(Kyoto University knee). The most outstanding feature of this model is that it has an auxiliary joint of a ball and socket at the center of the posterior part not only to facilitate a rollback movement but also to add a rotational function. During a gait under the load, the femorotibial articulation surface in a conventional design works as for standard design, but when the flexion becomes more, the auxiliary joint takes a part as a rotation center in the flexion motion. This auxiliary joint represents a certain type of posterior-stabilized knee and works to achieve a rollback, and when in flexion, rotation of tibia can be also achieved. Because this knee was unique in its biphasic surface structure for the different purposes, weight bearing, and flexion movement, it was later called bisurface knee (BS knee). Another characteristic of this prosthesis is the presence of zirconia ceramics (ZrO2) for femoral component.

Others companies modified design incorporating a lateral compartment which is fully congruent in extension, but relatively lax in flexion (Fig.12) (Mikashima et al., 2010).

Fig. 12. From Mikashima: the lateral tibiofemoral joint is completely conforming in extension (a), but less conforming at 90 degrees of flexion (b); the tibial insert has an AP curved medial surface and a spherically recessed lateral surface (c).

This lateral congruency constrains the lateral condyle to a central antero-posterior (AP) position in extension, but allows posterior translation in flexion. This articular geometry provides antero-posterior stability and acts through the lateral femoral condyle, thus there is rough analogy with the location and stabilizing role of the anterior cruciate ligament (ACL). In addition, the modified design has a more posterior tibial sulcus (Banks & Hodge, 2004) and the maximum femoral posterior condylar offset occurs later in the flexion arc (Bellemans et al., 2002).

TKA is an effective, well-established treatment for severe arthrythis of the knee. However, further improvement in the longevity in the longevity of the arthroplasty can be achieved with more durable bearing materials.

Due to the non-conforming shape of the bearing surface, hard-on-hard bearing are unlikely to have a role in TKA and polyethylene (PE) still remain an important bearing surface material.

Despite the improvement in manufacturing and elimination of gamma-irradiation in air have already resulted in fewer wear-related problems, concerns remain about adhesive and abrasive wear caused by the hard counterface of the femoral component.

(Kyoto University knee). The most outstanding feature of this model is that it has an auxiliary joint of a ball and socket at the center of the posterior part not only to facilitate a rollback movement but also to add a rotational function. During a gait under the load, the femorotibial articulation surface in a conventional design works as for standard design, but when the flexion becomes more, the auxiliary joint takes a part as a rotation center in the flexion motion. This auxiliary joint represents a certain type of posterior-stabilized knee and works to achieve a rollback, and when in flexion, rotation of tibia can be also achieved. Because this knee was unique in its biphasic surface structure for the different purposes, weight bearing, and flexion movement, it was later called bisurface knee (BS knee). Another characteristic of this prosthesis is the presence of zirconia ceramics (ZrO2) for femoral

Others companies modified design incorporating a lateral compartment which is fully

congruent in extension, but relatively lax in flexion (Fig.12) (Mikashima et al., 2010).

Fig. 12. From Mikashima: the lateral tibiofemoral joint is completely conforming in extension (a), but less conforming at 90 degrees of flexion (b); the tibial insert has an AP

This lateral congruency constrains the lateral condyle to a central antero-posterior (AP) position in extension, but allows posterior translation in flexion. This articular geometry provides antero-posterior stability and acts through the lateral femoral condyle, thus there is rough analogy with the location and stabilizing role of the anterior cruciate ligament (ACL). In addition, the modified design has a more posterior tibial sulcus (Banks & Hodge, 2004) and the maximum femoral posterior condylar offset occurs later in the flexion arc

TKA is an effective, well-established treatment for severe arthrythis of the knee. However, further improvement in the longevity in the longevity of the arthroplasty can be achieved

Due to the non-conforming shape of the bearing surface, hard-on-hard bearing are unlikely to have a role in TKA and polyethylene (PE) still remain an important bearing surface

Despite the improvement in manufacturing and elimination of gamma-irradiation in air have already resulted in fewer wear-related problems, concerns remain about adhesive and

abrasive wear caused by the hard counterface of the femoral component.

curved medial surface and a spherically recessed lateral surface (c).

component.

(Bellemans et al., 2002).

material.

with more durable bearing materials.

Previous studies have shown that roughening of the cobalt-chromiun (CoCr) alloy can potentiate wear of the PE (Fisher et al., 2004; White et al., 1994).

This wear can then lead to osteolysis, instability, and loosening of the implants from the underlying bone.

Designers are now concentrated on the research of different alloys for femoral components, alternative to the classic CoCrMo one (Stellite), both for complete ceramic or for ceramic surfaces.

A longer lasting of prosthesis with ceramic femoral components should be useful for younger patients with higher functional demands.

Moreover ceramic is useful when dealing with patients affected by allergies to metallic iones (Stellite) (Spector et al., 2001).

The advantages of ceramic bearing surfaces in terms of superior lubrication, friction, and wear properties compared to cobalt-chrome alloy (CoCr) surfaces in total joint arthroplasty are well recognized (Greenwald et al., 2001; Jacobs et al., 1994).

Laboratory and clinical data have demonstrated that ceramic bearings are associated with fewer wear particles that incite a less intense inflammatory host immune response than the metal-on-polyethylene articulations that are the accepted standard in total hip arthroplasty and total knee arthroplasty (Mont et al., 2003; Spector et al., 2001). The brittle nature of ceramics and the inability of ceramic materials to withstand high-impact tensile forces is of concern in clinical applications.

However, more than 10 years' long-term follow-up of cemented different ceramic knees, were performed in Japan and showed satisfactory results with low rate fractures of ceramic component (Akagi et al., 2000; Koshino et al., 2002).

An important improvement has been recently introduced in Europe by CeramTec (AG, Polchingen, Germany) with the BIOLOX Delta a composite matrix material containing 82% vol. alumina (Al2O3) and 17% vol. zirconia (ZrO2) providing good mechanical characteristics in terms of strength and resistance (Dalla Pria, 2007).

Using this material it was possible to develop a femoral component with a tensile strength that meets the demands for application in TKR (Kluess et al., 2009).

Fig. 13. a) Intraoperative photo of Biolox Delta ceramic femoral component.

History of Condylar Total Knee Arthroplasty 219

In USA an alternative strategy has been followed to decrease PE wear in THA and TKA, which consists in the surface transformation of metal to oxidized zirconium. A wrought zirconium alloy (Zr-2.5% Niobium) is oxidized by thermal diffusion to create a 5-mm oxidized zirconium layer (Oxinium, Smith & Nephew, Memphis, TN; Fig.14) (Laskin,

Although existing data are encouraging, with both strategies (Innocenti et al., 2010), further studies are needed to define the precise indications and outcomes of ceramic surfaces in

Technological developments in the field of knee replacement continues to increase the range

Particularly research and development efforts are focusing on designing effective prosthesis, allowing the movement ever closer to physiological ones, which are well tolerated and long

Explains the considerable attention, first, the morphological aspects of prosthetic components, and second, the quality of materials, with the aim of ensuring greater wear resistance and improved biocompatibility. This is a necessary condition for stability of the

Abdeen, AR., Collen, SB., & Vince, KG. (2010). Fifteen-year to 19-year follow-up of the Insall-Burstein-1 total knee arthroplasty. *J Arthroplasty,* Vol.25, No.2, pp. 173-178. Akagi, M., Nakamura, T., Matsusue Y., Ueo, T., Nishijyo, K., & Ohnishi, E. (2000). The

Anouchi, YS., Whiteside, LA., Kaiser, AD., & Milliano, MT. (1993). The effects of axial

Banks, SA., & Hodge, WA. (2004). Implant design affects knee arthroplasty kinematics

Bellemans, J., Banks, S., Victor, J., Vandenneucker, H., & Moemans, A. (2002). Fluoroscopic

Buechel, FF., & Pappas, MJ. (1986). The New Jersey Low-Contact-Stress Knee Replacement

Dalla Pria, P. (2007). Evolution and new application of the alumina ceramics in joint replacement. *Eur J Orthop Surg Traumatol,* 17:253-256 Vol.17, pp. 253-256.

follow-up study. *J Bone Joint Surg Am,* Vol.82, No.11, pp. 1626-1633.

during stair-stepping. *Clin Orthop Relat Res,* Vol.426, pp. 187-193.

posterior condylar offset. *J Bone Joint Surg Br,* Vol.84, No.1, pp. 50-53. Bindelglass, DF., & Dorr, LD. (1998). Current concepts review: symmetry versus asymmetry

Bisurface total knee replacement: a unique design for flexion. Four-to-nine-year

rotational alignment of the femoral component on knee stability and patellar tracking in total knee arthroplasty demonstrated on autopsy specimens. *Clin Orthop*

analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of

in the design of total knee femoral components - an unresolved controversy. *J*

System: biomechanical rationale and review of the first 123 cemented cases. *Arch.*

of solutions for the recovery of joint mobility of the painful knee arthritis.

lasting, and are implanted with less invasive interventions.

prosthetic implant and for the success of the intervention.

*Relat Res,* Vol.287, pp. 170-177.

*Arthroplasty,* Vol.13, No.8, pp. 939-944.

*Orthop Trauma Surg,* Vol.105, No.4, pp. 197-204.

2003).

TKA.

**8. References**

**7. Conclusions and future perspective**

A prospective international multicentre study started in 2008 with the aim to evaluate the clinical and radiological outcomes of the unconstrained Multigen Plus total knee system (Lima-Lto) with the new BIOLOX Delta ceramic femoral component (Fig.12a-b).

Fig. 13. b) Post-operative x-Ray of Multigen Plus total knee system (sagittal view).

Fig. 14. Intraoperative photo of Genesis II: Oxinium femoral component.

A prospective international multicentre study started in 2008 with the aim to evaluate the clinical and radiological outcomes of the unconstrained Multigen Plus total knee system

(Lima-Lto) with the new BIOLOX Delta ceramic femoral component (Fig.12a-b).

Fig. 13. b) Post-operative x-Ray of Multigen Plus total knee system (sagittal view).

Fig. 14. Intraoperative photo of Genesis II: Oxinium femoral component.

In USA an alternative strategy has been followed to decrease PE wear in THA and TKA, which consists in the surface transformation of metal to oxidized zirconium. A wrought zirconium alloy (Zr-2.5% Niobium) is oxidized by thermal diffusion to create a 5-mm oxidized zirconium layer (Oxinium, Smith & Nephew, Memphis, TN; Fig.14) (Laskin, 2003).

Although existing data are encouraging, with both strategies (Innocenti et al., 2010), further studies are needed to define the precise indications and outcomes of ceramic surfaces in TKA.

## **7. Conclusions and future perspective**

Technological developments in the field of knee replacement continues to increase the range of solutions for the recovery of joint mobility of the painful knee arthritis.

Particularly research and development efforts are focusing on designing effective prosthesis, allowing the movement ever closer to physiological ones, which are well tolerated and long lasting, and are implanted with less invasive interventions.

Explains the considerable attention, first, the morphological aspects of prosthetic components, and second, the quality of materials, with the aim of ensuring greater wear resistance and improved biocompatibility. This is a necessary condition for stability of the prosthetic implant and for the success of the intervention.

### **8. References**

History of Condylar Total Knee Arthroplasty 221

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Mont, MA., Booth, RE. Jr, Laskin, RS., Stiehl, JB., Ritter, MA., Stuchin, SA., & Rajadhyaksha,

Muratoglu, OK., Mark, A., Vittetoe, DA., Harris, WH., & Rubash, HE. (2003). Polyethylene

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Sledge, CB., & Ewald, FC. (1979). Total knee arthroplasty experience at the Robert Breck

Spector, BM., Ries, MD., Bourne, RB., Sauer, WS., Long, M., & Hunter, G. (2001) Wear

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Grace, JN., & Rand, JA. (1988). Patellar instability after total knee arthroplasty. *Clin Orthop*

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**15**

*Germany*

**The UniSpacer™: Correcting Varus**

Joern Bengt Seeger1 and Michael Clarius2

*2Department of Orthopaedic and Trauma Surgery,*

*Campus Charité Mitte (CCM), Berlin*

*Vulpius Klinik GmbH, Bad Rappenau*

**Malalignment in Medial Gonarthrosis**

*1Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin,*

The most commonly used operative treatments of osteoarthritis of the medial compartment of the knee joint, especially in younger patients, are arthroscopy, high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA). The last two procedures require

Fig. 1. Typical arthroscopic view of a patient with anteromedial osteoarthritis of the knee

**1. Introduction**

resection of bone stock (Iorio & Healy, 2003).

and degenerative lesion of the medial meniscus

Yoshii, I., Whiteside, LA., & Anouchi, YS. (1992). The effect of patellar button placement and femoral component design on patellar tracking in total knee arthroplasty. *Clin Orthop Relat Res,* Vol.275, pp. 211-219.

