Retrieval studies have shown that the use of fully congruent meniscal bearings reduces wear in knee replacements. We report the outcome of 143 knees with anteromedial osteoarthritis and normal anterior cruciate ligaments treated by unicompartmental arthroplasty using fully congruous mobile polyethylene bearings. At review, 34 knees were in patients who had died and 109 were in those who were still living. The mean elapsed time since operation was 7.6 years (maximum 13.8). We established the status of all but one knee. There had been five revision operations giving a cumulative prosthetic survival rate at ten years (33 knees at risk) of 98% (95% CI 93% to 100%). Considering the knee lost to follow-up as a failure, the ‘worst-case’ survival rate was 97%. No failures were due to polyethylene wear or aseptic loosening of the tibial component. One bearing which dislocated at four years was reduced by closed manipulation. The ten-year survival rate is the best of those reported for unicompartmental arthroplasty and not significantly different from the best rates for total knee replacement

Satisfactory selection criteria are essential for the successful outcome of unicompartmental knee arthroplasty (UCA). We report the frequency of revision of the Oxford medial unicompartmental arthroplasty in knees previously treated for anteromedial osteoarthritis by high tibial osteotomy (HTO). The combined results from three sources were used to allow statistical analysis of this uncommon subgroup. In the combined series of 631 knees (507 patients) which had medial unicompartmental replacement, 613 were primary procedures and 18 were for a failed HTO. The mean follow-up times of the two groups were similar (5.8 years and 5.4 years, respectively). At review, 19 (3.1%) of the primary procedures and five (27.8%) of those undertaken for a failed HTO had been revised to total knee replacement. Survival analysis revealed the ten-year cumulative survivals to be 96% and 66%, respectively. The log-rank comparison of these survivals revealed a highly significant difference (p < 0.0001). We recommend that the Oxford UCA should not be used in knees which have previously undergone an HTO

Objective: To report the survivorship rate and clinical outcome of a large series of lateral unicompartmental replacements. Method: 88 lateral St Georg Sled LTKRS were performed between 1978 and 1999. Clinical and radiological data was prospectively recorded at regular follow up and only 5 knees were lost during the 22 year period. Results: 15 knees were revised after an average of 8 years. (eight for progressive arthritis, six for loosening and four for femoral fracture) 29 patients (30 knees) died during the course of the study. At final follow up (average 9 years) 50 of the 63 remaining knees were rated as good or excellent, nine as fair and nine poor. The mean range of flexion was 110°. At 10 years the cumulative survival rate was 83% and at 15 years 78% (10 knees at risk). The “worst case scenario” where knees with pain or lost to follow up are added to revisions shows a 10 year survivorship of 74%. Conclusion: Although the results are not as good as medial UKR. These clinical outcomes suggest that the conservative surgical procedure of lateral UKR with the fixed bearing St George Sled prosthesis can give acceptable results in the uncommon situation of severely symptomatic isolated lateral tibio femoral arthritis

One hundred-one knees with medial compartmental osteoarthrosis were treated by unicompartmental arthroplasty with the Oxford Knee. The strict selection criteria were: (1) the presence of functioning anterior cruciate ligament, (2) correctable deformity and (3) full thickness of articular cartilage in the lateral compartment. The mean elapsed time from surgery was 28 months. One knee required revision for a loose tibial component; one had meniscal bearing dislplacement 1 month after the operation and was revised succesfully by replacing the meniscal implant with a thicker one. One implant was revised to a tricompartmental prosthesis. The femoral component has a spherical articular surface. The meniscal bearing is made of high-density polyethylene and is concave superiorly and flat inferiorly to fit exactly the metal femoral and tibial components. The meniscal bearing is not attached to either metal component but is held in place by its reciprocal shape and the tension in the ligaments. The bearing, which is avaliable in nine thicknesses, is inserted after the metal components have been fixed, allowing the ligaments to be restored to their physiologic tension. No femoral component was radiographically loose. Loosening was observed in two cases only in the tibial component. There were radiolucent lines more than 2 mm thick around two other tibial components, involving less than 15% of the component’s surface in each case. In none of these cases was the leg misaligned. There was no radiographic evidence of disease progression in the lateral compartment of any joint and the Ahlback grades remained unchanged. All the patients were evaluated 2 years after surgery according to the Oxford Knee Score. Our scores ranged from 40 to 48. In our opinion medial unicompartmental arthroplasty is the appropriate treatment in approximately one third of patients undergoing surgery for osteoarthrosis of the knee. Key point of this operation is: the surgical technique is less invasive and preserves all the structures of the knee so that a short patient recovery time is allowed. Furthermore, unicompartmental implants cost less than tricompartmental prostheses and revision surgery is relatively easy if performed early and before extensive bone erosion has occurred

