Early experiences with robot-assisted total knee arthroplasty using the DigiMatch™ ROBODOC® surgical system. Robot-assisted Total Knee Arthroplasty Achieving Accurate Ligament Balancing Using Robotic-Assisted Unicompartmental Knee Arthroplasty Comparative study between computer assisted-navigation and conventional technique in minimally invasive surgery total knee arthroplasty, prospective control study. Navigation Improves Accuracy of Rotational Alignment in Total Knee Arthroplasty Alignment in total knee arthroplasty. A comparison of computer-assisted surgery with the conventional technique. Image Guided Navigation System to Measure Intraoperatively Acetabular Implant Alignment Robotic-assisted TKA Reduces Postoperative Alignment Outliers and Improves Gap Balance Compared to Conventional TKA Comparison between computer-assisted-navigation and conventional total knee arthroplasties in patients undergoing simultaneous bilateral procedures: a randomized clinical trial. Technique and first clinical results of robot-assisted total knee replacement. Comparison between two computer-assisted total knee arthroplasty: gap-balancing versus measured resection technique Computer-assisted total knee arthroplasty using mini midvastus or medial parapatellar approach technique Comparison of robot-assisted and conventional total knee arthroplasty: A controlled cadaver study using multiparameter quantitative three-dimensional CT assessment of alignment Leg axis after computer-navigated total knee arthroplasty: a prospective randomized trial comparing computer-navigated and manual implantation. Accuracy of manual instrumentation of tibial cutting guide in total knee arthroplasty Comparison between patient-specific instruments and conventional instruments and computer navigation in total knee arthroplasty: a randomized controlled trial The reversed gap technique produces anatomical alignment with less midflexion instability in total knee arthroplasty: a prospective randomized trial Two-year Outcomes of Computed Tomography-based and Computed Tomography Free Navigation for Total Knee Arthroplasties Reliability of templating with patient-specific instrumentation in total knee arthroplasty. Are systemic emboli reduced in computer-assisted knee surgery?: A prospective, randomised, clinical trial. No difference between tibia-first and femur-first techniques in TKA using computer-assisted surgery Navigated total knee arthroplasty: a radiological analysis of 42 randomised cases. Surgically modifiable factors measured by computer-navigation together with patient-specific factors predict knee society score after total knee arthroplasty Robot-assisted total knee arthroplasty accurately restores the joint line and mechanical axis. A prospective randomised study. Conventional versus computer-navigated TKA: a prospective randomized study Reduction in variability of acetabular cup abduction using computer assisted surgery: a prospective and randomized study. Hands-on robotic unicompartmental knee replacement: a prospective, randomised controlled study of the acrobot system. What do we get from navigation in primary THA? Navigated intraoperative analysis of lower limb alignment Computer-assisted gap balancing technique improves outcome in total knee arthroplasty, compared with conventional measured resection technique Navigation of total knee arthroplasty: rotation of components and clinical results in a prospectively randomized study Patient-specific instrumentation for total knee arthroplasty does not match the pre-operative plan as assessed by intra-operative computer-assisted navigation Computer-navigated versus conventional total knee arthroplasty a prospective randomized trial. Comparison of Outcome and Survival After Unicompartmental Knee Arthroplasty Between Navigation and Conventional Techniques With an Average 9-Year Follow-Up. Patient-specific Guides Do Not Improve Accuracy in Total Knee Arthroplasty: A Prospective Randomized Controlled Trial Comparison of radiographic alignment of imageless computer-assisted surgery vs conventional instrumentation in primary total knee arthroplasty.
INTRODUCTION The use of robotics in total knee arthroplasty ( TKA ) has been shown to minimise human error , as well as improve the accuracy and precision of component implantation and mechanical axis alignment . The present study aim ed to demonstrate that robot-assisted TKA using ROBODOC ® is safe and capable of producing a consistent and accurate postoperative mechanical axis . METHODS We prospect ively recruited 27 consecutive patients who underwent robot-assisted TKA between May and December 2012 . Two patients were excluded from the study due to intraoperative technical problems with the robot .  Long-leg radiography and computed tomography were performed prior to surgery , and used for mechanical axis measurements and component sizing . DigiMatch ™ ROBODOC ® Surgical System software version 4.3.6 ( Curexo Technology Corp , Fremont , CA , USA ) was used in all cases to perform bone cuts in accordance with the preoperative plan . RESULTS The postoperative coronal mechanical alignment was within 3 degrees , with a mean alignment of -0.4 ± 1.7 degrees , confirming the accuracy of the preoperative surgical plan and bone cuts . The mean operating time was 96 ± 15 min , and preoperative planning yielded 100 % implant sizing accuracy . CONCLUSION Robotics has the potential to enable surgeons to consistently attain ideal postoperative alignment . The use of bone movement monitors and an integrated navigation system enhances the safety profile of ROBODOC ® by minimising errors . However , the role of the surgeon in TKA is still vital , as the surgeon is ultimately in charge of planning the surgery , its execution and ensuring soft tissue balance during TKA Increasing evidence suggests performing  total knee arthroplasty  using computer navigation can lead to more accurate surgical positioning of the components and knee alignment compared to a conventional operating technique without computer assistance . The use of robotic technology could theoretically take this accuracy one level further because it uses navigation in combination with ultimate mechanical precision , which could eliminate or reduce the inevitable margin of error during mechanical preparation of the bony cuts of total knee arthroplasty by the surgeon . We prospect ively followed 25 consecutive cases using an active surgical robot . The minimum followup was 5.1 years ( mean , 5.5 years ; range , 5.1 - 5.8 years ) . Our results demonstrate excellent implant positioning and alignment was achieved within the 1 ° error of neutral alignment in all three planes in all cases . Despite this technical precision , the excessive operating time required for the robotic implantation , the technical complexity of the system , and the extremely high operational costs have led us to ab and on this procedure and direct our interest more toward smart semiactive robotic systems . Level of Evidence : Level IV , therapeutic study . See the Guidelines for Authors for a complete description of levels of evidence Unicompartmental knee arthroplasty ( UKA ) allows replacement of a single compartment in patients with limited disease . However , UKA is technically challenging and relies on accurate component positioning and restoration of natural knee kinematics . This study examined the accuracy of dynamic , real-time ligament balancing  using a robotic-assisted UKA system . Surgical data obtained from the computer system were prospect ively collected from 51 patients ( 52 knees ) undergoing robotic-assisted medial UKA by a single surgeon .  Dynamic ligament balancing of the knee was obtained under valgus stress prior to component implantation and then compared to final ligament balance with the components in place . Ligament balancing was accurate up to 0.53 mm compared to the preoperative plan , with 83 % of cases within 1 mm at 0 ° , 30 ° , 60 ° , 90 ° , and 110 ° of flexion . Ligamentous laxity of 1.31 ± 0.13 mm at 30 ° of flexion was corrected successfully to 0.78 ± 0.17 mm ( P < 0.05 ) . Robotic-assisted UKA allows accurate and precise reproduction of a surgical balance plan using dynamic , real-time soft-tissue balancing to help restore natural knee kinematics , potentially improving implant survival and functional outcomes BACKGROUND Both Minimally Invasive surgery ( MIS ) and Computer-Assisted Surgery ( CAS ) are useful in Total Knee Arthroplasty ( TKA ) . Minimally invasive total knee arthroplasty was associated with decreased blood loss , shorter hospital stays , and increased range of motion .  