## **The UniSpacer™: Correcting Varus Malalignment in Medial Gonarthrosis**

Joern Bengt Seeger1 and Michael Clarius2

*1Center for Musculoskeletal Surgery, Charité - Universitätsmedizin Berlin, Campus Charité Mitte (CCM), Berlin 2Department of Orthopaedic and Trauma Surgery, Vulpius Klinik GmbH, Bad Rappenau Germany*

## **1. Introduction**

222 Recent Advances in Hip and Knee Arthroplasty

Yoshii, I., Whiteside, LA., & Anouchi, YS. (1992). The effect of patellar button placement and

*Orthop Relat Res,* Vol.275, pp. 211-219.

femoral component design on patellar tracking in total knee arthroplasty. *Clin*

The most commonly used operative treatments of osteoarthritis of the medial compartment of the knee joint, especially in younger patients, are arthroscopy, high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA). The last two procedures require resection of bone stock (Iorio & Healy, 2003).

Fig. 1. Typical arthroscopic view of a patient with anteromedial osteoarthritis of the knee and degenerative lesion of the medial meniscus

The UniSpacer™: Correcting Varus Malalignment in Medial Gonarthrosis 225

 Fig. 4. and 5. Patient with medial osteoarthritis of the knee: a.p. stance and lateral view of

Contraindications are inflammatory arthritis, severe instability due to advanced loss of osteochondral structure or the absence of collateral cruciate ligament integrity, as well as

Fig. 3. UniSpacer™ metallic interpositional device

the knee

flexion/contracture greater than 15 degrees.

A less invasive alternative to these procedures has been introduced in 2000 by Rick Hallock and Barry Fell: the UniSpacer™ implant (Zimmer, Inc., Warsaw, IN, USA), which is essentially a modern version of early metallic hemiarthroplasty as described by McKeever (McKeever, 1960) or MacIntosh (MacIntosh, 1958). However, due to a high failure rate between 16 and 44% as described by Bailie and Sisto, the implant is not available any more (Bailie et al., 2008; Sisto & Mitchel 2005).

Implantation of this self-centering, one-piece interpositional device into the knee joint does not require any resection of bone stock and is performed via minimally-invasive surgery (Scott, 2003). Initially, a cementless metal or polyethylene interpositional device has been implanted into the medial or lateral compartment.

The Unispacer is available in several thicknesses (between 2 and 5 mm) and sizes (38 – 58 mm) and adapts to knee kinematics (Marx et al., 2009). There are special models for the left and ride side.

The UniSpacer™ is a device that is not fixed to any structures and therefore self-centering; it is used to relieve pain and to correct or minimize varus malalignment in unicompartmental osteoarthritis of the knee. The upper surface of the implant postoperatively adapts to the femoral condylus (Scott, 2003).

The UniSpacer™ is indicated in patients with isolated moderate degeneration of the medial compartment with minimal degeneration, and no significant loss of joint space in the patellofemoral compartment.

A less invasive alternative to these procedures has been introduced in 2000 by Rick Hallock and Barry Fell: the UniSpacer™ implant (Zimmer, Inc., Warsaw, IN, USA), which is essentially a modern version of early metallic hemiarthroplasty as described by McKeever (McKeever, 1960) or MacIntosh (MacIntosh, 1958). However, due to a high failure rate between 16 and 44% as described by Bailie and Sisto, the implant is not available any more

(Bailie et al., 2008; Sisto & Mitchel 2005).

Fig. 2. Early interpositional hemiarthroplasty (Springer et al., 2006)

implanted into the medial or lateral compartment.

and ride side.

femoral condylus (Scott, 2003).

patellofemoral compartment.

Implantation of this self-centering, one-piece interpositional device into the knee joint does not require any resection of bone stock and is performed via minimally-invasive surgery (Scott, 2003). Initially, a cementless metal or polyethylene interpositional device has been

The Unispacer is available in several thicknesses (between 2 and 5 mm) and sizes (38 – 58 mm) and adapts to knee kinematics (Marx et al., 2009). There are special models for the left

The UniSpacer™ is a device that is not fixed to any structures and therefore self-centering; it is used to relieve pain and to correct or minimize varus malalignment in unicompartmental osteoarthritis of the knee. The upper surface of the implant postoperatively adapts to the

The UniSpacer™ is indicated in patients with isolated moderate degeneration of the medial compartment with minimal degeneration, and no significant loss of joint space in the

Fig. 3. UniSpacer™ metallic interpositional device

Fig. 4. and 5. Patient with medial osteoarthritis of the knee: a.p. stance and lateral view of the knee

Contraindications are inflammatory arthritis, severe instability due to advanced loss of osteochondral structure or the absence of collateral cruciate ligament integrity, as well as flexion/contracture greater than 15 degrees.

The UniSpacer™: Correcting Varus Malalignment in Medial Gonarthrosis 227

Clinical Scores preoperative 1 year postop. 2 years postop. 5 years postop

Fig. 8. and 9. Movement of the device during flexion due to the self-centering effect of the

Fig. 6. and 7. Postoperative implant position

Unispacer

Lysholm 59.1 85.4 90.2 97.2 AKS knee 60.1 87.4 88.7 96.6 AKS function 70.0 93.8 98.5 96.4 Table 1. Clinical scores preoperative, at 1 year-, 2 year- and 5 year follow-up

## **2. Operation technique (Hallock & Fell, 2003)**

An arthroscopy is performed in order to prove the correct indication, intact ACL and PCL and medial meniscectomy of the posterior horn. After arthroscopy a 6-7cm medial parapatellar arthrotomy is performed. The rest of the medial meniscus is resected and osteophytes of the medial tibial plateau, the notch and around the patella are removed in order to avoid an impingement of the Unispacer. The size of the tibial plateau is measured with a special device and a probe is implanted. The correct size of the implant is controlled under fluoroscopy and the movement of the Unispacer in flexion and extension is documented. The whole medial tibial plateau should be covered in a.p. radiographs and a ventral impingement of the Unispacer with the femoral condyle should be ruled out. After implanting the original Unispacer, the wound closure is performed under usual conditions.

## **2.1 Rehabilitation**

Weight bearing as tolerated can be performed with the use of crutches. A thrombosis prophylaxis is obligatory.

## **3. Results**

The first results have been published by the designers group on 71 Unispacer knee system implants implanted in 67 patients. (Hallock & Fell, 2003).

The mean Knee Society knee score improved 169% in the 1-year group and 193% in the 2 year group. The mean Knee Society function score improved 31% and 65%, respectively. The mean Lysholm score improved 88% and 140%, respectively. Five implants (7%) were revised to total knee arthroplasty (TKA) and 10 implants (14%) were revised to another Unispacer Knee System implant.

Marx et al. implanted 14 Unispacer in 13 patients (4 women and 9 men). In 8 cases the left and in 6 cases the right knee joint was operated. There were no intra- or postoperative complications. There was no mobilization under anesthesia necessary. A dislocation of the spacer was not observed.

The notion of a self-centering mobile component correcting the varus knee internally without any need for bone resection has been, and still is, appealing. Clarius et al. evaluated clinical and radiological results and whether appropriate alignment change can be achieved by UniSpacer™ implantation (Clarius et al., 2003). In addition they examined the alignment change in the first 5 years after surgery.

In a retrospective study, 18 patients (19 legs) presenting with moderate stage isolated medial gonarthrosis, who had received UniSpacer™ hemiarthroplasty between 2002 and 2004, were assessed (implant thickness: 2, 3 or 4 mm); one patient received bilateral implantation; 12 right and 7 left knees had been treated. The average age of the patients (7 women and 11 men) at the time of surgery was 60.8 (48 to 72) years.

The clinical scores (Lysholm, AKS knee and function) preoperatively and at 1-, 2- and 5 year follow-up are shown in tab. 1.

Only 15 legs could be evaluated, as 4 patients had undergone revision UKA or TKA due to persistent pain. Average time to revision for the knees revised to TKA or UKA was 23.8 (±18.0) months. So far, no dislocations have been observed in this study.

An arthroscopy is performed in order to prove the correct indication, intact ACL and PCL and medial meniscectomy of the posterior horn. After arthroscopy a 6-7cm medial parapatellar arthrotomy is performed. The rest of the medial meniscus is resected and osteophytes of the medial tibial plateau, the notch and around the patella are removed in order to avoid an impingement of the Unispacer. The size of the tibial plateau is measured with a special device and a probe is implanted. The correct size of the implant is controlled under fluoroscopy and the movement of the Unispacer in flexion and extension is documented. The whole medial tibial plateau should be covered in a.p. radiographs and a ventral impingement of the Unispacer with the femoral condyle should be ruled out. After implanting the original Unispacer, the wound closure is performed under usual

Weight bearing as tolerated can be performed with the use of crutches. A thrombosis

The first results have been published by the designers group on 71 Unispacer knee system

The mean Knee Society knee score improved 169% in the 1-year group and 193% in the 2 year group. The mean Knee Society function score improved 31% and 65%, respectively. The mean Lysholm score improved 88% and 140%, respectively. Five implants (7%) were revised to total knee arthroplasty (TKA) and 10 implants (14%) were revised to another Unispacer

Marx et al. implanted 14 Unispacer in 13 patients (4 women and 9 men). In 8 cases the left and in 6 cases the right knee joint was operated. There were no intra- or postoperative complications. There was no mobilization under anesthesia necessary. A dislocation of the

The notion of a self-centering mobile component correcting the varus knee internally without any need for bone resection has been, and still is, appealing. Clarius et al. evaluated clinical and radiological results and whether appropriate alignment change can be achieved by UniSpacer™ implantation (Clarius et al., 2003). In addition they examined the alignment

In a retrospective study, 18 patients (19 legs) presenting with moderate stage isolated medial gonarthrosis, who had received UniSpacer™ hemiarthroplasty between 2002 and 2004, were assessed (implant thickness: 2, 3 or 4 mm); one patient received bilateral implantation; 12 right and 7 left knees had been treated. The average age of the patients (7 women and 11

The clinical scores (Lysholm, AKS knee and function) preoperatively and at 1-, 2- and 5 year

Only 15 legs could be evaluated, as 4 patients had undergone revision UKA or TKA due to persistent pain. Average time to revision for the knees revised to TKA or UKA was 23.8

(±18.0) months. So far, no dislocations have been observed in this study.

**2. Operation technique (Hallock & Fell, 2003)**

implants implanted in 67 patients. (Hallock & Fell, 2003).

conditions.

**3. Results**

**2.1 Rehabilitation**

prophylaxis is obligatory.

Knee System implant.

spacer was not observed.

change in the first 5 years after surgery.

follow-up are shown in tab. 1.

men) at the time of surgery was 60.8 (48 to 72) years.

Table 1. Clinical scores preoperative, at 1 year-, 2 year- and 5 year follow-up

Fig. 6. and 7. Postoperative implant position

Fig. 8. and 9. Movement of the device during flexion due to the self-centering effect of the Unispacer

The UniSpacer™: Correcting Varus Malalignment in Medial Gonarthrosis 229

Bailie AG, Lewis PL, Brumby SA et al (2008) The Unispacer knee implant: early clinical

Cooke TD, Li J, Scudamore RA (1994) Radiographic assessment of bony contributions to

Cooke TD, Scudamore RA, Bryant JT et al (1991) A quantitative approach to radiography of

Cooke TD, Scudamore RA, Li J et al (1997) Axial lower-limb alignment: comparison of knee

Coventry MB, Ilstrup DM, Wallrichs SL (1993) Proximal tibial osteotomy. A critical longterm study of eighty-seven cases. *J Bone Joint Surg Am* 75(2), pp. 196-201 Deshmukh RV, Scott RD (2001) Unicompartmental Knee Arthroplasty: Long-Term Results.