Aim. To assess the survivorship of unicompartmental replacements (UKR) revised to UKR. Background: Partial revision of UKR, or revision to a further UKR is a rarely performed procedure with some data from the Australian registry suggesting that results are not good, with early revision being required. Method. All revision procedures from initial UKR are prospectively followed and scored as part of our department's knee database. We analysed the 37 cases in our database that showed revision of UKR to UKR. These included cases in the following categories: a) Mobile bearing revised to mobile bearing (n=8) b) Mobile bearing revised to fixed bearing (n=20) c) Fixed bearing revised to fixed bearing (n=9). Results. The survivorship of revisions of mobile UKR to mobile UKR was 87.5% at a mean of 5 yrs. The survivorship of revisions from mobile UKR to fixed bearing UKR was 95% at a mean of 8 yrs. The survivorship of revisions from fixed bearing UKR to fixed bearing UKR was 78% at 15 yr (1 revised at 9yrs, 1 at 12 yrs). Conclusion. Despite the perception that revision of a UKR to another UKR is likely to fail and require early revision, our results suggest that in specific circumstances acceptable survivorship and outcome are possible. MULTIPLE DISCLOSURES

This paper reports the authors’ experience of over 850 unicompartmental knee replacements beginning in 1985 with the MG2 uni and then the LCS uni in 1995, and more recently with the Allegretto, Oxford and PFC minimally invasive uni. Minimally invasive unicompartmental knee arthroplasty (MIU) offers the knee arthritis patient significant benefits compared with total knee arthroplasty. Some of these are especially important for Asian patients, in particular range of movement and ability to squat. The ideal indications for the MIU are not yet fully established but are becoming clearer. Contraindications are also clearer. These issues will be discussed in detail. The results in 100 cases of unicompartmental arthroplasty will be presented and discussed along with the complications in these patients. Special considerations and recommendations for the commencement of MIU will also be discussed. This recent and popular procedure also presents the knee surgeon with significant challenges. However, there are also disadvantages which will be outlined. The surgical technique of the MIU will be shown in detail. The paper closes on a brief discussion into recent developments by an 8 member international group of knee surgeons of a new MIU offering a choice of fixed or mobile bearing MIU, with precise instrumentation of both the femoral and tibial sides, and the early result of the first 18 procedures in 15 patients (3 bilateral)

When the Oxford unicompartmental meniscal bearing arthroplasty is used in the lateral compartment of the knee, 10% of the bearings dislocate. A radiological review was carried out to establish if dislocation was related to surgical technique. The postoperative radiographs of 46 lateral unicompartmental arthroplasties were analysed. Five variables which related to the position and alignment of the components were measured. Dislocations occurred in six knees. Only one of the five variables, the proximal tibial varus angle, had a statistically significant relationship to dislocation. This variable quantifies the height of the lateral joint line. The mean proximal tibial varus angle for knees the bearings of which had dislocated was 9° and for those which had not it was 5°. In both groups it was greater than would be expected in the normal knee (3°). Our study suggests that a high proximal tibial varus angle is associated with dislocation. The surgical technique should be modified to account for this, with care being taken to avoid damage to or over-distraction of the lateral soft tissues

