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)

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

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

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

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

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

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

The knee is one of the most commonly affected joints in osteoarthritis. Unicompartmental knee replacement (UKA) was developed to address patients with this disease in only one compartment. The conventional knee arthroplasty jigs, while usually being accurate, may result in the prosthesis being inserted in an undesired alignment which may lead to poor post-operative outcomes. Common modes of failure in UKA include edge loading due to incorrect sizing or positioning, development of disease in the other compartment due to over-stuffing or over-correction and early loosening or stress fractures due to inaccurate bone cuts.

Computer navigation and robotically assisted unicompartmental knee replacement were introduced in order to improve the surgical accuracy of both the femoral and tibial bone cuts. The aim of this study was to assess accuracy and reliability of robotic assisted, unicondylar knee surgery in producing reported bony alignment.

Two hundred and twenty consecutive patients with a mean age of 64 + 11 years who underwent successful medial robotic assisted unicondylar knee surgery performed by two senior total joint arthroplasty surgeons were identified retrospectively. The mean body mass index of the cohort was 33.5 + 8 kg/m² with a minimum follow-up of 6 months (range: 6–18 months). Femoral and tibial sagittal and coronal alignments as well as the posterior slope of the tibial component were measured in the post-operative radiographs. These measurements were compared with the equivalent measurements collected during intra-operative period by the navigation to study the reliability and accuracy of femoral and tibial cuts. Radiographic evaluation was independently conducted by two observers.

There was an average difference of 2.2 to 3.6 degrees between the intra-operatively planned and post-operative radiological equivalent measurements. For the femur, mean varus/valgus angulation was 2.8 + 2.5 degrees with 83% of those measured within 5% of planned. For the tibia mean varus/valgus angulation was 2.4 + 1.9 degrees with 93% within 5% of planned resection. There was minimal inter-observer variability between radiographic measurements. There were no infections in the evaluated group at the time of radiographic examination.

Alignment for unicondylar knee arthroplasty is important for implant survival and is a more difficult procedure to instrument as it is a minimally invasive surgery. Assuming appropriate planning, robotically assisted surgery in unicondylar knee replacement will result in reliably accurate positioning of component and reduce early component failures caused by malpositioning. A mismatch between pre-planning and post-operative radiography is often caused by poor cementing technique of the prosthesis rather than incorrect bony cuts. Addressing these factors can lead to greater success and improved outcomes for patients.

To our knowledge in medial unicompartmental knee arthroplasty (UKA) no study has specifically assessed the difference in outcome between matched gender groups. Previous unmatched gender studies have indicated more favourable results for women.

Aims

Mobile-bearing unicompartmental knee arthroplasty (UKA) with a flat tibial plateau has not performed well in the lateral compartment, leading to a high rate of dislocation. For this reason, the Domed Lateral UKA with a biconcave bearing was developed. However, medial and lateral tibial plateaus have asymmetric anatomical geometries, with a slightly dished medial and a convex lateral plateau. Therefore, the aim of this study was to evaluate the extent at which the normal knee kinematics were restored with different tibial insert designs using computational simulation.

INTRODUCTION

Wear and polyethylene damage have been implicated in up to 22% of revision surgeries after unicompartmental knee replacement. Two major design rationales to reduce this rate involve either geometry and/or material strategies. Geometric options involve highly congruent mobile bearings with large contact areas; or moderately conforming fixed bearings to prevent bearing dislocation and reduce back-side wear, while material changes involve use of highly crosslinked polyethylene. This study was designed to determine if a highly crosslinked fixed-bearing design would increase wear resistance.

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment of the knee 10% of the bearings dislocate. An in-vitro cadaveric study was performed to investigate if the anatomy and joint geometry of the lateral compartment was a contributory factor in bearing dislocation. More specifically, the study investigated if the soft tissue tension of the lateral compartment, as determined by the length of the lateral collateral ligament (LCL), was related to bearing dislocation. A change in length of greater than 2 mm is sufficient to allow the bearing to dislocate.

The Vicon Motion Analysis System (Oxford Metrics, Oxford, UK) was used to assess length changes in the LCL of seven cadaveric knees. Measurements were made of the LCL length through knee flexion and of the change in LCL length when a varus force was applied at a fixed flexion angle. Measurements were made in the normal knee and with the knee implanted with the Oxford prosthesis.

In the intact knee the mean LCL change was 5.5mm (8%) over the flexion range. After implantation with the Oxford UCA the mean change in length was only 1 mm (1%). There was a significant difference in the LCL length at 90° (p=0.03) and 135° (p=0.01) of knee flexion compared to the intact knee. When a varus force was applied the LCL length change of the intact knee (5.4 mm) was significantly different (p=0.02) to that of the knee with the prosthesis implanted (2.7 mm)

This study used a new method to dynamically measure LCL length. It found that after implantation of the Oxford lateral UCA the LCL remains isometric over the flexion range and does not slacken in flexion as it in the normal knee. This would suggest that the soft tissue tension was adequate to contain the bearing within the joint.

However, when a varus force was applied the LCL did not sufficiently resist a displacing force producing an LCL length change greater than 2 mm.

The evidence provided by this study is contradictory. The “lack of change in LCL length through flexion” suggests that the ligament remains tight through range and is unlikely to allow dislocation. However, the amount of distraction possible when an adducting moment is applied is sufficient to allow bearing dislocation. The length tension properties of the lateral structures are therefore implicated in the mechanism of dislocation.

Introduction: This study assesses the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK, Ahlback grades III & IV).

Methods: A total of 29 knees (27 patients) with SONK were assessed using the Oxford Knee Score. Twenty-six had osteonecrosis of the medial femoral condyle; 3 had osteonecrosis of the medial tibial plateau. This group was compared to a similar group who had undergone Oxford Medial UKA for primary osteoarthritis. Patients were matched for age, sex and time since operation.

Results: Mean length of follow-up was 5.2 years (range 1–13 years). There were no implant failures in either group, but there was one death 9 months post-arthroplasty from unrelated causes in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 37.8 (± 7.6) and 40.0 (± 6.6) in the group with osteoarthritis. There was no significant difference between the two groups using Student’s t-test (p=0.31).

Interpretation: Use of the Oxford Medial UKA for focal spontaneous osteonecrosis of the knee is reliable in the short to medium term, and gives similar results to when used for patients with primary osteoarthritis.

Introduction This study assesses the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK, Ahlback grades III & IV).

Methods A total of 29 knees (27 patients) with SONK were assessed using the Oxford Knee Score. Twenty-six had osteonecrosis of the medial femoral condyle; 3 had osteonecrosis of the medial tibial plateau. This group was compared to a similar group who had undergone Oxford Medial UKA for primary osteoarthritis. Patients were matched for age, sex and time since operation.

Results Mean length of follow-up was 5.2 years (range 1–13 years). There were no implant failures in either group, but there was one death 9 months post-arthroplasty from unrelated causes in the group with osteonecrosis. The mean Oxford Knee Score (SD) in the group with osteonecrosis was 37.8 (7.6) and 40.0 (6.6) in the group with osteoarthritis. There was no significant difference between the two groups using Student’s t-test (p=0.29).

Interpretation Use of the Oxford Medial UKA for focal spontaneous osteonecrosis of the knee is reliable in the short to medium term, and gives similar results to when used for patients with primary osteoarthritis.

The aim of this study was to investigate the hypothesis that unicompartmental knee replacement (UKR) of a single arthritic tibio femoral compartment can slow the progression of arthritis to the other compartment.

Method: Since 1974, a prospective database has been established in Bristol to register and follow up the results of unicompartmental knee replacement. Forty two prostheses that had survived for more than 10 years were examined using the Ahlbach radiological scoring system and compared to a control group of patients from the Bristol “OA 500” series, in which patients being treated conservatively for gonarthritis were regularly reviewed by clinical scoring and radiological analysis. The groups were sex matched.

All AP and lateral standing knee radiographs at entry and 8 years were scored using the Ahlbach scoring system. The Ahlbach system has been shown to have good inter and intra observer correlation, and to relate closely to pathological findings at operation. An intra and inter observer error study of our results confirmed good correlation.

Results: The groups were well matched but the OA 500 group showed a lower average age, though not a significant difference (62 years compared to 67 years). The lateral compartment of all knees in both groups were Ahlbach grade 0 or 1 group before operation or entry to the OA 500 register.

In the UKR group, four out of 42 knees showed progression of a single Ahlbach grade (9.5%). 2 revisions for arthritic progression were added to this group making a total of six out of 42 (14.3%). In the control group 12 of the 42 knees progressed by one or two Ahlbach grades and a further case underwent surgery making a total of 13 (31%). This difference was significant (p< 0.01).

Conclusion: Recent studies have shown that with a better understanding of design, improved selection of patients and better surgical technique, a UKR can have at least as good, if not better, results than a TKR at 5 year follow up, and has benefits of preservation of anatomy, earlier rehabilitation, preservation of bone stock and easier revision. Our radiological findings in this study will need to be correlated with further randomised prospective clinical studies, but suggest that progression of Osteoarthritis is reduced by UKR, and that this should be an additional stated benefit of this surgical technique.

Recently in Europe, Unicompartmental Knee Arthroplasty (UKA) has regained interest in the orthopedic community; however, based on various reports, results concerning UKA for isolated lateral compartment arthritis seemed to be not as good as for medial side. In 1988 our department started using Unicondylar Knee Pros-thesis with a fixed all polyethylene bearing tibial component and resurfacing of the distal femoral condyle. The aim of this study is to report on our personal experience using this type of implant for lateral osteoarthritis with a long follow-up period.

Between January 1988 and October 2003, we performed 54 lateral UKAs (52 patients) and all were implanted for lateral osteoarthritis (3 cases of which were posttraumatic). 52 knees in 50 patients were available after a minimum duration of follow-up of five years (96.3 %). The mean age of the patients at the time of the index procedure was 72.2±1.5 years. The mean duration of follow-up was 100.9 months (range 64 – 189 months).

At follow up, 4 underwent a second surgery: one conversion to TKA for tibial tray loosening at 2 years and 3 revisions for UKA in the medial compartment. No revision surgery was necessary for wear of either of the two components, nor for infection. The mean IKS knee score was 94.9 points, with mean range of motion 132.6° (range, 115–150) and a mean IKS function score totaling 81.8 points. The average femorotibial alignment was 1.8° (range −6° to 12°). Radiolucent lines in relation to the tibial component were appreciated in 6 knees and to the femoral component in 1 knee. Implant survival was 98.08% at ten years.

The UKA with a fixed bearing tibial component and a femoral resurfacing implant is a reliable option for management of isolated lateral knee osteoarthritis. It offers excellent medium-term results for both functional level and implant survival which even currently enable us to widen our selection criteria to include younger patients or those associated with starting patellofemoral osteoarthritis.

Introduction

Recent studies have indicated that healthy and willing patients above 80 years have similar outcomes as younger patients following arthroplasty. We wished to investigate the outcomes in a cohort of patients above 80 years who underwent medial unicompartment knee replacement (UKA).

Proprioception protects joints against injurious movements and is critical for joint stability maintenance under dynamic conditions. Knee replacement effect on proprioception in general remains elusive. This study aimed to evaluate the changes in proprioceptive performance after knee replacement; comparing Total (TKA) to Unicompartmental Knee Arthroplasty (UKA).

Thirty-four patients with osteoarthritis were recruited; 15 patients underwent TKA using the AGC prosthesis and 19patients underwent UKA using the Oxford prosthesis. Both cruciate ligaments were preserved in the UKA group, while only the PCL was preserved in TKA patients. Patients’ age was similar in both groups.> Joint Position Sense (JPS) and postural sway were used as measures of proprioception. Both groups were assessed pre- and 6 months post-operatively in both limbs. JPS was measured as the error in actively and passively reproducing five randomly ordered knee flexion angles between 30 and 70°using an isokinetic dynamometer. Postural sway (area and path) was measured during single leg stance using a Balance Performance Monitor. Functional outcome was assessed using the Oxford Knee Score (OKS).

Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb (UKA mean4.64°, SD1.44° and TKA mean5.18°, SD1.35°). No changes in JPS were seen in the control side. A significant improvement (P< 0.0001) in sway area and path was found in the UKA group only in both limbs. No significant changes in sway occurred in either limb of TKA patients. The OKS improved from 21.4 to 35.5 for TKA patients and from 23.9 to 38for UKA patients.

Both UKA and TKA improve proprioception as assessed by JPS. However, UKA alone improves postural sway in both limbs. This may impart explain why UKA patients function better than TKA patients

INTRODUCTION

we have previously reported that bone preparation is quite precise and accurate relative to a preoperative plan when using a robotic arm assisted technique for UKA. However, in that same study, we found a large variation between intended and final tibial implant position, presumably occuring during cement curing. In this study, we reviewed a subsequent cohort of patients in which the tibial and femoral components were cemented individually with ongoing evaluation of tibial component position during cement curing.

Introduction: Knee joint arthroplasty (total or unicompartmental) is the standard operative treatment for osteoarthritis (OA). Survival rate is good for both types but functional outcome is different. The function of unicompartmental knee arthroplasty (UKA) is substantially better than that of total knee arthroplasty (TKA). As function can be strongly influenced by proprioceptive ability, it is possible that improved outcome seen in patients with UKA results from retaining proprioceptive function associated with the cruciate ligaments. This prospective longitudinal study aimed to evaluate the change in proprioceptive performance after knee replacement; comparing TKA to UKA.

