Unicompartmental knee replacement (UKR) is an established treatment for single compartment end-stage knee arthrosis with good recorded survivorship. Although often used in more active, younger patients, patient selection remains controversial. To identify risk factors for early failure we compared patients with UKR failure requiring revision to total knee replacement (TKR) with a control group.

Between September 2002 and 2008, 812 Oxford Mobile Bearing Medial UKRs were implanted. 21 implants (20 patients) required revision to TKR within 5 years. The leading cause for revision was lateral compartment disease progression (11 patients). In the revision group, 17 patients were female (81%), average age at index surgery was 64.1 (range 48–81) and average BMI 31.8 (range 24.4–41.5).

Our UKR patients with early failure requiring revision were more likely to be female (p=0.0012) whilst age and BMI were similar between groups. Although the change in tibio-femoral valgus angle was similar, control group patients started in varus becoming valgus post-operatively, whereas revision group patients started in valgus and became more valgus post-operatively. This might explain lateral compartment disease progression as our leading cause of early failure. We believe females with medial compartment disease but valgus alignment are at greater risk of early failure and it is particularly important not to overstuff the medial compartment.