Computer-assisted surgery in total knee arthroplasty was developed to improve the positioning of implants during surgery . OBJECTIVE To evaluate radiographic results relative to component position and limb alignment when using a navigation system compared with conventional technique in MIS-TKA . MATERIAL AND METHOD A prospect i ve control study was performed in 180 patients who underwent total knee arthroplasty by one surgeon . All patients were r and omly divided into two groups , Conventional and Navigation TKA .  Intra- , post-operative data , and postoperative limb alignment were recorded for comparison in both groups . RESULTS The postoperative mechanical axis was within 3 degrees of neutral mechanical alignment in 94 % of the navigation group and 87 % in conventional group ( p = 0.13 ) . Registration time of navigation group is 13.58 minutes . No statistical significant difference was found in tourniquet time and postoperative blood loss in both groups . CONCLUSION The use of navigation in total knee arthroplasty increases accuracy in limb and implants alignment , and does not increase complications and surgical times Successful total knee arthroplasty is dependent on the correct alignment of implanted prostheses . Major clinical problems can be related to poor femoral component positioning , including sagittal plane and rotational malalignment . A prospect i ve r and omized study was design ed to test whether an optical navigation system for total knee arthroplasty achieved greater implantation precision than a nonnavigated technique . The primary variable was rotation of the femoral component in the transverse plane , measured from postoperative radiographs and computed tomography images . Sixty-four patients were included in the study . All patients received the Duracon total knee prosthesis .  The patients were r and omly divided into two groups : Group C patients had conventional total knee arthroplasty without navigation ; Group N patients had total knee arthroplasty using a computer-assisted knee navigation system . Analysis showed that patients in Group N had significantly better rotational alignment and flexion angle of the femoral component than patients in Group C. In addition , superior postoperative alignment of the mechanical axis , posterior tibial slope , and rotational alignment was achieved for patients in Group N. The use of a navigation system provides improved alignment accuracy , and can help to avoid femoral malrotation and errors in axial alignment Restoration of neutral alignment of the leg is an important factor affecting the long-term results of total knee arthroplasty ( TKA ) . Recent developments in computer-assisted surgery have focused on systems for improving TKA . In a prospect i ve study two groups of 80 patients undergoing TKA had operations using either a computer-assisted navigation system or a conventional technique .  Alignment of the leg and the orientation of components were determined on post-operative long-leg coronal and lateral films . The mechanical axis of the leg was significantly better in the computer-assisted group ( 96 % , within + /- 3 degrees varus/valgus ) compared with the conventional group ( 78 % , within + /- 3 degrees varus/valgus ) . The coronal alignment of the femoral component was also more accurate in the computer-assisted group . Computer-assisted TKA gives a better correction of alignment of the leg and orientation of the components compared with the conventional technique . Potential benefits in the long-term outcome and functional improvement require further investigation There has been little clinical research to examine the effects of patient positioning and pelvic motion on the alignment of the acetabular implant during total hip replacement surgery . Until now , no tools were capable of accurately measuring these variables during the actual procedure . As part of a broader program in medical robotics and computer assisted surgery , a clinical system has been developed that includes several enabling technologies . The hip navigation system ( HipNav ) continuously and precisely measures pelvic location and tracks relative implant alignment intraoperatively . HipNav technology is used to gauge current clinical practice and provide intraoperative feedback to surgeons with the goal of improving the precision and accuracy of acetabular alignment during total hip replacement . This system provides surgeons with a new class of image guided measurement tools and assist devices . These tools successfully were introduced into the clinical practice of surgery with results showing the following : ( 1 ) There exist unpredictable and large variations in the initial position of patients ' pelves on the operating room table and significant pelvic movement during surgery and during intraoperative range of motion testing ; ( 2 ) current mechanical acetabular alignment guides do not account for these variations , and result in variable and in the majority of cases unacceptable acetabular alignment ; and ( 3 ) press fitting oversized acetabular components influences the final cup orientation Background Several studies have shown mechanical alignment influences the outcome of TKA . Robotic systems have been developed to improve the precision and accuracy of achieving component position and mechanical alignment . Questions / purpose sWe determined whether robotic-assisted implantation for TKA ( 1 ) improved clinical outcome ; ( 2 ) improved mechanical axis alignment and implant inclination in the coronal and sagittal planes ; ( 3 ) improved the balance ( flexion and extension gaps ) ; and ( 4 ) reduced complications , postoperative drainage , and operative time when compared to conventionally implanted TKA over an intermediate-term ( minimum 3-year ) followup period . Methods We prospect ively r and omized 100 patients who underwent unilateral TKA into one of two groups : 50 using a robotic-assisted procedure and 50 using conventional manual techniques .  Outcome variables considered were postoperative ROM , WOMAC scores , Hospital for Special Surgery ( HSS ) knee scores , mechanical axis alignment , flexion/extension gap balance , complications , postoperative drainage , and operative time . Minimum followup was 41 months ( mean , 65 months ; range , 41–81 months ) . Results There were no differences in postoperative ROM , WOMAC scores , and HSS knee scores . The robotic-assisted group result ed in no mechanical axis outliers ( > ± 3 ° from neutral ) compared to 24 % in the conventional group . There were fewer robotic-assisted knees where the flexion gap exceeded the extension gap by 2 mm . The robotic-assisted procedures took an average of 25 minutes longer than the conventional procedures but had less postoperative blood drainage . There were no differences in complications between groups . Conclusions Robotic-assisted TKA appears to reduce the number of mechanical axis alignment outliers and improve the ability to achieve flexion-extension gap balance , without any differences in clinical scores or complications when compared to conventional manual techniques . Level of Evidence Level I , therapeutic study . See Instructions for Authors for a complete description of levels of evidence BACKGROUND Total knee arthroplasty has been increasingly used for young and active patients , and prosthesis durability is important in these patients . The accuracy of implant placement has been one of the major factors that determine the long-term survival of the prosthesis . The purpose of this study was to compare the accuracy of prosthetic alignment between computer-assisted-navigation and conventional total knee arthroplasties . METHODS From March 2007 to June 2008 , thirty-two patients with bilateral knee osteoarthritis underwent simultaneous bilateral total knee arthroplasty with the same type of implant in each knee .  