Methods and Materials: Two groups of patients with OA as diagnosed clinically and by X-ray were recruited. Group 1 consisted of 15 patients (mean age 65.8 years range 57–72 years, 10 females and 5 males) listed for TKA with the AGC prosthesis (Biomet, UK). Group 2 consisted of 19 patients (mean age 65.5 years range 52–75 years; 9 females and 10 males) listed for UKA with the Oxford UKA (Biomet, UK) for medial compartment OA. The ACL and PCL were present and preserved in all patients in Group 2, while only the PCL was preserved in Group 1 patients. Joint Position Sense (JPS) and postural sway were used as measures of proprioception performance. Both groups were assessed pre-and 6 months post-operatively in both limbs. JPS was measured using a dynamometer (KinCom, Chatanooga Ltd) as the error in actively and passively reproducing five randomly ordered knee flexion angles (30°, 40°, 50°, 60° and 70°). Postural sway (area, path and velocity) was measured during single leg stance using a Balance Performance Monitor (SMS Medical) for 30 seconds interval. Functional outcome was assessed using the Oxford Knee Score (OKS).

Results: Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb only (Mean ± standard deviation for UKA 4.64±1.44° and for TKA 5.18±1.35°). No changes in JPS were seen in the control side. An improvement in sway was found in the UKA group only. UKA patients showed significant improvement in both sway area and path (p< .0001) for both limbs post-operatively. No significant post-operative changes in sway occurred in either limb of TKA patients. The OKS improved postoperatively in both groups, rising from 21.4 to 35.5 for TKA patients and from 23.9 to 38 for UKA patients.

Conclusion: Interestingly, joint position sense improved for both groups but did not seem to show any difference between UKA and TKA. Postural sway was influenced by joint replacement type. Ligament retention may contribute to improved global postural control seen after unicompartmental knee arthroplasty and may explain the higher level of function seen in these patients.

Aims

To compare a randomised group of patients undergoing UKA to investigate the advantages of the minimal invasive approach in the early post-operative stage.

Purpose of the study Function is strongly infl uenced by proprioceptive ability, this prospective longitudinal study aimed to evaluate the change in proprioceptive performance after knee replacement; comparing total to unicompartment replacement.

Methods and Results Two groups of patients with OA as diagnosed clinically and by X-ray were recruited. Group 1 consisted of 15 patients (mean age 65.8yrs range 57-72yrs, 10 females & 5 males) listed for Total Knee Arthroplasty (TKA) with the AGC (Biomet, UK). Group 2 consisted of 19 patients (mean age 65.5yrs range 52–75yrs; 9 females & 10 males) listed for Oxford Uni-compartmental Knee Arthroplasty (OUKA) for medial compartment OA. The ACL and PCL were present and preserved in all patients in Group 2, while only the PCL was preserved for Group 1 patients.

Joint Position Sense (JPS) & sway were used as measures of proprioception performance. Both groups were assessed pre- and 6 months post-op. JPS was measured using an isokinetic dynamometer (KinCom, Chatanooga Ltd) as the error in actively and passively reproducing fi ve randomly ordered knee fl exion angles (30°, 40°, 50°, 60° and 70°). Sway (area, path and velocity) was measured during single leg stance using a Balance Performance Monitor (SMS Medical) for 30-second interval. Functional outcome was assessed using the Oxford Knee Score (OKS).

Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups.

Post-operatively, both groups had signifi cant improvement of JPS in the operated limb only (Mean ± standard deviation for UKA 4.64±1.44° and for TKA 5.18±1.35°). No changes in JPS were seen in the control side. Group 2 patients showed signifi cant improvement in both sway area and path (p< .0001) for both limbs post-operatively. No signifi cant post-operative changes in sway occurred in either limb of Group 1 patients.

The OKS improved post-operatively in both groups, rising from 21.4 to 35.5 for Group 1 patients and from 23.9 to 38 for Group 2 patients.

Conclusion Interestingly, joint position sense improved for both groups but did not seem to show any difference between UKA and TKA. Postural sway was infl uenced by joint replacement type. Ligament retention may contribute to improved global postural control seen after unicompartmental knee arthroplasty and may explain the higher level of function seen in these patients.

The objective of the present study was to analyse kinematics of subjects having a UKA during stance phase of gait, where the ACL was intact at the time of the operative procedure.

Femorotibial contact positions for nineteen subjects (15 medial UKA (MUA); 14 lateral UKA (LUA); HSS > 90, post-op > 3 yrs) were analysed using video fluoroscopy.

During stance-phase of gait, on average, subjects having a medial UKA experienced 0.8 mm of anterior motion (7.7 to – 2.3 mm), while subjects having a lateral UKA experienced −0.4 mm (0.9 to – 2.1 mm) of posterior femoral rollback (PFR). Eight of 15 subjects having a medial UKA and two out of four lateral UKA experienced PFR. Eight of 15 subjects having a medial UKA experienced normal axial rotation (average = 0.9 degrees) and one out of four subjects having a lateral UKA experienced normal axial rotation (average = −6.0 degrees).

High variability in the kinematic data for subjects experiencing an anterior slide and opposite axial rotation suggests that these subjects had an ACL that was not functioning properly and was unable to provide an anterior constraint force with the necessary magnitude to thrust the femur in the anterior direction at full extension. Progressive laxity of the ACL may occur over time, and at least in part, lead to premature polyethylene wear occasionally seen in UKA. Our results support the findings of other studies that the ACL plays a significant role in maintaining satisfactory knee kinematics, which may also, in part, contribute to UKA longevity.

Since 1974, we have made a prospective study in Bristol of the results of unicompartmental knee replacement using the St Georg sledge prosthesis. A total of 115 knees in 100 patients have been followed up for 2 to 12 years (mean, 4 years 9 months). Results have assessed both by the Bristol knee score and by survivorship studies on the total series of 138 knees. Results were excellent or good in 86% and fair or poor in 14%. The survivorship study (based on a definition of failure which included significant pain or a dissatisfied patient or the need for revision) showed a cumulative success rate of 76.4% at six years, with no further failures after that time. Seven knees have been revised, in most cases for deterioration of the contralateral compartment. The operation is recommended as a satisfactory and durable form of treatment for osteoarthritis affecting a single tibiofemoral compartment.

AIMS: To compare a randomised group of patients undergoing UKA to investigate the advantages of the minimal invasive approach in the early post-operative stage.

METHODS & RESULTS: 100 patients on the waiting list for UKA were recruited into the trial. Patients were randomised into 2 groups: Group 1 – longitudinal skin incision with dislocation of the patella, Group 2 – the minimally invasive approach. Standard milestones were recorded post-operatively: time to achieve IRQ, independent stair climbing and to discharge. Additionally, patients were scored with the AKSS and Oxford knee questionnaire pre-operatively, at 6 weeks, 6 months and 1 year.

No significant differences were found between the 2 groups in the measured parameters.

CONCLUSION: To our knowledge, there has been no previous randomised trial to investigate the results of less invasive surgery for UKA. We have been unable to demonstrate a significant advantage of this approach. With the continued drive for early return to function, some centres incorporate a 24hr accelerated discharge protocol. The less invasive approach may make this more achievable. We recommend however that the surgical procedure and implant position must not be compromised for the benefit of rapid discharge to the deficit of long term results.

Introduction The accuracy of UCA implantation is an important prognostic factor in survivorship. Previously, conventional instrumentation was adapted for UCA, possibly contributing to a lower long-term survivorship. This study aims to assess UCA position on x-rays, performed through a minimally invasive approach, in comparison to UCAs utilising an open approach.

Methods Patients were selected for UCA according to strict criteria. In particular, a varus knee < 15 and correct-able,< 15 fixed flexion deformity, intact cruciate ligaments and weight bearing knee x-rays indicating osteoarthritis in the antero-medial region and relative lateral compartment sparing. Patello-femoral joint disease was not an exclusion criterion. Ultimately, the decision to proceed with UCA was made at the time of surgery where the cruciates and lateral compartment could be inspected directly. Data was retrieved retrospectively for a continuous cohort of patients. Radiographs of component alignment were measured by an independent observer not involved in the surgery. Radiographs were measured for 56 UCAs, performed by one of the authors. Twelve patients had bilateral UCAs at the same surgery and one patient had a combined UCA/TKR. Short knee x-rays (anterior-posterior and lateral views) were used to estimate the axes of the femur and tibia as the reference points for component measurements.

Results The femoral component varus/valgus angle was 5.6° (range: 2 to 10) and flexion/extension angle was 4.9° (range: 0 to 11). The tibial component varus/valgus angle was 86.4° (range: 80 to 89°) and the postero-inferior tilt angle was 83° (range: 80 to 85). There was no radiolucency at the tibial plateau interface greater than one millimetre. One patient was treated for deep vain thrombosis and two patients underwent manipulations due to reduced range of motion. There were no deep or superficial infections and no UCA revisions.

Conclusions Radiological analysis of Oxford UCAs using a minimally invasive technique demonstrates similar implant positioning compared to the open approach. Patients gain the advantage of earlier recovery due to less synovial and quadriceps disturbance and no patella dislocation. Ongoing follow-up is required to determine whether these benefits extend to improved prosthesis survivorship.

Introduction: The ten-year survivorship of Oxford Unicompartmental Knee Arthroplasty (OUKA) has ranged from 98% in the hands of the developers to only 82–90% in reports from independent centers and national registries. This study was performed to investigate the effects of surgeon training and correct patient selection on the expected outcome of this procedure.

Methods: We created a computer-simulated joint registry consisting of 20 surgeons who performed OUKA on 1,000 patients. Mathematical models of the patient and surgeon populations and corresponding hazard functions were formulated using data from the Swedish and Australian joint registries. The long-term survivorship of UKA was assumed to average 94% at 10 years and was modeled as the product of hazard functions quantifying risk factors under the surgeon’s control, risk factors presented by the patient, and the inherent revision risk of the procedure. We performed four simulations looking at the effect of surgeon training by pairing surgeons and patients based on surgeon experience and patient risk factors.

Results: When experienced surgeons (> 40 cases) performed OUKA on low risk patients (bottom quintile), the revision rate dropped from 6.0% to 4.5%. The same surgeons had a revision rate of 7.5% when assigned to the highest risk patient group (top quintile). Conversely, when the least experienced surgeons (< 10 cases) selected the least fit patients, the revision rate increased from 6% to 8.25%. However, when these surgeons were assigned to the lowest risk group, only 5.25% of patients were revised. Taken simultaneously, these results indicate that the overall revision rate of this procedure can vary between 4.5% to 8.25%, depending upon the experience of the surgeon and the patients selected.

Conclusions:

Mathematical models of patients and surgeons can be built using joint registry data. These models can then be used in a computer simulation yielding results comparable to what has been reported in the literature.

Aim: Cementation of tibial implants in total knee arthroplasty is a gold-standard considering the high loosening rates of cementless implants. In contrast, only sparse data exist regarding unicondylar arthroplasty due to limited use. In this study, we compare cemented with cementless unicondylar knee arthroplasty and aim to define both clinical and radiological differences in treatment outcome.

Materials and Methods: In a retrospective study, 106 patients who had undergone a medial unicondylar replacement were examined after a mean postoperative period of 8 years. Of these, 42 patients (median age 81±7 years) had received a cemented and 64 (median age 73±7 years) a cementless knee arthroplasty by the same surgeon while 7 patients were deceased or could not be reached. Well-established clinical (VAS, HSS, KSS, UCLA, WOMAC) and quality of life (SF-36) scores were used to evaluate treatment outcome. X-rays were performed to evaluate periprosthetic loosening zones, according to Ewald’s criteria.

Results: The cementless patient group presented significantly better clinical scores (HSS, KSS, UCLA, WOMAC), except in the Visual Analogue Scale (VAS) for pain assessment. The quality of life was significantly better in the cementless group except in the subgroups concerning physical function, vitality and social role, which resembled normal population. Moreover, radiographic analysis using antero-posterior X-rays revealed significantly more and larger periprosthetic loosening areas in tibial zone 2 in the cementless group.

Conclusion: The inferior clinical results characterising the cemented group could be attributed to the higher mean age. Regarding the radiological loosening zones, we did not detect any differences in the techniques of fixation, although physical activity and mechanical stresses were higher in the cementless group.