Hallock RH, Fell BM (2003) Unicompartmental Tibial Hemiarthroplasty. Early Results of the

Hernigou P, Medevielle D, Debeyre J et al (1987) Proximal tibial osteotomy for osteoarthritis

Insall JN, Joseph DM, Msika C (1984) High tibial osteotomy for varus gonarthrosis. A long-

Iorio R, Healy WL (2003) Unicompartmental Arthritis of the Knee. *J Bone Joint Surg Am* 85(7),

Kennedy WRMD, White RPMD (1987) Unicompartmental Arthroplasty of the Knee

Koeck F, Perlick L, Luring C et al (2009) Leg axis correction with ConforMIS iForma™

MacIntosh DL (1958) Hemiarthroplasty of the knee using a space occupying prosthesis for

Moreland JR, Bassett LW, Hanker GJ (1987) Radiographic analysis of the axial alignment of

Scott RD (2003) UniSpacer: insufficient data to support its widespread use. *Clin Orthop Relat*

Scott RD (2003) UniSpacer(TM): Insufficient Data to Support its Widespread Use. *Clin*

Scott RD, Deshmukh RV (2005) Metallic hemiarthroplasty of the knee. *Curr Opin Orthop*

Sisto DJ, Mitchell IL (2005) UniSpacer Arthroplasty of the Knee. *J Bone Joint Surg Am* 87(8),

Springer BD, Scott RD, Thornhill TS (2006) Conversion of Failed Unicompartmental Knee

with varus deformity. A ten to thirteen-year follow-up study. *J Bone Joint Surg Am*

Postoperative Alignment and its Influence on Overall Results. *Clin Orthop Relat Res*

(interpositional device) in unicompartmental arthritis of the knee. *Int Orthop* 33(4),

painful varus and valgus deformities. In: of the Joint Meeting of the Orthopaedic Associations of the English-Speaking World. *J Bone Joint Surg Am* 40(6), pp. 1428-

the lower limb. Principles and applications. *J Bone Joint Surg Br* 73-B(5), pp. 715-720

geometry in normal volunteers and osteoarthritis patients. *Osteoarthritis Cartilage*

results. *J Bone Joint Surg Br* 90(4), pp. 446-450

*Clin Orthop Relat Res* 392, pp. 272-278

knee deformity. *Orthop Clin North Am* 25(3), pp. 387-393

UniSpacer(TM) Knee. *Clin Orthop Relat Res* 416, pp. 154-163

term follow-up study. *J Bone Joint Surg Am* 66(7), pp. 1040-1048

McKeever DC (1960) Tibial plateau prosthesis. *Clin Orthop Relat Res* 18, pp. 86-95

the lower extremity. *J Bone Joint Surg Am* 69(5), pp. 745-749

Arthroplasty to TKA. *Clin Orthop Relat Res* 446, pp. 214-220

**5. References**

5(1), pp. 39-47

69(3), pp. 332-354

pp. 1351-1364

221, pp. 278-285

*Res* 416, pp. 164-166

16(1), pp. 35-37

pp. 1706-1711

*Orthop Relat Res* 416, pp.164-166

pp. 955-960

1441

## **4. Conclusion**

The use of HTO in the treatment of symptomatic varus malaligned knees has been propagated and thoroughly documented for several decades: it is a well-established therapeutic option (Nelissen et al., 2009). UKA has recently experienced a renewal of interest, with improved prostheses and techniques used. There have been reports of good long-term results for these methods. However, both can lead to distinct issues patients may be troubled with over the course of time. UKA comes with loss of bone matter in the medial compartment and, if conversion to TKA becomes necessary, bone grafts or metal wedge augmentation might be required in some cases (Springer et al., 2006).

Hemiarthroplasty with metallic interpositional devices, while first described over half a century ago, is also currently experiencing a renaissance as a treatment option of varus unicompartmental OA, the idea being to provide a means of treatment that minimizes the disadvantages of other procedures. It is used in cases where HTO is contraindicated or patients are too young for TKA. The ConforMIS iForma™ device, following the MacIntosh and McKeever rationale in being functionally fixed to the tibial surface, has had one favorable review; altogether, there are still few reports examining the use of the selfcentering UniSpacer™ device in medial gonarthrosis.

Use of the UniSpacer™ in unicompartmental OA was initially recommended for young and active patients (Hallock & Fell, 2003). The role of this procedure still is not certain as it has been considered suitable for only few patients (1%) (Scott & Deshmukh, 2005) and there have been reports of poor postoperative results due to implant dislocation (up to 44%) (Bailie et al., 2005; Sisto & Mitchell, 2005).

Clarius et al. showed in their study a significant, slightly over-adjusting, correction of moderate varus alignment by UniSpacer™ arthroplasty, which does not correlate with the thickness of the implant used (Clarius et al., 2003). In the first postoperative year, a varus shift into a more neutral position could be observed, which is most likely due to adaptation of the implant to the joint. This effect is partly reversed in the following years by another slight valgus change, resulting, 5 years after surgery, in an average leg axis close to the one first achieved by UniSpacer™ implantation.

A high revision rate of 4 out of 19 UniSpacer™ implants in the first 5 postoperative years has been shown, which is unacceptably high compared to other treatment options. The reason for revision was persistent pain. There were no cases of dislocations. All revisions were technically easy to operate and uncomplicated. In all cases either UKA (2) or TKA (2) was performed and the patients were satisfied with the clinical results achieved after revision.

Looking at the high revision rates of the UniSpacer implant reported in the literature and in our study this metallic interposition arthroplasty does not seem to be a treatment option for patients with medial osteoarthritis of the knee. As there are reproducible good and excellent clinical and functional results reported with UKA after 10-15 years this operation should be preferred. However the clinical results of our remaining 14 patients with 15 operated knees were good and comparable to patients after UKA. Similar to the results of the metallic interpositional device of Mc Keever good results can be possible however the results are not predictable.

As a minimally invasive procedure, UniSpacer™ arthroplasty was seen as an alternative for treatment of varus malaligned knees in isolated medial gonarthrosis, due to good revision and conversion options.

#### **5. References**

228 Recent Advances in Hip and Knee Arthroplasty

The use of HTO in the treatment of symptomatic varus malaligned knees has been propagated and thoroughly documented for several decades: it is a well-established therapeutic option (Nelissen et al., 2009). UKA has recently experienced a renewal of interest, with improved prostheses and techniques used. There have been reports of good long-term results for these methods. However, both can lead to distinct issues patients may be troubled with over the course of time. UKA comes with loss of bone matter in the medial compartment and, if conversion to TKA becomes necessary, bone grafts or metal wedge

Hemiarthroplasty with metallic interpositional devices, while first described over half a century ago, is also currently experiencing a renaissance as a treatment option of varus unicompartmental OA, the idea being to provide a means of treatment that minimizes the disadvantages of other procedures. It is used in cases where HTO is contraindicated or patients are too young for TKA. The ConforMIS iForma™ device, following the MacIntosh and McKeever rationale in being functionally fixed to the tibial surface, has had one favorable review; altogether, there are still few reports examining the use of the self-

Use of the UniSpacer™ in unicompartmental OA was initially recommended for young and active patients (Hallock & Fell, 2003). The role of this procedure still is not certain as it has been considered suitable for only few patients (1%) (Scott & Deshmukh, 2005) and there have been reports of poor postoperative results due to implant dislocation (up to 44%)

Clarius et al. showed in their study a significant, slightly over-adjusting, correction of moderate varus alignment by UniSpacer™ arthroplasty, which does not correlate with the thickness of the implant used (Clarius et al., 2003). In the first postoperative year, a varus shift into a more neutral position could be observed, which is most likely due to adaptation of the implant to the joint. This effect is partly reversed in the following years by another slight valgus change, resulting, 5 years after surgery, in an average leg axis close to the one

A high revision rate of 4 out of 19 UniSpacer™ implants in the first 5 postoperative years has been shown, which is unacceptably high compared to other treatment options. The reason for revision was persistent pain. There were no cases of dislocations. All revisions were technically easy to operate and uncomplicated. In all cases either UKA (2) or TKA (2) was performed and the patients were satisfied with the clinical results achieved after

Looking at the high revision rates of the UniSpacer implant reported in the literature and in our study this metallic interposition arthroplasty does not seem to be a treatment option for patients with medial osteoarthritis of the knee. As there are reproducible good and excellent clinical and functional results reported with UKA after 10-15 years this operation should be preferred. However the clinical results of our remaining 14 patients with 15 operated knees were good and comparable to patients after UKA. Similar to the results of the metallic interpositional device of Mc Keever good results can be possible however the results are not

As a minimally invasive procedure, UniSpacer™ arthroplasty was seen as an alternative for treatment of varus malaligned knees in isolated medial gonarthrosis, due to good revision

augmentation might be required in some cases (Springer et al., 2006).

centering UniSpacer™ device in medial gonarthrosis.

(Bailie et al., 2005; Sisto & Mitchell, 2005).

first achieved by UniSpacer™ implantation.

revision.

predictable.

and conversion options.

**4. Conclusion**

**16**

*USA*

Fabio Orozco and Alvin Ong

*University, Philadelphia, Pennsylvani*

**Posterior Stabilized Total Knee Arthroplasty**

The posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) functions to prevent posterior translation of the tibia and aids in femoral roll-back1. Roll-back allows for increased quadriceps lever arm and more efficient use of extensor musculature, permitting more normal stair climbing. Because of this, PCL retaining knees have the advantage of maintenance of ligamentous proprioception, load transfer by the native PCL and anteriorposterior stability. However, retaining the PCL also has several disadvantages. Surgical exposure of the tibia, gap balancing and reliance on diseased ligament morphology make consistent TKA results difficult. The posterior stabilized design in TKA was introduced in the mid-1970s. Surgeons who use this system believed that the results obtained are more consistent because they do not have to rely on abnormal PCL morphology. Consequently, exposure, joint line restoration and appropriate balancing of the knee are easier with PCL stabilized designs. These components are a popular treatment for patients requiring primary TKA. Improvements in implant design, a technically easier procedure in the face of deformity, restoration of knee kinematics and reported very good long-term outcomes may

Most of the current total knee implants were derived from the Total Condylar Prosthesis (TCP; Zimmer, Warsaw, Indiana, USA), which was introduced in 1974. This prosthesis was a cruciate sacrificing cemented design. Technique of implantation of the TCP requires excision of the PCL but without substitution. Stability in this implant design was achieved by soft tissue balance in flexion and extension and articular conformity in the coronal and sagittal plane2. Consequently, the success of this implant was highly dependent of surgical technique. In 1978, the TCP was modified to the Insall Burstein Posterior Stabilized Prosthesis (IB I) to address posterior subluxation of the tibia and instability. The IB I is the

1 Dorr LD Ochsner JL, Gronley J, Perry J. Functional comparison of posterior curciate-retained versus

2 Scuderi GR, Pagnano MR: Review Article: The rationale for posterior cruciate substituting total knee

**1. Introduction**

all be reasons for the increased use of this design.

cruciate-sacrificedot al knee arthroplasty. CORR 1988; 236:36-43.

arthroplasty. J Orthopedic Surgery 2001, 9(2):81-88

**2. History and design rationale**

*Atlanticare Care Regional Medical Center, Pomona, New Jersey*

*Joint Replacement, Rothman Institute, Thomas Jefferson*

## **Posterior Stabilized Total Knee Arthroplasty**

## Fabio Orozco and Alvin Ong

*Atlanticare Care Regional Medical Center, Pomona, New Jersey Joint Replacement, Rothman Institute, Thomas Jefferson University, Philadelphia, Pennsylvani USA*

## **1. Introduction**

230 Recent Advances in Hip and Knee Arthroplasty

Tunggal JA, Higgins GA, Waddell JP (2009) Complications of closing wedge high tibial

Whiteside LA (2005) Making Your Next Unicompartmental Knee Arthroplasty Last: Three Keys to Success. *The Journal of Arthroplasty* 20 (Supplement 2), pp. 2-3

osteotomy. *Int Orthop* 10.1007/s00264-009-0819-9

The posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) functions to prevent posterior translation of the tibia and aids in femoral roll-back1. Roll-back allows for increased quadriceps lever arm and more efficient use of extensor musculature, permitting more normal stair climbing. Because of this, PCL retaining knees have the advantage of maintenance of ligamentous proprioception, load transfer by the native PCL and anteriorposterior stability. However, retaining the PCL also has several disadvantages. Surgical exposure of the tibia, gap balancing and reliance on diseased ligament morphology make consistent TKA results difficult. The posterior stabilized design in TKA was introduced in the mid-1970s. Surgeons who use this system believed that the results obtained are more consistent because they do not have to rely on abnormal PCL morphology. Consequently, exposure, joint line restoration and appropriate balancing of the knee are easier with PCL stabilized designs. These components are a popular treatment for patients requiring primary TKA. Improvements in implant design, a technically easier procedure in the face of deformity, restoration of knee kinematics and reported very good long-term outcomes may all be reasons for the increased use of this design.

#### **2. History and design rationale**

Most of the current total knee implants were derived from the Total Condylar Prosthesis (TCP; Zimmer, Warsaw, Indiana, USA), which was introduced in 1974. This prosthesis was a cruciate sacrificing cemented design. Technique of implantation of the TCP requires excision of the PCL but without substitution. Stability in this implant design was achieved by soft tissue balance in flexion and extension and articular conformity in the coronal and sagittal plane2. Consequently, the success of this implant was highly dependent of surgical technique. In 1978, the TCP was modified to the Insall Burstein Posterior Stabilized Prosthesis (IB I) to address posterior subluxation of the tibia and instability. The IB I is the

<sup>1</sup> Dorr LD Ochsner JL, Gronley J, Perry J. Functional comparison of posterior curciate-retained versus cruciate-sacrificedot al knee arthroplasty. CORR 1988; 236:36-43.