The subjects included seven men and twenty-five women , with an average age of sixty-three years . For each patient , the bilateral total knee arthroplasty was performed with computer-assisted navigation in one knee and a conventional technique in the other . The operative technique and the order of the surgical procedures were r and omized . The patients and surgeons conducting the follow-up study and performing the imaging measurements were blinded to the type of surgical procedure . RESULTS There was a significant difference between the two groups with regard to the alignment of the knee prosthesis in the coronal and sagittal planes . Nine knee implants ( 28 % ) in the conventional group , compared with no knee implants in the computer-navigation group , deviated > 3 ° from the mechanical axis in the coronal plane . The coefficient variation of data in the conventional group was three times greater than that in the computer-navigation group . There was no significant difference in the rotational angle of the femoral component between the two groups . The Hospital for Special Surgery ( HSS ) scores at six months postoperatively were substantially increased compared with the preoperative scores in both groups . CONCLUSIONS Computer-assisted navigation consistently provided coronal plane alignment within 3 ° of the mechanical axis , which was significantly better than the alignment obtained with conventional total knee arthroplasty Total knee replacement ( TKR ) is a common procedure for treatment of severe gonarthrosis  , but the outcome may be unsatisfactory due to primary malalignment of the prosthetic components . In order to improve precision and accuracy of this surgical procedure , a commercial robotic surgical system ( CASPAR ) has been adapted to assist the surgeon in the preoperative planning and intraoperative execution of TKR . So far , 70 patients with idiopathic gonarthrosis were successfully treated with a robot-assisted technique in our institution . No major adverse events related to the use of the robotic system have been observed . The mean difference between preoperatively planned and postoperatively achieved tibiofemoral alignment was 0.8 degrees ( 0 - 4.1 degrees ) in the robotic group vs. 2.6 degrees ( 0 - 7 degrees ) in a manually operated historical control group of 50 patients . A clear advantage of robot-assisted TKR seems to be the ability to execute a highly precise preoperative plan based on computed tomography ( CT ) scans . Due to better alignment of the prosthetic components and improved bone-implant fit , implant loosening is anticipated to be diminished which may be most evident in non-cemented prostheses . Current disadvantages such as the need for placement of fiducial markers , increased operating times and higher overall costs have to be resolved in the future Two surgical strategies are possible in total knee arthroplasty ( TKA ) : a measured resection technique , in which bone l and marks are used to guide resections equal to the distal and posterior thickness of the femoral component , or a gap-balancing approach , in which equal collateral ligament tension in flexion and extension is sought before and as a guide to final bone cuts . In this study performed with computer assisted system , we compared the 2 different methods in 126 patients followed prospect ively in order to analyze the effect of both the techniques on joint-line ( JL ) maintenance , axial limb restoration and components position . The gap technique showed a statistical increase in the post-operative value when compared with the measured resection technique , ( P = 0.008 ) . When comparing the two groups regarding to the pre-operative deformity , we have found a statistical difference ( P = 0.001 ) in case of moderate pre-operative deformity ( less than 10 ° ) , and the measured resection technique showed a slight superiority in preserving a joint line more faithful to the pre-operative . We found an ideal alignment for the mechanical axis ( 180 ° ± 3 ° ) ( 95 % of cases ) . In six cases ( 5 % ) , the mean post-operative value exceeded ( varus or valgus ) the ideal value by more than 3 ° . In the frontal plane , a good alignment was observed for both femoral and tibial components without a significant difference between the two techniques . In the sagittal plane was found more alignment variability due to the different implants used and their ideal starting slope , from 7 ° to 3 ° . Finally , the surgeon can use the approach with which he has more confidence ; however , as the measured resection technique causes less reduction in the post-operative joint-line position , in case of shortening of patellar tendon or patella infera , this technique is preferable Background Despite the growing evidence in the literature there is still a lack of consensus regarding the use of minimally invasive surgical technique ( MIS ) in total knee arthroplasty ( TKA ) . Methods A prospect i ve , r and omized , international multicentre trial including 69 patients was performed to compare computer-assisted TKA ( CAS-TKA ) using either mini-midvastus ( MIS group ) or st and ard medial parapatellar approach ( conventional group ) .  Patients from 3 centers ( Maastricht , Zwickau , Adelaide ) with end-stage osteoarthritis of the knee were r and omized to either an MIS group with dedicated instrumentation or a conventional group to receive cruciate retaining CAS-TKA without patella resurfacing .  The primary outcome was to compare post operative pain and range of motion ( ROM ) . The secondary outcome was to measure the duration of surgery , blood loss , chair rise test , quadriceps strength , anterior knee pain , Knee Society Score (KSS),WOMAC scores , mechanical leg axis and component alignment . Results Patients in the MIS group ( 3.97 ± 2.16 ) had significant more pain at 2 weeks than patients in the conventional group ( 2.77 ± 1.43 ) p = 0.003 . There was no significant difference in any of the other primary outcome parameters . Surgery time was significantly longer ( p < 0.001 ) and there were significantly higher blood loss ( p = 0.002 ) in the MIS group as compared to the conventional group . The difference of the mean mechanical leg alignment between the groups was not statistically significant ( –0.43 ° ( 95 % CI –1.50 – 0.64 ) ; p = 0.43).There was no significant difference of component alignment between the two surgical groups with respect to flexion/extension ( p = 0.269 ) , varus/valgus ( p = 0.653 ) or rotational alignment ( p = 0.485 ) of the femur component and varus valgus alignment ( p = 0.778 ) or posterior slope ( p = 0.164 ) of the tibial component . Conclusion There was no advantage of the MIS approach compared to a conventional approach CAS-TKA in any of the primary outcome measurements assessed , however the MIS approach was associated with longer surgical time and greater blood loss . MIS-TKA in combination with computer navigation is safe in terms of implant positioning . Trial registration number Clinical Trials.gov NCT02625311 8 December Introduction : A functional total knee replacement has to be well aligned , which implies that it should lie along the mechanical axis and in the correct axial and rotational planes . Incorrect alignment will lead to abnormal wear , early mechanical loosening , and patellofemoral problems . There has been increased interest of late in total knee arthroplasty with robotic assistance . This study was conducted to determine whether robot-assisted total knee arthroplasty is superior to the conventional surgical method with regard to the precision of implant positioning . Material s and Methods : Twenty knee replacements , comprising ten robot-assisted procedures and ten conventional operations , were performed on ten cadavers . Two experienced surgeons performed the surgeries . Both procedures on each cadaver were performed by the same surgeon . The choice of which procedure was to be performed first was r and omized . Following implantation of the prosthesis , the mechanical axis deviation , femoral coronal angle , tibial coronal angle , femoral sagittal angle , tibial sagittal angle , and femoral rotational alignment were measured via 3D CT scanning . These variables were then compared