We describe a patient with multiple sclerosis (MS), who developed recurrent dislocations after total knee arthroplasty. She had both knees replaced using similar mobile-bearing knee prostheses, but the outcome was worse in the leg which was more severely affected with MS.

Background. Currently there are various knee prosthesis designs available each with its plus and minus points; there is no general consensus on whether mobile-bearing knees are functionally better than fixed-bearing ones. This study is designed to compare outcomes after total knee arthroplasty with both of the above prostheses. Materials & Methods. 50 patients (68 knees) who'd had a total knee arthroplasty between April 1999 and April 2008 at both Akhtar and Kian Hospitals for primary osteoarthritis were selected. In 30 cases a fixed-bearing knee (Scorpio(r), Stryker) and in the remaining 38 a mobile-bearing prosthesis (Rotaglide(r), Corin Group) was used. Patients' knees were scored before and after the operation according to the Knee Society Scoring System. The mobile-bearing group had an average age of 65 and 34 months' follow-up; in the fixed-bearing group the average age was 69 and the average follow-up 30 months. Results. The average knee score in the mobile-bearing group rose from 29 to 64 while in the fixed-bearing group the score changed from 31 to 68. The average functional score moved from 45 to 67 in the mobile-bearing group and from 34 to 57 in the fixed-bearing group. The average overall score, for the fixed-bearing group, moved from 65 to 125 and in the mobile-bearing group from 75 to 128. Conclusion. In both groups the average knee/functional knee scores increased after the operation and all patients were happy with the results, however statistically there was no meaningful relationship between pre-and post-operation scores. So regarding to our findings, there is no preference between these two types of prosthesis

Background. No study compared the clinical results of the posterior-stabilized mobile-bearing knee with those of nonposterior-stabilized mobile-bearing knee in the same patients. The purpose of this study was to examine whether the clinical and radiographic results, range of motion, patients satisfaction, and complication rates would be better in the knees with a posterior-stabilized mobile-bearing knee than in the knees with a nonposterior-stabilized mobile-bearing knee. Methods. One hundred and fourteen patients (mean age, 67.9 years) received a nonposterior-stabilized mobile-bearing knee prosthesis in one knee and a posterior-stabilized mobile-bearing knee prosthesis in the contralateral knee. Seven patients were men, and 107 were women. At the time of each follow-up (mean, 7.3 years; range, seven to 7.6 years), the patients were assessed clinically and radiographically. Results. The mean postoperative Knee Society knee score (95 points versus 96 points, p=0.176), Hospital for Special Surgery knee score (92 points versus 93 points, p=0.077), and Western Ontario and McMaster University Osteoarthritis score (21 versus 20 points, p=0.785) were similar between the two group. At the final follow-up, the average range of motion was 27.7° (range, 70° to 150°) in the knees with a nonposterior stabilized mobile-bearing prosthesis and it was 132° (range, 90 to 150 °) in the knees with a posterior-stabilized mobile-bearing prosthesis. Complication rates (2.6% versus 1.8%) were similar between the two groups. The estimated survival rate was 97.4% at eight years with an overall revision rate of 2.6% (three of 114 knees) in the nonposterior-stabilized mobile-bearing prosthesis group and 98.2% at eight years with an overall revision rate of 1.8% (two of 114 knees) in the posterior-stabilized mobile-bearing prosthesis group. Conclusions. After a minimum duration of follow-up of seven years, we found no significant differences between the two groups with regard to the clinical and radiographic results, or patient satisfaction, or complication rate. However, the posterior-stabilized mobile-bearing prosthesis group had a greater range of knee motion than the nonposterior-stabilized mobile-bearing prosthesis group

