Differences in long-term fixation between mobile-bearing and fixed-bearing knee prostheses at ten to 12 years' follow-up: a single-blinded randomised controlled radiostereometric trial. A prospective randomised study comparing rotating platform and fixed bearing total knee arthroplasty in a cruciate substituting design--outcomes at two year follow-up. Gait analysis of fixed bearing and mobile bearing total knee prostheses during walking: do mobile bearings offer functional advantages? Long-term comparison of fixed-bearing and mobile-bearing total knee replacements in patients younger than fifty-one years of age with osteoarthritis. Comparison of Fixed-Bearing and Mobile-Bearing Total Knee Arthroplasties Mobile-bearing prosthesis did not improve mid-term clinical results of total knee arthroplasty Mobile and fixed-bearing (all-polyethylene tibial component) total knee arthroplasty designs. A prospective randomized trial. Long-term comparison of mobile-bearing vs fixed-bearing total knee arthroplasty. Fixed-bearing versus mobile-bearing total knee arthroplasty: a prospective randomised, clinical and radiological study with mid-term results at 7 years. The John Insall Award: No Functional Advantage of a Mobile Bearing Posterior Stabilized TKA Staged bilateral mobile-bearing and fixed-bearing total knee arthroplasty in the same patients: a prospective comparison of a posterior-stabilized prosthesis Kinematics and early migration in single-radius mobile- and fixed-bearing total knee prostheses. A comparison of fixed-bearing and mobile-bearing total knee arthroplasty at a minimum follow-up of 4.5 years. Comparison of a mobile with a fixed tibial bearing unicompartimental knee prosthesis: a prospective randomized trial using a dedicated outcome score. One Year After Navigated Total Knee Replacement, No Clinically Relevant Difference Found Between Fixed Bearing and Mobile Bearing Knee Replacement in a Double-Blind Randomized Controlled Trial A randomised controlled clinical trial and gait analysis of fixed- and mobile-bearing total knee replacements with a five-year follow-up. [Knee arthroplasty. Mobile- and fixed-bearing design]. Prosthesis alignment affects axial rotation motion after total knee replacement: a prospective in vivo study combining computed tomography and fluoroscopic evaluations Mobile vs. fixed meniscal bearing in total knee replacement: a randomised radiostereometric study. Fixed versus mobile weight-bearing prosthesis in total knee arthroplasty [Fixed-bearing versus mobile-bearing total knee arthroplasty: a prospective randomized clinical and radiological study]. Comparison of mobile- and fixed-bearing cemented total knee arthroplasty. A mobile-bearing total knee prosthesis compared with a fixed-bearing prosthesis. A multicentre single-blind randomised controlled trial. A randomised controlled trial of the clinical effectiveness and cost-effectiveness of different knee prostheses: the Knee Arthroplasty Trial (KAT). Lateral unicompartmental knee replacement: fixed or mobile bearing? Gait analysis and electromyography in fixed- and mobile-bearing total knee replacement: a prospective, comparative study Less Anterior Knee Pain with a Mobile-bearing Prosthesis Compared with a Fixed-bearing Prosthesis Mobile- versus fixed-bearing total knee arthroplasty: a prospective randomized controlled trial featuring 6-10-year follow-up. Mobile Bearings Do Not Improve Fixation in Cemented Total Knee Arthroplasty Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study. Does circumpatellar electrocautery improve the outcome after total knee replacement?: a prospective, randomised, blinded controlled trial. Early clinical results of a high-flexion, posterior-stabilized, mobile-bearing total knee arthroplasty: a US investigational device exemption trial. Patient-reported outcomes after fixed- versus mobile-bearing total knee replacement: a multi-centre randomised controlled trial using the Kinemax total knee replacement. Real In Vivo Kinematic Differences between Mobile-Bearing and Fixed-Bearing Total Knee Arthroplasties
This single-blinded r and omised controlled trial investigated whether one design of mobile-bearing ( MB ) total knee replacement ( TKR ) has any advantage over a fixed-bearing ( FB ) design on long-term fixation as measured by radiostereometry . The amount of wear underneath the mobile bearing was also evaluated . A series of 42 knees was r and omised to MB or FB tibial components with appropriate polyethylene inserts and followed for between ten and 12 years , or until the death of the patient . The polyethylene in the MB group was superior in that it was gamma-irradiated in inert gas and was calcium-stearate free ; the polyethylene in the FB group was gamma-irradiated in air and contained calcium stearate . In theory this should be advantageous to the wear rate of the MB group . At final follow-up the overall mean migration was 0.75 mm ( SD 0.76 ) in the MB group and 0.66 mm ( SD 0.4 ) in the FB group , with the FB group demonstrating more posterior tilt and the MB group more internal rotation . In the FB group there was one revision for aseptic loosening , but none in the MB group . There were no significant differences in clinical or radiological scores . For the MB group , the mean linear wear rate on the under-surface was 0.026 mm/year ( SD 0.014 ) . This was significantly smaller than the wear rate of 0.11 mm/year ( SD 0.06 ) in the MB between femur and polyethylene ( p < 0.001 ) . Nevertheless , even in a best-case setting the mobile bearings of this TKR design had no apparent advantage in terms of fixation over the FB knee prosthesis at ten to 12 years . The wear underneath the mobile bearing was small and is unlikely to be clinical ly relevant BACKGROUND Fixed bearing ( FB ) total knee replacement is a well established technique against which new techniques must be compared . Mobile bearing ( MB ) prostheses , in theory , reduce polyethylene wear but the literature is yet to provide evidence that they are superior in terms of function or long-term survivorship . In addition there has been no comparison of patella resurfacing on the outcome of either design . The aims of this r and omised prospect i ve study were firstly to determine whether a mobile bearing prosthesis produced better clinical outcome and range of motion at two year follow-up and secondly to assess the effect of patella resurfacing on the outcomes of both types of bearing design . METHODS Three hundred fifty-two patients were r and omised into receiving either a PFC Sigma © cruciate sacrificing total knee arthroplasty either with a mobile bearing or a fixed bearing  , with a sub-r and omisation to either patella resurfacing or patella retention . All patients participated with st and ard clinical outcome measures and had their range of motion measured both pre-operatively and at follow-up . RESULTS The mobile bearing TKR design had no impact on range of motion ; Oxford Knee Score and American Knee Society knee and function scores when compared to its fixed bearing equivalent . CONCLUSIONS At two year follow-up there was no difference between the PFC Sigma © fixed and mobile bearing design s. With no clinical difference between the cohorts , we can not recommend one design over the other . Long term benefits , particularly with regards to polyethylene wear , may yet be demonstrated . Level of evidence --1B BACKGROUND Limited previous findings have detailed biomechanical advantages following implantation with mobile bearing ( MB ) prostheses after total knee replacement ( TKR ) surgery during walking . The aim of this study was to compare three dimensional spatiotemporal , kinematic , and kinetic parameters during walking to examine whether MBs offer functional advantages over fixed bearing ( FB ) design s. METHODS Sixteen patients undergoing primary unilateral TKR surgery were r and omised to receive either a FB ( n=8 ) or MB ( n=8 ) total knee prosthesis .  