with the preoperatively planned values . Results : In the knees that underwent robot-assisted surgery , the mechanical axis deviation ranged from −1.94 ° to 2.13 ° ( mean : −0.21 ° ) , the femoral coronal angle from 88.08 ° to 90.99 ° ( mean : 89.81 ° ) , the tibial coronal angle from 89.01 ° to 92.36 ° ( mean : 90.42 ° ) , the tibial sagittal angle from 81.72 ° to 86.24 ° ( mean : 83.20 ° ) , and the femoral rotational alignment from 0.02 ° to 1.15 ° ( mean : 0.52 ° ) in relation to the transepicondylar axis . In the knees that underwent conventional surgery  , the mechanical axis deviation ranged from −3.19 ° to 3.84 ° ( mean : −0.48 ° ) , the femoral coronal angle from 88.36 ° to 92.29 ° ( mean : 90.50 ° ) , the tibial coronal angle from 88.15 ° to 91.51 ° ( mean : 89.83 ° ) , the tibial sagittal angle from 80.06 ° to 87.34 ° ( mean : 84.50 ° ) , and the femoral rotational alignment from 0.32 ° to 4.13 ° ( mean : 2.76 ° ) in relation to the transepicondylar axis . In the conventional knee replacement group , there were two instances of outliers outside the range of 3 ° varus/valgus for the mechanical axis deviation . The robot-assisted knee replacements showed significantly superior femoral rotational alignment results compared with conventional surgery ( p = 0.006 ) . There was no statistically significant difference between robot-assisted and conventional total knee arthroplasty with regard to the other variables . All the measurements showed high intra-observer and inter-observer reliability . Conclusion : Robot-assisted total knee arthroplasty showed excellent precision in the sagittal and coronal planes of the 3D CT scan . In particular , the robot-assisted technique showed better accuracy in femoral rotational alignment compared to the conventional surgery , despite the fact that the surgeons who performed the operations were more experienced and familiar with the conventional method than with robot-assisted surgery . It can thus be concluded that robot-assisted total knee arthroplasty is superior to conventional total knee arthroplasty To compare the alignment after computer-navigated total knee arthroplasty , 52 patients were r and omly allocated to 2 groups . Twenty-seven patients received a total knee arthroplasty with the aid of a kinematic computer-navigation system , and 25 patients received a total knee arthroplasty with the conventional method . Both groups were well balanced concerning demographic data and preoperative scores . At 3-month follow-up , the mechanical alignment of the leg reached the desired straight axis in more cases with the computer-navigated implantation . This difference was statistically significant . The femoral and tibial mechanical anteroposterior axis and the femoral and tibial sagittal tilt ( slope ) measured on sagittal x-rays were not significantly improved in this patient group Purpose The aim of this study was to evaluate the accuracy of conventional instrumentation for tibial resection in total knee arthroplasty ( TKA ) as assessed by a computer-based navigation system during each phase of the surgical procedure . The hypothesis is that conventional instrumentation fails to achieve optimal accuracy in final implant positioning , thus leading to surgical errors . Methods Forty primary TKAs were performed .  The resection guide was placed using an extramedullary guide . Accurate guide positioning was assessed by the navigation system prior to the osteotomy . The alignment measurement was repeated after resection and after component implantation in order to quantify the deviation caused by the manual positioning of the prosthetic components . A deviation ≥2 ° was considered unsatisfactory . Results In the frontal plane , unsatisfactory results observed were as follows : 15 % with reference to manual positioning of the resection guide and 10 % with reference to definition of the resection plane with a tendency towards varus malalignment . In the sagittal plane , unsatisfactory results were as follows : 45 % with reference to manual positioning of the resection guide and 40 % with reference to definition of the resection plane with a trend of decreased tibial slope angle . The deviation between bone resection and subsequent implant placement was ≥2 ° in none of the cases . Conclusions The study confirms the hypothesis that conventional instrumentation fails to achieve optimal accuracy in the positioning of the tibial component . During each phase of the surgical procedure , a tendency towards varus malalignment and a decreased tibial slope angle were observed . Levels of evidence II Abstract Purpose The current study investigated the accuracy in achieving proper lower limb alignment and individual component positions after total knee arthroplasty ( TKA ) with 3 different instrumentation techniques . It was hypothesized that patient-specific instruments ( PSI ) would achieve more accurate lower limb alignment and component positions compared to conventional instruments ( CON ) . Methods Ninety knees in 81 patients were r and omized in 1:1:1 ratio into  CON , computer navigation ( NAV )  and PSI  groups to receive TKA . The surgical routines were st and ardized . The lower limb mechanical axis and individual component positions were assessed on st and ard radiographs . Tourniquet time , operation time and patients ’ functional scores were documented . Results Conventional instruments and PSI were more likely to result in an excessively flexed femoral component ( p = 0.001 ) compared to NAV . Number of outliers in postoperative lower limb alignment , and other components positions in the coronal and sagittal plane showed no statistically significant difference . The mean tourniquet time and operation time was significantly shorter in CON and PSI groups than NAV group ( p < 0.001 ) . Four early complications occurred in the PSI group ( p = 0.015 ) . At 3-month follow-up , there was no difference in terms of the knee range of motion and patients ’ function among the 3 groups . Conclusion No significant radiological and clinical benefit could be demonstrated in using PSI over CON or NAV in TKA . Routine use of PSI is not recommended because of the extra cost and waiting time . Level of evidence Purpose No surgical technique is capable of controlling the stability of the joint in midflexion . The purpose of the present study was to present and evaluate a surgical technique that aims to reduce the need for soft-tissue release and optimize stability in midflexion . Methods Sixty knee joints were included in this prospect i ve r and omized study . Surgery was performed either according to a classical gap ( GT ) technique or using the reversed gap ( RG ) technique . In the RG , the femoral component was positioned parallel to the surgical transepicondylar axis using a preoperative MRI and a navigation system . The frontal alignment of the tibia was then selected to produce a symmetric flexion gap . Then , the frontal alignment of the femoral component was adjusted to produce a symmetric extension gap . Soft-tissue release was defined to be extensive if more than two steps or stabilizing structures were involved . Joint stability was measured at different flexion angles ( −5 ° to 120 ° ) using a gap tensioning device and the trial femoral implant . Results In the GT group , 16 knee joints ( 53 % ) showed an instability of more than 2 mm at 5 ° , 30 ° or 60 ° , compared with 8 knee joints ( 27 % ) in the RG group ( p = 0.035 ) . The RG did not lead to a reduction in the number of soft-tissue releases , but they were less extensive . Conclusion RG reduced midflexion instability and the number of extensive soft-tissue releases . It may simplify the operation by reducing the extent of soft-tissue releases and avoid instability-related problems of knee arthroplasty . Nevertheless , it should only be performed under controlled conditions until long-term clinical data are available . Level of evidence Optimal component position in all planes and well-balanced soft tissues facilitate a good clinical outcome and long-term survival after total knee arthroplasties . We investigated the accuracy of implantation of navigated total knee arthroplasties at 3 months followup and the influence on the clinical