<sup>2</sup> Scuderi GR, Pagnano MR: Review Article: The rationale for posterior cruciate substituting total knee arthroplasty. J Orthopedic Surgery 2001, 9(2):81-88

Posterior Stabilized Total Knee Arthroplasty 233

stabilized TKA experienced AP femoro-tibial translation more similar to the normal knee during normal gait and deep knee bend.9 Moreover, studies have shown no significant difference between posterior stabilized TKA and normal knees with regard to spatiotemporal gait parameters, knee range of motion during stair climbing or in isokinetic

A study comparing cruciate retaining, cruciate sacrificing and posterior stabilized TKA found that posterior stabilized designs produced more roll back and better quadriceps efficiency than cruciate retaining knee designs11. Posterior stabilized TKA predictably restores more normal knee kinematics when compared to either PCL substituting or PCL

Both cruciate retaining and posterior stabilized TKA designs can provide excellent range of motion. However, range of motion may be better when a posterior stabilized TKA is used to maintain femoral roll back. It appears, according to most comparative studies, that posterior stabilized designs may provide more predictable motion, with greater flexion under fluoroscopic visualization.12 13 In a very well done meta-analysis Jacobs *et al.* analyzed eight randomized controlled trials comparing posterior stabilized with cruciate retaining TKA and found that the range of motion was 8° higher (105 versus 113°) in the posterior stabilized group than the cruciate retaining group (*P* = 0.01, 95% confidence interval 1.7-

Retention of the PCL requires that the prosthetic kinematics closely match that of the normal knee. This obligates the implant to have a "flat" polyethylene component relative to the radius of curvature of the femur. This "round on flat" design allows for minimal constraint on tibial component enabling roll back of the femur on tibia with knee flexion. This less forming design can lead to excessive point contact pressure and increase polyethylene wear. In contrast, in posterior-stabilized design, it is possible to use more conforming polyethylene articulation with minimal point contact stress. Increasing the conformity of the implant, increases the contact area, and decreases the stress to which the polyethylene is subjected. This can potentially minimize polyethylene wear and increase the long-term survival of the TKA. Cases of severe polyethylene wear in cruciate retaining implants with less conforming

10 Wilson SA, McCann PD, Gotlin RS, Ramakrishnan HK, Wootten ME and Insall JN. Comprehensive

11 Mahoney OM, Noble PC, Rhoads DD, Alexander JW, Tullos HS. Posterior cruciate function following

12 Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement: a systematic literature review within the Cochrane framework. Acta Orthop

13 Maruyama S, Yoshiya S, Matsui N, Kuroda R, Kurosaka M. Functional comparison of posterior cruciate retaining versus posterior stabilized total knee arthroplasty. J Arthroplasty 2004; 19:349-353. 14 Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement: a systematic literature review within the Cochrane framework. Acta Orthop

9 Udomkiat P, Meng BJ, Dorr LD, Wan Z. Clin Orthop 2000 Sep;(378):192-201

total knee arthroplasty: A biomechanical study. J Arthroplasty 1994, 9:569-78.

gait analysis in posterior stabilized knee arthroplasty. J Arthroplasty 1996, 11:359–67.

muscle strength.10

sacrificing designs.

15).14

2005; 76:757-768.

2005; 76:757-768.

**3.3 Improved range of motion**

**3.4 Less polyethylene wear**

first posterior stabilized/substituting TKA design. It incorporated a femoral cam that articulates with a polyethylene tibial post to act as a substitute for the excised native PCL. Most posterior stabilized knee designs evolved from the IB I - incorporating a cam-post mechanism to aid in roll back, increase the amount of distraction tolerated before subluxation occurs, and increase varus-valgus constraint. The cam-post mechanism improves both anterior-posterior and translational stability. Multiply studies have shown that function of the TKA is improved with PCL substitution. PCL substitution allowed for better stability, increased ROM, reduced quadriceps force in extension, improved stairclimbing ability, and improved patellofemoral function.3 <sup>4</sup> 5

## **3. Advantages of posterior stabilized TKA**

There are several advantages with use of posterior stabilized TKA designs. These include: I) easier surgical exposure and ligament balancing, II) predictable restoration of knee kinematics, III) improved range of motion, IV) less polyethylene wear, and V) avoiding the possibility of PCL rupture.

### **3.1 Easier surgical exposure and ligament balancing**

Adequate exposure of the tibia may not be possible with PCL retention. Excision of the PCL aids in exposing the tibia for adequate visualization by releasing the tethering effect of a tight contracted PCL. Moreover, the PCL can be excised from the femoral and tibial attachment in a reproducible way, making the ligamentous balancing and correction of the deformity easier since it is not complicated by the tethering effect of the PCL. Abnormal PCL morphology is often encountered in the diseased knee making predictable gap balancing difficult in PCL retaining designs. If the patient has a "tight", contracted PCL, the knee may be relatively tight in flexion with excessive femoral roll-back. On the other hand, if the PCL is lax or incompetent, the knee may experience posterior sag with no roll-back with knee flexion. Thus, use of posterior stabilized TKA makes balancing more predictable eliminating the reliance on abnormal PCL morphology and function.

### **3.2 Predictable restoration of knee kinematics**

In posterior stabilized TKA, the tibial post articulates with the transverse femoral cam predictably with knee flexion, preventing posterior subluxation of the tibia while maintaining femoral roll back. Many studies report more normal kinematics with the use of posterior stabilized designs.6 7 8 Fluoroscopic kinematics showed that the posterior

<sup>3</sup> Insall JN, Lachiewicz PF, Burstein AH. The posterior stabilized condylar prosthesis: a modification of the total condylar design. J Bone Joint Surg Am. 1982;64:1317

<sup>4</sup> Scott WN, Rubinstein M, Scuderi G. Results after knee replacement with a posterior cruciatesubstituting prosthesis. J Bone Joint Surg Am. 1998;70:1163

<sup>5</sup> Scuderi GR, Insall JN. The posterior stabilized knee prosthesis. Orthop Clin North Am. 1989;20:71

<sup>6</sup> Stiehl JB, Komistek RD, Dennis DA, et al. Fluoroscopic analysis of kinematics after posterior cruciate retaining knee arthroplasty. J Bone Joint Surg Br 1995; 77B:884-889.

<sup>7</sup> Dennis DA, Komistek RD, Hoff WA. In vivo knee kinematics derived using an inverse perspective technique. Clin Orthop 1996; 331:107-117.

<sup>8</sup> Ranawat CS, Komistek RD, Rodriguez JA, et al. In vivo kinematics for fixed and mobile-bearing posterior stabilized knee prostheses. Clin Orthop Relat Res 2004; 418:184-190.

first posterior stabilized/substituting TKA design. It incorporated a femoral cam that articulates with a polyethylene tibial post to act as a substitute for the excised native PCL. Most posterior stabilized knee designs evolved from the IB I - incorporating a cam-post mechanism to aid in roll back, increase the amount of distraction tolerated before subluxation occurs, and increase varus-valgus constraint. The cam-post mechanism improves both anterior-posterior and translational stability. Multiply studies have shown that function of the TKA is improved with PCL substitution. PCL substitution allowed for better stability, increased ROM, reduced quadriceps force in extension, improved stair-

There are several advantages with use of posterior stabilized TKA designs. These include: I) easier surgical exposure and ligament balancing, II) predictable restoration of knee kinematics, III) improved range of motion, IV) less polyethylene wear, and V) avoiding the

Adequate exposure of the tibia may not be possible with PCL retention. Excision of the PCL aids in exposing the tibia for adequate visualization by releasing the tethering effect of a tight contracted PCL. Moreover, the PCL can be excised from the femoral and tibial attachment in a reproducible way, making the ligamentous balancing and correction of the deformity easier since it is not complicated by the tethering effect of the PCL. Abnormal PCL morphology is often encountered in the diseased knee making predictable gap balancing difficult in PCL retaining designs. If the patient has a "tight", contracted PCL, the knee may be relatively tight in flexion with excessive femoral roll-back. On the other hand, if the PCL is lax or incompetent, the knee may experience posterior sag with no roll-back with knee flexion. Thus, use of posterior stabilized TKA makes balancing more predictable

In posterior stabilized TKA, the tibial post articulates with the transverse femoral cam predictably with knee flexion, preventing posterior subluxation of the tibia while maintaining femoral roll back. Many studies report more normal kinematics with the use of posterior stabilized designs.6 7 8 Fluoroscopic kinematics showed that the posterior

3 Insall JN, Lachiewicz PF, Burstein AH. The posterior stabilized condylar prosthesis: a modification of

4 Scott WN, Rubinstein M, Scuderi G. Results after knee replacement with a posterior cruciate-

7 Dennis DA, Komistek RD, Hoff WA. In vivo knee kinematics derived using an inverse perspective

8 Ranawat CS, Komistek RD, Rodriguez JA, et al. In vivo kinematics for fixed and mobile-bearing

5 Scuderi GR, Insall JN. The posterior stabilized knee prosthesis. Orthop Clin North Am. 1989;20:71 6 Stiehl JB, Komistek RD, Dennis DA, et al. Fluoroscopic analysis of kinematics after posterior cruciate

climbing ability, and improved patellofemoral function.3 <sup>4</sup> 5

**3.1 Easier surgical exposure and ligament balancing**

eliminating the reliance on abnormal PCL morphology and function.

**3.2 Predictable restoration of knee kinematics**

the total condylar design. J Bone Joint Surg Am. 1982;64:1317

substituting prosthesis. J Bone Joint Surg Am. 1998;70:1163

technique. Clin Orthop 1996; 331:107-117.

retaining knee arthroplasty. J Bone Joint Surg Br 1995; 77B:884-889.

posterior stabilized knee prostheses. Clin Orthop Relat Res 2004; 418:184-190.

**3. Advantages of posterior stabilized TKA**

possibility of PCL rupture.

stabilized TKA experienced AP femoro-tibial translation more similar to the normal knee during normal gait and deep knee bend.9 Moreover, studies have shown no significant difference between posterior stabilized TKA and normal knees with regard to spatiotemporal gait parameters, knee range of motion during stair climbing or in isokinetic muscle strength.10

A study comparing cruciate retaining, cruciate sacrificing and posterior stabilized TKA found that posterior stabilized designs produced more roll back and better quadriceps efficiency than cruciate retaining knee designs11. Posterior stabilized TKA predictably restores more normal knee kinematics when compared to either PCL substituting or PCL sacrificing designs.

#### **3.3 Improved range of motion**

Both cruciate retaining and posterior stabilized TKA designs can provide excellent range of motion. However, range of motion may be better when a posterior stabilized TKA is used to maintain femoral roll back. It appears, according to most comparative studies, that posterior stabilized designs may provide more predictable motion, with greater flexion under fluoroscopic visualization.12 13 In a very well done meta-analysis Jacobs *et al.* analyzed eight randomized controlled trials comparing posterior stabilized with cruciate retaining TKA and found that the range of motion was 8° higher (105 versus 113°) in the posterior stabilized group than the cruciate retaining group (*P* = 0.01, 95% confidence interval 1.7- 15).14

#### **3.4 Less polyethylene wear**

Retention of the PCL requires that the prosthetic kinematics closely match that of the normal knee. This obligates the implant to have a "flat" polyethylene component relative to the radius of curvature of the femur. This "round on flat" design allows for minimal constraint on tibial component enabling roll back of the femur on tibia with knee flexion. This less forming design can lead to excessive point contact pressure and increase polyethylene wear. In contrast, in posterior-stabilized design, it is possible to use more conforming polyethylene articulation with minimal point contact stress. Increasing the conformity of the implant, increases the contact area, and decreases the stress to which the polyethylene is subjected. This can potentially minimize polyethylene wear and increase the long-term survival of the TKA. Cases of severe polyethylene wear in cruciate retaining implants with less conforming

<sup>9</sup> Udomkiat P, Meng BJ, Dorr LD, Wan Z. Clin Orthop 2000 Sep;(378):192-201

<sup>10</sup> Wilson SA, McCann PD, Gotlin RS, Ramakrishnan HK, Wootten ME and Insall JN. Comprehensive gait analysis in posterior stabilized knee arthroplasty. J Arthroplasty 1996, 11:359–67.

<sup>11</sup> Mahoney OM, Noble PC, Rhoads DD, Alexander JW, Tullos HS. Posterior cruciate function following total knee arthroplasty: A biomechanical study. J Arthroplasty 1994, 9:569-78.

<sup>12</sup> Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement: a systematic literature review within the Cochrane framework. Acta Orthop 2005; 76:757-768.

<sup>13</sup> Maruyama S, Yoshiya S, Matsui N, Kuroda R, Kurosaka M. Functional comparison of posterior

cruciate retaining versus posterior stabilized total knee arthroplasty. J Arthroplasty 2004; 19:349-353. 14 Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement: a systematic literature review within the Cochrane framework. Acta Orthop 2005; 76:757-768.