Background. The cemented mobile bearing metal backed low contact stress patellofemoral arthroplasty (LCS PFA) is a newer design belonging to the second generation of inlay type implant, based on the more successful knee arthroplasty model. The advantage is the patella can articulate with the trochlear implant as well as the femoral component of a total knee replacement (TKR). Patients. This series is a cohort of 21 patients who underwent 24 (3 bilateral) unicompartmental PFA replacements for isolated patellofemoral osteoarthritis. We have used the mobile bearing LCS PFA in all of them. There were 3 males and 18 females. Average age was 51(40-58) years. The Oxford Knee score was used to assess the results. Results. At the latest follow-up averaging 2.7 (0.5 to 4) years, 9 patients showed excellent improvement in their knee scores, 5 patients showed fair improvement and 7 patients very little. There were 9 revisions in 7 patients either due to mechanical problems or with persistent symptoms. We had 4 patients with mechanical complications who underwent revision and 4 patients had a conversion to TKR. The revision rate at 2 years was 33%. There were no infections or loosening of trochlear implants. Conclusion. The revision rate for this implant seems to be very high and mainly with the patellar implant (at the metal polyethylene interface). The Australian Orthopaedic association annual joint registry report 2008 reported a higher revision rate for the same implant at 5% from a pool of 1057 patients. The young active patient having a patellofemoral replacement may put extreme force on their patellar implant. We strongly advocate patellofemoral arthroplasties to be analysed separately from the unicompartmental knees in the National Joint Registries to highlight any persistent issues with this implant

Unicompartmental knee replacement components have gained favor because they replace only the most damaged areas of articular cartilage and the less invasive operation results in a faster patient recovery than traditional TKR. Additionally, they can provide a solution when a full TKR is not yet needed. However, the wear magnitude of such implants is not well understood, primarily due the variation in design and the difficulty of testing them in knee simulators designed to test full TKRs. Modern innovative partial cartilage replacement knee components which are typically even smaller and more bone conservative than unicompartmental implants, are even less common in testing with added challenges. This study investigates the fatigue characteristics of partial cartilage replacement knee components, and the wear of the UHMWPE bearing of a new, truly less invasive unicompartmental design by Arthrex Inc./Florida. Fatigue testing was performed on MTS 858 MiniBionix machines. Two 12mm diameter UHMWPE tibial components were cemented into jigs at 0° posterior slope and were axially loaded at 2Hz for 10 million cycles (Mc) with a sinusoidal profile peaking at 60% of 8 average human bodyweights (3800N) and a load ratio R of 0.1. Two femoral components were tested with the same load profile at 10Hz for 10 million loading cycles (Mc). The femoral components were mounted at 15° flexion and only the anterior half of the implant was supported, replicating a worst-case scenario where fixation had failed on the posterior half of the implant. This resulted in a large bending moment when force was applied that would fatigue the femoral implant. Following the fatigue test, two full wear simulation tests were conducted on four 12mm and four 20mm unicompartmental components on a four-station Instron-Stanmore force-control knee simulator. The spring-based system to simulate soft-tissue restraining forces and torques was adapted to operate the machine in a displacement control mode to achieve the motions of the medial compartment based on ISO 14243-3. The specimens were lubricated with bovine serum (20g/L protein, 37°C) and the simulator was operated at 1Hz. Liquid absorption was corrected through passive-soak-control bearing inserts. The tibial specimens were cleaned and weighed at standard intervals with the usual ISO test protocols. After 10Mc of fatigue testing, both tibial components had deformed by some flattening out but were able to sustain the full load without failure and displayed average stiffness (over the whole 10Mc) of 27,600±1,180 N/mm. Neither partially supported femoral component failed, and the femorals displayed average stiffness (over 10Mc) of 37,500 ±3,280N/mm. After 5Mc of wear testing, the 12mm tibial components displayed a wear rate of 4.56±1.45mg/Mc while the larger 20mm size wore at a lower 2.80±0.39mg/Mc. The results from the fatigue test suggest that this unicompartmental cartilage replacement design will not fail under simple axial loading, even under the extreme case where the tibial implant is receiving the entire share of the load, and the femoral component is only partially supported. In the clinical application, of course some load-sharing with the native unworn cartilage would occur, reducing the stresses on the implant. The results from the wear test showed very low wear for tibial components of this design, lower than many successful TKRs. The larger size tibial components wore less likely due to reduced contact stress. Based on the results of this test, an implant of this type could be a viable option prior to TKR

Background: Symptomatic patellofemoral osteoarthritis is a challenge to the orthopaedic surgeon. In comparison to Total Knee Arthroplasty (TKA), little has been written about unicompartmental patellofemoral arthroplasty. Although, recent reports have shown more promise, the procedure has not gained wide acceptance.

Materials and Methods: We present the outcome of 23 unicompartmental patellofemoral arthroplasties on 19 patients performed in a district general hospital in the UK. The procedures were performed by a single surgeon (RSG), with a special interest in knee surgery. All the patients had failed a trial of non-operative treatment which included non-steroidal anti-inflammatory analgesia and physiotherapy. Some knees had undergone previous surgical procedures including arthroscopy (12), carbon fibre patch implantation (5), tibial tubercle transfer (1), lateral release (1), medial release (1) and excision of patellar bursa (1). Multiple arthroscopies had been performed on 4 knees.

The arthroplasty was performed via an anterior midline incision and medial parapatellar approach. All patients received Leicester Patellofemoral Prosthesis (Corin). One patient had a revision procedure following a failed PFJR performed elsewhere. The age of the patient at the time of operation ranged from 31–68 years (Mean age 50.3 years). The duration of follow-up was 6 months to 88 months (Mean 36 months). The results were evaluated using the Oxford Knee Score.

Results: One patellofemoral arthroplasty was converted to TKA after 41 months. There was no infection or loosening of the components in any patient. All patients reported relief of post-operative discomfort by 6 months except for one patient who developed hypersensitive skin lateral to the scar at 6 months. All patients said that their knees were significantly better after the procedure. Oxford Knee Scores ranged from 17 to 54 (Median 29). All except one patient reported that they would to undergo the procedure on their other knee (unilateral cases) and would recommend the procedure to friends/family.

Conclusion: The early and medium term results of uni-compartmental patellofemoral arthroplasty in our study are encouraging with patients reporting significant improvement in knee symptoms. We feel that careful patient selection and meticulous attention to surgical detail contribute to better outcomes.

The aim of this study was to assess the increase in the anterior diameter of the knee and the impact of this increase on the range of motion and function of the knee.

Twenty-eight patients (34 knees) who underwent Patello-femoral replacement with FPV (Wright Medical) prosthesis between 2005 and 2009 who 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. Trochlear height was compared pre and postoperatively. Patellar height was also measured in preoperative and postoperative skyline view and was compared. The range of movement at six weeks and the Oxford and American knee society knee scores at six months postoperatively were noted. Association between increased anterior height and improved range of motion was studied.

All but three-knees regained full knee extension. Postoperative mean range of flexion of the knee joint was 116 degrees. The mean Oxford knee and the mean American Knee Society Knee Scores significantly improved post-operatively

The trochlear height was increased by 4mms. Patellar height was also increased by 3 mms resulting in average total increase of 7 mms in the anterior-posterior diameter of the knee. We found no relationship between range of motion of the knee and the increase in the anterior-posterior diameter. We found a negative correlation between increase in the antero-posterior and preoperative trochlear and patellar height.

We conclude that FPV Patello-femoral replacement results in correct anatomical reconstruction of the trochlear height rather than ‘overstuffing’ of the patellofemoral joint which can lead to stiffness and failure of resolution of pain post-operatively. This should in turn result in durable improvements in pain and function.

Aims. There has been a recent resurgence in interest in combined partial knee arthroplasty (PKA) as an alternative to total knee arthroplasty (TKA). The varied terminology used to describe these procedures leads to confusion and ambiguity in communication between surgeons, allied health professionals, and patients. A standardized classification system is required for patient safety, accurate clinical record-keeping, clear communication, correct coding for appropriate remuneration, and joint registry data collection. Materials and Methods. An advanced PubMed search was conducted, using medical subject headings (MeSH) to identify terms and abbreviations used to describe knee arthroplasty procedures. The search related to TKA, unicompartmental (UKA), patellofemoral (PFA), and combined PKA procedures. Surveys were conducted of orthopaedic surgeons, trainees, and biomechanical engineers, who were asked which of the descriptive terms and abbreviations identified from the literature search they found most intuitive and appropriate to describe each procedure. The results were used to determine a popular consensus. Results. Survey participants preferred “bi-unicondylar arthroplasty” (Bi-UKA) to describe ipsilateral medial and lateral unicompartmental arthroplasty; “medial bi-compartmental arthroplasty” (BCA-M) to describe ipsilateral medial unicompartmental arthroplasty with patellofemoral arthroplasty; “lateral bi-compartmental arthroplasty” (BCA-L) to describe ipsilateral lateral unicompartmental arthroplasty with patellofemoral arthroplasty; and tri-compartmental arthroplasty (TCA) to describe ipsilateral patellofemoral and medial and lateral unicompartmental arthroplasties. “Combined partial knee arthroplasty” (CPKA) was the favoured umbrella term. Conclusion. We recommend bi-unicondylar arthroplasty (Bi-UKA), medial bicompartmental arthroplasty (BCA-M), lateral bicompartmental arthroplasty (BCA-L), and tricompartmental arthroplasty (TCA) as the preferred terms to classify CPKA procedures. Cite this article: Bone Joint J 2019;101-B:922–928

Purpose

To identify the incidence and reasons for revision of the Oxford prosthesis (OXF) in New Zealand.

There are now a number of controlled prospective trials comparing the advantages of unicompartmental arthroplasty versus total knee replacement (Rougraff 1991, Lawrencin 1991, Newman 1998, and Price 2000). These studies all favour unicompartmental arthroplasty over total knee replacement in terms of the following. The kinematics of uncompartmental arthroplasty are better and more normal for the surgery retains both cruciate ligaments with proprioceptive input. The range of motion tends to be greater in the unicompartmental group and the function better. This is especially true of demanding activities such as ascending and descending stairs, and has been shown using gait study analysis (O’Connor 1986). The pain relief is as good, or better, with unicompartmental arthroplasty in these studies when compared to total knee replacement, and in particular there is “a better feel” with unicompartmental arthroplasty. The complications with the smaller procedure tend to be less frequent and severe and the recovery more rapid, with a potential benefit allowing for a lower cost. There are however certain disadvantages encountered in using unicompartmental arthroplasty when compared to total knee replacement. In general there is a higher revision rate with the unicompartmental arthroplasty and this is particularly borne out in the Swedish Knee Arthroplasty Register. Using the strict criteria of Insal/Stern they suggest an incidence of 1:20 patients suitable for unicompartmental arthroplasty, and with such small numbers it is hardly surprising that there is a higher complication rate. The advantages of unicompartmental arthroplasty in the young remains controversial. In particular there are few comparative studies (Broughton and Newman 1988). In a small study from Oxford we have found that the pain relief and function in the unicompartmental arthroplasty group were substantially better with an age match comparison group using a patient based question score (The Oxford Knee Score 0–48). We sent the Oxford questionnaire to the HTO patients of the main proponent of osteotomy surgery in the UK, who has devoted a lifetime to perfecting the art of osteotomy surgery. These patients represent the “best case scenario” and his patients at five year follow up scored 27/48 on the Oxford Knee Score. Age match group of young uni-compartmental arthroplasty patients scored 38. Comparison of total knee replacement group would score 35, and it is of interest to note that those patients revised from a failed high tibial osteotomy to a total knee replacement raised their scores from 27 to 33. There are of course disadvantages comparing unicompartmental arthroplasty and high tibial osteotomy in the young. The main disadvantages that artificial material is implanted and there is the potential for infection. What remains debatable and controversial is the outcome of procedures when converting them to a total knee replacement. In terms of 10 year survivorship most of the published literature suggests that with high tibial osteotomy there is a two-thirds survivorship, one-third being converted to a total knee replacement by 10 years (range 51% to 80%) (Naudie 1999, Coventry 1993, Rudan 1991). The similar 10 year survivorship of unicompartmental arthroplasty in patients under 65 years is in the order of 80%. This is borne out in the Swedish Knee Registry. In general the problem with unicompartmental arthroplasty seems to centre around a higher revision rate, and faced with this problem there are a number of solutions. One can accept this and abandon the procedure, which has happened until recently in the United States. One can suggest that a unicompartmental arthroplasty is used as a pre-knee replacement, which has been forwarded by Repicci in the States. Alternatively one can try to minimise the failure rate by employing an implant with very good wear characteristics, one can concentrate on appropriate indications and one can define an accurate reproducible technique. One can seek to achieve a survival rate that is similar to that of the best total knee replacement. The Oxford unicompartmental knee replacement was deigned first by Goodfellow and O’Connor 25 years ago. It employs a spherical femoral component articulating on a flat tibial component. There is a fully mobile bearing, which is unconstrained. This bearing is fully congruent in all positions, which minimises wear. In two published retrieval studies (Argenson and Psychoyios) 10 year wear rate was 0.03mm per year. In those cases with no impingement the rate was 0.01mm per year. There was no correlation with thickness and we now feel comfortable advising a 3.5mm bearing for long term survivorship. The indications for unicompartmental arthroplasty in essence centre around medial compartment osteoarthritis with a functionally intact ACL. Some superficial damage to the ligament is acceptable, but in essence the structure needs to be intact to be functioning. There needs to be a correctable varus deformity with full thickness lateral compartment articular cartilage and this is best demonstrated on stress x-ray. A fixed flexion deformity of less than 15° is usual and employing the above indications we find that a unicompartmental arthroplasty is suitable for 1:4 knees presenting with osteoarthritis. We do not feel that the state of the patellofemoral joint is a contraindication to unicompartmental arthroplasty. We have significant evidence to corroborate this statement. In Mr Goodfellow’s published series in 1998 the state of the patellofemoral joint and the clinical results did not correlate. The study by Weale (1999) there was no progression of patellofemoral osteoarthritis over 10 years. On the Swedish Registry there have been no cited revisions for progression of patellofemoral arthritis. The age and the activity of the patient does not seem to be an obvious contraindication. In particular in the old and unfit using the minimal invasive approach there is a low morbidity, with all its attendant advantages. In the young patient (less than 50 years), the 10 year survivorship is 92% in two published series (Murray et al 1998 and Price 2000). The published 10 year results of the designers patient (Murray et al 1998) details the follow up of 144 unicompartmental arthroplasties with a 10 year survivorship. At 10 years there were 34 knees at risk giving a 98% 10 year survivorship 95%, confidence levels 93–100%. There was one case lost to follow up giving a worse case scenario of 97%. Of much more relevance concerns an independent series from Sweden (Svard et al 2001). These series is of 420 Oxford unicompartmental arthroplasties from a single centre performed by four surgeons. None lost to follow up. A 10+ year follow up involved 122 Oxford unis reviewed, with 92% good or excellent HSS scores. The 15 year survivorship was 94% with confidence levels 86 to 100%, there were none lost to follow up so the 15 year worse case scenario was 94%. This is better than fixed bearing unis and as good as the best total. The Swedish Knee Arthoplasty Register however gave a different picture, and was published in 1995 (Lewald et al), reported poor early results with no learning curve and advised that the difficult implant should not be used. We in fact have gained data from 944 rather than 699 from the register. It concluded that at these centres they had very reasonable results, but one or two centres had catastrophically poor results, in the order of 30% failure. We can only conclude that these poor results were due to inappropriate indications or technique. More recently in January 2001 Robertson et al have published an update of the Swedish Knee Arthroplasty Register citing good to excellent results in those centres performing more than 23 Oxford unicompartmental arthroplasties a year. Good results were possible, but there is a definite learning curve. The phase 3 tradition of the Oxford was introduced in 1998. The aim of this introduction was to make the operation simpler and more consistent. We have consistently employed a minimally invasive approach, but we have sought to keep the advantages of phase 2 Oxford unicompartmental arthroplasty. In effect there has been minor modifications to the instruments with an increased range of sizes. Our early phase 3 results, published in 1999 (Price et al) have compared the early recovery. This is the time taken to functional recovery, by which time the patient is ready for discharge. We compared the first 40 minimals with the last 20 opens and used 40 knee replacements taken as controls performed at the same time. We have shown that the minimally invasive unis recover three times faster than the totals (p< 0.001) and twice as fast as the open unis (p< 0.001). Finally our one year follow up of the first 58 phase 3 Oxford unicompartmental arthroplasties reveal increase in the mean flexion from pre-operative 123° to postoperative 135°. A high proportion of the patients gained at least 130° of flexion and 50% were 140+. A mean AKS score rose from a pre of 37 to one year of 98. The AKS function score raised from a pre 53 to one year 94, with a very high proportion of patients scoring 95+ score out of 100 on the AKS. In summary unicompartmental arthroplasties offer many potential advantages over TKR in terms of:. - Recovery, function. - The best long term results of uni (Oxford) are now as good as best TKR. - Unis in general are technically demanding and there is a definite learning curve