outcome at 2 years followup . Forty-four patients ( 44 procedures ) were enrolled in our prospect i ve study . One half of the surgeries were performed using a computed tomography-based navigation system , and half were performed with im-ageless navigation . Outcomes were based on the Insall knee score parameters , anterior knee pain , patient satisfaction , feeling of instability , and step test . The radiographic parameters were the mechanical axis , tibial slope , lateral distal femoral angle , and medial proximal tibial angle . The radio-graphic measurements were similar in both groups ( patients within ± 3 ° inaccuracy range in computed tomography-based/imageless groups ; mechanical axis 86%/81 % , tibial slope 95%/91 % , lateral distal femoral angle 95%/91 % , medial proximal tibial angle 91%/95 % ) . The imageless system provided equal radiographic results , but we found improved ligament balancing in the computed tomography free group . The computed tomography-based approach has a good pre-operative planning procedure , but is more expensive and time consuming . Level of Evidence : Therapeutic Study , Level II . See the Guidelines for Authors for a complete description of levels of evidence Magnetic resonance imaging ( MRI ) or computed tomography-based patient-specific instrumentation ( PSI ) may allow for reliable alignment and fewer outliers when compared with conventionally instrumented total knee arthroplasty ( TKA ) . However , some authors have suggested that frequent intraoperative surgeon-directed changes may still be required . This study evaluated the accuracy of  PSI  to predict component sizing and alignment during TKA . A total of 84 patients ( 89 knees ) who underwent a TKA using a PSI system were evaluated . An MRI-based preoperative plan of every knee was provided and approved by the surgeons . This demonstrated the proposed prosthetic component alignment , as well as the femoral , tibial , and bearing insert component size and position . Intraoperative changes to these components were prospect ively recorded and compared with the computerized preoperative plan . Major changes were defined as any changes in femoral or tibial resection , size , and position of the components . Minor changes were defined as any change in the size of the polyethylene bearing insert . The preoperative plan was able to correctly predict the size of the implanted tibial and femoral component in 93 and 95.5 % of the cases , respectively . Thirteen major intraoperative changes were made . In one knee , the proposed femoral resection was not acceptable ( because of the presence of significant amount of osteophytes ) and was ab and oned in favor of a manual extramedullary guide . In another patient , the proposed femoral and tibial components were upsized . In two other patients , the femoral components were downsized , in four patients , the tibial components were downsized , and in another patient , it was upsized . There were also 16 minor changes , which included 2-mm upsizing of the polyethylene liner in 13 knees and 4-mm upsizing in 3 knees . Surgical experience is necessary to recognize improper component size , incorrect surgical resection , or nonideal alignment when performing TKA using PSI . The authors believe that the design and manufacture of PSI combined with a comprehensive templating result ed in excellent intraoperative concordance of the preoperative plan at the default setting s with minimal changes We undertook a prospect i ve , r and omised study using a non-invasive transcranial Doppler device to evaluate cranial embolisation in  computer-assisted navigated total knee arthroplasty ( n = 14 ) and compared this with a st and ard conventional surgical technique using intramedullary alignment guides ( n = 10 ) . All patients were selected r and omly without the knowledge of the patient , anaesthetists ( before the onset of the procedure ) and ward staff . The operations were performed by a single surgeon at one hospital using a uniform surgical approach , instrumentation , technique and release sequence . The only variable in the two groups of patients was the use of single tracker pins of the imageless navigation system in the tibia and femur of the navigated group and intramedullary femoral and tibial alignment jigs in the non-navigated group . Acetabular Doppler signals were obtained in 14 patients in the computer-assisted group and nine ( 90 % ) in the conventional group , in whom high-intensity signals were detected in seven computer-assisted patients ( 50 % ) and in all of the non-navigated patients . In the computer-assisted group no patient had more than two detectable emboli , with a mean of 0.64 ( SD 0.74 ) . In the non-navigated group the number of emboli ranged from one to 43 and six patients had more than two detectable emboli , with a mean of 10.7 ( sd 13.5 ) . The difference between the two groups was highly significant using the Wilcoxon non-parametric test ( p = 0.0003).Our findings show that computer-assisted total knee arthroplasty , when compared with conventional jig-based surgery , significantly reduces systemic emboli as detected by transcranial Doppler ultrasonography Purpose The measured resection technique and the gap-balancing technique are two philosophies used in total knee surgery . It is still unknown whether one or the other technique provides superior results when computer-assisted surgery is performed . We hypothesized that the gap-balancing technique improves joint stability because the technique relies primarily on the soft tissue . Methods A prospect i ve controlled study was performed in 116 patients using the tibia-first or femur-first technique .  The ColumbusTM total knee system and the Orthopilot ® ( Aesculap ® AG , Tuttlingen , Germany ) navigation system were used in all cases . Sixty-three patients were allocated to the femur-first technique ( group F ) and 53 patients to the tibial first technique ( group T ) . The mean follow-up time was 11.4 ± 1.1 months . The KSS , KOOS and SF-36 were taken prior to surgery and at the time of follow-up for clinical assessment . Long-leg weight-bearing radiographs were performed to assess ligament alignment . Radiographs in varus and valgus stress were performed using the Telos ® -Instrument ( Telos ® GmbH , Greisheim , Germany ) under a force of 15 N at the time of follow-up for the assessment of medial – lateral stability . The nonparametric t test ( Mann – Whitney U-test ) was used in order to compare the ligament stability and the scores between group F and group T. Results The lateral joint space opening for groups F and T was 3.4 ° ± 1.4 ° and 3.9 ° ± 1.7 ° , respectively ( n.s . ) , and the medial joint space opening for groups F and T was 4 ° ± 1.4 ° and 4.1 ° ± 1.7 ° , respectively ( n.s . ) . The femorotibial mechanical axis for groups F and T revealed 1.4 ° ± 1.2 ° and 0.7 ° ± 2.0 ° of varus , respectively ( p = 0.138 ) . The clinical assessment showed significant improvement according to KSS , KOOS and SF-36 in all subscales . Neither of the sores showed significant differences between the two groups . Conclusion The surgeon should use his/her preferred surgical technique providing the implantation is performed with computer assistance . It remains unclear whether the same findings will occur after conventional surgery . Level of evidence II The purpose of this study was to evaluate the use of a  navigation device  in a cohort of 42 total knee arthroplasties ( TKA ) . The patients were r and omised into two groups . Total knee arthroplasties performed using the conventional technique formed the control group ( 21 knees ) ; the experimental group included 21 knees performed with the aid of a computed navigation system .  