Posterior Stabilized Total Knee Arthroplasty 235

constant size for each femoral component size.20 The consequence is that there will be a relatively large notch cut for a small femoral component greatly weakening the condyle and increasing the risk of femoral condyle bone loss and periprosthetic fracture. Surgeons who chose to use posterior stabilized TKA should familiarize themselves with relative "box" cut volume to avoid intra-operative and post-operative periprosthetic fractures, especially in

Patella clunk is a complication that is more prevalent in posterior stabilized TKA designs. A prominent fibrous nodule can form at the junction of the proximal patellar pole and the quadriceps tendon. During deep flexion, this fibrous nodule can "catch" in the intercondylar notch of the femoral component causing a catching sensation on the end of the groove as the patella moves back with knee extension. It is this catching and then forceful release with extension that results in the "clunk" and pain characteristic of this condition.21 Recommended treatment consists of physical therapy and arthroscopic debridement. Arthrotomy and possible revision surgery is reserved for recurrent clunks, malposition or

One of the disadvantages of posterior stabilized TKA is the potential for dislocation in flexion as the tibial post rides underneath the femoral cam. This occurs when there is significant extension-flexion gap mismatch. More specifically, dislocations occur when the flexion gap is larger than the corresponding extension gap, allowing the post to "jump" over the cam. The incidence of dislocation with posterior stabilized TKA is very rare with modern designs (0.2%).23 To prevent knee dislocation it is mandatory that the surgeon balance the knee both in flexion and extension. When dislocation occurs, closed and sometimes open reduction is required. If recurrent dislocation occurs, revision surgery to

The "deep-dish" tibial insert, introduced by Hoffman et al in 2000, is an alternative to the cam post posterior stabilized TKA design. This type of design eliminated the need for resection of the intercondylar notch bone stock and use of a tibial post. AP stability is achieved by using highly conforming tibial inserts with anterior build-up24. Some advantages of this ultra-congruent design include: bone preservation by eliminating the

20 Haas S, Nelson C, Laskin R. Posterior stabilized TKA: an assessment of bone resection. The Knee 2000;

21 Hozack WJ, Rothman RH, Booth RE Jr, Balderston RA. The patellar clunk syndrome. A complication of posterior stabilized total knee arthroplasty. Clin Orthop Relat Res 1989; 241:203-208. 22 Beight JL, Yao B, Hozack WJ, et al. The patellar 'clunk' syndrome after posterior stabilized total knee

23 Lombardi AV Jr, Mallory TH, Vaughn BK, et al. Dislocation following primary posterior-stabilized

24 Hofmann AA, Tkach TK, Evanich CJ, Camargo MP: Posterior stabilization in total knee arthroplasty

with use of an ultracongruent polyethylene insert. J Arthroplasty 2000;15:576-583

small, osteoporotic femurs.

**4.3 Patellar clunk**

loose components.22

7: 25-29.

**4.4 Tibio-femoral dislocations**

correct flexion extension mismatch is imperative.

arthroplasty. Clin Orthop Relat Res 1994; 299:139-142.

total knee arthroplasty. J Arthroplasty 1993; 8:633-639.

**5. Alternative to cam post design**

tibial inserts have been reported.15 16 Additionally, technical issues may contribute to wear in cruciate retaining TKA if the PCL is left too tight in flexion. This can lead to asymmetric posterior polyethylene wear from posterior femoral subluxation and may predispose to osteolysis.

## **3.5 Avoiding the possibility of posterior cruciate ligament rupture**

The PCL can rupture postoperatively with the use of cruciate retaining TKA. This can occur by trauma or inflammatory disease process. Late flexion instability can occur if the PCL fails over time. This complication can also occur iatrogenically when the PCL it is overzealously recessed intraoperatively or excessive proximal tibial resection is perfomed. When too much proximal tibia is resected, the PCL insertion site can be jeopardized. The PCL can also be is damaged by synovitis from inflammatory arthropathy, resulting in failure.17 Thus, avoiding the use PCL retaining implants can eliminate failure and instability by avoiding reliance on the integrity of the native PCL.

## **4. Disadvantages of posterior stabilized TKA**

There are several disadvantages with use of posterior stabilized TKA designs. These include: I) tibial post wear and breakage, II) excessive bone resection, III) patellar clunk syndrome, and IV) tibio-femoral dislocations.

## **4.1 Tibial post wear and breakage**

A potential problem with posterior stabilized design is tibial post polyethylene wear from the cam-post articulation. Excessive wear particulate debris can lead to osteolysis. In a wear analysis of retrieved posterior stabilized TKA components, evidence of wear or damage was observed on all specimens of stabilizing posts, including those revised because of infection.18 Wear caused premature failure and early revision. Moreover, wear can lead to catastrophic failure of the tibial post through fracture. The authors concluded that the cam-post articulation in posterior stabilized implants can be an additional source of polyethylene wear debris. The variability in wear patterns observed among designs may be due to differences in cam-post mechanics, post location, and post geometry. 19

#### **4.2 Excessive bone resection**

It is necessary to remove bone from the intercondylar notch inorder to accommodate the tibial post in most posterior stabilized TKA designs. This obligatory "box" cut can be significant in smaller sized femurs especially is TKA systems where the post remains a

<sup>15</sup> Collier JP, Mayor MB, McNamara JL, et al. Analysis of the failure of 122 polyethylene inserts from uncemented tibial knee components. Clin Orthop Relat Res 1991; 273:232-242.

<sup>16</sup> Kilgus DJ, Moreland JR, Finerman GA, et al. Catastrophic wear of tibial polyethylene inserts. Clin Orthop Relat Res 1991; 273:223-231.

<sup>17</sup> Waslewski GL, Marson BM, Benjamin JB. Early, incapacitating instability of posterior cruciate ligament-retaining total knee arthroplasty. J Arthroplasty 1998; 13:763-767.

<sup>18</sup> Puloski SK, McCalden RW, MacDonald SJ, et al. Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris. J Bone Joint Surg Am 2001; 83A:390-397.

<sup>19</sup> Dolan MM, Kelly NH, Nguyen JT, Wright TM, Haas SB. Implant design influences tibial post wear damage in posterior-stabilized knees. Clin Orthop Relat Res. 2011 Jan;469(1):160-7.

constant size for each femoral component size.20 The consequence is that there will be a relatively large notch cut for a small femoral component greatly weakening the condyle and increasing the risk of femoral condyle bone loss and periprosthetic fracture. Surgeons who chose to use posterior stabilized TKA should familiarize themselves with relative "box" cut volume to avoid intra-operative and post-operative periprosthetic fractures, especially in small, osteoporotic femurs.

### **4.3 Patellar clunk**

234 Recent Advances in Hip and Knee Arthroplasty

tibial inserts have been reported.15 16 Additionally, technical issues may contribute to wear in cruciate retaining TKA if the PCL is left too tight in flexion. This can lead to asymmetric posterior polyethylene wear from posterior femoral subluxation and may predispose to

The PCL can rupture postoperatively with the use of cruciate retaining TKA. This can occur by trauma or inflammatory disease process. Late flexion instability can occur if the PCL fails over time. This complication can also occur iatrogenically when the PCL it is overzealously recessed intraoperatively or excessive proximal tibial resection is perfomed. When too much proximal tibia is resected, the PCL insertion site can be jeopardized. The PCL can also be is damaged by synovitis from inflammatory arthropathy, resulting in failure.17 Thus, avoiding the use PCL retaining implants can eliminate failure and instability by avoiding reliance on

There are several disadvantages with use of posterior stabilized TKA designs. These include: I) tibial post wear and breakage, II) excessive bone resection, III) patellar clunk

A potential problem with posterior stabilized design is tibial post polyethylene wear from the cam-post articulation. Excessive wear particulate debris can lead to osteolysis. In a wear analysis of retrieved posterior stabilized TKA components, evidence of wear or damage was observed on all specimens of stabilizing posts, including those revised because of infection.18 Wear caused premature failure and early revision. Moreover, wear can lead to catastrophic failure of the tibial post through fracture. The authors concluded that the cam-post articulation in posterior stabilized implants can be an additional source of polyethylene wear debris. The variability in wear patterns observed among designs may be due to

It is necessary to remove bone from the intercondylar notch inorder to accommodate the tibial post in most posterior stabilized TKA designs. This obligatory "box" cut can be significant in smaller sized femurs especially is TKA systems where the post remains a

15 Collier JP, Mayor MB, McNamara JL, et al. Analysis of the failure of 122 polyethylene inserts from

16 Kilgus DJ, Moreland JR, Finerman GA, et al. Catastrophic wear of tibial polyethylene inserts. Clin

17 Waslewski GL, Marson BM, Benjamin JB. Early, incapacitating instability of posterior cruciate

18 Puloski SK, McCalden RW, MacDonald SJ, et al. Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris. J Bone Joint Surg Am 2001; 83A:390-397. 19 Dolan MM, Kelly NH, Nguyen JT, Wright TM, Haas SB. Implant design influences tibial post wear

**3.5 Avoiding the possibility of posterior cruciate ligament rupture**

differences in cam-post mechanics, post location, and post geometry. 19

uncemented tibial knee components. Clin Orthop Relat Res 1991; 273:232-242.

ligament-retaining total knee arthroplasty. J Arthroplasty 1998; 13:763-767.

damage in posterior-stabilized knees. Clin Orthop Relat Res. 2011 Jan;469(1):160-7.

osteolysis.

the integrity of the native PCL.

**4. Disadvantages of posterior stabilized TKA**

syndrome, and IV) tibio-femoral dislocations.

**4.1 Tibial post wear and breakage**

**4.2 Excessive bone resection**

Orthop Relat Res 1991; 273:223-231.

Patella clunk is a complication that is more prevalent in posterior stabilized TKA designs. A prominent fibrous nodule can form at the junction of the proximal patellar pole and the quadriceps tendon. During deep flexion, this fibrous nodule can "catch" in the intercondylar notch of the femoral component causing a catching sensation on the end of the groove as the patella moves back with knee extension. It is this catching and then forceful release with extension that results in the "clunk" and pain characteristic of this condition.21 Recommended treatment consists of physical therapy and arthroscopic debridement. Arthrotomy and possible revision surgery is reserved for recurrent clunks, malposition or loose components.22

#### **4.4 Tibio-femoral dislocations**

One of the disadvantages of posterior stabilized TKA is the potential for dislocation in flexion as the tibial post rides underneath the femoral cam. This occurs when there is significant extension-flexion gap mismatch. More specifically, dislocations occur when the flexion gap is larger than the corresponding extension gap, allowing the post to "jump" over the cam. The incidence of dislocation with posterior stabilized TKA is very rare with modern designs (0.2%).23 To prevent knee dislocation it is mandatory that the surgeon balance the knee both in flexion and extension. When dislocation occurs, closed and sometimes open reduction is required. If recurrent dislocation occurs, revision surgery to correct flexion extension mismatch is imperative.

## **5. Alternative to cam post design**

The "deep-dish" tibial insert, introduced by Hoffman et al in 2000, is an alternative to the cam post posterior stabilized TKA design. This type of design eliminated the need for resection of the intercondylar notch bone stock and use of a tibial post. AP stability is achieved by using highly conforming tibial inserts with anterior build-up24. Some advantages of this ultra-congruent design include: bone preservation by eliminating the

<sup>20</sup> Haas S, Nelson C, Laskin R. Posterior stabilized TKA: an assessment of bone resection. The Knee 2000; 7: 25-29.

<sup>21</sup> Hozack WJ, Rothman RH, Booth RE Jr, Balderston RA. The patellar clunk syndrome. A complication

of posterior stabilized total knee arthroplasty. Clin Orthop Relat Res 1989; 241:203-208. 22 Beight JL, Yao B, Hozack WJ, et al. The patellar 'clunk' syndrome after posterior stabilized total knee arthroplasty. Clin Orthop Relat Res 1994; 299:139-142.

<sup>23</sup> Lombardi AV Jr, Mallory TH, Vaughn BK, et al. Dislocation following primary posterior-stabilized total knee arthroplasty. J Arthroplasty 1993; 8:633-639.

<sup>24</sup> Hofmann AA, Tkach TK, Evanich CJ, Camargo MP: Posterior stabilization in total knee arthroplasty with use of an ultracongruent polyethylene insert. J Arthroplasty 2000;15:576-583

Posterior Stabilized Total Knee Arthroplasty 237

versus cruciate retaining designs Joint position sense, the threshold to detect joint motion, and the patient's ability to balance on an unstable platform were assessed prior to and at least 6 months after the operation. They found that after TKA all patients detected motion significantly faster, reproduced joint position with less error and had balance improvement. The group treated with the posterior stabilized TKA more accurately reproduced joint position when the knee was extended from a flexed position. The authors conclude that retention of the PCL does not appear to improve proprioception

At long-term follow-up there appears to be no significant difference in the aseptic loosening rates of posterior stabilized and cruciate retaining TKA designs. The cemented posterior stabilized TKA has a reported 98.1% survival rate at 14 years [19]. In the most recent study Rasquinha *et al.* [20••] reported the long-term results of a series of 150 consecutive posterior stabilized TKA that were performed in 118 patients They found a good to excellent result in 90% of patients at mean follow-up of 12 years. At 12 years, the survival rate was 94.6 ± 4.0% with failure for any reason as the end point and 98.3 ± 2.4% with mechanical failure as the end point. Revision surgery was necessary in five cases: two because of infection, one for

As mentioned above with posterior stabilized TKA if the knee is not properly balanced dislocation in flexion can occur. This a very rare event, and can be avoided with careful balancing of the flexion and extension gaps. In terms of instability, posterior or flexion instability may in fact be a greater, although less recognized, problem with cruciate retaining TKA designs. Rupture of the PCL after surgery can cause pain and disability. Flexion instability can also result when the flexion space is left too loose, resulting in marked anterior-posterior translation of the tibia on the femur in flexion. Pagnano *et al.* [21] reported on 25 cruciate retaining TKAs treated for flexion instability. These patients presented with a typical constellation of symptoms that included a sense of knee instability without true give-way, recurrent knee joint effusions, and anterior knee pain. On exam, these knees had obvious anteroposterior instability when tested at 90° of flexion, and even demonstrated a marked posterior sag sign. They all underwent revision surgery to a posterior stabilized design and 22 of the 25 had significant symptomatic

Most series of patients with varus deformities have shown excellent results after 10-15 years, with either cruciate retaining or posterior stabilized TKA. There is, however, only one comparative study [22] that evaluated the results of cruciate retaining and posterior stabilized implants in the context of severe varus or varus-flexion deformities. In this series, survivorship, range of motion, and pain-related outcomes were worse in patients with fixed varus (or varus-flexion) deformities over 15° who were treated with cruciate retaining devices, compared with patients treated with posterior stabilized implants or with those who did not have such varus deformities and were treated with cruciate

dislocation and two for polyethylene wear and osteolysis.

improvement after revision surgery.