Eight age and gender matched controls underwent the same protocol on one occasion . A 12 camera Vicon system integrated with four force plates was used . Patients were tested pre-surgery and nine months post-surgery . RESULTS No significant differences between FB and MB groups were found at any time point in the spatiotemporal parameters . The MB group was found to have a significantly reduced frontal plane knee range of motion ( ROM ) at pre-surgery than the FB group ( FB=14.92±4.02 ° ; MB=8.87±4.82 ° ) , with the difference not observed post-surgery . No further significant kinematic or kinetic differences were observed between FB and MB groups . Fixed bearing and MB groups both displayed spatiotemporal , kinematic , and kinetic differences when compared to controls . Fixed bearing and MB groups differed from controls in six and five parameters at nine months post-surgery , respectively . CONCLUSIONS No functional advantages were found in knees implanted with MB prostheses during walking , with both groups indicative of similar differences when compared to normal knee biomechanics following prosthesis implantation . LEVEL OF EVIDENCE Level II BACKGROUND There is limited information comparing the results of fixed-bearing total knee replacement and mobile-bearing total knee replacement in patients with osteoarthritis who are younger than fifty-one years and who have a fixed-bearing implant in one knee and a mobile-bearing implant  in the other . The purpose of this study was to compare our long-term clinical and radiographic results of fixed-bearing total knee replacement and mobile-bearing total knee replacement in a group of patients from this population . METHODS We prospect ively compared the results of 108 patients with osteoarthritis who were younger than fifty-one years ( mean age , forty-five years ) who had received a fixed-bearing prosthesis in one knee and a rotating platform mobile-bearing prosthesis in the other .  The mean follow-up was 16.8 years ( range , fifteen to eighteen years ) . The patients were assessed clinical ly and radiographically . Knee motion and function were assessed as a primary outcome . Patients were assessed with question naires , and each knee was assessed separately . RESULTS Although there was significant improvement in both groups of knees , there was no significant difference between the groups ( i.e. , fixed-bearing and mobile-bearing knees ) with regard to the mean postoperative knee motion ( 126 ° and 128 ° , respectively ; p = 0.79 ) , the mean Knee Society knee clinical score ( 95 and 94 points , respectively ; p = 0.79 ) , or the Knee Society knee functional score ( 84 and 85 points , respectively ; p = 0.19 ) at the latest follow-up . In the fixed-bearing group , one knee was revised because of infection , two for aseptic loosening of the tibial component , and two because of wear of the tibial polyethylene insert . In the rotating platform mobile-bearing group , two knees were revised because of instability and one because of infection . The Kaplan-Meier survivorship for revision at 16.8 years of follow-up was 95 % ( 95 % confidence interval , 91 to 100 ) for the fixed-bearing prosthesis and 97 % ( 95 % confidence interval , 93 to 100 ) for the rotating platform mobile-bearing prosthesis . CONCLUSIONS Long-term results of both fixed and mobile-bearing total knee arthroplasties were encouraging in patients who were younger than fifty-one years of age with osteoarthritis . However , we found no superiority of the mobile-bearing total knee prosthesis over the fixed-bearing total knee prosthesis The purpose of the current study was to directly compare the results of fixed-bearing and mobile-bearing total knee arthroplasties in the same patient who had bilateral simultaneous total knee replacements . A fixed-bearing total knee prosthesis ( AMK ) was implanted in one knee and a mobile-bearing total knee prosthesis ( LCS ) was implanted in the other knee in 116 patients . The average age of the patients was 65 years ( range , 33–70 years ) . The average followup was 7.4 years ( range , 6–8 years ) .  Clinical and radiographic followup was done using Knee Society and Hospital for Special Surgery knee rating systems at 6 weeks , 3 months , 6 months , 1 year after surgery , and yearly thereafter . Total knee score , pain score , mean functional score , and range of motion were comparable in both groups . Two knee replacements ( 2 % ) in one patient with AMK prostheses were revised because of complete wear of tibial bearing polyethylene . One knee replacement ( 1 % ) in one patient with an LCS prosthesis was revised because of dislocation of the medial tibial bearing polyethylene and one knee replacement ( 1 % ) in one patient with an LCS prosthesis was revised because of complete wear of the medial tibial bearing polyethylene . No knee had aseptic loosening or osteolysis in either group . After a minimum followup of 6 years , the results of fixed- and mobile-bearing total knee prostheses in the current series are favorable . However , there is no evidence to prove the superiority of the mobile-bearing total knee design A prospect i ve study was performed to compare the clinical and radiological results of mobile- and fixed-bearing total knee arthroplasty  with specific attention to rotational alignment and range of motion . Sixty-one knees were assigned to total knee arthroplasty with either the NexGen LPS Flex fixed-bearing or with the NexGen LPS Flex mobile-bearing prosthesis . Postoperatively , knees were compared with regard to range of motion , clinical score , and radiographic findings . Rotational alignment of the femoral and tibial components was evaluated by computed tomography . The median follow-up period was 5.9 years ( range 2.1–8.8 years ) . Median postoperative Knee Society scores were 99 points ( 68–100 ) for the fixed-bearing group and 100 points ( 66–100 ) for the mobile-bearing group ( n.s . ) . The median postoperative flexion angles of 120 ° ( 90 ° –150 ° ) for the fixed-bearing group and 125 ° ( 90 ° –145 ° ) for the mobile-bearing group were not significantly different from each other ( n.s . ) . No knee required revision surgery due to wear of polyethylene or loosening of the component in either group . Computed tomography showed that 11 knees had rotational mismatches of more than 10 ° between the femoral and tibial components , but no significant difference was found in the postoperative extension and flexion angles or in the clinical score between the two treatment groups . Using the identical design for both fixed- and mobile-bearing prostheses , this prospect i ve , r and omized study did not show any clinical advantages of the mobile-bearing