Postoperative mean values for the various measurements showed no significant difference in component alignment . However , the range of individual measurements for coronal and sagittal plane positioning was smaller in the navigated group , in which there were no outliers . Rotational alignment was not different between the two groups . This confirms the advantages and limitations of navigated TKA presented in larger studies Background The purpose was to investigate whether patient-specific factors ( PSF ) and surgically modifiable factors ( SMF ) , measured by means of a computer-assisted navigation system , can predict the Knee Society Scores ( KSS ) after total knee arthroplasty ( TKA ) . Methods Data from 99 patients collected during a r and omized clinical trial were used for this secondary data analysis . The KSS scores of the patients were measured preoperatively and at 4-years follow-up . Multiple regression analyses were performed to investigate which combination of variables would be the best to predict the 4-years KSS scores . Results When considering SMF alone the combination of four of them significantly predicted the 4-years KSS-F score ( p = 0.009 ) , explaining 18 % of its variation . When considering only PSF the combination of age and body weight significantly predicted the 4-years KSS-F ( p = 0.008 ) , explaining 11 % of its variation . When considering both groups of predictors simultaneously the combination of three PSF and two SMF significantly predicted the 4-years KSS-F ( p = 0.007 ) , explaining 20 % of its variation . Conclusions Younger age , better preoperative KSS-F scores and lower BMI before surgery , a positive tibial component slope and small changes in femoral offset were predictors of better KSS-F scores at 4-years Robot-assisted Total Knee Arthroplasty ( TKA ) improves the accuracy and precision of component implantation and mechanical axis ( MA ) alignment . Joint-line restoration in robot-assisted TKA is not widely described and joint-line deviation of>5 mm results in mid-flexion instability and poor outcomes . We prospect ively r and omised 60 patients into two groups : 31 patients ( robot-assisted ) , 29 patients ( conventional ) .  No MA outliers ( > ±3 ° from neutral ) or notching was noted in the robot-assisted group as compared with 19.4 % ( P=0.049 ) and 10.3 % ( P=0.238 ) respectively in the conventional group . The robot-assisted group had 3.23 % joint-line outliers ( > 5 mm ) as compared to 20.6 % in the conventional group ( P=0.049 ) . Robot-assisted TKA produces similar short-term clinical outcomes when compared to conventional methods with reduction of MA alignment and joint-line deviation outliers Purpose The purpose of this study was to assess the midterm results of total knee arthroplasty ( TKA ) implanted with  a specific computer navigation system in a group of patients ( NAV ) and to assess the same prosthesis implanted with the conventional technique in another group ( CON ) ; we hypothesized that computer navigation surgery would improve implant alignment , functional scores and survival of the implant compared to the conventional technique . Methods From 2008 to 2009 , 225 patients were enrolled in the study and r and omly assigned in CON and NAV groups ; 240 consecutive mobile-bearing ultra-congruent score ( Amplitude , Valence , France ) TKAs were performed by a single surgeon , 117 using the conventional method and 123 using the computer-navigated approach .  Clinical outcome assessment was based on the Knee Society Score ( KSS ) , the Hospital for Special Surgery Knee Score and the Western Ontario Mac Master University Index score . Component survival was calculated by Kaplan – Meier analysis . Results Median follow-up was 6.4 years ( range 6–7 years ) . Two patients were lost to follow-up . No differences were seen between the two groups in age , sex , BMI and side of implantation . Three patients of CON group referred feelings of instability during walking , but clinical tests were all negative . NAV group showed statistical significant better KSS Score and wider ROM and fewer outliers from neutral mechanical axis , lateral distal femoral angle , medial proximal tibial angle and tibial slope in post-operative radiographic assessment . There was one case of early post-operative superficial infection ( caused by Staph . Aureus ) successfully treated with antibiotics . No mechanical loosening , mobile-bearing dislocation or patellofemoral complication was seen . At 7 years of follow-up , component survival in relation to the risk of aseptic loosening or other complications was 100 % . There were no implant revisions . Conclusion This study demonstrates superior accuracy in implant positioning and statistical significant better functional outcomes of computer-navigated TKA . Computer navigation for TKAs should be used routinely in primary implants . Level of evidence II Optimal orientation of the acetabular component of a  total hip prosthesis  is an important factor in determining the early and long-term result of a  total hip arthroplasty ( THA ) . Conventional positioning of the cup component is usually done using a free-h and method , or with the help of a mechanical acetabular alignment guide . However , these methods have proven to be inaccurate , and a great variation in orientation of the cup is found postoperatively . In this study , we wished to determine if the variability of the abduction angle of acetabular cups could be reduced with the use of computer navigation . The abduction angles of the acetabular components of three groups of 50 THAs were assessed . In the first group , a free-h and method was used to position the cup component . This group was operated in the period before we started using computer navigation for hip surgery . In the second group , CT-based computer navigation was used to plan and help position the cup . The third group consisted of 50 THA cases in which a free-h and method was used to position the cup , although these procedures were performed in the period after we had begun using the Computer Assisted Surgery ( CAS ) system . The variability in cup abduction angle was assessed in all three groups and compared . There was a significant reduction in variability in the CAS group compared to the first group . There was also a reduction in variability in the CAS group compared to the third group , although this was not statistically significant . It is concluded that the use of computer navigation helped the surgeon to place the cup component with less variability of the abduction angle , and , more importantly , we found that no cups were placed in the more extreme positions ( outliers ) We performed a prospect i ve , r and omised controlled trial of unicompartmental knee arthroplasty comparing the performance of the Acrobot system with conventional surgery . A total of 27 patients ( 28 knees ) awaiting unicompartmental knee arthroplasty were r and omly allocated to have the operation performed conventionally or with the assistance of the Acrobot . The primary outcome measurement was the angle of tibiofemoral alignment in the coronal plane , measured by CT . Other secondary parameters were evaluated and are reported . All of the Acrobot group had tibiofemoral alignment in the coronal plane within 2 degrees of the planned position , while only 40 % of the conventional group achieved this level of accuracy . While the operations took longer , no adverse effects were noted , and there was a trend towards improvement in performance with increasing accuracy based on the Western Ontario and McMaster Universities Osteoarthritis Index and American Knee Society scores at six weeks and three months . The Acrobot device allows the surgeon to reproduce a pre-operative plan more reliably than is possible using conventional techniques which may have clinical advantages Navigation in primary total hip arthroplasty has a history of over 20 years . During this process , imageless computer navigation can be particularly helpful in optimally restoring the hip ’s biomechanics . This involves the accurate placement of the acetabular component with the determination of the anteversion and abduction , whereby the navigated femur-first technique also allows for a calculation of the combined anteversion . Additional critical parameters such as the reconstruction of the rotation centre , as well as the femoral and acetabular offset , can also be optimally adjusted . Last but not least , an intra-operative evaluation and equalisation of the leg length is possible . Nonetheless , the disadvantages of this surgical technique in terms of the high costs in the acquisition and preservation of the necessary devices , as well as the longer operation time , must be taken into account . However , economic aspects are not the only thing preventing widespread use of the navigation technique . Determining the plane of reference ( APP ) for the optimal orientation of the implants is based on palpation of the bony l and marks – and this is influenced by the thickness of the soft tissue layer . Furthermore , the experience of the surgeon constitutes a variable that influences the accuracy of navigation . In summary , hip navigation certainly offers an interesting technique for the optimisation of  total hip arthroplasty with reconstruction of proper biomechanics . At the same time , there is currently a lack of high- quality r and omised controlled long-term trials that evaluate the clinical advantage for the patients , together with cost utility and survival rates . Cite this article : Renner L , Janz V , Perka C , Wassilew GI . What do we get from navigation in primary THA ? EFORT Open Rev 2016;1:205 - 210 . 