Aims. In-hospital length of stay (LOS) and discharge dispositions following arthroplasty could act as surrogate measures for improvement in patient pathways, and have major cost saving implications for healthcare providers. With the ever-growing adoption of robotic technology in arthroplasty, it is imperative to evaluate its impact on LOS. The objectives of this study were to compare LOS and discharge dispositions following robotic arm-assisted total knee arthroplasty (RO TKA) and unicompartmental arthroplasty (RO UKA) versus conventional technique (CO TKA and UKA). Methods. This large-scale, single-institution study included patients of any age undergoing primary TKA (n = 1,375) or UKA (n = 337) for any cause between May 2019 and January 2023. Data extracted included patient demographics, LOS, need for post anaesthesia care unit (PACU) admission, anaesthesia type, readmission within 30 days, and discharge dispositions. Univariate and multivariate logistic regression models were also employed to identify factors and patient characteristics related to delayed discharge. Results. The median LOS in the RO TKA group was 76 hours (interquartile range (IQR) 54 to 104) versus 82.5 (IQR 58 to 127) in the CO TKA group (p < 0.001) and 54 hours (IQR 34 to 77) in the RO UKA versus 58 (IQR 35 to 81) in the CO UKA (p = 0.031). Discharge dispositions were comparable between the two groups. A higher percentage of patients undergoing CO TKA required PACU admission (8% vs 5.2%; p = 0.040). Conclusion. Our study showed that robotic arm assistance was associated with a shorter LOS in patients undergoing primary UKA and TKA, and no difference in the discharge destinations. Our results suggest that robotic arm assistance could be advantageous in partly addressing the upsurge of knee arthroplasty procedures and the concomitant healthcare burden; however, this needs to be corroborated by long-term cost-effectiveness analyses and data from randomized controlled studies. Cite this article: Bone Jt Open 2023;4(10):791–800

Abstract. Objectives. There is renewed interest in bi-unicondylar arthroplasty (Bi-UKA) for patients with medial and lateral tibiofemoral osteoarthritis, but a spared patellofemoral compartment and functional cruciate ligaments. The bone island between the two tibial components may be at risk of tibial eminence avulsion fracture, compromising function. This finite element analysis compared intraoperative tibial strains for Bi-UKA to isolated medial unicompartmental arthroplasty (UKA-M) to assess the risk of avulsion. Methods. A validated model of a large, high bone-quality tibia was prepared for both UKA-M and Bi-UKA. Load totalling 450N was distributed between the two ACL bundles, implant components and collateral ligaments based on experimental and intraoperative measurements with the knee extended and appropriately sized bearings used. 95th percentile maximum principal elastic strain was predicted in the proximal tibia. The effect of overcuts/positioning for the medial implant were studied; the magnitude of these variations was double the standard deviation associated with conventional technique. Results. For all simulations, strains were an order of magnitude lower than that associated with bone fracture. Highest strain occurred in the spine, under the anteromedial ACL attachment, adjacent to transverse overcut of the medial component. Consequently, Bi-UKA had little effect on strain: <10% increases were predicted when compared to UKA-M with equivalent medial cuts/positioning. However, surgical overcutting/positional variation that resulted in loss of anteromedial bone in the spine increased strain. The biggest increase was for lateral translation of the medial component: 44% and 42% for UKA-M and Bi-UKA, respectively. Conclusions. For a large tibia with high bone quality, Bi-UKA with a well-positioned lateral implant had no tangible effect on the risk of tibial eminence avulsion fracture compared to UKA-M. Malpositioning of the medial component that removes bone from the anterior spine could prove problematic for smaller tibiae. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

The indications for unicompartmental replacement are quite specific. Overall there should be involvement of one tibiofemoral compartment, mild malalignment, and ligamentous stability. In a review of 250 osteoarthritic knees these pathologic findings were present in 9% of patients. If the average orthopaedic surgeon performs 25 total knee replacements per year only 2–3 patients will be ideally suited for this procedure. Technique, despite improvement in instrumentation, is still more demanding than tricompartmental knee replacement and therefore failure to achieve an optimal arthroplasty is higher. Overall results with unicompartmental replacement in the literature have been inferior to tricompartmental replacement (82% versus 97%). The concept that unicompartmental replacement is a temporising procedure is not a valid one in that the patient has to undergo another arthroplasty with all the risks of revision arthroplasty surgery. Tibial osteotomy remains the procedure of choice in the younger, active patient with unicompartmental replacement and tricompartmental replacement in the older, lower demand patient

Total knee arthroplasty has been demonstrated to provide durable results with excellent pain relief and improvement in function. Our institution has studied and published the longest follow-up of mobile bearing TKR, fixed bearing modular TKR, and unicompartmental replacement. Indeed these studies support the durability of the operation and the improvement in function and relief of pain. They, however, are not perfect. In tricompartmental replacement, up to 5 or 6% are revised for loosening and or wear and in unicompartmental replacement, up to 25% are revised for loosening. There are also one or two percent of cases revised for periprosthetic fracture and one or two percent for hematogenous infection. One must remember these cases were performed in patients of average age 71. When one looks at our results in more active patients with osteoarthritis who are less than 55, the results are less spectacular with 15% revised at 10 to 15 years for loosening. We all hope that better polyethylene and better tibial tray locking mechanisms (in fixed bearing modular designs) will improve these results, but to predict there will be no failures is a “leap of faith”. Long-term follow-up of cemented TKA in patients under 55 where monolithic tibial trays were utilised have demonstrated better results at 20 years (92.3%) survivorship versus those where modular tibial trays (68%) were utilised. Long-term studies of cementless total knee replacement, especially in younger patients are needed to see if this approach provides better results

Purpose. The aim of the present study was to look at survivorship and patient satisfaction of a fixed bearing unicompartmental knee arthroplasty with an all-polyethylene tibial component. Materials and Methods. We report the survivorship of 91 fixed bearing unicompartmental arthroplasties with all-polyethylene tibial components (Preservation DePuy UK), which were used for medial compartment osteoarthritis in 79 patients between 2004 and 2007. The satisfaction level of patients who had not undergone revision of the implant was also recorded. For comparison, we reviewed 49 mobile bearing unicompartmental arthroplasties (Oxford UKA Biomet UK Ltd), which had been used in 44 patients between 1998 and 2007. Results. Mean length of follow up of patients with the fixed bearing implant was 44.7 months (range 24 - 74 months) and for the mobile bearing replacement, the mean follow up was 67.6 months (24 - 119). In the fixed bearing design, at maximum follow up period of 74 months, 8 implants (8.8%) had been revised (or were listed for revision) to total knee replacement and in the mobile bearing design over the maximum follow up period of 119 months there had been only one revision (2.0%). Patients who had not undergone revision were asked if they were satisfied with their knee following the unicompartmental arthroplasty. In the fixed bearing design, 83.5% said that they were satisfied with the outcome of the operation compared to 93.9% of the patients receiving the mobile bearing design. Conclusion. We conclude that there is a higher incidence of revision of this fixed bearing design using an all-polyethylene tibial component compared to the mobile bearing design. We found that those patients who had not required revision had a lower rate of satisfaction with the fixed bearing compared to the mobile bearing design

Introduction: Minimally invasive surgery (MIS) has recently been proposed for unicompartmental arthroplasty to allow quick function recovery. The purpose of this study is to evaluate retrospectively the indications in which this technique would have been possible and successful. Methods: The requirements for the minimal invasive technique are: a pre-operative flexion of 100° and a lesion limited to one compartment of the knee. The preoperative status, operative findings and clinical outcome of 160 cases of unicompartmental knee arthroplasty (MG, Zimmer) were analyzed to determine whether the criteria for MIS would have been possible. Results: Preoperatively 12 knees had a flexion less than 100°. Postoperatively four of them had a limited flexion ranging from 90° to 100°. In 53 knees (33 %), peripheral osteophytes were removed on the opposite tibiofemoral joint. None of them were revised for progression of osteoarthritis. In 33 knees (21 %) a patelloplasty was associated to the procedure for peripheral osteophytes. Two of them were revised at 12 and 20 months for osteoarthritis progression. Discussion: Removal of peripheral osteophytes can be successfully associated to the unicompartmental procedure when using a conventional surgical approach. In 96 of the 160 knees (60 %) MIS was not recommended either for limited preoperative flexion or for peripheral osteophytes. In 2 knees unicompartmental arthroplasty itself was not the correct indication and total knee arthroplasty would have been the right solution. Finally, in 62 of the 160 knees (39 %) unicompartmental arthroplasty using MIS was indicated. In conclusion unicompartmental knee arthroplasty may be either performed by conventional or minimal approach based on the preoperative clinical and radiological evaluation

Introduction: A subjective observation suggests that a significant percentage of patients offered a TKR could benefit from a relatively more conservative, less invasive unicompartmental knee arthroplasty. We set out to challenge this hypothesis. Materials & Methods: 1147 TKRs were performed between 2002 and 2005 at Ravenscourt Park Hospital. 50 consecutive knee x-rays of patients who underwent a TKR were reviewed by three independent observers. Medial and lateral articular cartilage height, varus angulation, and femero-tibial anteroposterior and mediolateral translation were measured on antero-posterior and lateral weight bearing radiographs. Skyline views were analysed for patellofemoral disease. The most appropriate procedure according to local radiological criteria was recorded for all three observers. Unicompartmental arthroplasty was considered when the following criteria was met 1) anteromedial disease with preservation of posterior slope, 2) preservation of the tibial spines, 3) no anteroposte-rior or mediolateral translation, 4) normal tibiofemoral alignment and 5) preservation of patellofemoral joint. Osteophytes were disregarded. Tricompartmental disease merited a TKR while isolated patellofemoral (PFJ) disease considered for PFJ replacement. Patients were not formally examined. Preoperative Knee Society Scores (KSS) and WOMAC scores were noted. Results: The three observers indicated that 26 (52%), 21 (42%) and 22 (44%) patients respectively could potentially benefit from a unicompartmental arthroplasty given the right clinical setting. Consensus was reached for unicompartmental replacement in 16 (31.2%) and for TKR in 18 (36%) of cases. There was no correlation between the operation performed and operation proposed (42% ± 8) suggesting that the surgeon’s preference is a dominating factor. Interestingly within the proposed unicompartmental group Knee Society Scores were higher (100 ± 22 vs 71 ± 26) giving an indication to the disease severity. Conclusion: The clinical benefit and economic value of opting for a unicondylar knee arthroplasty when indicated is considerable. None the less it was only considered by a minority of surgeons who undertake knee arthroplasty

There is suggestion our National Joint Replacement Registry (ANJRR) does not recognize ‘the surgical learning curve’ for new prostheses. Prostheses introduced post-Registry have the learning curve revisions captured. Prostheses introduced pre-Registry will not and will be advantaged. This paper presents the evidence for this and makes suggestions to correct this issue. A literature search was made for surgery learning curve references. The Swedish Knee Arthroplasty Register was reviewed for learning curve references. The ANJRR reports were examined for evidence of learning curve revisions inclusion in cumulative revision rate curves using Unicompartmental Arthroplasty data. An Internet search reveals 212 references on ‘surgery learning curve’. Some discuss the particular issue of minimally invasive surgery (MIS). The 2004 Swedish Knee Arthroplasty Register (SKAR) report mentions the trend towards increased revision rates when Unicompartmental Arthroplasty was inserted with MIS. The 2006 SKAR report discussed this issue further suggesting the method may initiate a new learning process which can be shortened if the surgeons are offered training before they start using the method. In 2004 the Australian National Joint Replacement Registry report showed that a new Unicompartmental Arthroplasty (Preservation) had a high early revision rate. This prosthesis was launched in 2002 as a minimally invasive product. That report data was used by several prostheses companies and surgeons to widely highlight the prosthesis “poor performance”. The 2007ANJRR report shows that Preservation now has the lowest 2 to 4 year revision rate of all Unicompartmental prostheses. If the surgery learning curve was excluded the prosthesis would not have been disadvantaged in its early data reports. The evidence is that the learning curve exists and disadvantages new prostheses in ANJRR reporting. This now discourages prosthesis companies from launching new products here. Solutions recommend are:. The ANJRR accept and support the issue of “the learning curve” and the adverse impact this has on post ANJRR prosthesis revision rate data & graphs compared with pre ANJRR prostheses. The first 2 years results of the new prostheses be monitored and discussed with vendors and early evaluators but not reported. The first 2 years of revisions be “quarantined” from subsequent ANJRR reporting so that pre and post ANJRR prostheses are on an “level playing field.”