knee . Analysis of rotational alignment by CT scan did not reveal a particular advantage of the self-aligning mechanism of mobile-bearing implants BACKGROUND Proponents of mobile-bearing total knee arthroplasty believe that it has potential advantages over a fixed-bearing design in terms of diminished wear and improved motion and /or function , but these advantages have not been demonstrated in a r and omized clinical comparison to our knowledge . We conducted a patient-blinded , prospect i ve , r and omized clinical trial to compare mobile-bearing and fixed-bearing cruciate-substituting total knee arthroplasties of the same design . METHODS Patients between the ages of sixty and eighty-five years were prospect ively r and omized to receive a cruciate-substituting rotating-platform design or a fixed-bearing design with an all-polyethylene tibial component . There were no significant differences in the demographic characteristics ( mean age , 72.2 years ; mean American Society of Anesthesiologists score , 2.7 ; mean body mass index , 31.8 kg/m(2 ) ) or preoperative clinical or radiographic measures between the groups . Routine clinical and radiographic follow-up measures included the Knee Society score ( KSS ) , Western Ontario and McMaster Universities Osteoarthritis Index ( WOMAC ) , and Short Form-36 ( SF-36 ) outcome measures . RESULTS The results of 312 arthroplasties ( 136 with an all-polyethylene tibial component  and 176 rotating-platform design s ) in 273 patients were analyzed at a minimum of two years ( mean , forty-two months ) postoperatively . Although there was significant improvement in both groups , there was no significant difference between the groups with regard to the mean postoperative range of motion ( 110.9 degrees and 109.1 degrees , respectively ; p = 0.21 ) , the mean KSS clinical score ( 90.4 and 88.2 points ; p = 0.168 ) , or the mean KSS pain score ( 44.9 and 43.1 points ; p = 0.108 ) at this follow-up point . There were ten revisions : seven because of infection , one because of patellar fracture , one because of instability , and one because of aseptic loosening . CONCLUSIONS The two design s functioned equivalently at the time of early follow-up in this low-to-moderate-dem and patient group . The rotating-platform design had no significant clinical advantage over the design with the all-polyethylene tibial component Few published reports have been published regarding a comparison of the long-term outcomes between mobile- ( MB ) and fixed-bearing component design s for knee arthroplasty . The minimum 10-year clinical and radiologic follow-up of an unselected consecutive series of 89 patients ( 107 knees ) who were r and omized to have one of these different design s for primary arthroplasty was done . Twenty-six patients ( 30 knees ) who had a fixed-bearing design and 24 patients ( 33 knees ) who had an MB prosthesis were available for follow-up . Two MB knees were revised for aseptic loosening of a tibial component in one and femoral component fracture in the other . In patients who did not have revision surgery , there were no differences between the groups with respect to mean Knee Society scores , knee flexion , or pain scores Mobile-bearing ( MB ) total knee arthroplasty ( TKA ) was developed as an alternative to the established fixed-bearing ( FB ) design because of theoretical advantages . Short-term studies comparing these design s have not shown any differences in clinical and radiographic results . We compared the results at 7 years of a r and omised study of patients undergoing TKA using either a FB or a MB variant of the same prosthesis . Fifty-two patients ( 52 knees ) with an average age of 70 years received a FB posterior-stabilized prosthesis , and 50 patients ( 52 knees ) with an average age of 72 years , a MB prosthesis .  All implants were cemented and the patella was routinely resurfaced . Preoperatively , there were no differences between the two groups , and surgical procedure and postoperative protocol were the same for both . At an average follow-up of 7.1 years , no significant differences of FB over MB design could be demonstrated with respect to the American Knee Society score ( AKSS ) , pain score , a question naire of general health ( SF-12 score ) , range of motion ( ROM ) , or complication rates . Radiographs showed no significant difference in prosthetic alignment or evidence of loosening . Two knees with a MB design required reoperation , one for persistent joint stiffness and another to treat septic loosening . One patient with a MB prosthesis with signs of tibial component loosening was asymptomatic . We conclude that at mid-term follow-up there is no evidence to prove the superiority of MB over FB TKA with regard to the clinical and radiographic results Background Mobile bearing ( MB ) total knee design has been advocated as a means to enhance the functional characteristics and decrease the wear rates of condylar total knee arthroplasty ( TKA ) . However , it is unclear if these design s achieve these goals . Questions / purpose sWe asked whether function of patients or survivorship would be greater or complications would be lesser in groups of patients with MB compared with fixed bearing ( FB ) TKA .  We also sought to describe retrieval findings . Methods We r and omized 507 primary TKAs in 416 eligible patients to receive MB ( n = 252 ) or FB ( n = 255 ) devices from November 2001 to August 2007 ( Investigational Device Exemption G000180 , Clinical Trials.gov registration number NCT00946075 ) . Patients were blinded to treatment allocation . WOMAC Index , SF-12 Health Survey , knee range of motion , and Knee Society scores were collected and compared preoperatively and at 6 , 12 , and 24 months postoperatively . We recorded device failures and complications until October 2009 . Kaplan-Meier survivorship was compared using the log rank test . Twelve retrieved MB devices underwent pathologic analysis . The minimum postoperative time was 2.2 years ( mean , 5.9 years ; range , 2.2–7.9 years ) . Results We found no differences in mean clinical assessment scores or mean score changes from baseline at any postoperative interval through 2 postoperative years . Nineteen of the 252 MB and 13 of the 255 FB knees had undergone revision of any component . Estimated survival at 6 postoperative years was similar for the two devices : 90.1 % ( 95 % confidence interval [ CI ] , 84.1–93.9 ) for MB and 94.2 % ( 95 % CI , 90.1–96.6 ) for FB . Two MB and no FB tibial components were revised for loosening . There was one case of MB insert dislocation . Retrieved MB devices demonstrated no unexpected wear or mechanical device failures . Conclusion We found no evidence of functional advantage of the MB design . Survivorship was similar , although the study is limited by short duration of followup . Level of Evidence Level I , therapeutic study . See Guidelines for Authors for a complete description of levels of evidence Mobile-bearing total knee arthroplasty ( TKA ) has several theoretical advantages over fixed-bearing TKA . We conducted a prospect i ve r and omized trial to compare the results of mobile-bearing and fixed-bearing posterior-stabilized TKA in the same patients using the same femoral component design of a mobile-bearing prosthesis in one knee and a fixed-bearing prosthesis