Aims. Implant failure has become more common as the number of primary total ankle arthroplasties (TAAs) performed has increased. Although revision arthroplasty has gained attention for functional preservation, the long-term results remain unclear. This study aimed to assess the long-term outcomes of revision TAA using a mobile-bearing prosthesis in a considerably large cohort; the risk factors for failure were also determined. Methods. This single-centre retrospective cohort study included 116 patients (117 ankles) who underwent revision TAA for failed primary TAA between July 2000 and March 2010. Survival analysis and risk factor assessment were performed, and clinical performance and patient satisfaction were evaluated preoperatively and at last follow-up. Results. The mean duration from initial revision TAA to last follow-up was 15.0 years (SD 3.0; 11.2 to 20.5). The cumulative survival rates of the revised ankles were 81% (95% confidence interval (CI) 74% to 88%), 74% (65% to 82%), and 70% (61% to 79%) at five, ten, and 15 years, respectively. Comorbidities prior to primary TAA, aseptic loosening, instability, or grafting of cysts were found to be the most common risk factors for secondary revision. The median value for preoperative pain, as assessed using the visual analogue scale, declined from 6 (interquartile range (IQR) 5 to 8) to 2 (IQR 0 to 5) (p < 0.001) and the mean American Orthopaedic Foot and Ankle Society ankle-hindfoot score improved from 43 (SD 17) preoperatively to 70 (SD 20) (p < 0.001) at last follow-up. Conclusion. Revision TAA offers acceptable survival rates after 15 years; it therefore offers a valuable option for treatment of implant failure in carefully selected cases. Although patient-reported outcomes improve substantially, the degree of improvement reported following primary TAA is not achieved. Cite this article: Bone Joint J 2024;106-B(1):46–52

We compared patient-reported outcomes of the Kinemax fixed- and mobile-bearing total knee replacement in a multi-centre randomised controlled trial. Patients were randomised to the fixed- or the mobile-bearing prosthesis via a sealed envelope method after the bone cuts had been made in the operating theatre. Randomisation was stratified by centre and diagnosis. Patients were assessed pre-operatively and at eight to 12 weeks, one year and two years post-operatively. Validated questionnaires 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 validated 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

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 prospectively evaluated. Comparative analysis of both designs 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 designs 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

Clinical implantation represents the ultimate experiment of any component and often demonstrates areas of strengths and weaknesses not predicted from in vitro testing. Mobile bearing knees incorporate an additional articulating interface between the flat distal PE insert and a highly polished metal tibial tray. This can allow the proximal interface to retain high conformity whilst leading to reduced stresses at the bone – prosthesis interface by permitting complex distal interface compensatory motion to occur (rotation and/or translation). Retrieval reports on many of the new generation of mobile bearing implants remains scarce. This study presented a retrieval analysis of 9 mobile bearing inserts that had be in situ for less than 24 months. Nine cemented mobile bearing implants (6 AP Glide, 1 LCS, 1 MBK and 1TRAK) were received into our Implant Retrieval Program. The femoral component, tibial tray and PE insert were macroscopically examined under a stereo-zoom microscope for evidence of damage. The PE inserts were graded for wear based on optical and SEM assessments. The proximal and distal surfaces of the PE inserts were subsequently assessed for surface roughness following ISO 97 (Ra and Rp) using a Surfanalyzer 5400 (Federal Products, Providence, RI). Virgin, unused PE inserts were analysed and served as a comparison to the retrieved implants. Time in situ time for these implants ranged from 6 months to 24 months (mean 18.6). The implants were revised for instability and pain (AP glide) or dislocation (TRAK). Damage to the femoral components, in general, was minimal with some evidence of a transfer film of PE. The proximal surface of the tibial trays presented evidence of PE transfer as well as some scratches but in general were intact. The proximal PE and distal PE articulating surfaces demonstrated significant areas of damage due to third body wear which was identified on EDAX to be PMMA. Areas of burnishing were also present at the proximal and distal interface. The damage, in part, correlated with the complex kinematics of each design

Between April 2004 and July 2007, we performed 241 primary total knee replacements in 204 patients using the e.motion posterior cruciate-retaining, multidirectional mobile-bearing prosthesis. Of these, 100 were carried out using an image-free navigation system, and the remaining 141 with the conventional technique. We conducted a retrospective study from the prospectively collected data of these patients to assess the early results of this new mobile-bearing design. At a mean follow-up of 49 months (32 to 71), 18 knees (7.5%) had mechanical complications of which 13 required revision. Three of these had a peri-prosthetic fracture, and were removed from the study. The indication for revision in the remaining ten was loosening of the femoral component in two, tibiofemoral dislocation in three, disassociation of the polyethylene liner in four, and a broken polyethyene liner in one. There were eight further mechanically unstable knees which presented with recurrent disassociation of the polyethylene liner. There was no significant difference in the incidence of mechanical instability between the navigation-assisted procedures (8 of 99, 8.1%) and the conventionally implanted knees (10 of 139, 7.2%). In our view, the relatively high rate of mechanical complications and revision within 30 months precludes the further use of new design of knee replacement