**7.3 Correction of deformity**

retaining devices.

and balance.

**7.1 Loosening**

**7.2 Stability**

need for box cut, elimination of post breakage and wear, elimination of tibio-femoral dislocation and patella clunk syndrome. In addition, the ultracongruent tibial component has the advantage of distributing the loads over a larger surface area of the polyethylene insert, hypothetically limiting and distributing more evenly the loads at the bone—implant interface. Moreover, because femoral box preparation is eliminated, femoral bone stock is preserved, decreasing the potential for fracture and operative time.25 Several studies comparing the stability, range of motion and stair climbing ability found no significant difference with ultracongruent design TKA when compared to traditional cam post design TKA.

## **6. Outcomes**

Despite the dissimilarities between cruciate retaining and posterior stabilized TKA designs, most comparative studies have found no significant differences in function, patient satisfaction, or survivorship of the two designs in unselected patient cohorts.26 We have divided the reported results after posterior stabilized TKA into specific outcomes to facilitate the review. Specific outcomes include the performance of posterior stabilized TKA designs in terms of proprioception, wear, loosening, and stability. Also the results with the use of posterior stabilized TKA in two particular subgroups of patients: varus-flexion deformity and postpatellectomy are included in this section.

## **7. Proprioception**

Proprioception after TKA may be improved with the preservation of the native PCL. Mechanoreceptors have been identified in the native posterior cruciate ligament may aid in feedback mechanism improving proprioception.27 Hystological analysis, however, suggests that marked neurologic degeneration occurs within the posterior cruciate ligament as part of the arthritic process [13]. Clinical studies are not conclusive as to which implant design has better proprioception. Warren *et al.* [14] observed that proprioception improved after TKA with either a posterior stabilized or cruciate retaining design, but suggested that greater improvement occurred in the cruciate retaining group. In contrast, Simmons *et al.* [15] noted that in patients with severe arthritis better postoperative proprioception was obtained with a posterior stabilized TKA. Becker *et al.* [16] compared patients with bilateral paired cruciate retaining and posterior stabilized TKA. Fifty percent of the patients were unable to express a preference for one knee or the other. The other 50% were equally divided between those who preferred the cruciate retaining and those who preferred the posterior stabilized knee. Most recently Swanik *et al.* [17] performed a prospective, randomized study on 20 patients to assess proprioception, kinesthesia, and balance following TKA comparing posterior stabilized

<sup>25</sup> Laskin RS, Maruyama Y, Villaneuva M, Bourne R. Deep-dish congruent tibial component use in total knee arthroplasty: a randomized prospective study. Clin Orthop Relat Res. 200 Nov;(380):36-44.

<sup>26</sup> Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement: a systematic literature review within the Cochrane framework. Acta Orthop 2005; 76:757-768.

<sup>27</sup> Warren PJ, Olanlokun TK, Cobb AG, Bentley G. Proprioception after knee arthroplasty: the influence of prosthetic design. Clin Orthop Relat Res. 1993;297:182-187.

versus cruciate retaining designs Joint position sense, the threshold to detect joint motion, and the patient's ability to balance on an unstable platform were assessed prior to and at least 6 months after the operation. They found that after TKA all patients detected motion significantly faster, reproduced joint position with less error and had balance improvement. The group treated with the posterior stabilized TKA more accurately reproduced joint position when the knee was extended from a flexed position. The authors conclude that retention of the PCL does not appear to improve proprioception and balance.

#### **7.1 Loosening**

236 Recent Advances in Hip and Knee Arthroplasty

need for box cut, elimination of post breakage and wear, elimination of tibio-femoral dislocation and patella clunk syndrome. In addition, the ultracongruent tibial component has the advantage of distributing the loads over a larger surface area of the polyethylene insert, hypothetically limiting and distributing more evenly the loads at the bone—implant interface. Moreover, because femoral box preparation is eliminated, femoral bone stock is preserved, decreasing the potential for fracture and operative time.25 Several studies comparing the stability, range of motion and stair climbing ability found no significant difference with ultracongruent design TKA when compared to traditional cam post design

Despite the dissimilarities between cruciate retaining and posterior stabilized TKA designs, most comparative studies have found no significant differences in function, patient satisfaction, or survivorship of the two designs in unselected patient cohorts.26 We have divided the reported results after posterior stabilized TKA into specific outcomes to facilitate the review. Specific outcomes include the performance of posterior stabilized TKA designs in terms of proprioception, wear, loosening, and stability. Also the results with the use of posterior stabilized TKA in two particular subgroups of patients: varus-flexion

Proprioception after TKA may be improved with the preservation of the native PCL. Mechanoreceptors have been identified in the native posterior cruciate ligament may aid in feedback mechanism improving proprioception.27 Hystological analysis, however, suggests that marked neurologic degeneration occurs within the posterior cruciate ligament as part of the arthritic process [13]. Clinical studies are not conclusive as to which implant design has better proprioception. Warren *et al.* [14] observed that proprioception improved after TKA with either a posterior stabilized or cruciate retaining design, but suggested that greater improvement occurred in the cruciate retaining group. In contrast, Simmons *et al.* [15] noted that in patients with severe arthritis better postoperative proprioception was obtained with a posterior stabilized TKA. Becker *et al.* [16] compared patients with bilateral paired cruciate retaining and posterior stabilized TKA. Fifty percent of the patients were unable to express a preference for one knee or the other. The other 50% were equally divided between those who preferred the cruciate retaining and those who preferred the posterior stabilized knee. Most recently Swanik *et al.* [17] performed a prospective, randomized study on 20 patients to assess proprioception, kinesthesia, and balance following TKA comparing posterior stabilized

25 Laskin RS, Maruyama Y, Villaneuva M, Bourne R. Deep-dish congruent tibial component use in total knee arthroplasty: a randomized prospective study. Clin Orthop Relat Res. 200 Nov;(380):36-44. 26 Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior cruciate ligament in total knee replacement: a systematic literature review within the Cochrane framework. Acta Orthop

27 Warren PJ, Olanlokun TK, Cobb AG, Bentley G. Proprioception after knee arthroplasty: the influence

deformity and postpatellectomy are included in this section.

of prosthetic design. Clin Orthop Relat Res. 1993;297:182-187.

TKA.

**6. Outcomes**

**7. Proprioception**

2005; 76:757-768.

At long-term follow-up there appears to be no significant difference in the aseptic loosening rates of posterior stabilized and cruciate retaining TKA designs. The cemented posterior stabilized TKA has a reported 98.1% survival rate at 14 years [19]. In the most recent study Rasquinha *et al.* [20••] reported the long-term results of a series of 150 consecutive posterior stabilized TKA that were performed in 118 patients They found a good to excellent result in 90% of patients at mean follow-up of 12 years. At 12 years, the survival rate was 94.6 ± 4.0% with failure for any reason as the end point and 98.3 ± 2.4% with mechanical failure as the end point. Revision surgery was necessary in five cases: two because of infection, one for dislocation and two for polyethylene wear and osteolysis.

#### **7.2 Stability**

As mentioned above with posterior stabilized TKA if the knee is not properly balanced dislocation in flexion can occur. This a very rare event, and can be avoided with careful balancing of the flexion and extension gaps. In terms of instability, posterior or flexion instability may in fact be a greater, although less recognized, problem with cruciate retaining TKA designs. Rupture of the PCL after surgery can cause pain and disability. Flexion instability can also result when the flexion space is left too loose, resulting in marked anterior-posterior translation of the tibia on the femur in flexion. Pagnano *et al.* [21] reported on 25 cruciate retaining TKAs treated for flexion instability. These patients presented with a typical constellation of symptoms that included a sense of knee instability without true give-way, recurrent knee joint effusions, and anterior knee pain. On exam, these knees had obvious anteroposterior instability when tested at 90° of flexion, and even demonstrated a marked posterior sag sign. They all underwent revision surgery to a posterior stabilized design and 22 of the 25 had significant symptomatic improvement after revision surgery.

#### **7.3 Correction of deformity**

Most series of patients with varus deformities have shown excellent results after 10-15 years, with either cruciate retaining or posterior stabilized TKA. There is, however, only one comparative study [22] that evaluated the results of cruciate retaining and posterior stabilized implants in the context of severe varus or varus-flexion deformities. In this series, survivorship, range of motion, and pain-related outcomes were worse in patients with fixed varus (or varus-flexion) deformities over 15° who were treated with cruciate retaining devices, compared with patients treated with posterior stabilized implants or with those who did not have such varus deformities and were treated with cruciate retaining devices.

Posterior Stabilized Total Knee Arthroplasty 239

[1] Stiehl JB, Komistek RD, Dennis DA, *et al*. Fluoroscopic analysis of kinematics after

[2] Dennis DA, Komistek RD, Hoff WA. In vivo knee kinematics derived using an inverse

[3] Ranawat CS, Komistek RD, Rodriguez JA, *et al*. *In vivo* kinematics for fixed and mobile-

[4] Jacobs WC, Clement DJ, Wymenga AB. Retention versus removal of the posterior

[5] Collier JP, Mayor MB, McNamara JL, *et al*. Analysis of the failure of 122 polyethylene

[6] Kilgus DJ, Moreland JR, Finerman GA, *et al*. Catastrophic wear of tibial polyethylene

[7] Waslewski GL, Marson BM, Benjamin JB. Early, incapacitating instability of posterior

[8] Puloski SK, McCalden RW, MacDonald SJ, *et al*. Tibial post wear in posterior stabilized

[9] Hozack WJ, Rothman RH, Booth RE Jr, Balderston RA. The patellar clunk syndrome. A

[10] Beight JL, Yao B, Hozack WJ, *et al*. The patellar 'clunk' syndrome after posterior stabilized total knee arthroplasty. Clin Orthop Relat Res 1994; 299:139-142. [11] Lombardi AV Jr, Mallory TH, Vaughn BK, *et al*. Dislocation following primary posterior-stabilized total knee arthroplasty. J Arthroplasty 1993; 8:633-639. [12] Fantozzi S, Catani F, Ensini A, *et al*. Femoral rollback of cruciate-retaining and

[13] Kleinbart FA, Bryk E, Evangelista J, *et al*. Histologic comparison of posterior cruciate

[14] Warren PI, Olanlokun TK, Cobb AG, Bentley G. Proprioception after knee arthroplasty:

[15] Simmons S, Lephart S, Rubash H, *et al*. Proprioception after unicondylar knee arthroplasty versus total knee arthroplasty. Clin Orthop 1996; 331:179-184. [16] Becker MW, Insall JN, Faris PM. Bilateral total knee arthroplasty: one cruciate retaining

[17] Swanik CB, Lephart SM, Rubash HE. Proprioception, kinesthesia, and balance after

total knee arthroplasty with cruciate-retaining and posterior stabilized prostheses. J

The influence of prosthetic design. Clin Orthop 1993; 297:182-187.

and one cruciate substituting. Clin Orthop 1990; 271:122-124.

Bone Joint Surg Am 2004; 86A:328-334.

perspective technique. Clin Orthop 1996; 331:107-117.

the Cochrane framework. Acta Orthop 2005; 76:757-768.

activities of daily living. J Orthop Res 2006; 24:2222-2229.

inserts. Clin Orthop Relat Res 1991; 273:223-231.

Joint Surg Am 2001; 83A:390-397.

posterior cruciate retaining knee arthroplasty. J Bone Joint Surg Br 1995; 77B:884-

bearing posterior stabilized knee prostheses. Clin Orthop Relat Res 2004; 418:184-

cruciate ligament in total knee replacement: a systematic literature review within

inserts from uncemented tibial knee components. Clin Orthop Relat Res 1991;

cruciate ligament-retaining total knee arthroplasty. J Arthroplasty 1998; 13:763-767.

total knee arthroplasty. An unrecognized source of polyethylene debris. J Bone

complication of posterior stabilized total knee arthroplasty. Clin Orthop Relat Res

posterior-stabilized total knee replacements: *in vivo* fluoroscopic analysis during

ligaments from arthritic and age matched knee specimens. J Arthroplasty 1996;

**10. References**

889.

190.

273:232-242.

1989; 241:203-208.

6:726-731.

### **7.4 Postpatellectomy patients**

Most authors suggest that a posterior stabilized design is most appropriate in patients with previous patellectomy. The tibial post and femoral cam mechanism limits the posterior translation of the tibia that can occur without the patella. Patellectomy leads to the disruption of the normal kinematics of the knee. In the context of knee replacement, it has been hypothesized that loads on the PCL in the years following surgery may be increased, potentially resulting in late attenuation and instability [23,24]. Patellectomy also can cause decreased extensor mechanism power because of the loss of the fulcrum provided by the intact patella. A retrospective study showed that patellectomized patients treated with posterior stabilized implants had better functional and pain scores than did those treated with cruciate retaining implants [23]. In comparison to cruciate retaining designs, posterior stabilized devices lead to better results when TKA is performed in patients with prior patellectomies [25].