in the other knee in 25 patients with osteoarthritis . The mean follow-up was 40 months . No significant differences were found in the mobile-bearing and fixed-bearing knees in terms of clinical and radiographic results . No osteolysis , loosening , or revision occurred . One knee with a mobile-bearing prosthesis had a dislocation of the rotating bearing ; however , spontaneous reduction occurred and the dislocation did not recur . Satisfactory early results can be achieved in both mobile-bearing and fixed-bearing knees . We could not demonstrate an advantage of a mobile-bearing TKA BACKGROUND The mobile-bearing variant of a single-radius design is assumed to provide more freedom of motion compared to the fixed-bearing variant because the insert does not restrict the natural movements of the femoral component . This would reduce the contact stresses and wear which in turn may have a positive effect on the fixation of the prosthesis to the bone and thereby decreases the risk for loosening . The aim of this study was to evaluate early migration of the tibial component and kinematics of a mobile-bearing and fixed-bearing total knee prosthesis of the same single-radius design . METHODS Twenty Triathlon single-radius posterior-stabilized knee prostheses were implanted ( 9 mobile-bearing and 11 fixed-bearing ) .  Fluoroscopy and roentgen stereophotogrammetric analysis ( RSA ) were performed 6 and 12 months post-operatively . FINDINGS The 1 year post-operative RSA results showed considerable early migrations in 3 out of 9 mobile-bearing patients and 1 out of 11 fixed-bearing patients . The range of knee flexion was the same for the mobile-bearing and fixed-bearing group . The mobile insert was following the femoral component during motion . INTERPRETATION Despite the mobile insert following the femoral component during motion , and therefore performing as intended , no kinematic advantages of the mobile-bearing total knee prosthesis were seen . The fixed-bearing knee performed as good as the mobile-bearing knee and maybe even slightly better based on less irregular kinematics and less early migrations BACKGROUND Durable long-term independent results with the Low Contact Stress rotating-platform ( mobile-bearing ) and the Insall Burstein-II ( fixed-bearing ) total knee prostheses have been reported , but no studies describing either the mid-term or long-term results and comparing the two prostheses are available , to our knowledge . METHODS Thirty-two patients who had bilateral arthritis of the knee with similar deformity and preoperative range of motion on both sides and who agreed to have one knee replaced with a mobile-bearing total knee design and the other with a fixed-bearing design were prospect ively evaluated . Comparative analysis of both design s was done at a mean follow-up period of six years , minimizing patient , surgeon , and observer-related bias . Clinical and radiographic outcome , survival , and complication rates were compared . RESULTS Patients with osteoarthritis had better function scores and range of motion compared with patients with rheumatoid arthritis . However , with the numbers available , no benefit of mobile-bearing over fixed-bearing design s could be demonstrated with respect to Knee Society scores , range of flexion , subject preference , or patellofemoral complication rates . Radiographs showed no difference in prosthetic alignment . Two knees with a mobile-bearing prosthesis required a reoperation : one had an early revision because of bearing dislocation and another required conversion to an arthrodesis to treat a deep infection . CONCLUSIONS We found no advantage of the mobile-bearing arthroplasty over the fixed-bearing arthroplasty with regard to the clinical results at mid-term follow-up . The risk of bearing subluxation and dislocation in knees with the mobile-bearing prosthesis is a cause for concern and may necessitate early revision . LEVEL OF EVIDENCE Therapeutic Level II Between February 1996 and December 1997 , forty consecutive patients with medial compartment knee arthritis were assigned r and omly into two groups . All underwent a unicompartimental knee replacement . The tibial prosthesis in group A ( 20 knees ) had a fixed bearing and in group B ( 20 knees ) a mobile bearing . The average age was 69 . Five in group A and 71 in group B. Pre-operatively , and at an average follow-up of 5.7 years , all the knees were assessed using both a dedicated UKR score specifically developed and adopted by the Italian Orthopaedic Unicompartimental Knee Replacement Users Group ( GIUM ) and the Knee Society Score . During surgery in group B we experienced a medial tibial plateau fracture fixed intra-operatively . One prosthesis in group A required an early revision to a TKR because of a continuous pain without any evident sign of loosening . There were no meniscal dislocations in group B. No statistically significant difference in outcome was observed between the two groups at the latest follow-up Background : The mobile bearing design s have not yet been shown to improve clinical outcome of total knee arthroplasty ( TKA ) . In this prospect i ve r and omized study , we compared the short-term clinical results of a mobile bearing implant with those of the fixed bearing version of the same implant . Methods : We r and omized 100 knees into two double-blind groups who received either the fixed ( FB , 52 knees ) or the mobile bearing ( MB , 48 knees ) version of the same implant .  We used navigation to st and ardize the surgical technique . For up to one year , we recorded the Knee Society ( KSS ) and Oxford ( OXF ) scores . We performed an exploratory analysis of variance ( ANOVA ) to determine the influence of baseline scores as covariate and the extent of improvement in clinical outcome over time . Results : After one year , we did not detect any statistically significant difference between the two groups . The KSS scores differed by 2 points , the OXF scores by 1.1 points . Conclusion : Even with identical geometry of implant surfaces and a navigated surgical technique , first-year results do not support a preference for either a fixed or a mobile design This study compared the outcome of  total knee replacement ( TKR ) in adult patients with fixed- and mobile-bearing prostheses during the first post-operative year and at five years ' follow-up , using gait parameters as a new objective measure . This double-blind r and omised controlled clinical trial included 55 patients with mobile-bearing ( n = 26 ) and fixed-bearing ( n = 29 ) prostheses of the same design , evaluated pre-operatively and post-operatively at six weeks , three months , six months , one year and five years . Each participant undertook two walking trials of 30 m and completed the EuroQol question naire , Western Ontario and McMaster Universities osteoarthritis index , Knee Society score , and visual analogue scales for pain and stiffness . Gait analysis was performed using five miniature angular rate sensors mounted on the trunk ( sacrum ) , each thigh and calf . The study population was divided into two groups according to age ( ≤ 70 years versus > 70 years ) .  