The Self Aligning (SAL I) total knee prosthesis (Sulzer, Winterthur) is a first generation cruciate retaining mobile bearing implant allowing unrestricted rotation and up to 5 mm. of translation. A consecutive series of two hundred and three SAL I components in one hundred and sixty- seven patients were implanted between 1990 and 1994 and were reviewed clinically and radiographically. Quality of life outcomes (SF-12 and WOMAC) were also reviewed pre-operatively and regular intervals. This first generation mobile bearing knee implant in this series, continues to function well at a minimum ten years follow-up, with a mechanical failure rate (8%) comparable to fixed bearing designs. A consecutive series of SAL I total knee arthroplasties were performed between 1990 and 1994 and were reviewed clinically, radiographically and with standardized quality of life outcome tools, including the SF-12 and the Western Ontario MacMaster Osteoarthritis Index (WOMAC). Patient demographics, radiographs, and multiple validated outcome measures (WOMAC, SF12, Knee Society Clinical Rating System) were evaluated pre-operatively, at three, twelve, and twenty-four months and every two years thereafter. The series included two hundred and three SAL I implants in one hundred and sixy-sevenpatients. There have been sixty-nine patient deaths (eighty-five procedures), nine patients (eleven procedures) now reside in nursing homes and are unable to return due to medical complications, two patients (three procedures) could not be located. Nine-teen patients/procedures have had revision surgery. Therefore, seventy-six patients (ninety-three procedures) were evaluated with over ten year follow-up (average 10.89 years, range 10.03–13.72). Indications for revision included, sepsis (three), aseptic loosening (eight), instability (two) and poly-wear (six). The KSCRS was assessed for all remaining patients at greater than ten years including pain (45.83), function(65.60), range of motion extension(0.13) and flexion(113.82) as well as the results of the WOMAC (pain-4.36, joint stiffness-2.29, function-18.66, total- 15.92) and SF-12 (Mental-55.37 Physical- 34.99). The SAL I mobile bearing implant continues to perform comparably to fixed bearing cruciate retaining designs. This first generation mobile bearing knee implant continues to function well at a minimum ten years follow-up, with a mechanical failure rate (8%) comparable to fixed bearing designs

The posterior-stabilized knee prosthesis is designed specifically to provide the posterior stability to a knee arthroplasty when PCL is deficient or has to be sacrificed. Posterior dislocation of such prosthesis is rare but dreaded complication. There are several causes of postoperative dislocation such as malposition of the prosthesis, preoperative valgus deformity, a defect of the extensor mechanism and overwidening of the flexion gap. Posterior-stabilized rotating-platform mobile-bearing knee implants have been widely used to further improve the postoperative range of motion by incorporation of the post and cam mechanism to improve the posterior roll back during flexion and to overcome the wear and osteolysis problems due to significant undersurface micromotion of posterior-stabilized fixed-bearing knees. But, spin-out or rotatory dislocation of the polyethylene insert can occurs as result of excessive rotation of the rotating platform accompanied by translation of the femur on the tibia after mobile-bearing total knee arthroplasty, but that is very rare. Here, authors describe an unusual case of acute 180° rotatory dislocation of the rotating platform after posterior dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty. A 71-year-old male with knee osteoarthritis underwent a TKRA using posterior-stabilized mobile-bearing prosthesis. The posterior dislocation of the total knee arthroplasty occurred 5 weeks postoperatively(Fig. 1). We underwent closed reduction of posterior dislocated total knee arthroplasty resulting in a complete 180° rotatory dislocation of the rotating platform (Fig. 2). He was treated with open exploration and polyethylene exchange with a larger component. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty can occur with valgus laxity, cause 90° spin-out of the polyethylene insert and closed reduction attempts may contribute to complete 180° rotatory dislocation of the rotating platform. Special attention needs to be paid to both AP and lateral view to ensure that the platform is truly reduced and not just rotated 180° as was in this case