Purpose: To evaluate the feasibility and short term outcomes of bilateral medial unicompartmental replacement, undertaken with the patient positioned to allow simultaneous procedures in a safe and appropriate fashion. Methods: The use of the minimally invasive approach for implantation of the Oxford unicompartmental replacement (Biomet, UK) has become increasingly popular over the past few years, though this requires a specific knee positioning for optimal implantation to allow the leg to remain dependant and a full range of flexion. We describe a previously unreported method of positioning to allow bilateral procedures. Fifteen patients have undergone bilateral medial unicompartmental replacements (ie 30 knees), using the minimally invasive approach, with our appropriate positioning technique. Early results in terms of complications, post-operative radiographs and Oxford knee score were noted. A comparison with groups of an age and sex-matched bilateral total knee replacement group and a group of single unicompartmental knees was also undertaken. Results: The mode of patient positioning for the bilateral procedure is described. There were no noted complications in the operative or early post-operative periods. Review of the radiographs demonstrates 4 minimally malpositioned implants with no symptomatic correlation. In early follow, from 6 months to 2 years, there has been 1 moderate result, with a patient requiring an MUA for 1 knee. 12 of 15 patients report good or excellent post-operative results in both knees. Three patients report problems with 1 knee only. The age matched group of bilateral total knee replacements had longer hospital stays, greater blood transfusion requirements and minor post-operative complications. There were a similar number of radiographic abnormalities and 1 re-operation in the single unicompartmental group. Conclusion: It is possible to safely undertake bilateral simultaneous Oxford unicompartmental knee replacements using a minimally invasive technique using our described method, with obvious benefits for patients with symmetrical knee arthrosis. (299 words)

Aims: The purpose of this study was to analyse the clinical and radiological results and revision rate of Oxford II unicompartmental arthroplasty in a community hospital setting. Methods: 46 unicompartmental arthroplasties were evaluated after mean 8.4-year follow-up. Clinical results were analysed according to Knee Society and Lysholm scores. Radiologically tibiofemoral axis and possible radiolucent lines were measured. Kaplan-Meier survivorship curves, using revision of any reason as an end point, were also analysed and compared to overall results from the Finnish Arthroplasty Register. Results: During the follow-up there were six revisions (13.0%): one of them for primary deep infection, menis-ceal bearing was repeatedly dislocated in one knee. Four conversions to TKA were made because of ongoing lateral osteoarthritis and an average time for revision surgery was 63.8 months (1,5- 120 months). The survivorship calculated at þve years was 90.5% (95%Cl 81.6–99.4; 33 cases at risk), and after eight years 87.6% (95%Cl 77.3–97,9; 19 cases at risk). Follow-up showed no clinical or radiological signs of solution of components. The angle of tibiofemoral axis was also not altered signiþcantly during this observation period. Conclusions: We conclude that the unicompartmental Oxford arthroplasty is a potential alternative in the treatment of unicompartmental medial osteoarthritic knee. Indications and patient selection should be carefully considered. The survivorship was in accordance with most of the previous series

The February 2015 Knee Roundup. 360 . looks at: Intra-operative sensors for knee balance; Mobile bearing no advantage; Death and knee replacement: a falling phenomenon; The swings and roundabouts of unicompartmental arthroplasty; Regulation, implants and innovation; The weight of arthroplasty responsibility!; BMI in arthroplasty

The purpose of our study was to compare the alignment achieved by navigated mobile bearing unicompartmental arthroplasty with that of standard instrumentation. We looked at postoperative X-Rays of 18 unicompartmental mobile bearing arthroplasties performed by two surgeons. 12 of these performed by one surgeon, consisting of 6 navigated E-Motion™ mobile bearing knees and 6, Phase 3 Oxford™ unicompartmental mobile bearing knees. The remaining 6 were Phase 3 Oxford™ unicompartmental mobile bearing knees, performed by a different surgeon. Radiological measurements using the criteria in the Oxford™ manual were taken. All navigated E-motion™ components were within the defined Oxford™ parameters, while a quarter of both all the femoral and all tibial implants were malaligned using standard instrumentation. Our study shows that better and more consistent alignment was achieved when navigation was used for mobile bearing unicompartmental arthroplasty as opposed to the use of standard instrumentation

Medial tibial plateaux excised during 46 unicompartmental arthroplasties for osteoarthritis were collected and photographed. The anterior cruciate ligament was intact in all joints. In every case the cartilage and bone erosion was centred anteriorly on the plateau and the posterior cartilage was intact. The site of the lesion and the intact state of the cruciate ligaments taken together explain why varus deformity was observed only in the extended knee, and why the deformity was correctable and had not become fixed. Failure of the anterior cruciate ligament may allow the erosion to extend posteriorly, producing fixed varus deformity and leading to degeneration of the lateral compartment. Anteromedial osteoarthritis is a distinct clinicopathological entity; its radiographic features enable it to be diagnosed from lateral radiographs; its anatomical features render it suitable for treatment by unicompartmental arthroplasty

The purpose of this paper was to investigate the predictability of outcome of a consecutive series of cemented unicompartmental or total knee replacements in a single surgeon series. Between September 2006 and February 2009, ninety-nine cemented, fixed bearing TKR were performed with patellar resurfacing. 52 cemented Miller Galante (Zimmer) Tibio-femoral UKR were performed in the same time interval. The minimum follow up was 6 months. Oxford and AKSS knee scores were collected prospectively at pre-operative and at routine follow up appointments. Pre-operative mean AKSS Knee score for TKR group was 33.9 and improved to 84.2 at 1 year. Mean scores for Tibiofemoral UKR were 40.4 improving to 84.3 at 1 year. Pre-operative mean Oxford knee score for TKR group was 34.6 (28%) and improved to 16.6 (65%) at 1 year. Mean scores for UKR were 28.5 (41%) improving to 14.0 (71%) at 1 year. These data would suggest that unicompartmental replacement performs as well as TKR. However, in the TKR group, 59% achieved a knee score >85 and 23% an Oxford score >80%. In the UKR group, 67% achieved knee score >85 and 45% an Oxford score >80%. Conversely, only 5% of TKR achieved knee score <50 and 20% Oxford score <50% whilst 10% of UKR had a knee score <50 and 26% and Oxford score <50%. These data show that whilst mean outcomes for TKR and UKR look similar, TKR offers a more predictable outcome with fewer clinical failures but also fewer excellent results. UKR offers a more polarised set of outcomes with far more clinically excellent results but also more clinical failures. These data can inform the ongoing debate regarding the role of unicompartmental arthroplasty. Patient selection is clearly critical but remains an inexact process

In a systematic review, reports from national registers and clinical studies were identified and analysed with respect to revision rates after joint replacement, which were calculated as revisions per 100 observed component years. After primary hip replacement, a mean of 1.29 revisions per 100 observed component years was seen. The results after primary total knee replacement are 1.26 revisions per 100 observed component years, and 1.53 after medial unicompartmental replacement. After total ankle replacement a mean of 3.29 revisions per 100 observed component years was seen. The outcomes of total hip and knee replacement are almost identical. Revision rates of about 6% after five years and 12% after ten years are to be expected

Purpose: Unicompartmental replacement for medial compartment arthrosis of the knee has become popular with eligible patients because of the shortened recovery time, decreased tissue damage and easier future revision. Contemporary multimodal anesthesia has added the potential to safely perform this as outpatient surgery reducing inpatient bed burden. We describe our initial pilot experience with this approach. Method: The first 25 patients who fulfilled the criteria developed underwent same day surgery for unicompart-mental arthroplasty for medial (19) or lateral (3) compartment replacement with either the Oxford knee (20) or the Uniglide (2). All patients were treated with an indwelling femoral nerve catheter supplied by Ropivacaine through a constant release pump (Stryker) which was discontinued at 48 hours. Home care support was made available in first 72 hours by way of RN and physiotherapy visits and mandatory use of walker or crutches for the first 48 hours. Results: Patients in this cohort were universally very satisfied with the model of postop care as described and particularly pleased to avoid a hospital stay. Eighty percent of those who were offered this model chose it. The use of narcotic oral medication was consistently about 50% less than that observed to similar inpatients treated without catheter, and eight patients had complete opioid sparing experience. There were no complications related to the catheter, in particular serious falls or longer term neurologic sequelae. The clinical results were very good and equal to those who were in patients. Conclusion: Outpatient unicompartmental replacement can be performed safely recognizing the decreased surgical trauma and pain stimuli associated with UKR and a relatively younger and healthier cohort screened for this alternative. These patients are amongst the most satisfied with their perioperative course and all would do the same again if given the chance. Other models of analgesia could be considered, though the catheter does seem to have a large opioid sparing effect that likely contributed to patient well being and satisfaction

The options for treatment of the young active patient with isolated symptomatic osteoarthritis of the medial compartment and pre-existing deficiency of the anterior cruciate ligament are limited. The potential longevity of the implant and levels of activity of the patient may preclude total knee replacement, and tibial osteotomy and unicompartmental knee arthroplasty are unreliable because of the ligamentous instability. Unicompartmental knee arthroplasties tend to fail because of wear or tibial loosening resulting from eccentric loading. Therefore, we combined reconstruction of the anterior cruciate ligament with unicompartmental arthroplasty of the knee in 15 patients (ACLR group), and matched them with 15 patients who had undergone Oxford unicompartmental knee arthroplasty with an intact anterior cruciate ligament (ACLI group). The clinical and radiological data at a minimum of 2.5 years were compared for both groups. The groups were well matched for age, gender and length of follow-up and had no significant differences in their pre-operative scores. At the last follow-up, the mean outcome scores for both the ACLR and ACLI groups were high (Oxford knee scores of 46 (37 to 48) and 43 (38 to 46), respectively, objective Knee Society scores of 99 (95 to 100) and 94 (82 to 100), and functional Knee Society scores of 96 and 96 (both 85 to 100). One patient in the ACLR group needed revision to a total knee replacement because of infection. No patient in either group had radiological evidence of component loosening. The radiological study showed no difference in the pattern of tibial loading between the groups. The short-term clinical results of combined anterior cruciate ligament reconstruction and unicompartmental knee arthroplasty are excellent. The previous shortcomings of unicompartmental knee arthroplasty in the presence of deficiency of the anterior cruciate ligament appear to have been addressed with the combined procedure. This operation seems to be a viable treatment option for young active patients with symptomatic arthritis of the medial compartment, in whom the anterior cruciate ligament has been ruptured

The purpose was to assess the effect of the posterior slope on the long-term outcome of unicompartmental arthroplasty in knees with intact and deficient anterior cruciate ligaments. We retrospectively reviewed ninety-nine unicompartmental arthroplasties after a mean duration of follow-up of sixteen years (12 to 20 years). At the time of the arthroplasty, the anterior cruciate ligament was considered to be normal in fifty knees, damaged in thirty-one, and absent in eighteen. At the most recent follow-up, we measured the posterior tibial slope and the anterior tibial translation on standing lateral radiographs. In the group of seventy-seven knees that had not been revised by the time of the most recent follow-up, there was a significant linear relationship between anterior tibial translation (mean, 3.7 mm) and posterior tibial slope (mean, 4.3) (p = 0.01). The mean posterior slope of the tibial implant was significantly less in the group of seventy-seven knees without loosening of the implant than it was in the group of seventeen knees with loosening of the implant (p = 0.03). Five ruptures of the anterior cruciate ligament occurred in knees in which the ligament had been considered to be normal at the time of implantation; the posterior tibial slope in these five knees was greater than 13 degrees. Clinical evaluation revealed normal or nearly normal anteroposterior stability at the time of the most recent follow-up in all sixty-six unrevised knees in which the anterior cruciate ligament had been present at the time of implantation. Of the eighteen knees in which the anterior cruciate ligament had been absent at the time of the arthroplasty, eleven still had the implant in situ at the time of the most recent follow-up; the mean posterior tibial slope in these 11 knees was less than 5 degrees. Seven knees in which the anterior cruciate ligament had been absent at the time of the arthroplasty were revised. In these 7 knees, the tibial prosthesis was implanted with a posterior slope greater than 8 degrees. These findings suggest that more than 7 degrees of posterior slope of the tibial implant should be avoided, particularly if the anterior cruciate ligament is absent at the time of implantation. An intact anterior cruciate ligament, even when partly degenerated, was associated with the maintenance of normal anteroposterior stability of the knee for an average of sixteen years following unicompartmental knee arthroplasty