Improvements in most gait parameters at five years ' follow-up were greater for fixed-bearing TKRs in older patients ( > 70 years ) , and greater for mobile-bearing TKRs in younger patients ( ≤ 70 years ) . These findings should be confirmed by an extended age controlled study , as the ideal choice of prosthesis might depend on the age of the patient at the time of surgery After the introduction of  mobile-bearing knee arthroplasty  in the late 1970s , he benefits were discussed in comparison to the well-established modular fixed-bearing systems . The hypothetical advantages of mobile-bearing design s are the ability of axial rotation and a greater articular conformity , which reduces significantly fatigue failure of the polyethylene . Biomechanical analyses showed for each system characteristic features , which are not concordant with the aim of restoring normal knee kinematics . In both groups the long-term clinical results were excellent with 10-year survival rates of 95 - 98 % . Ligamentous stability and a perfect operative technique are key factors in mobile-bearing knee arthroplasty . Prospect i ve r and omized clinical trials are necessary to find answers concerning backside and volumetric polyethylene wear and the detrimental effects of wear particle size . Before this is accomplished , the indication for a  mobile-bearing knee arthroplasty  , especially in young patients , should be carefully considered in each case Background Clinical consequences of alignment errors in  total knee replacement ( TKR ) have led to the rigorous evaluation of surgical alignment techniques . Rotational alignment in the transverse plane has proven particularly problematic , with errors due to component malalignment relative to bone anatomic l and marks and an overall mismatch between the femoral and tibial components ’ relative positions . Ranges of nominal rotational alignment are not well defined , especially for the tibial component and for relative rotational mismatch , and some studies advocate the use of mobile-bearing TKR to accommo date the result ing small rotation errors . However , the relationships between prosthesis rotational alignment and mobile-bearing polyethylene insert motion are poorly understood . This prospect i ve , in vivo study evaluates whether component malalignment and mismatch affect axial rotation motions during passive knee flexion after TKR . Methods Eighty patients were implanted with mobile-bearing TKR .  Rotational alignment of the femoral and tibial components was measured from postoperative CT scans . All TKR were categorized into nominal or outlier groups based on defined norms for surgical rotational alignment relative to bone anatomic l and marks and relative rotational mismatch between the femoral and tibial components . Axial rotation motion of the femoral , tibial and polyethylene bearing components was measured from fluoroscopic images acquired during passive knee flexion . Results Axial rotation motion was generally accomplished in two phases , dominated by polyethylene bearing rotation on the tibial component in early to mid-flexion and then femoral component rotation on the polyethylene articular surface in later flexion . Opposite rotations of the femur-bearing and bearing-baseplate articulations were evident at flexion greater than 80 ° . Knees with outlier alignment had lower magnitudes of axial rotation and distinct transitions from external to internal rotation during mid-flexion . Knees with femoral-tibial rotational mismatch had significantly lower total axial rotation compared to knees with nominal alignment . Conclusions Maintaining relative rotational mismatch within ±5 ° during TKR provided for controlled knee axial rotation during flexion . TKR with rotational alignment outside of defined surgical norms , with either positive or negative mismatch , experienced measurable kinematic differences and presented different patterns of axial rotation motions during passive knee flexion compared to TKR with nominal mismatch . These findings support previous studies linking prosthesis rotational alignment with inferior clinical and functional outcomes .Trial Registration Clinical Trials 52 knees scheduled for a total knee arthroplasty were r and omised to either a fixed or a mobile polyethylene bearing . The design was identical in all parts . The knee systems used were the Rotaglide Total Knee System ( RTK ) and the Nuffield Total Knee System ( NTK ) , both from the same manufacturer ( Corin Medical Ltd. , UK ) . All knees implanted were uncemented . The patients were followed for 2 years clinical ly and with radiostereometric analyses to assess migration over time and inducible displacement of the tibial component . Separate analysis of the mobility of the tibial insert in the knees with a mobile bearing was also made . The migration measured with RSA between the 1st and 2nd year expressed as maximum total point motion ( MTPM ) might predict the risk of loosening of the implant . There were no differences between the groups regarding clinical outcome ( HSS Knee score ) , migration or inducible displacement during the 2 years follow-up . The movement between the tibial tray and the mobile meniscal insert expressed as maximum total point motion ( MTPM ) was 6.8+/-3.3 mm at the 1st year follow-up Purpose This study was design ed to compare clinical , radiological , and general health results of two prostheses ( mobile vs. fixed weight-bearing devices ) that are used in total knee arthroplasty with a 5-year follow-up . Methods This r and omized controlled study was conducted from 2004 to 2010 in the Department of Orthopedic Surgery at two university hospitals in Isfahan , Iran . Three hundred patients with expected primary total knee arthroplasty ( TKA ) without severe deformity ( a fixed varus or valgus deformity greater than 20 ° ) received fixed weight-bearing ( n = 150 ) or mobile weight-bearing ( n = 150 ) devices . Clinical , radiological , and quality of life outcomes were compared between the two groups at six-month intervals for the first year , after which the comparisons were made annually for the next 4 years . Results Both groups had similar baseline characteristics . Although there was significant improvement in both groups , there was no significant difference between the groups with regard to the means of the Knee Society Scores , which were 92 ( SD : 12.1 ) for the fixed weight-bearing device and 93 ( SD : 14.2 ) for the mobile weight-bearing device ( n.s . ) at the final follow-up point . Radiographs showed that there was no significant difference in prosthetic alignment and no evidence of loosening . After TKA , the SF-36 score increased in both groups , but there was no statistical difference between the groups in quality of life at the final follow-up ( 62 ( 12.2 ) vs. 64 ( 14.3 ) , n.s . ) . There was no revision after 5 years . Conclusions In terms of clinical , radiological or general health outcomes for people who underwent TKA , the results of this study showed no clear advantage of mobile weight-bearing over the fixed weight-bearing prosthesis at the five-year follow-up . Level of evidence PURPOSE OF THE STUDY Mobile-bearing total knee arthroplasty has become increasingly popular over the last few years since this option presents several theoretical advantages compared with the fixed-bearing models . The clinical advantage remains to be demonstrated . We therefore conducted a prospect i ve r and omized trial to ascertain the potential