Introduction. In total knee arthroplasty, the alignment of leg depends on the alignment of the component. In unicompartmental knee arthroplasty, it is determined by the thickness of the implant relative to the bone excised mostly. After initial scepticism, UKA is increasingly accepted as a reliable procedure for unicompartmental knee osteoarthritis with the improvements in implant design, surgical technique and appropriate patient selection. Recently, computer assisted UKA is helpful in accuracy and less invasive procedure. But, fixed bearing or mobile bearing in UKA is still controversy. We compared the early clinical and radiological results of robot-assisted unicompartmental knee arthroplasty using a fixed bearing design versus a mobile type bearing design. Materials and Methods. A data set of 50 cases of isolated compartmental degenerative disease that underwent robot-assisted UKA using a fixed bearing design were compared to a data set of 50 cases using a mobile bearing type design. The operations were performed by one-senior author with the same robot system. The clinical evaluations included the Knee Society Score (knee score, functional score) and postoperative complications. The radiological evaluations was assessed by 3-foot standing radiographs using the technique of Kennedy and White to determine the mechanical axis and femoro-tibial angle for knee alignment. Operative factors were evaluated including length of skin incision, operation time, blood loss, hospital stay and intraoperative complications. Results. There were no statistically significant differences in operation time, skin incision size, blood loss and hospital stay. (p > 0.05) There were no significant differences in Knee Society Scores at last follow up. An average preoperative femorotibial alignment was varus alignment of −1° in both groups. Postoperative patients with fixed-bearing implants had an average +2.1° valgus and the patients with mobile bearing implants had +5.4° valgus in femorotibial alignment, which was different.(p<0.05) There was one case of medial tibia plateau fracture in fixed bearing group in 3 months postoperatively. And there were one case of liner dislocation with unstable knee in 6 weeks postoperatively and one case of femoral component loosening in 1 year postoperatively in mobile bearing group. There was no intraoperative complication. The average preoperative knee score was 45.8, which improved to 89.5 in fixed bearing group and 46.5, which improved to 91.2 in mobile bearing group at last followup. The average preoperative function score was 62.4 which improved to 86.5 in fixed bearing group and 60.7 which improved to 88.2 in mobile bearing group at last followup. Conclusion. In ourearly experience, two types of bearing of robot-assisted UKA groups showed no statistical differences in clinical assessment but there was statistical difference in postoperative radiological corrected alignment. But in aspect of early complications, we think that mobile bearing seems to be requiring more attention in surgery

Aims

Unicompartmental knee arthroplasty (UKA) is the preferred treatment for anterior medial knee osteoarthritis (OA) owing to the rapid postoperative recovery. However, the risk factors for UKA failure remain controversial.

The April 2023 Foot & Ankle Roundup³⁶⁰ looks at: Outcomes following a two-stage revision total ankle arthroplasty for periprosthetic joint infection; Temporary bridge plate fixation and joint motion after an unstable Lisfranc injury; Outcomes of fusion in type II os naviculare; Total ankle arthroplasty versus arthrodesis for end-stage ankle osteoarthritis; Normal saline for plantar fasciitis: placebo or therapeutic?; Distraction arthroplasty for ankle osteoarthritis: does it work?; Let there be movement: ankle arthroplasty after previous fusion; Morbidity and mortality after diabetic Charcot foot arthropathy.

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 random 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 standard implant. It demonstrates a small but significant clinical advantage for the mobile-bearing design

There is ample data to confirm that Computer-assisted total knee replacement improves alignment of the limb when compared with the conventional technique. There is also published evidence that optimum alignment correlates with longevity of implants. CAS enables accurate component alignment of both femoral and tibial components. It enables accurate restoration of the posterior tibial slope which has important consequences for flexion range and stability of the component in flexion especially if mobile bearing implants are considered. CAS also aids in correctly orienting rotation of the femoral component; this has value in minimizing patellar maltracking. We will present our data showing accurate restoration of joint line and posterior femoral offset. As CAS ensures alignment, rotation, sizing and positioning of components, the surgeon is free to devote his efforts to ensuring soft-tissue balance and stability, since TKA is really a ‘soft-tissue’ operation. How CAS is of immense value in deformity correction and soft-tissue balancing will be illustrated with examples. It helps in better understanding and quantification of the effects of soft-tissue release on flexion-extension gaps and this is of great value not only for minimal deformities (to minimise releases) but also for severe deformities (to ensure complete correction by adequate release). CAS is invaluable in helping equalize flexion-extension gaps; how it can help balance the flexion gap to the extension gap by ‘virtual surgery’ will be depicted with examples. It is particularly useful in presence of hardware in the femur or tibia and for concomitant extra-articular deformity. We have also found a consistent improvement in recovery of functional milestones with CAS with similar results for both unilateral and bilateral TKAs. Furthermore, there is evidence to support that ensuring alignment has important benefits in improving functional and quality of life scores. In addition, those with alignment of mechanical axis within 3 degrees of normal have been shown to have a shorter stay in hospital by 2 days. Studies have shown reduced blood loss and incidence of emboli after CAS TKA. Using CAS routinely for all cases, the author is ‘time neutral’. While there is always room for improvement with evolving technologies and CAS is no exception, it already has enormous benefits in the performance and outcome of TKA, and is an important part of the surgical armamentarium for a successful knee arthroplasty

