A review of current literature describes varying 10-year survival rates for the Oxford Unicompartmental Knee Replacement (Biomet Orthopedics Inc, Warsaw, Ind). Application of rigorous indications and meticulous surgical technique are two factors considered to reduce revision rates. A retrospective case-note review was conducted for 96 patients (128 knees) aged 42–89 (mean 57) who had an Oxford unicompartmental knee replacement for medial compartment osteoarthritis between January 2000 and January 2011. All procedures were performed, or directly supervised, by one 5 surgeons. The aim of the study was to ascertain the rate of revision to bicompartmental knee replacement and any associated contributory factors. Of the 128 unicompartmental knees, 10.9% were revised to either mobile- or fixed-bearing total knee replacements due to septic (0.5%) and aseptic (1.5%) loosening, patello-femoral pain (3.9%), periprosthetic fracture (0.8%) and bearing dislocation (3.1%). Of those knees requiring revision, mean patient age was 73 years, 50% had wound complications and 42% were performed by senior trainees. All patients had intact ACL and medial osteoarthritis. Mean time to revision was 2.7 years. In conclusion, revision of the unicompartmental knee was related to patient age > 65 years and early post-operative complications; grade of operating surgeon had little apparent effect

Introduction. Unicompartmental knee arthroplasty (UKA) in patients with isolated medial osteoarthritis of the knee is nowadays a standard procedure with good results, especially with the minimally-invasive approach. However, the survival rate of the unicompartmental knee prostheses is inferior to that of total knee prostheses. Therefore, further studying of UKA is still necessary. In most mobile bearing designs the femoral component has a spherical surface and therefore its positioning is not crucial. The role of the tibial slope in UKA has not been investigated so far. The manufacturers recommend tibial slopes with values between 10° positive slope and 5° negative slope. Most surgeons try to reconstruct the anatomical slope with a high failure by measuring the slope on x-rays. The aim of this study was to investigate the influence of the tibial slope on the wear rate of a medial UKA. Materials and methods. In vitro wear simulation of medial mobile bearing unicompartmental knee prosthesis with a spherical femoral surface (Univation ®) was performed with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243–1:2002(E). The tibial tray was inserted with 2 different medial tibial slopes: 0°, 8° (n=3 for each group). The lateral tibial slope of the space-holder was not changed (0° for every group). We performed a total of 5 million cycles for every different slope, the gravimetric wear rate was determined gravimetrically using an analytical balance every 500 000 cycles according to the ISO 14243–2. Results. The wear rate in the 0° slope group was 3.46±0.59 mg/million cycles, and in the 8° slope group it was 0.99±0.42 mg/million cycles. The difference between the 0° tibial slope group and the 8° tibial slope group was highly significant (p<0.01, alternate t-test). Discussion. An increase of the tibial slope leads to a reduced wear rate in a mobile bearing UKA. Therefore, a higher tibial slope should be recommended for mobile bearing UKA. However, the influence on the ligaments has to be considered as a higher tibial slope leads to an increased strain on the anterior cruciate ligament. This influences needs to be investigated in further studies before a definite optimal range for the tibial slope can be recommended