10.1302/2058 - 5241.1.000034 Introduction : Accurate intraoperative assessment of lower limb alignment is crucial for the treatment of long bone fractures , implantation of knee arthroplasties and correction of deformities . During orthopaedic surgery , exact real time control of the mechanical axis is strongly desirable . The aim of this study was to compare conventional intraoperative analysis of the mechanical axis by the cable method with continuous , 3-dimensional imaging with a navigation system . Material s and methods : Twenty legs of fresh human cadaver were r and omly assigned to conventional analysis with the cable method ( n=10 ) or navigated analysis with a fluoroscopy based navigation system ( n=10 ) . The intersection of the mechanical axis with the tibia plateau was presented as percentage of the tibia plateau ( beginning with 0 % at the medial border and ending with 100 % laterally ) . CT-scans were performed for all legs and the CT-values of the mechanical axis were compared to the measurements after cable method and navigation . Furthermore , the radiation time and dose area product of both groups for single analysis of the mechanical axis was compared . Results : Conventional evaluation of the mechanical axis by the cable method showed 6.0±3.1 % difference compared to the analysis by CT . In the navigated group the difference was 2.6±1.8 % ( P=0.008 ) . Radiation time and dose area product were highly significantly lower after conventional measurement . Conclusions : Navigated intraoperative evaluation of the mechanical axis offers increased accuracy compared to conventional intraoperative analysis . Furthermore , navigation provides continuous control not only of the mechanical axis , but also of the sagittal and transverse plane . Using the cable method , radiation exposure depends on the number of measurements and is lower compared to the navigation system for single intraoperative analysis of the mechanical axis , but may be higher in case of repeated intraoperative measurements Purpose The objective of this prospect i ve study was to compare the functional outcome of conventional measured resection technique and computer-assisted gap balancing technique in TKA . Methods 140 patients were r and omized into two groups . The conventional measured resection technique without computer navigation was performed in Group 1 and the computer-assisted gap balancing technique in Group 2 . Range of motion , clinical laxity assessment with KT-1000 arthrometer , postoperative radiological films and various functional knee scores were documented at 6 months and 2 years . Results At 2 years , there were significantly more patients ( five patients , 7 % ) in the Group 1 with flexion contractures of more than 5 ° ( P = 0.05 ) . There were significantly more outliers in the Group 1 ( eight patients , 11 % ) , who demonstrated anterior tibial translation > 5 mm , than Group 2 ( two patients , 3 % ) ( P = 0.041 ) . The total excursion at 20 ° was significantly higher in Group 1 at 6 months ( P = 0.012 ) and after 2 years ( P = 0.031 ) . Group 2 was able to demonstrate significantly better limb alignment with fewer outliers ( more than 3 ° varus/valgus ) than Group 1 . At 6-month follow-up , Group 2 demonstrated better outcomes in Function Score ( P = 0.040 ) and Total Oxford Score ( P = 0.031 ) . At 2-year review , Group 2 had better outcome in the Total Oxford Score ( 0.030 ) . Conclusion Computer-assisted gap balancing technique was able to achieve more precise soft tissue balance and restoration of limb alignment with better knee scores as compared to the conventional measured resection technique in total knee arthroplasty . Level of evidence Background Navigation was introduced into  total knee arthroplasty ( TKA ) to improve accuracy of component position , function and survival of implants . This study was design ed to assess the outcome of navigated TKA in comparison with conventional implantation with the focus on rotational component position and clinical mid-term results . Methods In a prospect ively r and omized single-blinded approach , 90 patients with primary gonarthrosis were assigned to three different groups . Thirty patients each were assigned to NexGen LPS without and with navigation ( groups 1 and 2 ) , and 30 patients to navigation with the Stryker Scorpio PS ( group 3 ) . The navigation system used was the imageless Stryker KneeTrac , version 1.0 . Clinical outcome was assessed by a blinded observer applying the Knee Society Score ( KSS ) and a visual analogue scale ( VAS ) for pain . CT scans and radiographs were conducted prior to and 12 weeks after index surgery . Results Seventy-nine patients were available for clinical evaluation at 3 ± 0.4 years follow-up . Four implants had to be revised for early loosening or infection ( 4.4 % ) . Four patients had died and three patients were not able to follow the invitation for clinical assessment . Functional results in the KSS were significantly lower after navigated TKA . Operation time and incisions with navigation were significantly longer . Significantly less radiological outliers with navigation were found for coronal alignment of the femur , only . Conclusion In this series , no beneficial effect for navigation in TKA could be shown assessing clinical data , as functional results in the presented series seemed to be lower after first generation navigated TKA . The clinical mid- to long-term value of navigation remains to be evaluated in larger patient series or meta-analyses at longer follow-up . Trial registration numberDRKS Abstract Purpose The introduction of patient-specific instruments ( PSI ) for guiding bone cuts could increase the incidence of malalignment in primary total knee arthroplasty . The purpose of this study was to assess the agreement between one type of patient-specific instrumentation ( Zimmer PSI ) and the pre-operative plan with respect to bone cuts and component alignment during TKR using imageless computer navigation . Methods A consecutive series of 30 femoral and tibial guides  were assessed in-theatre by the same surgeon using computer navigation . Following surgical exposure , the PSI cutting guides were placed on the joint surface and alignment assessed using the navigation tracker . The difference between in-theatre data and the pre-operative plan was recorded and analysed . Results The error between in-theatre measurements and pre-operative plan for the femoral and tibial components exceeded 3 ° for 3 and 17 % of the sample , respectively , while the error for total coronal alignment exceeded 3 ° for 27 % of the sample . Conclusion The present results indicate that alignment with Zimmer PSI cutting blocks , assessed by imageless navigation , does not match the pre-operative plan in a proportion of cases . To prevent unnecessary increases in the incidence of malalignment in primary TKR , it is recommended that these devices should not be used without objective verification of alignment , either in real-time or with post-operative imaging . Further work is required to identify the source of discrepancies and vali date these devices prior to routine use . Level of evidence II BACKGROUND The literature lacks studies that confirm whether the improved radiographic alignment that can be achieved with