The purpose of this study was to determine the rate of polyethylene wear in a fixed bearing knee replacement in order to establish a norm against which mobile bearing implants can be judged. Method: Eighteen all polyethylene tibial components were retrieved when a St Georg Sled unicompartmental replacement was being revised. This prosthesis has a biconvex femoral component and a totally flat tibia; thus point loading occurs on at implantation. The implants had been in situ between 6 and 110 months, revision was predominantly for progression of the arthritic process. Linear wear was measured using an electronic micrometer and volumetric wear by creating a mould of the defect using dental wax, and subsequently weighing the wax. Results: All components developed dishing which varied in orientation but matched the alignment of the femoral component. A near congruous articulation was thus produced correctly aligned for that particular arthroplasty. The mean linear penetrative wear for the group was 0.33mm (0.09mm per year) and the volumetric wear 124mm³ (26mm³ per year). The rate of wear seemed greatest during the second year. Conclusion: The wear rate for this totally non congruous implant was much less than anticipated. The linear penetrative wear is comparable to that reported for Charnley hip replacement though more than for a fully congruent mobile UKR. The volumetric wear is much lower than that thought to cause osteolysis. The surprisingly low wear rate suggests that the need for mobile bearing UKRs, with their greater technical demands, should be questioned

Introduction: Unicompartmental knee arthroplasty (UKA) is an increasingly popular procedure for young osteoarthritic patients whose age and activity levels preclude the use of a total knee arthroplasty (TKA). However, successful reconstruction using an unconstrained mobile bearing implant requires an intact and functioning ACL. Patients with isolated medial compartment OA and an absent ACL therefore provide a management dilemma for the treating surgeon. One option is to perform a combined ACL reconstruction and mobile bearing UKA. This paper presents early results of this new procedure using an Oxford UKA and ACL reconstruction using an autograft. Materials and Methods: Eleven patients who underwent one or two-staged ACL reconstruction and Oxford UKA for treatment of symptomatic medial compartment OA were reviewed at one year after surgery. The combined procedure required specific precautions and considerations; care had to be taken to place the tibial tunnel as far laterally as possible to avoid impingement of the graft by the tibial implant. Also, the presence of a posteromedial, rather than an anteromedial cartilage defect has the potential to reduce accuracy for placement of the initial tibial cut. Results: All patients were male with an average age of 49 years (range: 36 – 52) and mean follow up of 1.3 years. One patient needed revision to TKA due to infection. The objective and functional knee society scores improved pre to post operatively from 55 to 98, and 85 to 100, respectively. Conclusions: ACL reconstruction and simultaneous or staged UKA is a viable treatment option for patients with symptomatic medial compartment arthritis in whom the ACL is absent. Early results of this technically demanding procedure are encouraging but longer follow-up is required

Static finite-element (FE) analysis has been extensively used to examine polyethylene stresses in Total Knee Arthroplasty (TKA). The aim of this study was to use an explicit-dynamic FE approach with force driven models to simulate both the kinematics and the internal stresses within a single analysis of the Meniscal Bearing Knee (MBK, Zimmer, Warsaw, IN) prosthesis. The MBK is a mobile-bearing prosthesis (rotating and AP-gliding) with complete femorotibial conformity throughout motion owing to spherical femoral condyles. The FE meshes of the MBK were created from data obtained from the manufacturer as Initial Graphics Exchange Specification (IGES) files. Three-dimensional FE models of the original MBK design and of two modified versions (MBK-Flex and MBK-PS) were generated in Hypermesh 5.1 software. The tibial insert was modeled as a flexible body with 82212 noded solid tetrahedral elements (Poisson ratio: 0.46). The femoral and tibial components were modeled as rigid bodies. No abnormal alignment or soft tissue imbalance were assumed. Linear soft tissue constraints (30 N/mm AP and 0.6 N-m/degree rotational displacements) were included. Axial load was 4.9mm medially displaced to achieve amedially-biased (60–40) condylar load allocation. Waveforms to simulate gait, stair-climbing and deep-knee-bending with the FE models were obtained from the proposed International Standards Organization 14243–1 and from literature data. Peak contact stresses for each activity evaluated were below 11 MPa for both the original and modified MBK versions. Kinematics analysis showed similar amount of displacements (average rotations: 3.7°: average AP-glide: 2.5mm) for the various design during gait. In simulated stair-climbing and deep-knee-bending the PS version showed a more reproducible pattern of posterior rollback in flexion without increasing contact stresses. Explicit FE analysis is an efficient screening tool before in-vivo or in-vitro testing. It provides a means of testing the effect of variables such as change in prosthetic design, surgical techniques and applied loads on knee forces and kinematics