Intro/Purpose. Lateral partial knee replacement is indicated as an alternative to total knee replacement for isolated end stage lateral compartment degenerative joint disease. The purpose of this study is to report the surgical technique and clinical results of a large series of lateral partial knee replacements from two institutions. Methods. A retrospective review identified 205 lateral unicompartmental arthroplasty procedures performed in two practices over a six-year period (Aug 2011 – June 2017). Patients indicated for surgery met specific preoperative clinical and radiographic criteria confirming lateral compartment arthritic disease with a correctable deformity, intact full-thickness medial cartilage, competent anterior cruciate ligament, and minimal disease in the patellofemoral compartment. A single cemented fixed bearing tibial component design was used in all cases specifically designed for lateral compartment anatomy. Results. The average age was 65 years old and 76% were female. Average follow-up in the lateral partials was 1.7 years (range 0.5 years to 6 years). Knee Society Scores improved from 45 (pre-op) to 88 points (post-op). Range of motion improved from 6–115o (pre-op) to 0–122 o (post-op). No knees were revised to a TKA. One knee had an additional medial partial knee placed at 1.1 years post lateral partial knee replacement for medial disease progression. Two knees required an irrigation and debridement for traumatic wound dehiscence. Conclusion. This is the largest series of lateral partial knee replacements reported. Clinical improvements, range of motion, and survivorship were excellent at short-term follow-up. Long-term follow-up is needed for additional understanding of a novel implant designed specifically for the lateral compartment and the survivorship of the unreplaced compartments. We believe the lateral partial knee replacement to be a viable option for isolated lateral compartment disease in approximately 4% of patients

Purpose: To compare the ten-year survivorship results of an established total and medial compartment knee replacement performed in a single centre over an eighteen year period. Method: Since 1978 knee replacements have been prospectively recorded in Bristol on a database. Regular clinical and radiological review has been undertaken every two or three years up to twenty years. 408 medial St Georg Unicompartmental replacements and 531 Kinematic total knee replacements have been subject to survivorship analysis using three failure end points. One - revision or removal of the implant. Two – revision or removal and moderate or severe pain. Three – the worst case including all patients lost to follow-up. Results: The follow-up rate was 97% in both groups. 212 patients (562 knees) died and 31 patients (35 knees) were lost to follow-up. At ten years 25 medial Sled and 20 Kinematic knee arthroplasties had been revised. There was no significant difference (p > 0.05) in the number of good and excellent results. The mean range of movement at the last follow-up was 109 degrees for the medial Sled and 100 degrees for the Kinematic (p< 0.01). 94% of the medial Sled patients obtained a range of movement equal to or greater than 90 degrees whereas only 84% of Kinematic patients obtained this range (p < 0.05). The ten-year survivorship figures were similar for both groups. Revision as the end point was 87.5% for the medial Sled and 89.6% for the Kinematic knees. When moderate and severe pain was considered in addition to revision ten-year survivorship was 79.4% in both groups. The worst case survivorship was also 74% in both groups. Conclusion: The ten-year survivorship results of a fixed bearing, non-congruous, Unicompartmental arthroplasty are as good as those of a total knee replacement when performed in a single centre by two consultant surgeons and a variety of trainees. The advantages of a more rapid recovery and better quality result are offset by an easier though slightly higher revision rate

Robotic arm-assisted total knee replacement is performed as a semi-active system in which haptic guidance is used to precisely position and align components. This is based on pre-operative planning based on CT imaging and can be modified as needed throughout the procedure. This technology, as shown with unicompartmental arthroplasty, is more accurate than conventional and even computer navigated instrumentation and will decrease variability. The knee can be planned to a neutral mechanical alignment. Intra-operatively, the computer will demonstrate compartment gap measurements to assist with soft tissue balancing. Alternatively, limb and component alignment can be accurately adjusted several degrees off the neutral axis to balance the knee and avoid or minimise soft tissue releases. This allows a more constitutional alignment within the alignment parameters accepted by the surgeon. This technique was utilised commonly in the first 60 robotic total knee replacements performed. We will now have the ability to collect accurate component positioning, alignment, and soft tissue balance data that can be correlated to outcomes of total knee replacements

We present a comparison of the results of the Oxford unicompartmental knee arthroplasty in patients younger and older than 60 years of age. The ten-year all-cause survival of the < 60 years of age group (52) was 91% (95% confidence interval (CI) 12), while in the ≥ 60 years of age group (512), the figure was 96% (95% CI 3). For the younger group, the mean Hospital for Special Surgery score at ten-year follow-up (n = 21) was 94 of 100, compared with a mean of 86 of 100 for the older group (n = 135). The results show that the Oxford unicompartmental arthroplasty can achieve ten-year results that are comparable to total knee arthroplasty in patients < 60 years of age. We conclude that for patients aged over 50, age should not be considered a contraindication for this procedure

Total knee arthroplasty is a successful procedure with good long-term results. Studies indicate that 15% – 25% of patients are dissatisfied with their total knee arthroplasty. In addition, return to sports activities is significantly lower than total hip arthroplasty with 34% – 42% of patients reporting decreased sports participation after their total knee arthroplasties. Poor outcomes and failures are often associated with technical errors. These include malalignment and poor ligament balancing. Malalignment has been reported in up to 25% of all revision knee arthroplasties, and instability is responsible for over 20% of failures. Most studies show that proper alignment within 3 degrees is obtained in only 70% – 80% of cases. Navigation has been shown in many studies to improve alignment. In 2015, Graves examined the Australian Joint Registry and found that computer navigated total knee arthroplasty was associated with a reduced revision rate in patients under 65 years of age. Navigation can improve alignment, but does not provide additional benefits of ligament balance. Robotic-assisted surgery can assist in many of the variables that influence outcomes of total knee arthroplasty including: implant positioning, soft tissue balance, lower limb alignment, proper sizing. The data on robotic-assisted unicompartmental arthroplasty is quite promising. Cytech showed that femoral and tibial alignment were both significantly more accurate than manual techniques with three times as many errors with the manually aligned patients. Pearle, et al. compared the cumulative revision rate at two years and showed this rate was significantly lower than data reported in most unicompartmental series, and lower revision rates than both Swedish and Australian registries. He also showed improved satisfaction scores at two years. Pagnano has noted that optimal alignment may require some deviation from mechanically neutral alignment and individualization may be preferred. This is also likely to be a requirement of more customised or bi-cruciate retaining implant designs. The precision of robotic surgery may be necessary to obtain this individualised component alignment. While robotic total knee arthroplasty requires further data to prove its value, more precise alignment and ligament balancing is likely to lead to improved outcomes, as Pearl, et al. and the Australian registry have shown. While it is difficult to predict the future at this time, I believe robotic-assisted total knee arthroplasty is the future and that future begins now

Since 2005, the author has performed nearly 1000 Oxford medial unicompartmental arthroplasties (UKA) using a mobile bearing. The indications are 1) Isolated medial compartment osteoarthritis with ‘bone-on-bone’ contact, which has failed prior conservative treatment, 2) Medial femoral condyle avascular necrosis or spontaneous osteonecrosis, which has failed prior conservative treatment. Patients are recommended for UKA only if the following anatomic requirements are met: 1) Intact ACL, 2) Full thickness articular cartilage wear limited to the anterior half of the medial tibial plateau, 3) Unaffected lateral compartment cartilage, 4) Unaffected patellar cartilage on the lateral facet, 5) Less than 10 degrees of flexion deformity, 6) Over 100 degrees of knee flexion, and 7) Varus deformity not exceeding 15 degrees. Exclusion criteria for surgery are BMI of more than 30, prior high tibial osteotomy, and inflammatory arthritis. All cases were performed with a tourniquet inflated using a minimally-invasive incision with a quadriceps-sparing approach. Both femoral and tibial components were cemented. Most patients were discharged home the next morning; bilaterals usually stayed a day longer. We have previously described our results and the factors determining alignment. In a more recent study, we have compared the coronal post-operative limb alignment and knee joint line obliquity after medial UKA with a clinically and radiologically (less than Grade 2 medial OA) normal contralateral lower limb. In our series, we have had 1 revision for aseptic loosening of both components, conversion to TKRs in a patient with bilateral UKAs who developed rheumatoid arthritis 3 years later, and 9 meniscal dislocations. There have been no cases of wound infections and thromboembolism. We have reviewed our patients with a minimum 10-year follow-up which will be presented. The vast majority of our patients have been generally very satisfied with the results. Our study shows that most patients (who have no disease in the contralateral knee) regain their ‘natural’ alignment and joint line obliquity comparable to their contralateral limb. Over the past few years our percentage of UKAs has been steadily rising to about a third of our knee cases. UKA serves as a definitive procedure in the elderly. We see it as a suitable procedure in middle-aged patients who want an operation that provides a quick recovery, full function and range of motion, and near-normal kinematics, with the understanding that they have a small chance of conversion to a total knee arthroplasty in the future

Twenty patients underwent simultaneous bilateral medial unicompartmental knee arthroplasty. Pre-operative hip-knee-ankle alignment and valgus stress radiographs were used to plan the desired post-operative alignment of the limb in accordance with established principles for unicompartmental arthroplasty. In each patient the planned alignment was the same for both knees. Overall, the mean planned post-operative alignment was to 2.3° of varus (0° to 5°). The side and starting order of surgery were randomised, using conventional instrumentation for one knee and computer-assisted surgery for the opposite side. The mean variation between the pre-operative plan and the achieved correction in the navigated and the non-navigated limb was 0.9° (. sd. 1.1; 0° to 4°) and 2.8° (. sd. 1.4; 1° to 7°), respectively. Using the Wilcoxon signed rank test, we found the difference in variation statistically significant (p < 0.001). Assessment of lower limb alignment in the non-navigated group revealed that 12 (60%) were within ± 2° of the pre-operative plan, compared to 17 (87%) of the navigated cases. Computer-assisted surgery significantly improves the post-operative alignment of medial unicompartmental knee arthroplasty compared to conventional techniques in patients undergoing bilateral simultaneous arthroplasty. Improved alignment after arthroplasty is associated with better function and increased longevity

The United States is in the midst of an opioid epidemic, with the World Health Organization reporting that American's consume 99% of the world's supply of hydrocodone and 83% of the world's oxycodone. Additionally, pre-operative opioid use has been associated with worse clinical outcomes and higher rates of complications following TKA. This is especially important in the TKA population given that approximately 15% of patients are either dissatisfied or very dissatisfied at least one year after their TKA procedure. Given the concerning rise is opioid use the American Academy of Orthopaedic Surgeons (AAOS) has recently released an information statement with practice recommendations for combating this excessive and inappropriate opiate use. However, little is known regarding peri-operative opioid use for TKA patients. Therefore, the purpose of this study was to: 1) identify rates of opioid use prior to primary TKA, 2) evaluate post-operative trends in opioid use throughout the year following TKA and 3) identify risk factors for prolonged opioid use following TKA. Overall, 31% of TKA patients are prescribed opioids within 3-months prior to TKA; this percentage has increased over 9% during the years included in this study. Pre-operative opioid use was most predictive of increased refills of opioids following TKA, however, other intrinsic patient characteristics were also predictive of prolonged opioid use. These characteristics remained predictive after controlling for opioid user status. The increasing rates of opioid prescribing prior to TKA are concerning, especially given literature concluding opioids have minimal effect on pain or function in patients with osteoarthritis and pre-operative opioid use is associated with poor outcomes and more complications following TKA. This data provides an important baseline for opioid use trends following TKA that can be used for future comparison and identifies risk factors for prolonged use that will be helpful to prescribers as the AAOS works to decreased opioid use, misuse and abuse within the United States. Our data on THA and unicompartmental arthroplasty is similar with an increase in pre-THA use of 9% with 38% receiving narcotics within 3 months of surgery and continued use in opioid users (9 times non-opioid users at 12 months)

Lateral unicompartmental replacement is performed less frequently than medial replacement and is technically more difficult. The ratio of medial to lateral arthroplasties is approximately 10:1. Differences in technique include the following:. The patella is more vulnerable to impingement on the leading edge of the femoral component and must be carefully recessed. Because the wear pattern in lateral disease is more posterior than in medial disease, there is often residual cartilage on the distal femoral condyle. This is also the case when UKA is performed for the sequella of a lateral plateau fracture. To avoid this impingement, residual cartilage should probably be removed from the distal condyle before its resection and the femoral component should be under-sized anteriorly. Initial tibial resection should be very conservative to avoid the need for very thick tibial components to restore alignment and stability. Err toward shifting the femoral component laterally and the tibial component medially to maximise M-L congruency. Consider a medial parapatellar approach (avoiding the anterior horn of the medial meniscus) to facilitate visibility and component alignment

It is important to remember that osteoarthritis is a noninflammatory condition that can affect 1, 2 or all 3 compartments of the knee. Moreover, this disease is a continuum from very mild to very severe involvement of the soft tissue, articular cartilage and bone. For this reason, a variety of nonsurgical and surgical options are indicated. The rheumatologist and/or orthopedist must understand the stage of the disease and fit that both to the pathology, age, activity level, and functional needs of the patient. For that reason, each of the options discussed today have an indication. The important issue about tricompartmental replacement is that we have improved technology and technique and the indications of today are broader than those of 20 years ago. Hopefully, they will continue to evolve both in terms of materials and instruments. The American Rheumatologic Association (ARA) has stated that joint replacement has been the major improvement in the care of the arthritic patient. The tricompartmental solution is the treatment of choice in patients with inflammatory arthritis such as rheumatoid arthritis as well as the solution in osteoarthritic patients with tricompartmental disease. There is an indication for osteotomy, unicompartmental replacement and perhaps patellofemoral replacement. I think the next frontier will be to find disease modifying osteoarthritic drugs (DMOADS) that will provide disease intervention as the DMARDs have done in rheumatoid arthritis. Moreover, cartilage repair combined with osteotomy will hopefully allow us to prevent progression of this disease