Patellofemoral unicompartmental joint replacement is a controversial subject with a relatively small evidence base. Of the 50,000 total knee arthroplasties performed each year in the UK, approximately 10% are performed for predominantly patellofemoral arthritis. There are several patellofemoral unicompartmental prostheses on the market with the National Joint Registry recording 745 such prostheses used in 2007. Most evidence in favour of this procedure comes from experience with the Avon prosthesis (Stryker) predominantly from designer-surgeons. The FPV patellofemoral joint replacement (Wright Medical) has been in use in Europe for several years. The instruments have recently been redesigned and the device marketed in the UK. In 2007 the FPV had 5.9% market share (n=44). We present our early experience with the FPV patellofemoral joint replacement, which to our knowledge, is the first clinical outcome series for this prosthesis. 33 consecutive FPV joint replacements in 29 patients were performed between April 2007 and September 2009 for unicompartmental patellofemoral OA. All cases were performed or directly supervised by the senior author. Results are presented with a minimum follow-up of six months. Oxford and American Knee Society scores (AKSS) were obtained on all patients preoperatively and at subsequent outpatient visits. Mean preoperative AKSS knee score was 49.7 points and postoperative scores at 6 months and 1 year were 82.5 and 86.4 respectively. Mean Oxford score preoperatively was 30.4 (37%) and at 6 months and 1 year were 21.3 (56%) and 11.2 (77%) respectively. There were no complications related to the implant. One knee required a secondary open lateral release due to inadequate balancing at the index procedure. Further medium to long-term follow up data are required, but our initial experience with this device is encouraging

Patellofemoral unicompartmental joint replacement is a controversial subject with a relatively small evidence base. Of the 50,000 total knee arthroplasties performed each year in the UK, approximately 10% are performed for predominantly patellofemoral arthritis. There are several patellofemoral unicompartmental prostheses on the market with the National Joint Registry recording 745 such prostheses used in 2007. Most evidence in favour of this procedure comes from experience with the Avon prosthesis (Stryker) predominantly from designer-surgeons. The FPV patellofemoral joint replacement (Wright Medical) has been in use in Europe for several years. The instruments have recently been redesigned and the device marketed in the UK. In 2007 the FPV had 5.9% market share (n=44). We present our early experience with the FPV patellofemoral joint replacement, which to our knowledge, is the first clinical outcome series for this prosthesis. 33 consecutive FPV joint replacements in 29 patients were performed between April 2007 and September 2009 for unicompartmental patellofemoral OA. All cases were performed or directly supervised by the senior author. Results are presented with a minimum follow-up of six months. Oxford and American Knee Society scores (AKSS) were obtained on all patients preoperatively and at subsequent outpatient visits. Mean preoperative AKSS knee score was 49.7 points and postoperative scores at 6 months and 1 year were 82.5 and 86.4 respectively. Mean Oxford score preoperatively was 30.4 (37%) and at 6 months and 1 year were 21.3 (56%) and 11.2 (77%) respectively. There were no complications related to the implant. One knee required a secondary open lateral release due to inadequate balancing at the index procedure. Further medium to long-term follow up data are required, but our initial experience with this device is encouraging

Purpose: Varus deformity after total knee replacement (TKR) is associated with poor outcome. This aim of this study was to determine whether the same is true for medial unicompartmental arthroplasty (UKA). Methods: 158 patients implanted with the Oxford UKA, using a minimally invasive approach, were studied prospectively for five years. Leg alignment was measured with a long-arm goniometer referenced from Anterior Superior Iliac Spine, centre of patella and centre of ankle. Patients were grouped according to the American Knee Society Score (AKSS). Group A: > 0° varus (n=13, 8.2%); Group B: 0 to 4° valgus (n=39, 24.7%); Group C: 5–10° valgus (normal alignment, n=106, 67.12%). Comparisons were made between the three groups in terms of the absolute and the change in Oxford Knee Score (OKS) and AKSS over the five year period, and the presence of radiolucency. Results: There was no significant difference in any outcome measure except for Objective-AKSS (p< 0.001). The means and standard deviations of the ΔOKS for the groups were:. 24 ± 5,. 22 ± 10, and. 22 ± 9 and for Objective-AKSS were 84 ± 12, 82 ± 15 and 91 ± 11 respectively. The frequency of five year radiolucency for the groups A, B, and C were 42%, 35%, and 45% respectively. Conclusion: The aim of the Oxford UKA is to restore knee kinematics and thus knee alignment to the pre-disease state. Therefore, as demonstrated by this study, about 30% of patients have varus alignment. This study also demonstrates that post-operative varus alignment does not compromise the outcome. The only score which did show worse outcome was the Objective-AKSS. This is because 10 or 20 points are deducted for varus alignment, which is not appropriate following UKA. Therefore, AKSS in its present form is not a reliable tool for assessment of UKA