benefits . MATERIAL AND METHODS This study included patients treated by three senior orthopedic surgeons . Each group included 52 prostheses in 52 patients in the fixed-bearing group and 50 patients in the mobile-bearing group . The per- and postoperative protocol s were the same for both groups . Implants were cemented in all cases and patellae were resurfaced . The SF-12 , the Knee Society Score ( KSS ) , the Hospital of Special Surgery score ( HSS ) and pain and joint motion were noted before and after surgery . RESULTS Among the 104 prostheses implanted , 100 were review ed at mean follow-up of 36 months ( range 24 - 41 ) . One patient in the fixed-bearing group died six months after surgery from an unrelated cause . Three patients were lost to follow-up : one in the fixed-bearing group and two in the mobile-bearing group . There was no difference between groups for the SF-12 , KSS , HSS , pain and joint motion measured postoperatively . Postoperative femorotibial alignment was one degree varus on average in the fixed-bearing group and zero degree in the mobile-bearing group . At last follow-up , there were no radiological signs of prosthesis loosening . One patient in the fixed-bearing group developed a deep venous thrombosis , complicated by pulmonary embolism . Two of the mobile-bearing prostheses were revised , one for patellar fracture caused by a bicycle accident and one for prosthesis infection in a patient with endocarditis 1.5 years after implantation . DISCUSSION The clinical results were similar for the two groups in terms of function , pain , general status and complications . The outcome at 36 months was considered excellent or good in 90 % of the fixed-bearing group and 88 % in the mobile-bearing group . This study did not reveal any difference between the two groups regarding maximal flexion and anterior knee pain , two parameters which would theoretically show short-term improvement with the mobile bearing . Mid- and long-term follow will be required to confirm these findings and to determine the survival of these two types of implants Concern about polyethylene wear and related osteolysis after knee arthroplasty has developed in the last years . Mobile-bearing knee prostheses were design ed in order to reduce the influence of this critical factor on long-term success of total knee replacement . We present a prospect i ve study comparing clinical and radiological results with a mobile-bearing ( Ceragyr ) and a fixed-bearing knee prosthesis ( posterior stabilized Hermes ) . Clinical results did not show any significant differences in Knee Society scores . We found better results in the mobile-bearing group for pain scores and subjective preference , but the difference did not reach statistical significance . Within the time limits of this study , radiological analysis showed no osteolysis in either group , but longer follow-up will be needed to confirm this Before proceeding to longer-term studies , we have studied the early clinical results of a new mobile-bearing total knee prosthesis in comparison with an established fixed-bearing device .  Patients requiring bilateral knee replacement consented to have their operations under one anaesthetic using one of each prosthesis . They also agreed to accept the r and om choice of knee ( right or left ) and to remain ignorant as to which side had which implant . Outcomes were measured using the American Knee Society Score ( AKSS ) , the Oxford Knee Score ( OKS ) , and determination of the range of movement and pain scores before and at one year after operation . Preoperatively , there was no systematic difference between the right and left knees . One patient died in the perioperative period and one mobile-bearing prosthesis required early revision for dislocation of the meniscal component . At one year the mean AKSS , OKS and pain scores for the new device were slightly better ( p < 0.025 ) than those for the fixed-bearing device . There was no difference in the range of movement . We believe that this is the first controlled , blinded trial to compare early function of a new knee prosthesis with that of a st and ard implant . It demonstrates a small but significant clinical advantage for the mobile-bearing design BACKGROUND In the late 1990s , new developments in knee replacement were identified as a priority for research within the NHS . The newer forms of arthroplasty were more expensive and information was needed on their safety and cost-effectiveness . OBJECTIVES The Knee Arthroplasty Trial examined the clinical effectiveness and cost-effectiveness of four aspects of knee replacement surgery : patellar resurfacing , mobile bearings , all-polyethylene tibial components and unicompartmental replacement . DESIGN This study comprised a partial factorial , pragmatic , multicentre r and omised controlled trial with a trial-based cost-utility analysis which was conducted from the perspective of the NHS and the patients treated . Allocation was computer generated in a 1 : 1 ratio using a central system , stratified by eligible comparisons and surgeon , minimised by participant age , gender and site of disease . Surgeons were not blinded to allocated procedures . Participants were unblinded if they requested to know the prosthesis they received . SETTING The setting for the trial was UK secondary care . PARTICIPANTS Patients were eligible for inclusion if a decision had been made for them to have primary knee replacement surgery . Patients were recruited to comparisons for which the surgeon was in equipoise about which type of operation was most suitable . INTERVENTIONS Patients were r and omised to receive a knee replacement  with the following : patellar resurfacing or no patellar resurfacing irrespective of the design of the prosthesis used ; a mobile bearing between the tibial and femoral components or a bearing fixed to the tibial component ; a tibial component made of either only high-density polyethylene ( ' all polyethylene ' ) or a polyethylene bearing fixed to a metal backing plate with attached stem ; or unicompartmental or total knee replacement . MAIN OUTCOME MEASURES The primary outcome was the Oxford Knee Score ( OKS ) . Other outcomes were Short Form 12 ; EuroQol 5D ; intraoperative and postoperative complications ; additional surgery ; cost ; and cost-effectiveness . Patients were followed up for a median of 10 years ; the economic evaluation took a 10-year time horizon , discounting costs and quality -adjusted life-years ( QALYs ) at 3.5 % per annum . RESULTS A total of 116 surgeons in 34 centres participated and 2352 participants were r and omised : 1715 in patellar resurfacing ; 539 in mobile bearing ; 409 in all-polyethylene tibial component ; and 34 in the unicompartmental comparisons . Of those r and omised , 345 were r and omised to two comparisons . We can be more than 95 % confident that patellar resurfacing is cost-effective , despite there being no significant difference in clinical outcomes , because of increased QALYs [ 0.187 ; 95 % confidence interval ( CI ) -0.025 to 0.399 ] and reduced costs ( -£104 ; 95 % CI -£630 to £ 423 ) . We found no definite advantage or disadvantage of mobile bearings in OKS , quality of life , reoperation and revision rates or cost-effectiveness . We found improved functional results for metal-backed tibias : complication , reoperation and revision rates were similar . The metal-backed tibia was cost-effective ( particularly in the elderly ) , costing £ 35 per QALY gained . CONCLUSIONS The results provide evidence to support the routine resurfacing of the patella and the use of metal-backed tibial components even in the elderly . Further follow-up is required to assess the stability of these findings over time and to inform the decision between mobile and fixed bearings . TRIAL REGISTRATION Current Controlled Trials IS RCT N45837371 . FUNDING This project was funded by the NIHR Health Technology Assessment programme and the orthopaedic industry . It will be published in full in Health Technology Assessment ; Vol . 