Since 2005, the author has performed 422 Oxford medial unicompartmental arthroplasties (UKA) using a mobile bearing. There were 263 females and 119 males, (40 patients had bilateral UKAs) with a mean age of 62 years. The indications were: Isolated medial compartment osteoarthritis with ‘bone-on-bone’ contact, which had failed prior conservative treatment; Medial femoral condyle avascular necrosis or spontaneous osteonecrosis, which had failed prior conservative treatment. Patients were recommended UKA only if the following anatomic requirements were met: Intact ACL, Full thickness articular cartilage wear limited to the anterior half of the medial tibial plateau, Unaffected lateral compartment cartilage, Unaffected patellar cartilage on the lateral facet, Less than 10 degrees of flexion deformity, Over 100 degrees of knee flexion, Varus deformity not exceeding 15 degrees. Exclusion criteria for surgery were BMI of more than 30, prior high tibial osteotomy, and inflammatory arthritis. All cases were performed with a tourniquet inflated using a minimally-invasive incision with a quadriceps-sparing approach. Both femoral and tibial components were cemented. Rehabilitation consisted of teaching the patients 6 exercises to regain strength and range of motion, and weight-bearing as tolerated with a cane began from the evening of surgery. Most patients were discharged home the next morning; bilaterals usually stayed a day longer. We have previously described our results and the factors determining alignment. In a more recent study we have compared the coronal postoperative limb alignment and knee joint line obliquity after medial UKA with a clinically and radiologically (less than Grade 2 medial OA) normal contralateral lower limb. In our series of 423 cases, we have had 1 revision for aseptic loosening of both components, and 4 meniscal dislocations. There have been no cases of wound infections and thromboembolism. We are currently undertaking a review of the 2–10 year follow-up of our cases. The vast majority of our patients have been generally very satisfied with the results. Our study shows that most patients (who have no disease in the contralateral knee) regain their ‘natural’ alignment and joint line obliquity comparable to their contralateral limb. Over the past few years our percentage of UKAs has been steadily rising. UKA serves as a definitive procedure in the elderly. We see it as a suitable procedure in middle-aged patients who want an operation that provides a quick recovery, full function and range of motion, and near-normal kinematics, with the understanding that they have a small chance of conversion to a total knee arthroplasty in the future

This randomised trial evaluated the outcome of a single design of unicompartmental arthroplasty of the knee (UKA) with either a cemented all-polyethylene or a metal-backed modular tibial component. A total of 63 knees in 45 patients (17 male, 28 female) were included, 27 in the all-polyethylene group and 36 in the metal-backed group. The mean age was 57.9 years (39.6 to 76.9). At a mean follow-up of 6.4 years (5 to 9.9), 11 all-polyethylene components (41%) were revised (at a mean of 5.8 years; 1.4 to 8.0) post-operatively and two metal-backed components were revised (at one and five years). One revision in both groups was for unexplained pain, one in the metal-backed group was for progression of osteoarthritis. The others in the all-polyethylene group were for aseptic loosening. The survivorship at seven years calculated by the Kaplan–Meier method for the all-polyethylene group was 56.5% (95% CI 31.9 to 75.2, number at risk 7) and for the metal-backed group was 93.8% (95% CI 77.3 to 98.4, number at risk 16) This difference was statistically significant (p <  0.001). At the most recent follow-up, significantly better mean Western Ontario and McMaster Universities Arthritis Index Scores were found in the all-polyethylene group (13.4 vs 23.0, p = 0.03) but there was no difference in the mean Knee injury and Osteoarthritis Outcome scores (68.8; 41.4 to 99.0 vs 62.6; 24.0 to 100.0), p = 0.36). There were no significant differences for range of movement (p = 0.36) or satisfaction (p = 0.23). This randomised study demonstrates that all-polyethylene components in this design of fixed bearing UKA had unsatisfactory results with significantly higher rates of failure before ten years compared with the metal-back components. Cite this article: Bone Joint J 2015;97-B:786–92

The osteonecrosis of the medial femoral condyle, depending on the area occupied, causes pain and may progress into osteoarthritis. For the management of osteonecrosis numerous treatment methods have been described, as conservative, drilling, osteotomy and others. The aim of our study is to evaluate the results of management of knee osteonecrosis with unicompartmental arthroplasty. We studied 16 knees in 15 patients (all women) with osteonecrosis of the medial femoral condyle. The size of osteonecrosis was greater than 3.5 cm, as revealed by MRI. The mean age of patients was 72 years (range 64–80 years). The time elapsed from the onset of symptoms to surgical treatment ranged from 3 to 10 months. All patients were followed clinically and by X-ray 1 to 6 years post-operatively and scored with Knee Society Score. The result in 14 patients was excellent and in 1 was good. In conclusion, unicompartmental knee arthroplasty is a satisfactory method of treatment of osteonecrosis, which provides immediate relief from pain, long-term satisfactory outcome and avoids multiple operations

Background. Wear and fatigue damage to polyethylene components remain major factors leading to complications after total knee and unicompartmental arthroplasty. A number of wear simulations have been reported using mechanical test equipment as well as computer models. Computational models of knee wear have generally not replicated experimental wear under diverse conditions. This is partly because of the complexity of quantifying the effect of cross-shear at the articular interface and partly because the results of pin-on-disk experiments cannot be extrapolated to total knee arthroplasty wear. Our premise is that diverse experimental knee wear simulation studies are needed to generate validated computational models. We combined five experimental wear simulation studies to develop and validate a finite-element model that accurately predicted polyethylene wear in high and low crosslinked polyethylene, mobile and fixed bearing, and unicompartmental (UKA) and tricompartmental knee arthroplasty (TKA). Methods. Low crosslinked polyethylene (PE). A finite element analysis (FEA) of two different experimental wear simulations involving TKA components of low crosslinked polyethylene inserts, with two different loading patterns and knee kinematics conducted in an AMTI knee wear simulator: a low intensity and a high intensity. Wear coefficients incorporating contact pressure, sliding distance, and cross-shear were generated by inverse FEA using the experimentally measured volume of wear loss as the target outcome measure. The FE models and wear coefficients were validated by predicting wear in a mobile bearing UKA design. Highly crosslinked polyethylene (XLPE). Two FEA models were constructed involving TKA and UKA XLPE inserts with different loading patterns and knee kinematics conducted in an AMTI knee wear simulator. Wear coefficients were generated by inverse FEA. Results. Predicted wear rates were within 5% of experimental wear rates during validation tests. Unicompartmental mobile bearing back-side wear accounted for 46% of the total wear in the mobile bearing. Wear during the swing phase was 38% to 44% of total wear. Discussion & Conclusions. Crosslinking polyethylene primarily decreased (by nearly 10-fold) the wear generated by cross-shear. This result can be explained by the reduced propensity of crosslinked polyethylene molecules to orient in the dominant direction of sliding. A highly crosslinked fixed-bearing polyethylene insert can provide high wear performance without the increased risk for mobile bearing dislocation. Finite element analysis can be a robust and efficient method for predicting experimental wear. The value of this model is in rapidly conducting screening studies for design development, assessing the effect of varying patient activity, and assessing newer biomaterials. This FEA model was experimentally validated but requires clinical validation

No, Neutral mechanical axis has never been regarded as “necessary” to the success of TKA. In fact it has never been established as “ideal” with published data. Tibial femoral alignment after TKA is important, but it is also an issue that we do not understand completely. Neutral mechanical alignment refers to the relationship between the mechanical axes of the femur and tibia as shown on full length radiographs. “Neutral” means that these axes are collinear, i.e. that a line may be drawn from the center of the hip to the center of the ankle and it will intersect the center of the knee joint. The allure of the “straight line” has led many surgeons to regard a neutral mechanical axis as “perfection” for TKA surgery, but indeed, it is not the usual “normal” alignment for most human knees, nor is it the target for many conventional knee replacements. The “neutral mechanical axis” represents OVERCORRECTION for most knees. Moreland demonstrated in 1987 that few human knee joints are naturally aligned “in neutral”, but with the line from center of hip to center of ankle passing through the medial compartment. This tendency to relative varus mechanical axis in most human knees was corroborated by Bellemans et al in 2012. They substituted the word “constitutional varus” for what would otherwise be known as “normal alignment”. In general, patients with pathologic or significant varus alignment, whose arthroplasties have been performed competently, are at greatest risk for failure by wear, osteolysis and loosening. This is the prototypical failure mechanism that pre-occupied the surgeons responsible for making knee arthroplasty successful in the 1970s. The first paper to identify varus TKA alignment and failure due to loosening was Lotke and Ecker in 1977. They worked from short radiographs and ushered in an era of careful attention to valgus TKA alignment-not neutral alignment. Correction of varus deformity combined with ligament balancing was probably responsible for making condylar type knee arthroplasties work durably in the early days. Full length radiographs, used by Kennedy and White in 1987 to study alignment in unicompartmental arthroplasties, provide a more sophisticated method of evaluating knee alignment. These studies must be aligned with correct rotation to be valid. Computerised navigation was probably responsible for some surgeon's dedication to the neutral mechanical axis. The study of Parratte et al from Mayo has received much attention and argued that a neutral mechanical axis did NOT improve success rates at 15 years. It should be noted that these TKA's were expertly performed and even the less well-aligned cases were not “excessively” malaligned. This study does not state that alignment is irrelevant to the success of TKA, but rather that a range of alignments (with stability) might be expected to produce a durable arthroplasty. Concurrent with these developments has been an interest in “under-correcting” knee deformity or allowing osseous anatomy (with compensation for cartilage loss) guide component position. In truth, it is inaccurate to describe conventional “align and balance” techniques as necessarily seeking a neutral mechanical axis. Most classical alignment techniques do, however, alter the angle of component position from the original articular surface angles and theoretically may not function as well with the native soft tissue environment. Surgeons who would align the TKA identically to the arthritic knee may credit previous generations with improving the technology such that this is a possibility. If every patient is to be aligned with this technique, however, this suggests that soft tissue pathology does not exist. As with all complex issues, glib answers are to be avoided and deep analysis is appropriate

Aims

With up to 40% of patients having patellofemoral joint osteoarthritis (PFJ OA), the two arthroplasty options are to replace solely the patellofemoral joint via patellofemoral arthroplasty (PFA), or the entire knee via total knee arthroplasty (TKA). The aim of this study was to assess postoperative success of second-generation PFAs compared to TKAs for patients treated for PFJ OA using patient-reported outcome measures (PROMs) and domains deemed important by patients following a patient and public involvement meeting.

Between 1989 and 1992 102 knees adjudged suitable for Unicompartmental replacement (UKR) were randomised to receive either a St Georg Sled UKR or a Kinematic modular total knee replacement (TKR). The early results demonstrated that the UKR group had less complications, and more rapid rehabilitation. At 5 years there were equal failures but the UKR group had more excellent results and a greater range of movement. Despite this doubt persisted about whether these advantages would be maintained these cases have been followed regularly by a research nurse at 8, 10, 12 years. We now report the final outcome at 15 years. 43 patients (45 knees) have died with all their knees intact. Throughout the review period the Bristol Knee Scores (BKS) of the UKR group have been better and at 15 years 77% and 53% of the surviving UKRs and TKRs achieve an excellent score. 6 TKRs and 4 UKRs have failed during the 15 years of the review. Conclusion. The better early results with UKR are maintained at 15 years with no greater failure rate. The median BKS scores of the UKR group was 91.1 at five years and 92 at 15 years suggesting little functional deterioration in either the prosthesis or remainder of the joint. These results would seem to justify the increased use of UKR

Aims

The aim of this study was to determine the risk of tibial eminence avulsion intraoperatively for bi-unicondylar knee arthroplasty (Bi-UKA), with consideration of the effect of implant positioning, overstuffing, and sex, compared to the risk for isolated medial unicondylar knee arthroplasty (UKA-M) and bicruciate-retaining total knee arthroplasty (BCR-TKA).

The options for treatment of the young active patient with isolated symptomatic osteoarthritis of the medial compartment and pre-existing deficiency of the anterior cruciate ligament are limited. The indications for the unicompartimental knee prosthesis are selective. Misalignment femoral-tibia, varo-valgus angle more than 7°, over-weight, and knee instability were considered to be a contraindication. The potential longevity of the implant and levels of activity of the patient may preclude total knee replacement, and tibial osteotomy and unicompartmental knee arthroplasty are unreliable because of the ligamentous instability. Therefore, we combined reconstruction of the anterior cruciate ligament first and unicompartmental arthroplasty of the knee. We included in this study six patients, three males and three female, mean age 53.6 years, that presented only osteoarthritis of medial femoral condyle and ACL deficiency. In the first group included 2 patients, we performed arthroscopy ACL reconstruction with hamstring and unicompartimental knee prosthesis one-step, and in the second group included 4 patients, we performed the same surgical procedure in two-step. The clinical and radiological data at a minimum of 1.5 years at follow-up. We evaluated all patients with KOOS score, and IKDC score. At the last follow-up, no patient had radiological evidence of component loosening, no infection, no knee remainder instability. The subjective and objective outcome assessed with the scale documented satisfactory average results, both in patients of first group and in those of second group. ACL deficiency induced knee osteoarthritis for incorrect knee biomechanics, and all patients could be submit a total knee replacement. What method for preventing it? This combined surgical treatment seems to be a viable treatment option for young active patients with symptomatic arthritis of the medial compartment, in whom the anterior cruciate ligament has been ruptured. Future developments and more data are necessary for standardised surgical approach

Aims

The impact of a diaphyseal femoral deformity on knee alignment varies according to its severity and localization. The aims of this study were to determine a method of assessing the impact of diaphyseal femoral deformities on knee alignment for the varus knee, and to evaluate the reliability and the reproducibility of this method in a large cohort of osteoarthritic patients.