Introduction This prospective outcome study presents the results and complications of 41 lateral unicompartmental knee joint replacements. Methods One surgeon operated on all the patients in this series. The surgery was performed through minimally invasive techniques wtih the patients being day-stay or overnight stay patients. Assessment was made using SF-36 and WOMAC questionnaires, physical examination, x-ray pre-operatively and at six monthly intervals. Kaplan-Meier survival analysis was carried out. Results Forty-one knees (39 patients) underwent surgery. There were 15 males (average age 64 years) and 26 females (average age 68 years). Mean follow-up time was 3.2 years (max 4.6 years). Of these four were Repicci inlay components, 10 were Repicci onlay components and 28 were Oxford mobile bearing implants. Three patients required reoperation, all having mobile bearings in place. One required revision to total knee replacement for progression of arthritis in the medial compartment, and two for bearing dislocation. The operation consisted of a change of bearing to a thicker one. One of these patients had a further complication, a deep infection which was treated successfully with arthroscopic debridement and antibiotics. Another of the mobile bearing patients had a DVT. WOMAC and SF36 show a reduction in pain and stiffness, and an increase in physical function and quality of life. Kaplan-Meier analysis shows 100% survival of the fixed implants but 96% in the mobile bearing group. However 11% of the mobile bearing group required reoperation. Conclusions Lateral compartment replacement is a technically demanding procedure. This study looks at the early results, and does not examine long-term wear. A significant difference in the complication rates for the different type of implant is noted, with the mobile bearing having a higher reoperation rate. In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source

Introduction: Static finite-element (FE) analysis has been extensively used to examine polyethylene stresses in Total Knee Arthroplasty (TKA). The aim of this study was to use an explicit-dynamic FE approach with force driven models to simulate both kinematics and internal stresses within a single analysis of the Meniscal Bearing Knee (MBK, Zimmer, Warsaw, IN). Material and methods: The MBK is a mobile-bearing prosthesis (rotating and AP-gliding) with complete femoro-tibial conformity throughout motion owing to spherical femoral condyles. The FE meshes of the MBK were created from data obtained from the manufacturer as Initial Graphics Exchange Specification (IGES) files. Three-dimensional FE models of the original MBK design and of two modified versions (MBK-Flex and MBK-PS) were generated in Hypermesh 5.1 software. The tibial insert was modeled as a flexible body with 82212 noded solid tetrahedral elements (Poisson ratio: 0.46). The femoral and tibial components were modeled as rigid bodies. Linear soft tissue constraints (30 N/mm AP and 0.6 N-m/degree rotational displacements) were included. Axial load was 4.9mm medially displaced to achieve a medially-biased (60–40) condylar load allocation. Waveforms to simulate gait, stair-climbing and deep-knee-bending with the FE models were obtained from the proposed International Standards Organization 14243–1 and from literature data. Results: Peak contact stresses for each activity evaluated were below 14 MPa for both the original and modified MBK versions. Kinematics analysis showed similar amount of displacements (average rotations: 3.7°: average AP-glide: 2.5mm) for the various design during gait. In simulated stair-climbing and deep-knee-bending the PS version showed a more reproducible pattern of posterior roll-back in flexion without increasing contact stresses. Conclusion: Explicit FE analysis is an efficient screening tool before in-vivo or in-vitro testing. It allows to test the effects of variables such as change in prosthetic design, surgical techniques and loads on knee forces and kinematics