computer-navigated total knee arthroplasty improves patients ’ activities of daily living or the durability of total knee prostheses . The purpose of this study was to determine whether computer-navigated total knee arthroplasty improves the clinical function , alignment , and survivorship of the components . METHODS We prospect ively compared the results of 520 patients with osteoarthritis who underwent computer-navigated total knee arthroplasty for one knee and conventional total knee arthroplasty for the other . The assignment of the knee to navigation or not was done r and omly . There were 452 women ( 904 knees ) and sixty-eight men ( 136 knees ) with a mean age of sixty-eight years ( range , forty-nine to eighty-eight years ) at the time of the index arthroplasty . The mean follow-up period was 10.8 years ( range , ten to twelve years ) . The patients were assessed clinical ly and radiographically with the rating system of the Knee Society and with the Western Ontario and McMaster Universities Osteoarthritis Index ( WOMAC ) score at three months , one year , and annually thereafter . RESULTS Total knee scores , knee function scores , pain scores , WOMAC scores , knee motion , and activity scores did not show statistically significant differences between the two groups preoperatively or at the time of the final follow-up . Alignment and the survivorship of the components were not significantly different between the two groups . The Kaplan-Meier survivorship with revision as the end point at 10.8 years was 98.8 % ( 95 % confidence interval [ CI ] , 0.96 to 1.00 ) in the computernavigated total knee arthroplasty group and 99.2 % ( 95 % CI , 0.96 to 1.00 ) in the conventional total knee arthroplasty group . CONCLUSIONS Our data demonstrated no difference in clinical function or alignment and survivorship of the components between the knees that underwent computer-navigated total knee arthroplasty and those that underwent conventional total knee arthroplasty BACKGROUND Unicompartmental knee arthroplasty(UKA ) has become a treatment of choice for many patients with isolated unicomparmental arthritis due to its specific advantages over total knee arthroplasty , but few studies have compared conventional and navigational UKA with similar instrumentation on mid- to long-term results . We investigated whether the use of imageless navigation can improve implant positioning and clinical outcomes of UKA at a long-term follow-up compared to the conventional technique . METHODS We prospect ively studied clinical and radiological results in 68 patients with an average age of 64.0 years ( range , 50 to 81 years ) who received UKA between January 2003 and December 2005 using the conventional or navigational technique .  Clinical evaluations were performed preoperatively and the last follow-up included knee range of motion , Hospital for Special Surgery ( HSS ) scores , Western Ontario and McMaster Universities Osteoarthritis Index ( WOMAC ) scores and Visual Analogue Scale ( VAS ) pain score . For radiologic evaluation , the mechanical alignment of the lower limb was measured using mechanical femoro-tibial angle ( mFTA ) and Kennedy protocol . RESULTS After an average 9-year follow-up ( range , 7.4 to 10.8 years ) , the navigation group showed better coronal alignments of the components , fewer radiological outliers and better clinical scores , but similar estimated 10-year prosthesis survival rates . CONCLUSION This study indicates that the use of navigation significantly contributes to the desired mechanical axis and improved component placement as compared to the conventional technique . LEVEL OF EVIDENCE Prospect i ve comparative study , Level III Background Recently , patient-specific guides ( PSGs ) have been introduced , cl aim ing a significant improvement in accuracy and reproducibility of component positioning in TKA . Despite intensive marketing by the manufacturers , this cl aim has not yet been confirmed in a controlled prospect i ve trial . Questions / purpose sWe ( 1 ) compared three-planar component alignment and overall coronal mechanical alignment between PSG and conventional instrumentation and ( 2 ) logged the need for applying changes in the suggested position of the PSG . Methods In this r and omized controlled trial , we enrolled 128 patients . In the PSG cohort , surgical navigation was used as an intraoperative control . When the suggested cut deviated more than 3 ° from target , the use of PSG was ab and oned and marked as an outlier . When cranial-caudal position or size was adapted , the PSG was marked as modified . All patients underwent long-leg st and ing radiography and CT scan .  Deviation of more than 3 ° from the target in any plane was defined as an outlier . Results The PSG and conventional cohorts showed similar numbers of outliers in overall coronal alignment ( 25 % versus 28 % ; p = 0.69 ) , femoral coronal alignment ( 7 % versus 14 % ) ( p = 0.24 ) , and femoral axial alignment ( 23 % versus 17 % ; p = 0.50 ) . There were more outliers in tibial coronal ( 15 % versus 3 % ; p = 0.03 ) and sagittal 21 % versus 3 % ; p = 0.002 ) alignment in the PSG group than in the conventional group . PSGs were ab and oned in 14 patients ( 22 % ) and modified in 18 ( 28 % ) . Conclusions PSGs do not improve accuracy in TKA and , in our experience , were somewhat impractical in that the procedure needed to be either modified or ab and oned with some frequency . Level of Evidence Level I , therapeutic study . See instructions for authors for a complete description of levels of evidence A total of 208 patients were enrolled in a multicenter , prospect i ve r and omized , institutional review board-approved study that compared preoperative surgical plan to postoperative 2-dimensional radiographic alignment measured by a blinded review er for  primary total knee arthroplasty ( TKA ) implanted using computer-assisted surgery ( CAS ) compared with conventional TKA instrumentation . The results demonstrated a statistically significant improvement in the coronal tibial component alignment ( P < .03 ) and failed to demonstrate a statistically significant improvement in the mechanical axis , femoral coronal/sagittal , and tibial sagittal alignment . Knee Society Score knee and function scores and 6-minute walk test were equivalent between the 2 treatment groups at all postoperative intervals . There was a statistically significant increase in the skin-skin time ( P < .0001 ) and the time until first bone cut ( P < .0001 ) for the CAS knees compared with those implanted with conventional instrumentation . The use of CAS in this r and omized clinical trial conducted at high-volume centers did not offer a clinical ly meaningful improvement in postoperative alignment , clinical , functional , or safety outcomes compared with conventional TKA
A literature review of robotic systems showed that these systems can , similarly to computer navigation , reliably improve lower leg alignment , component positioning and soft tissues balancing .
Findings in this study suggest that computer navigation or robotic assistance may help managing these multiple variables and could improve outcomes .
Recently , there is a growing interest in surgical variables that are intraoperatively controlled by orthopaedic surgeons , including lower leg alignment , component positioning and soft tissues balancing .
Since more tight control over these factors is associated with improved outcomes of unicompartmental knee arthroplasty and total knee arthroplasty ( TKA ) , several computer navigation and robotic-assisted systems have been developed .
Although mechanical axis accuracy and component positioning have been shown to improve with computer navigation , no superiority in functional outcomes has yet been shown .
This could be explained by the fact that many differences exist between the number and type of surgical variables these systems control .
Most systems control lower leg alignment and component positioning , while some in addition control soft tissue balancing .
Finally , robotic-assisted systems have the additional advantage of improving surgical precision .
Manually controlling all these surgical variables can be difficult for the orthopaedic surgeon .