The Oxford medial unicompartmental knee replacement was designed to reproduce normal mobility and forces in the knee, but its detailed effect on the patellofemoral joint has not been studied previously. We have examined the effect on patellofemoral mechanics of the knee by simultaneously measuring patellofemoral kinematics and forces in 11 cadaver knee specimens in a supine leg-extension rig. Comparison was made between the intact normal knee and sequential unicompartmental and total knee replacement. Following medial mobile-bearing unicompartmental replacement in 11 knees, patellofemoral kinematics and forces did not change significantly from those in the intact knee across any measured parameter. In contrast, following posterior cruciate ligament retaining total knee replacement in eight knees, there were significant changes in patellofemoral movement and forces. The Oxford device appears to produce near-normal patellofemoral mechanics, which may partly explain the low incidence of complications with the extensor mechanism associated with clinical use

Aims: The aim of our work was to measure, the necessary correction angle in unicompartmental knee prosthesis in order to make the patientñs functional result the best following the procedure. Method: We included all the medial and all the lateral unicompartmental arthroplasties in our department in 1999. For the analysis of the functional results, we have reviewed the patients and recorded the clinical data with the help of the New Jersey Knee Score. We have had the postoperative weight bearing AP knee X-rays also at the same time. Conclusion: This type of implant can be used with conþdence in medial unicompartmental knee arthroplasties up to 15 degrees of varus deformation preoperatively, according to the early postoperative results. We did not þnd any signiþcant difference in the early functional results between the 10 degrees or less and the more than 10 degrees corrected groups

Unicompartmental knee replacements have been performed since the 1970’s. Controversy still exists as to the indications and contra-indications for these procedures, and there is still no clarity as to whether the patient should have a high tibial osteotomy, a unicompartmental knee replacement, or a total knee replacement. It has been suggested that unicompartmental knee replacements are preferable to high tibial osteotomies, as conversion to a total knee replacement is easier following a unicompartmental replacement. Ten patients with unicompartmental knee replacements presented to the author requiring revision. All were revised to total knee replacements. In four a primary knee replacement could be performed, but the remaining six required a revision prosthesis on the tibial side, using stems and wedges. No revision prostheses were required on the femoral side. Revision of a unicompartmental total knee replacement is technically easier than the revision of a total knee replacement. Revision of a high tibial osteotomy to a total knee replacement can be difficult, particularly if a poorly performed HTO had been done, with residual significant ligament imbalance. The author feels that any type of revision surgery can be difficult. The author concludes that there is still no clarity as to whether one should do a unicompartmental knee replacement or a high tibial osteotomy, and that currently it is still the Surgeon’s choice as to which procedure he is going to perform

Osteoarthritis of the knee is a debilitating condition affecting millions of persons, often requiring arthroplasty to relieve pain and improve mobility. For those patients with disease in only one compartment of the knee, unicompartmental knee arthroplasty (UKA) can be a viable surgical alternative. To date, there has not been a large series reported in the literature of UKAs performed with robotic assistance. The aim of this study was to examine the clinical outcomes of patients who underwent this procedure. Five hundred and ten procedures in patients with a mean age of 63.7 years (range, 28 to 88 years) who underwent unicompartmental knee arthroplasty using a robotic-assisted system between July, 2008 and June, 2010 were identified. Clinical outcomes were evaluated using the Oxford Knee Score and patients without recent follow-up were contacted by telephone. The revision rate and time to revision were also examined. The average length of stay for patients who underwent robot-assisted UKA was 1.4 days (range, 1 to 7 days). There was minimal blood loss with most procedures. At latest clinical follow-up, most patients were doing well after UKA with a mean Oxford Knee Score of 36.1 + 9.92. The revision rate was 2.5% with 13 patients being either converted from an inlay to onlay prosthesis or conversion to total knee arthroplasty. The most common indication for revision was tibial component loosening, followed by progression of arthritis. Mean time to revision was 9.55 + 5.48 months (range, 1 to 19 months). Unicompartmental arthroplasty with a robotic system provides good pain relief and functional outcome at short-term follow-up. Ensuring correct component alignment and ligament balancing increases the probability of a favorable outcome following surgery. Proper patient selection for appropriate UKA candidates remains an important factor for successful outcomes

We describe 88 knees (79 patients) with lateral unicompartmental osteoarthritis which had been treated by the St Georg Sled prosthesis. At a mean follow-up of nine years (2 to 21) 15 knees had revision surgery, nine for progression of arthritis, six for loosening, four for breakage of a component and four for more than one reason. Six patients complained of moderate or severe pain at the final follow-up. Only five knees were lost to follow-up in the 21-year period. We performed survivorship analysis on the group using revision for any cause as the endpoint. At ten years the cumulative survival rate was 83%, and at 15 years, when ten knees were still at risk, it was 74%. Based on our clinical results and survival rate the St Georg Sled may be considered to be a suitable unicompartmental replacement for isolated lateral compartment osteoarthritis

Osteoarthritis of the medial compartment of the knee often shows a specific pattern of anterior wear. Review of our revisions from a series of medial metal-backed Brigham unicondylar knee replacements performed between 1983 and 1989 showed that this wear pattern was common on the tibial polyethylene surface. We reviewed these cases retrospectively to compare the pattern of preoperative erosion with the wear of the prosthesis. In all 14 knees with severe anterior wear in a unicompartmental replacement, the prearthroplasty radiographs showed similar patterns, suggesting that the implanted tibial component may continue to be subjected to the same localised stresses that precipitated the failure of the original articular cartilage. Many tibial components implanted during the 1980s had an unacceptably thin anterior rim of polyethylene and it seems that greater thickness is essential at the anterior and peripheral margins of the tibial plateau

We reviewed two similar groups of patients with medial osteoarthritis of the knee treated by unicompartmental arthroplasty. The group receiving an Oxford meniscal-bearing implant, with no medial release, showed significantly better mechanical alignment than that receiving a fixed-bearing implant. Under-correction, with its ominous mechanical implications, was much more common with the fixed-bearing design. Over-correction was rare and was seen in both designs about equally. Degenerative stenosis of the intercondylar notch was common and appeared to put the anterior cruciate ligament at risk of rupture, especially after correction of the varus deformity. We consider that postoperative leg alignment and soft-tissue balance after unicompartmental knee replacement are determined more by the implant design and the surgical technique than by any variation in soft-tissue contracture. Release of the medial collateral ligament is not necessary for realignment, but a generous notchplasty is often needed to allow normal anterior cruciate ligament function

Purpose. Late stage medial unicompartmental osteoarthritic disease of the knee can be treated by either Total Knee Replacement (TKR) or Unicompartmental Replacement (UKR). As a precursor to the TOPKAT study this work tested the postulate that individual surgeons show high variation in the choice of treatment for individual patients. Method. Four surgeons representing four different levels of expertise or familiarity with partial knee replacement (UKR design centre knee surgeon, specialist knee surgeon, arthroplasty surgeon and a year six trainee) made a forced choice decision of whether they would perform a TKR or UKR based on the same pre-operative radiographic and clinical data in 140 individual patients. Consistency of decision was also evaluated for each surgeon 3 months later and the effect of additional clinical data was also evaluated. The sample consisted of the 100 patients who had subsequently undergone UKR and 40 who had undergone TKR. Results. The specialist knee surgeon from the design centre would have performed UKR in 80% of the patients. The other surgeons would have performed a UKR in between 32-43% of the patients representing a variation in decision making of up to 59%. The choice of treatment for each surgeon remained unchanged in between 80-87% of cases after viewing additional clinical data. There was high intra surgeon repeatability in decision making when assessed 3 months later. Conclusion. Despite being given identical information, surgeons show high variability in decision making for patients with medial OA of the knee. A knee surgeon with a special interest in partial knee replacement is twice as likely to choose UKR for a patient with medial compartment OA than a non specialist surgeon. The choice is predominantly based on radiological findings but decision making for each individual surgeon is reassuringly consistent. The implications are that if TKR and UKR have unequal efficacy, some patients may be undergoing a suboptimal procedure

Using a new, non-invasive method, we measured the patellofemoral force (PFF) in cadaver knees mounted in a rig to simulate weight-bearing. The PFF was measured from 20° to 120° of flexion before and after implanting three designs of knee prosthesis. Medial unicompartmental arthroplasty with a meniscal-bearing prosthesis and with retention of both cruciate ligaments caused no significant change in the PFF. After arthroplasty with a posterior-cruciate-retaining prosthesis and division of the anterior cruciate ligament, the PFF decreased in extension and increased by 20% in flexion. Implantation of a posterior stabilised prosthesis and division of both cruciate ligaments produced a decrease in the PFF in extension but maintained normal load in flexion. There was a direct relationship between the PFF and the angle made with the patellar tendon and the long axis of the tibia. The abnormalities of the patellar tendon angle which resulted from implantation of the two total prostheses explain the observed changes in the PFF and show how the mechanics of the patellofemoral joint depend upon the kinematics of the tibiofemoral articulation

We randomised 102 knees suitable for a unicompartmental replacement to receive either a unicompartmental (UKR) or total knee replacement (TKR) after arthrotomy. Both groups were well matched with a predominance of females and a mean age of 69 years. Patients in the UKR group showed less perioperative morbidity, but regained knee movement more rapidly and were discharged from hospital sooner. At five years, two UKRs and one TKR had been revised; another TKR was radiologically loose. All other knees appeared to be clinically and radiologically sound. Pain relief was good in both groups but the number of knees able to flex ≥ 120° was significantly higher in the UKR group (p < 0.001) and there were more excellent results in this group. Our findings have shown that UKR gives better results than TKR and that this superiority is maintained for at least five years

We report the outcome of 135 knees with anteromedial osteoarthritis in which the Oxford meniscal-bearing unicompartmental arthroplasty was inserted in a district general hospital by a single surgeon. All the knees had an intact anterior cruciate ligament, a correctable varus deformity and the lateral compartment was uninvolved or had only minor osteoarthritis. The mean follow-up was 5.82 years (2 to 12). Using revision as the end-point, the outcome for every knee was established. Five knees have been revised giving a cumulative rate of survival of the prosthesis at ten years of 94.04% (95% confidence interval 84.0 to 97.8). Knee rating and patient function were assessed using the modified Knee Society scoring system. The mean knee score was 92.2 (51 to 100) and the mean functional score 76.2 (51 to 100). The survival of the implant is comparable to that reported by the designers of the prosthesis and not significantly different from that for total knee replacement. Unicompartmental knee replacement offers a viable alternative in patients with medial osteoarthritis. Appropriate selection of patients and good surgical technique are the key factors

Between February 2000 and August 2002, 60 Oxford unicompartment knee replacements were done on 51 patients, nine of whom had bilateral surgery. The mean age of patients, 82% of whom were women, was 66 years (45 to 83). Primary osteoarthritis was the pathology in 97% and post-traumatic arthritis in 3%. The mean range of movement increased from 113° preoperatively to 120° at the most recent follow-up. Complications included one case of deep vein thrombosis, one patient with bilateral tibial component loosening and three patients with loose cement particles in the joint. Most patients have no pain, but some have mild or occasional pain. One patient with bilateral unicompartmental replacements now has lateral knee pain. Unicompartment knee replacements are an alternative to total knee replacements, but there is a significant learning curve, particularly with regard to cementing techniques. Attention needs to be paid to removing all loose cement from the joint. Patient selection is critical. The complication rate remains low, however, and the results seem satisfactory

We describe the outcome of a series of 124 Oxford meniscal-bearing unicompartmental arthroplasties carried out for osteoarthritis of the medial compartment. They had been undertaken more than ten years ago in a non-teaching hospital in Sweden by three surgeons. All the knees had an intact anterior cruciate ligament, a correctable varus deformity and full-thickness cartilage in the lateral compartment. Thirty-seven patients had died; the mean time since operation for the remainder was 12.5 years (10.1 to 15.6). Using the endpoint of revision for any cause, the outcome for every knee was established. Six had been revised (4.8%). At ten years there were 94 knees still at risk and the cumulative survival rate was 95.0% (95% confidence interval 90.8 to 99.3). This figure is similar to that reported by the designers of the prosthesis and to the best published results for independent series of total knee replacement. If patients are selected appropriately, this implant is a reliable treatment for anteromedial osteoarthritis of the knee

A total of 10474 unicompartmental knee arthroplasties was performed for medial osteoarthritis in Sweden between 1986 and 1995. We sought to establish whether the number of operations performed in an orthopaedic unit affected the incidence of revision. Three different implants were analysed: one with a high revision rate, known to have unfavourable mechanical and design properties; a prosthesis which is technically demanding with a known increased rate of revision; and the most commonly used unicompartmental device. Most of the units performed relatively few unicompartmental knee arthroplasties per year and there was an association between the mean number carried out and the risk of later revision. The effect of the mean number of operations per year on the risk of revision varied. The technically demanding implant was most affected, that most commonly used less so, and the outcome of the unfavourable design was not influenced by the number of operations performed. For unicompartmental arthroplasty, the long-term results are related to the number performed by the unit, probably expressing the standards of management in selecting the patients and performing the operation