18 , No. 19 . See the NIHR Journals Library website for further project information Between May 2001 and May 2003 , 233 consecutive Preservation unicompartmental knee replacements ( UKR ) were performed . Of these , 30 were lateral UKRs ( 13 % ) performed in 12 men and 16 women ( 2 bilateral cases ) with a mean age of 67 years ( range 36–93 years ) . A metal-backed mobile bearing tibial component was used in 13 knees and an all-polyethylene fixed bearing tibial component in 17 knees . The patients were review ed prospect ively at 1 and 2 years . The 2 year results show no difference in range of motion or function between the mobile and fixed bearing versions of the Preservation knee when used on the lateral side . There were three early revisions , all in the mobile bearing group Purpose The theoretical superiority of mobile-bearing total knee arthroplasties ( TKAs ) has not yet been proven in clinical studies . The aim of the current study was to compare and to analyse in a patient population that had received either a fixed or a mobile TKA differences in gait analysis electromyography and clinical scores . Methods In a prospect i ve , r and omized , patient- and observer-blinded clinical study , 33 patients with primary osteoarthritis of the knee were included . All patients received a Genesis II total knee replacement . Sixteen patients received a mobile  and 17 a  fixed-bearing cruciate retaining Genesis II TKA .  Clinical and quality -of-life scores , electromyography and gait analysis were applied preoperatively and postoperatively with a follow-up of 24 months . Results In both groups , improvements from pre- to postoperative were detected . whereas the results of gait analysis and electromyography did not show any differences . The results from the clinical and the quality -of-life scores improved from pre- to postoperative , while the Knee Society Score showed a superiority of the mobile-bearing group ( mean 159 ± 28 ) over the fixed-bearing group ( mean 134 ± 41 ) . Conclusion No functional advantage of mobile over fixed-bearing TKA was detected , although the mobile-bearing group had better clinical results for which a reason could not be found . These results only apply to cruciate retaining mobile-bearing TKA with a bearing which allows both rotation and anteroposterior translation . Level of evidence Prospect i ve comparative study , Level II Abstract  Anterior knee pain is one of the major short-term complaints after TKA . Since the introduction of the mobile-bearing TKA , numerous studies have attempted to confirm the theoretical advantages of a mobile-bearing TKA over a fixed-bearing TKA but most show little or no actual benefits . The concept of self-alignment for the mobile bearing suggests the posterior-stabilized mobile-bearing TKA would provide a lower incidence of anterior knee pain compared with a fixed-bearing TKA . We therefore asked whether the posterior-stabilized mobile-bearing knee would in fact reduce anterior knee pain . We r and omized 103 patients scheduled for cemented three-component TKA for osteoarthrosis in a prospect i ve , double-blind clinical trial . With a 1-year followup , more patients experienced persistent anterior knee pain in the posterior-stabilized fixed-bearing group ( 10 of 53 , 18.9 % ) than in the posterior-stabilized mobile-bearing group ( two of 47 , 4.3 % ) . No differences were observed for range of motion , visual analog scale for pain , Oxford 12-item question naire , SF-36 , or the American Knee Society score . The posterior-stabilized mobile-bearing knee therefore seems to provide a short-term advantage compared with the posterior-stabilized fixed-bearing knee . Level of Evidence : Level I , therapeutic study . See the Guidelines for Authors for a complete description of levels of evidence OBJECTIVE The purpose of this study was to compare long-term clinical and radiographic outcomes of mobile- ( MB ) and fixed-bearing ( FB ) total knee arthroplasties ( TKA ) . METHODS A r and omized controlled study was conducted to compare the clinical and radiographic outcomes of MB and FB prostheses in 93 consecutive patients who underwent primary TKA for knee osteoarthritis . Mean follow-up of the patients was 100.9 months in the MB group ( range : 78 - 121 months ) and 93.7 months ( range : 78 - 120 months ) in the FB group . The clinical results were grade d according to the Knee Society Knee Score ( KSKS ) and the Knee Society Functional Score ( KSFS ) . Secondary outcomes included pain , patellofemoral joint function , quality of life ( QOL ) , and radiologic outcomes ( Knee Society 's roentgenographic evaluation system ) . RESULTS Although there was significant improvement in both groups , there were no significant differences between the groups with respect to mean KSFS and radiologic outcomes . However , mean pain score of the MB group was significantly higher than that of the FB group ( 48.83±0.62 vs 47.39±0.86 , respectively , p=0.011 ) , and mean KSKS was significantly higher than that of the FB group ( 93.5±6.2 vs 89.7±6.9 , respectively , p=0.007 ) . CONCLUSION TKA clinical results were satisfactory in both the MB and FB groups . KSKS and pain scores were significantly better in the MB than in the FB group . However , no differences were found in other assessment s. Thus , we conclude that the best design is the one with which the surgeon is most comfortable and most able to implant reproducibly Mobile bearings were introduced to improve wear and knee kinematics . By uncoupling the forces generated at the articulation from the implant-bone interface this would , theoretically , also improve the fixation of the implant to bone . We did this study to evaluate whether mobile bearings  improve the fixation of the tibial component to bone .  