## **8. Rheumatoid arthritis**

Total knee arthroplasty is a proven technique for the management of deformity and unremitting pain in the rheumatoid arthritic knee. Many important considerations must be taken into account in order to maximize the results of total knee replacement in this challenging patient population. In a retrospective study, Laskin et al28 reported that cruciate retaining implants in patients with rheumatoid arthritis were associated with inferior results compared with posterior stabilized implants, principally because of late instability and progressive recurvatum deformity. The tendency for generalized ligamentous laxity and attenuation and joint deformity in these patients make successful TKA difficult with PCL retaining designs. These patients may present with severe or fixed valgus deformities. Most patients with rheumatoid arthritis typically have poor quality of the soft tissues and the potential for synovitis to cause late attenuation and rupture of the PCL.

## **9. Conclusion**

The use of posterior stabilized TKA has several advantages. Potential benefits of a posterior stabilized TKA over a cruciate retaining TKA include easier surgical exposure and ligament balancing, predictable restoration of knee kinematics, improved range of motion, less wear, and avoiding the possibility of PCL rupture. In addition, the use of posterior stabilized TKA appears to be advantageous in correction of severe varus – valgus deformity. A potential problem with posterior stabilized TKA is tibial post polyethylene wear from the cam-post mechanism. Excessive wear can lead not only to osteolysis but also post fracture. Other disadvantage of posterior stabilized TKA is patellar 'clunk' syndrome, risk of dislocation or flexion instability and bone loss and peri-prosthetic condylar fracture. Despite the dissimilarities between cruciate retaining and posterior stabilized TKA designs, most studies have found no significant differences in function, patient satisfaction, or survivorship of the two designs in unselected patient cohorts. Posterior stabilized TKA outcomes appear to be better in a particular subgroup of patients including patients with patellectomy, large varus or varus-flexion deformity, and rheumatoid arthritis.

 28 Laskin RS, O'Flynn HM. The Insall Award. Total knee replacement with posterior cruciate ligament retention in rheumatoid arthritis: Problems and complications. Clin Orthop 1997; 345:24-28.

#### **10. References**

238 Recent Advances in Hip and Knee Arthroplasty

Most authors suggest that a posterior stabilized design is most appropriate in patients with previous patellectomy. The tibial post and femoral cam mechanism limits the posterior translation of the tibia that can occur without the patella. Patellectomy leads to the disruption of the normal kinematics of the knee. In the context of knee replacement, it has been hypothesized that loads on the PCL in the years following surgery may be increased, potentially resulting in late attenuation and instability [23,24]. Patellectomy also can cause decreased extensor mechanism power because of the loss of the fulcrum provided by the intact patella. A retrospective study showed that patellectomized patients treated with posterior stabilized implants had better functional and pain scores than did those treated with cruciate retaining implants [23]. In comparison to cruciate retaining designs, posterior stabilized devices lead to better results when TKA is performed in patients with prior

Total knee arthroplasty is a proven technique for the management of deformity and unremitting pain in the rheumatoid arthritic knee. Many important considerations must be taken into account in order to maximize the results of total knee replacement in this challenging patient population. In a retrospective study, Laskin et al28 reported that cruciate retaining implants in patients with rheumatoid arthritis were associated with inferior results compared with posterior stabilized implants, principally because of late instability and progressive recurvatum deformity. The tendency for generalized ligamentous laxity and attenuation and joint deformity in these patients make successful TKA difficult with PCL retaining designs. These patients may present with severe or fixed valgus deformities. Most patients with rheumatoid arthritis typically have poor quality of the soft tissues and the

The use of posterior stabilized TKA has several advantages. Potential benefits of a posterior stabilized TKA over a cruciate retaining TKA include easier surgical exposure and ligament balancing, predictable restoration of knee kinematics, improved range of motion, less wear, and avoiding the possibility of PCL rupture. In addition, the use of posterior stabilized TKA appears to be advantageous in correction of severe varus – valgus deformity. A potential problem with posterior stabilized TKA is tibial post polyethylene wear from the cam-post mechanism. Excessive wear can lead not only to osteolysis but also post fracture. Other disadvantage of posterior stabilized TKA is patellar 'clunk' syndrome, risk of dislocation or flexion instability and bone loss and peri-prosthetic condylar fracture. Despite the dissimilarities between cruciate retaining and posterior stabilized TKA designs, most studies have found no significant differences in function, patient satisfaction, or survivorship of the two designs in unselected patient cohorts. Posterior stabilized TKA outcomes appear to be better in a particular subgroup of patients including patients with

potential for synovitis to cause late attenuation and rupture of the PCL.

patellectomy, large varus or varus-flexion deformity, and rheumatoid arthritis.

retention in rheumatoid arthritis: Problems and complications. Clin Orthop 1997; 345:24-28.

28 Laskin RS, O'Flynn HM. The Insall Award. Total knee replacement with posterior cruciate ligament

**7.4 Postpatellectomy patients**

patellectomies [25].

**9. Conclusion**

**8. Rheumatoid arthritis**

**17**

*Israel*

**Mobile Bearing Concept in**

Arnan Greental1 and Michael Soudry1,2

*2Ruth and Bruce Rappaport Faculty of Medicine, Technion – Israel Institute of Technology, Haifa*

The rationale for mobile bearing design of knee replacement prosthesis is to increase its survival by reducing the rate of aseptic loosening and to improve the range of movement of the treated knee. The theoretical basis for the achievement of the first goal is the expected lower rates of the polyethylene insert wear in the mobile design in comparison to a fixed design, due to lower contact and constraint forces. A better range of movements following mobile bearing arthroplasty is expected as the result of additional moving surface between to fixed planes at the ends of the articulating bones, allowing mobility with congruency.These expected advantages of the mobile bearing design should be judged cautiously since the initial mobile bearing implants caused higher rates of breakage and disarrangement of the polyethylene inserts, when the implantation method wasn't strictly followed. In order to resolve these technical problems the rotating platform

Mobile bearing concept was implemented in a three compartment replacement prostheses and also in unicompartamental designs, especially for the medial compartment of the knee. Currently, following the more than two decades of the rising experience with implantation of a large number of mobile bearing prostheses, there is a significant amount of data for evaluation of the survival of these prosthetic designs. In order to declare on their higher expected efficiency these implants should show higher than 96-97% of ten year clinical survival, which should remain relatively stable up to 20 years of follow up, as reported in the several of fixed bearing designs. Unfortunately this data is not readily available, because only few well designed survivorship reports on mobile knee implants have been published yet. Furthermore the published data failed to provide a clear

The endoprosthetic arthroplasty is the most popular surgical modality for treatment of advanced knee joint disease, either degenerative or inflammatory. The reason for this clinical trend is the ability to reduce pain and to restore the patient's ability to walk.

**1. Introduction**

mobile prosthesis was developed.

evidence of the superiority of mobile bearing design.

**Knee Arthroplasty**

*1Orthopaedic Surgery "A" Dept., Rambam – Health Care Campus, Haifa*

Nahum Rosenberg1,2,

## **Mobile Bearing Concept in Knee Arthroplasty**

Nahum Rosenberg1,2, Arnan Greental1 and Michael Soudry1,2 *1Orthopaedic Surgery "A" Dept., Rambam – Health Care Campus, Haifa 2Ruth and Bruce Rappaport Faculty of Medicine, Technion – Israel Institute of Technology, Haifa Israel*

### **1. Introduction**

240 Recent Advances in Hip and Knee Arthroplasty

[18] Scott RD, Thornhill TS. Posterior cruciate supplementing total knee replacements using

[19] Colizza WA, Insall JN, Scuderi GR. The posterior stabilized total knee prosthesis:

[20] Rasquinha VJ, Ranawat CS, Cervieri CL, Rodriguez JA. The press-fit condylar modular

[24] Cameron HU, Hu C, Vyamont D. Posterior stabilized knee prosthesis for total knee replacement in patients with prior patellectomy. Can J Surg 1996; 39:469-473. [25] Bayne O, Cameron HU. Total knee arthroplasty following patellectomy. Clin Orthop

[26] Laskin RS, O'Flynn HM. The Insall Award. Total knee replacement with posterior

cruciate ligament retention in rheumatoid arthritis: Problems and complications.

radiolucent lines. Clin Orthop 1994; 309:146-149.

Joint Surg Am 1995; 77A:1708-1712.

1984; 186:112-114.

Clin Orthop 1997; 345:24-28.

follow-up. J Bone Joint Surg Am 1995; 77A:1713-1720.

conforming inserts and cruciate recession: effect on range of motion and

Assessment of polyethylene damage and osteolysis after a 10-year minimum

total knee system with a posterior cruciate-substituting design. A concise follow-up of a previous report. J Bone Joint Surg Am 2006; 88A:1006-1010. This was a longterm follow-up study with 118 patients that had a posterior stabilized TKA. [21] Pagnano MW, Hanssen AD, Stuart MJ, Lewallen DG. Flexion instability after primary posterior cruciate retaining total knee arthroplasty. Clin Orthop 1998; 356:39-46. [22] Laskin RS. The Insall Award. Total knee replacement with posterior cruciate ligament retention in patients with a fixed varus deformity. Clin Orthop 1996; 331:29-34. [23] Paletta GA Jr, Laskin RS. Total knee arthroplasty after a previous patellectomy. J Bone

> The rationale for mobile bearing design of knee replacement prosthesis is to increase its survival by reducing the rate of aseptic loosening and to improve the range of movement of the treated knee. The theoretical basis for the achievement of the first goal is the expected lower rates of the polyethylene insert wear in the mobile design in comparison to a fixed design, due to lower contact and constraint forces. A better range of movements following mobile bearing arthroplasty is expected as the result of additional moving surface between to fixed planes at the ends of the articulating bones, allowing mobility with congruency.These expected advantages of the mobile bearing design should be judged cautiously since the initial mobile bearing implants caused higher rates of breakage and disarrangement of the polyethylene inserts, when the implantation method wasn't strictly followed. In order to resolve these technical problems the rotating platform mobile prosthesis was developed.

> Mobile bearing concept was implemented in a three compartment replacement prostheses and also in unicompartamental designs, especially for the medial compartment of the knee. Currently, following the more than two decades of the rising experience with implantation of a large number of mobile bearing prostheses, there is a significant amount of data for evaluation of the survival of these prosthetic designs. In order to declare on their higher expected efficiency these implants should show higher than 96-97% of ten year clinical survival, which should remain relatively stable up to 20 years of follow up, as reported in the several of fixed bearing designs. Unfortunately this data is not readily available, because only few well designed survivorship reports on mobile knee implants have been published yet. Furthermore the published data failed to provide a clear evidence of the superiority of mobile bearing design.

> The endoprosthetic arthroplasty is the most popular surgical modality for treatment of advanced knee joint disease, either degenerative or inflammatory. The reason for this clinical trend is the ability to reduce pain and to restore the patient's ability to walk.

Mobile Bearing Concept in Knee Arthroplasty 243

mechanical properties of the bearing insert. For this reason this method is of limited role

Therefore other tribulogical factors should be addressed in order to reduce the cross shear and surface pressure of the polyethylene insert. High conformation between the femoral and tibial surfaces in the prosthesis can reduce the surface pressure and polyethylene wear. But in fixed bearing design the elevation of conformation causes restriction in the range of movement of the knee. Therefore in the fixed bearing prostheses some unconformity is deliberately allowed in order to provide a reasonable range of knee

Another mechanical concept to reduce the bearing component wear, which is mainly induced by the high point and line contact forces between moving metal femoral component and static polyethylene tibial insert, has been developed . By this concept an "area" contact pattern has been introduced (7). The rationale of the "area" contact pattern is based on the assumption that the forces between the prostheses components may be distributed more efficiently by using a mobile bearing polyethylene insert (8). Subsequently the hypothetical advantage is in reduction of material wear and elimination

According to this concept Pappas MJ and Buechel FF developed a total knee prosthesis with mobile bearing (7), and Goodfellow JW and O'Connor J developed the unicompartamental

The expectation from the later unicompartamental design was to develop a prosthetic method that will replace the technically demanding osteotomies in younger patients with unicompartamental degenerative disease. This goal was achieved only partially, since the unicompartamental design could be successful only in patients who answer to the very strict

The former, LCS® mobile meniscal bearing total knee replacement system, has been designed to lower contact stress with preservation of the crucial low constraint properties. Initially after the introduction of this system for the widespread clinical use in 1977-80 one large multicenter (10) and three independent (11,12,13) middle term follow up studies have been published showing favorable subjective outcome results in 90-97.5% of patients with 94.6 – 95.3% of six to eight years survivorship of cementless LCS® mobile bearing posterior cruciate retaining prostheses. These outcome results are close to the survivorship data reported by the system designers, that showed 97.9% and 95.1% of five and twelve years

Conversely there have been a number of reports of high rate mechanical failures of the LCS® system (8,15). These short term follow up studies showed a tendency for mobile bearing dislocation and breakage. These findings can also be supported by cadaveric biomechanical testing (16). Thus the potential susceptibility of LCS® posterior cruciate retaining design for early mechanical failure may overcome the benefits of long term low loosening rates. In an additional later report on a medium term experience with 35 cementless LCS® mobile meniscal bearing total knee replacements in patients with osteoarthritis there was an evidence of 97.1% five year survivorship (17). This high survival rate, with a satisfactory functional outcome, at middle term follow up, has been achieved by following an optimal technique of implantation, according to the designers recommendations, i.e. the tibial component should be situated perpendicularly to

in the knee prostheses.

of aseptic loosening (Figure 1).

clinical and radiographic criteria.

survivorship rates respectively (14).

mobile bearing "Oxford Knee" design (9).

movement.