We have made a retrospective comparison between the results of 49 high tibial osteotomies and 42 unicompartmental replacement arthroplasties performed for the treatment of osteoarthritis of the knee, assessed 5 to 10 years after operation. The type of operation depended on the policy of the consultant responsible for treatment but analysis of the pre-operative findings showed that the two groups were sufficiently similar for direct comparison between them. In the replacement group, 32 (76%) were good, 4 were fair, 3 were poor and 3 had been revised. In the osteotomy group 21 (43%) were good, 11 were fair, 7 were poor and 10 had been revised. It was concluded that, in this series, the results of unicompartmental replacement were significantly better and that this group had shown no sign of late deterioration

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

Unicompartmental arthroplasty of the knee (UKA) is technically challenging because the prosthetic devices must function in concert with a mostly normal joint. Malalignment is common, leading to patient dissatisfaction and early failures. However, UKA remains attractive as a temporizing treatment in early disease. Until now, resurfacing UKAs were performed with free-hand techniques. This study is only the second report investigating the use of a tactile guidance system (TGS—essentially, a robotically assisted surgery) for the performance of UKA. Methods. The first 20 patients who underwent resurfacing using a Mako Surgical Inc. TGS system by a single surgeon were studied. Surgical goals were to place the components to replicate closely the patient’s native bony architecture. The surgical plan was completed on a workstation, and then executed with the TGS system through a mini-arthrotomy. Stelkast, Inc resurfacing components were implanted with methymethacrylate. Intraoperative measurements of component position were obtained. Pre- and postoperative radiographs were also measured for alignment correction, change in angulation of the joint line relative to the femoral and tibial anatomic axes, femoral component alignment relative to the femoral anatomic axis, and change in tibial slope. Results. All cases could be completed as planned. None were converted to a full arthrotomy. None required conversion to a different implant. There were no failures of the TGS, associated navigation, or the CAT-scan based preoperative plan. Intraoperative measurements showed an average femoral component position of 0.89+3.36 degrees of varus relative to the mechanical axis, with 62.5% being varus and 37.5% being valgus. The average femoral component flexion was 11.1+2.11 degrees, with no outliers (less than 5 degrees; greater than 15 degrees). The tibial component position was 4.60+1.76 degrees of varus, with all components in varus as desired. There was an average of 5.00+2.37 degrees of slope, with 25% outliers (less than 3 or greater than 7 degrees). Postoperative measurements showed an overall limb alignment correction of 4.29+2.60 degrees, femoral joint line change of only 0.43+0.49 degrees, and an overall component alignment relative to the anatomic axis of 4.54+3.77 degrees of valgus. On the tibial side, the joint line varus was corrected by 3.00+2.04 degrees and the slope was changed by 4.29+3.24 degrees, including 19% outliers (less than 3 degrees, more than 7 degrees). However, 33% of the outliers were outliers preoperatively as well. Interestingly, the bone level after resection on the tibial side averaged 5.36+3.00 degrees of varus, suggesting that component placement must be carefully watched. Discussion. TGS seems to be extremely accurate and precise in recreating individual patient anatomy. This also applies to cases in which the patient anatomy dictates placement of components in so-called “outlier” positions. It is unknown whether these “outlier” positions really translate into poorer outcomes. Impressively, there were no failures to execute the intended surgical plan and no failures of the TGS system. Future research will attempt to correlate component placement in native anatomical positions with functional outcomes and failures, as well as cost-effectiveness of the system

We determined the outcome of 56 ‘Oxford’ unicompartmental replacements performed for anteromedial osteoarthritis of the knee between 1982 and 1987. Of these, 24 were in patients who had died without revision, one was lost to follow-up and two had been revised. Of the remaining 29 knees, 26 were examined clinically and radiologically, two were only examined clinically and one patient was contacted by telephone. The mean age of the patients was 80.3 years. At a mean follow-up of 11.4 years (10 to 14) the measurements of the knee score, range of movement and degree of deformity were not significantly different from those made one to two years after operation, except that the range of flexion had improved. Comparison of fluoroscopically-controlled radiographs at a similar interval of time showed no change in the appearance of the lateral compartments. The retained articular cartilage continued to function for ten or more years which suggests that anteromedial osteoarthritis may be considered as a focal disorder of the knee. This justifies continued efforts to develop methods of treatment which preserve intact joint structures