Fifty-two consecutive knees in 47 patients ( average age , 72 years ; range , 62 - 84 years ) with primary osteoarthrosis were r and omized into two groups to receive a cemented total knee arthroplasty with either a fixed-bearing or mobile-bearing tibial component . The quality of fixation was analyzed with radiostereometric analysis for up to 2 years . Mobile bearings did not improve fixation . Both magnitudes and directions of component rotations were similar , and the number of implants with continuous migration was almost identical . Both implant types had a combination of subsidence and lift-off , but where the mobile bearing implants displayed more of subsidence , the fixed bearing knees showed more lift-off . It might be that the somewhat stiffer cobalt-chromium baseplate or the different joint conformity used in the mobile-bearing knees counteracts any potential effects of the mobile bearing . Level of Evidence : Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence Unicompartmental knee replacement ( UKR ) for anteromedial osteoarthritis is a well-established technique . Numerous clinical outcome studies demonstrate good medium and long-term results . The aim of this prospect i ve study was to compare the complications and short-term clinical outcome of the St. Georg Sled , a fixed bearing UKR , with the Oxford mobile bearing UKR . Outcome at 2 years was assessed using the Bristol knee score and the Oxford knee score ; in addition , complications occurring since formal scoring at 2-year follow-up were recorded . A total of 47 Oxford UKRs and 57 St. Georg Sled UKRs were performed in 91 patients , none of whom were lost to follow-up . At 2 years , both outcome measures were better for the St. Georg Sled Group . The pain component of the Bristol knee score was significantly better for this group ( p-value = 0.013 ) . Three patients in the Oxford group had bearing dislocations and a further four patients required revision ( mean time to revision 3.0 years ) . In the St. Georg Sled group , three patients required revisions ( mean time to revision 3.4 years ) . These results demonstrate that in the short-term , the Oxford mobile bearing prosthesis has a higher re-operation rate and that the St. Georg Sled achieves better pain relief . The functional scores of the two groups were similar The incidence of  anterior knee pain following total knee replacement ( TKR ) is reported to be as high as 49 % . The source of the pain is poorly understood but the soft tissues around the patella have been implicated . In theory circumferential electrocautery denervates the patella thereby reducing efferent pain signals . However , there is mixed evidence that this practice translates into improved outcomes . We aim ed to investigate the clinical effect of intra-operative circumpatellar electrocautery in patients undergoing TKR  using the LCS mobile bearing or Kinemax fixed bearing TKR . A total of 200 patients were r and omised to receive either circumpatellar electrocautery ( diathermy ) or not ( control ) . Patients were assessed by visual analogue scale ( VAS ) for anterior knee pain and Oxford knee score ( OKS ) pre-operatively and three months , six months and one year post-operatively . Patients and assessors were blinded . There were 91 patients in the diathermy group and 94 in the control . The mean VAS improvement at one year was 3.9 in both groups ( control ; -10 to 6 , diathermy ; -9 to 8 , p < 0.001 in both cases , paired , two-tailed t-test ) . There was no significant difference in VAS between the groups at any other time . The mean OKS improvement was 17.7 points ( 0 to 34 ) in the intervention group and 16.6 ( 0 to 42 ) points in the control ( p = 0.36 ) . There was no significant difference between the two groups in OKS at any other time . We found no relevant effect of patellar electrocautery on either VAS anterior knee pain or OKS for patients undergoing LCS and Kinemax TKR Between May 2001 and June 2004 , 388 total knee arthroplasty cases were enrolled in a prospect i ve , r and omized , multicenter investigational device exemption trial . Patients received either the investigational high-flexion mobile-bearing knee or a fixed-bearing control . At 2 to 4 years of follow-up , results in 293 patients with degenerative joint disease were compared using Knee Society Assessment and Function scores , radiographic results , complications analysis , and survival estimates . The mobile-bearing and fixed-bearing groups demonstrated similar , significant improvement over preoperative assessment s in Knee Scores , maximum flexion , and range of motion . One mobile-bearing arthroplasty required revision . Radiographic results were unremarkable , and implant-related complications were rare in both groups . At this early follow-up , the investigational high-flexion mobile-bearing knee and its fixed-bearing counterpart demonstrated comparable , effective performance We compared patient-reported outcomes of the Kinemax fixed- and mobile-bearing total knee replacement in a multi-centre r and omised controlled trial . Patients were  r and omised to the fixed- or the mobile-bearing prosthesis via a sealed envelope method after the bone cuts had been made in the operating theatre . R and omisation was stratified by centre and diagnosis . Patients were assessed pre-operatively and at eight to 12 weeks , one year and two years post-operatively . Vali date d question naires were used which included the Western Ontario MacMasters University , Short-Form 12 , Mental Health Index-5 , Knee Injury and Osteoarthritis Outcome Score for Knee-Related Quality of Life and Function in Sport and Recreation scales and a vali date d scale of satisfaction post-operatively . In total , 242 patients ( 250 knees ) with a mean age of 68 years ( 40 to 80 ) were recruited from four NHS orthopaedic centres . Of these , 132 patients ( 54.5 % ) were women . No statistically significant differences could be identified in any of the patient-reported outcome scores between patients who received the fixed-bearing or the mobile-bearing knee up to two-years post-operatively We did an in vivo fluoroscopic study comparing the sagittal plane kinematics of mobile-bearing and fixed-bearing total knee arthroplasties in a unique group of patients . These patients were part of a larger bilateral r and omized controlled outcome trial with each patient having received both types of total knee arthroplasties . Invited patients did three exercises with each of their different knee replacements ; extension against gravity , flexion against gravity , and a step-up . These exercises were recorded using video fluoroscopy , and a series of still digital images over the flexion range were retrieved . The relationship of patella tendon angle to knee flexion angle for each patient was derived . The patella tendon angle to knee flexion angle of the mobile-bearing knee behaved in a linear manner more closely replicating the normal knee , whereas the fixed-bearing knee behaved in a nonlinear , more variable manner . This pattern of results was similar for all three exercises with each patient having one knee replacement that behaved differently in the sagittal plane when compared with their other knee replacement . These kinematic differences may explain the clinical differences observed in the r and omized controlled trials that compared these two total knee arthroplasties
Meta-analyses showed no clinical ly relevant differences in terms of revision rates , clinical outcome scores or patient-reported outcome measures between MB and FB TKRs .
It appears that theoretical assumptions of superiority of MB over FB TKR are not borne out in clinical practice
Mobile-bearing ( MB ) total knee replacement ( TKR ) was introduced to reduce the risk of aseptic loosening and wear of polyethylene inserts .
However , no consistent clinical advantages of mobile- over fixed-bearing ( FB ) TKR have been found .
In this study we evaluated whether mobile bearings have an advantage over fixed bearings with regard to revision rates and clinical outcome scores .
Furthermore , we determined which modifying variables affected the outcome .