Aims

The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position.

Introduction

Kozinn and Scott have made recommendations about contra-indications for unicompartmental knee replacement (UKR). They suggest that patients younger than 60, weight > 82 kilograms, patients with exposed bone in patella-femoral compartment or patients who are physically active/perform heavy labour should not be offered a UKR. In addition, chondrocalcinosis is a contra-indication. These strict selection criteria are based on the experience with fixed bearing UKAs and are more intuitive than evidence based. The Oxford UKR has a fully congruous mobile bearing and has been shown to have minimal wear. Over the past 25 years, the Oxford Group has followed a standardised protocol for patient selection for UKR. We ignore patella-femoral joint pathology, chondrocalcinosis, patient's age, weight and activity level when deciding the suitability for UKR.

Polyethylene particulate wear debris continues to be implicated in the aetiology of aseptic loosening following knee arthroplasty. The Oxford unicompartmental knee arthroplasty employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. This study measures the in vivo ten-year linear wear of the device, using a roentgenstereophotogrammetric technique.

In this in vivo study, seven medial Oxford unicompartmental prostheses, which had been implanted ten years previously were studied. Stereo pairs of radiographs were acquired for each patient and the films were analysed using a roentgen stereophotogrammetric analysis calibration and a computer-aided design model silhouette-fitting technique. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. In addition, eight control patients were examined less than three weeks post-insertion of an Oxford prosthesis, where no wear would be expected. The control group showed no measured wear and suggested a system accuracy of 0.1 mm. At ten years, the mean linear wear rate was 0.02 mm/year.

The results from this in vivo study confirm that the device has low ten-year linear wear in clinical practice. This may offer the device a survival advantage in the long term.

Introduction

The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from distal femur nor to over tighten the knee and thus ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component.

Objectives

The aim of this study was to determine the polyethylene wear rate of Phase 3 Oxford Unicompartmental Knee Replacement bearings and to investigate the effects of resin type and manufacturing process.

The Oxford mobile bearing unicompartmental knee replacement (UKR) is a validated, highly successful implant with an excellent ten-year survivorship. From November 2001 to September 2006 three hundred and eighty two patients who had a medial cemented Oxford Unicompartmental knee replacement (Biomet, Bridgend, UK) via a minimally invasive approach were prospectively entered into a database and followed up as per departmental policy in the specialist joint assessment clinic. We have noted a minority of patients have persistent postoperative pain and/or mechanical symptoms resistant to the standard postoperative therapies. We report the outcome of 22 patients who had an arthroscopy for persistent pain and/or mechanical symptoms a median of 15 months (range 4 months – 31 months) following medial unicompartmental knee replacement. The median follow up time following arthroplasty was 38 months (range 16 months – 63 months). Post arthroscopy we divided our study patients into two groups; those who had an improvement in symptoms and those who had none. These groups were then compared, with particular reference to demographics, check radiographs and arthroscopic findings. The results showed that patients with anterior or anteromedial symptoms in whom a medial rim of scar tissue was identified and debrided sixty seven percent had a significantly increased probability of symptomatic improvement (p<0.005). In addition men appeared to significantly improve more that women (p<0.043). When performed this therapeutic intervention many prevent or at least defer the need for early revision to total knee replacement in some cases and we have no complications as a result of the arthroscopic intervention. This observational study provides evidence for a role for arthroscopy in selected patients with pain following unicompartmental knee replacement

INTRODUCTION. Mobile bearing unicompartmental knee replacement (UKR) is an accepted treatment for patients with isolated medial unicompartmental knee osteoarthritis (OA) with a full thickness cartilage loss. The aim of this study was to determine if this recommendation was correct and if the procedure could be used for partial-thickness cartilage loss. METHODS. 1053 Oxford medial UKRs were studied prospectively. The knees were divided into two groups; partial-thickness cartilage loss (PTCL) group and the full thickness-cartilage loss (FTCL) group. The primary outcome measure was the total Oxford Knee Score (OKS, 0 to 48) at the time of final follow up. The groups were also compared for the change in OKS (?OKS) and the proportion of patients that were considered to have benefited substantially from surgery (?OKS >5). RESULTS. There were 21 knees in the PTCL group, with a mean age of 61 years (SD 13) and mean follow-up of 1.7 years (SD 1.0). There were 1032 knees in the FTCL group, with a mean age of 66 years (SD 10) and mean follow-up of 3.9 years (SD 2.5). The PTCL group had a significantly lower (p=0.03) total OKS (mean 35.8, SD 10.7) at final review than the FTCL group (mean 39.8, SD 8.5). There was no significant difference in pre-operative or ?OKS between the groups. However the proportion of patients that did not have substantial benefit from surgery (?OKS>5) was significant lower (p=0.04) in the PTCL group. CONCLUSIONS. The results confirm that a good outcome can routinely be achieved with UKR if there is bone-on-bone. If there is partial loss of cartilage the results are less predictable. Although some patients do well, a higher proportion do not benefit from the surgery. It may be that in a subgroup of these patients the pain did not initially arise from the partially damaged cartilage. We therefore recommend that the Oxford Knee should only be used for medial OA if there is bone on bone

Aims

Uncemented mobile bearing designs in medial unicompartmental knee arthroplasty (UKA) have seen an increase over the last decade. However, there are a lack of large-scale studies comparing survivorship of these specific designs to commonly used cemented mobile and fixed bearing designs. The aim of this study was to evaluate the survivorship of these designs.