A retrospective review of medial compartment arthroplasty in 22 patients (22 knees) is reported. The operations were performed between 1973 and 1978. Eighty-six per cent were rated good or excellent using the knee rating system devised by the Hospital for Special Surgery, New York. Excellent or good results were achieved in six patients who had previously had a high tibial osteotomy. At the time of follow-up significant loosening had not occurred, although progression of patellofemoral disease was noted. This study supports the promising results reported for unicompartmental resurfacing arthroplasty in the elderly

Medial unicompartmental replacement (UKR) has been shown to have superior functional results to total knee replacement (TKR) in appropriately selected patients, and this has been associated with a resurgence of interest in the procedure. This may relate to evidence showing that the kinematic profile of UKR is similar to the normal knee, in comparison to TKR, which has abnormal kinematics. Concerns remain over the survivorship of UKR and work has suggested the anterior cruciate ligament (ACL) may become dysfunctional over time. Cruciate mechanism dysfunction would produce poor kinematics and instability providing a potential mechanism of failure for the UKR. Aim: To test the hypothesis that the sagittal plane kinematics (and cruciate mechanism) of a fixed bearing medial UKR deteriorate over time (short to long term). A cross sectional study was designed in which 24 patients who had undergone successful UKR were recruited and divided into early (2–5 years) and late (> 9 years) groups according to time since surgery. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. This work suggests the sagittal plane kinematics of a fixed bearing UKR is maintained in the long term. There is no evidence that the cruciate mechanism has failed at ten years. However, increased tibial bearing conformity from ‘dishing’, and adequate muscle control, cannot be ruled out as possible mechanisms for the satisfactory kinematics observed in the long term for this UKA

Background

Lateral Unicompartmental Knee Arthroplasty (UKA) is a recognised treatment option in the management of lateral Osteoarthritis (OA) of the knee. Whilst there is extensive evidence on the indications and contraindcations in Medial UKA there is limited evidence on this topic in Lateral UKA. The aim of this study was to assess our experience of mobile lateral UKR and to look specifically at the effect of Contraindications on the outcome.

The aim of this study was to assess the perioperative complications associated with bilateral simultaneous UKR and compare them with those of unilateral UKR and bilateral TKRs. Over a 2 year period, 40 patients underwent bilateral simultaneous Preservation unicompartmental knee replacement UKR. They were compared to 40 matched unilateral UKRs and 28 bilateral simultaneous total knee replacement patients who had their operations during the same time period by the senior author. There was no significant difference between the groups in terms of age, weight, ASA grade and throm-boprophylaxis received. There was no statistically significant difference in the complication rates of all 3 groups. When compared to 2 unilateral UKRs, bilateral simultaneous UKR results in a reduced operative time, blood loss and hospital stay but more blood transfusion. When compared to bilateral TKRs, bilateral simultaneous UKR results in reduced blood loss, reduced blood transfusion and hospital stay but an increased operative time. Bilateral UKR is a useful option in selected patients with bilateral unicompartmental osteoarthritis.

The aim of this study was to document the thickness of the patellofemoral joint before and after unicompart-mental joint replacement and to correlate these data with knee outcome scores.

Seventeen patients (22 knees) who underwent Patello-femoral replacement with FPV (Wright Medical) prosthesis between 2006 and 2008 were identified retrospectively and analyzed using chart and radiological review. Oxford and AKSS knee scores were gathered prospectively pre-operative and at follow-up.

Trochlear height was measured using lateral radiograph of the knee by measuring the distance between anterior distal femoral cortex and the highest point of trochlea. Trochlear height was compared pre and postoperatively. The range of movement and the Oxford and American knee society knee scores at six weeks postoperatively were noted. Association between increased trochlear height and improved range of motion was studied.

All but two patients regained full knee extension. Postoperative mean range of flexion of the knee joint was 114 degrees. The mean Oxford knee score at 6 weeks postoperatively was 21 points. The mean American Knee Society Knee Score was 85 points and function score 60 points.

We found the average trochlear height to be 6.2 mms pre and 9.7 mms post operatively with an average increase of 3.5 mms. We found no relationship between range of motion of the knee and knee function and trochlear height. This is important because there has been concern that ‘overstuffing’ of the patellofemoral joint can lead to stiffness and failure of resolution of pain post-operatively. Rather it appears that the FPV prosthesis restores the previous anatomical thickness of this compartment.

We conclude that FPV Patello-femoral replacement results in correct anatomical reconstruction of the trochlear height. This should in turn result in durable improvements in pain and function