Although it has been shown that the improvement in ambulation, following knee arthroplasty, is mostly subjective, because other restrictions of a capacity to walk might be revealed following elimination of the pain in the knee (1), the reduction of the pain level while walking is considered by the patients as a significant improvement in the quality of life. For this reason a major effort is exerted by the clinicians and the industry to develop the most effective surgical techniques and prosthetic designs aiming to improve immediate postsurgical outcome of knee prosthetic arthroplasty and the longevity of the implanted prostheses. Several of the currently used prosthetic designs have already reached long term, above 10 years, survivorship of above 95%, therefore the "straggle" for the improvement in the prostheses longevity is aimed to the marginal 5% improvement of long term survivorship following the implantation by reducing the prostheses failure rate in long time scale. The success of this multidisciplinary effort of clinicians and engineers can't be overemphasized because the success will not only eliminate the need for revision surgery in patients, who are mostly in the age above sixty years, because of the expected prostheses' longevity consideration, but also will provide a prosthetic solutions for the younger patients with degenerative knees, who seek for a better treatment modality for their disability.

Therefore logically the widely used generic design of unconstrained knee prosthesis, with metal femoral component and polyethylene insert fixed on metal back-plate on tibia, with cemented or cementless fixation into articulating surfaces, should be improved in one or in several of its components in order to improve its long term clinical performance . Clearly these considerations do not related to the short term prosthetic failures, which are mostly attributed to a basically fault prosthetic design, as observed in the early constrained prostheses (2), to deficient surgical technique or to a complicated general medical condition of the patient that might lead to the prosthesis disarrangement, peri-prosthetic fracture or local infection.

Long standing clinical success of prosthetic knee replacement is dependent on the ability to provide stability with good range of movement, to resist the loosening processes and to provide material longevity of all prosthetic components. Near satisfactory range of movement and stability have been successfully achieved with widely used fixed bearing designs, however, component loosening remains their main long term problem (3,4). Although the early loosening processes, common in the original constrained designs, have been eliminated in the second generation unconstrained prostheses, late loosening, due to osteolysis caused by polyethylene wear of the fixed tibial bearings, remains unresolved (5). Therefore it is logical that the main target that should be addresses in order to reduce the late aseptic loosening of the knee prostheses would be the polyethylene insert and its susceptibility for wear following long standing and continuous exposure to compressing forces from the adjacent metal components. One of the steps for reducing the polyethylene wear was directed to improve the material characteristics of the polyethylene in order to avoid the free radicals release during the gamma sterilization by using a manufacturer process with high temperature towards the melting point with crosslinking induction and generation of ultrahigh molecular weight polyethylene that reduces the plastic insert susceptibility to mechanical wear (6). A high level of crosslinking had been used in several acetabular polyethylene designs in the last decade and showed less surface wear but, on the other hand, presented alteration in the

Although it has been shown that the improvement in ambulation, following knee arthroplasty, is mostly subjective, because other restrictions of a capacity to walk might be revealed following elimination of the pain in the knee (1), the reduction of the pain level while walking is considered by the patients as a significant improvement in the quality of life. For this reason a major effort is exerted by the clinicians and the industry to develop the most effective surgical techniques and prosthetic designs aiming to improve immediate postsurgical outcome of knee prosthetic arthroplasty and the longevity of the implanted prostheses. Several of the currently used prosthetic designs have already reached long term, above 10 years, survivorship of above 95%, therefore the "straggle" for the improvement in the prostheses longevity is aimed to the marginal 5% improvement of long term survivorship following the implantation by reducing the prostheses failure rate in long time scale. The success of this multidisciplinary effort of clinicians and engineers can't be overemphasized because the success will not only eliminate the need for revision surgery in patients, who are mostly in the age above sixty years, because of the expected prostheses' longevity consideration, but also will provide a prosthetic solutions for the younger patients with degenerative knees, who seek for a better treatment modality for

Therefore logically the widely used generic design of unconstrained knee prosthesis, with metal femoral component and polyethylene insert fixed on metal back-plate on tibia, with cemented or cementless fixation into articulating surfaces, should be improved in one or in several of its components in order to improve its long term clinical performance . Clearly these considerations do not related to the short term prosthetic failures, which are mostly attributed to a basically fault prosthetic design, as observed in the early constrained prostheses (2), to deficient surgical technique or to a complicated general medical condition of the patient that might lead to the prosthesis disarrangement, peri-prosthetic fracture or

Long standing clinical success of prosthetic knee replacement is dependent on the ability to provide stability with good range of movement, to resist the loosening processes and to provide material longevity of all prosthetic components. Near satisfactory range of movement and stability have been successfully achieved with widely used fixed bearing designs, however, component loosening remains their main long term problem (3,4). Although the early loosening processes, common in the original constrained designs, have been eliminated in the second generation unconstrained prostheses, late loosening, due to osteolysis caused by polyethylene wear of the fixed tibial bearings, remains unresolved (5). Therefore it is logical that the main target that should be addresses in order to reduce the late aseptic loosening of the knee prostheses would be the polyethylene insert and its susceptibility for wear following long standing and continuous exposure to compressing forces from the adjacent metal components. One of the steps for reducing the polyethylene wear was directed to improve the material characteristics of the polyethylene in order to avoid the free radicals release during the gamma sterilization by using a manufacturer process with high temperature towards the melting point with crosslinking induction and generation of ultrahigh molecular weight polyethylene that reduces the plastic insert susceptibility to mechanical wear (6). A high level of crosslinking had been used in several acetabular polyethylene designs in the last decade and showed less surface wear but, on the other hand, presented alteration in the

their disability.

local infection.

mechanical properties of the bearing insert. For this reason this method is of limited role in the knee prostheses.

Therefore other tribulogical factors should be addressed in order to reduce the cross shear and surface pressure of the polyethylene insert. High conformation between the femoral and tibial surfaces in the prosthesis can reduce the surface pressure and polyethylene wear. But in fixed bearing design the elevation of conformation causes restriction in the range of movement of the knee. Therefore in the fixed bearing prostheses some unconformity is deliberately allowed in order to provide a reasonable range of knee movement.

Another mechanical concept to reduce the bearing component wear, which is mainly induced by the high point and line contact forces between moving metal femoral component and static polyethylene tibial insert, has been developed . By this concept an "area" contact pattern has been introduced (7). The rationale of the "area" contact pattern is based on the assumption that the forces between the prostheses components may be distributed more efficiently by using a mobile bearing polyethylene insert (8). Subsequently the hypothetical advantage is in reduction of material wear and elimination of aseptic loosening (Figure 1).

According to this concept Pappas MJ and Buechel FF developed a total knee prosthesis with mobile bearing (7), and Goodfellow JW and O'Connor J developed the unicompartamental mobile bearing "Oxford Knee" design (9).

The expectation from the later unicompartamental design was to develop a prosthetic method that will replace the technically demanding osteotomies in younger patients with unicompartamental degenerative disease. This goal was achieved only partially, since the unicompartamental design could be successful only in patients who answer to the very strict clinical and radiographic criteria.

The former, LCS® mobile meniscal bearing total knee replacement system, has been designed to lower contact stress with preservation of the crucial low constraint properties. Initially after the introduction of this system for the widespread clinical use in 1977-80 one large multicenter (10) and three independent (11,12,13) middle term follow up studies have been published showing favorable subjective outcome results in 90-97.5% of patients with 94.6 – 95.3% of six to eight years survivorship of cementless LCS® mobile bearing posterior cruciate retaining prostheses. These outcome results are close to the survivorship data reported by the system designers, that showed 97.9% and 95.1% of five and twelve years survivorship rates respectively (14).

Conversely there have been a number of reports of high rate mechanical failures of the LCS® system (8,15). These short term follow up studies showed a tendency for mobile bearing dislocation and breakage. These findings can also be supported by cadaveric biomechanical testing (16). Thus the potential susceptibility of LCS® posterior cruciate retaining design for early mechanical failure may overcome the benefits of long term low loosening rates. In an additional later report on a medium term experience with 35 cementless LCS® mobile meniscal bearing total knee replacements in patients with osteoarthritis there was an evidence of 97.1% five year survivorship (17). This high survival rate, with a satisfactory functional outcome, at middle term follow up, has been achieved by following an optimal technique of implantation, according to the designers recommendations, i.e. the tibial component should be situated perpendicularly to

Mobile Bearing Concept in Knee Arthroplasty 245

longitudinal axis of tibial metaphysis with 5 O - 10 O of posterior inclination relatively to the anatomical axis of tibia in the sagittal plane, the sagittal flexion angle of the femoral component should be close to 5 O relatively to the anatomical axis of femur and overall coronal alignment of the components should be around 5 O of valgus (18). The average three dimensional component alignment in this study group has not deviated more than 3 O from the recommended by the designers' optimal orientation. Therefore it might be suggested that the high survival rates of the prosthesis and good functional outcome in the majority of evaluated patients in this study should be attributed to the effective surgical technique. This was reflected by the satisfactory functional knee scores in 77% and complete pain elimination in 89% of the evaluated knees. Therefore there is evidence that in the middle term the mobile bearing design of total knee replacement can be as effective as the conventional fixed bearing designs. Additional reports on short and middle term outcome of knee replacement with LCS® mobile meniscal bearing cementless design revealed rates of aseptic loosening in the range of 0.4 – 1.8% (8,14), which are compatible with most of the effective fixed bearing designs (19). However, the real advantage of mobile bearing system in reducing the rate of osteolysis should be established in the long term survivorship

The emerged susceptibility of mobile bearing meniscal surfaces to early failure due to dislocation or breakage (8) may provoke a reasonable hesitation to its widespread use. Although the designers of the LCS® mobile meniscal bearing prosthesis claimed that strict operative technique and precise prosthetic placement should avoid its mechanical failure (18), there are only few independent studies that support this claim by showing 0.6% rate of meniscal bearing failure in 2 – 10 years of follow up (13, 17). And on the other hand there is some evidence that greater deviation from the desired three dimensional placement of the mobile bearing prosthesis does not significantly reduce its 10 years survivorship and preferable functional outcome (20). Therefore there is no clear evidence of the precise precise factors contributing to the mobile inserts

In order to reduce the revealed possibility of mechanical failure of meniscal type mobile bearings, a more stable "rotating platform" mobile polyethylene bearing was designed. In this design a single polyethylene insert, without rotational constraint, was used. The rotating platform knee is assumed to follow the normal femoral rotation upon the tibial axis during knee flexion, which is normally between 160-230 degrees (21). But it was found that the measured rotation of the bearing surface in the implanted prostheses is significantly less than expected, e.g. only in 12% of the knees there was more than 10

Additional theoretical advantage of a mobile bearing prosthesis is the expected better patellar tracking due to the self-alignment of the mobile bearing. But this assumption has not been proven in patients, because there was no clinical evidence of a diminished post-

The cautious approach for the efficiency of mobile bearing prostheses is even supported by the results of their biomechanical testing. It has been shown by a simulator based experiment, utilizing six million cycles of repetitive testing of prosthesis movement of mobile bearing designs with rotating platform and one fixed bearing implant, that there was

operative anterior knee pain even in the first year after surgery (22).

no difference in the amount of in vitro wear (23).

studies.

disarrangement.

degrees of rotation.

A: A schematic representation of vectors of forces on a unit of polyethylene tibial insert in a sagittal plane during knee loading. Blue arrows are the vectors of forces in fixed bearing design and red arrows in a mobile bearing insert, where less magnitude of force from the peripheral constrain should reduce the overall magnitude of force and to reduce the development of the polyethylene insert wear, as represented in B.

A

B: Reprehensive example of an advanced wear of a polyethylene insert of a fixed bearing design. Fig. 1. Rationale for mobile bearing concept in knee arthroplasty prosthesis:

A A: A schematic representation of vectors of forces on a unit of polyethylene tibial insert in a sagittal plane during knee loading. Blue arrows are the vectors of forces in fixed bearing design and red arrows in a mobile bearing insert, where less magnitude of force from the peripheral constrain should reduce the overall magnitude of force and to reduce the development of the polyethylene insert wear, as

B

B: Reprehensive example of an advanced wear of a polyethylene insert of a fixed bearing design.

Fig. 1. Rationale for mobile bearing concept in knee arthroplasty prosthesis:

represented in B.