Abstract
Background
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.
Methods & Results
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). In the control group of all patients who underwent UKR during this period, 348 patients were female (44%), average age was 65.0 (range 36-89) and average BMI 31.2 (range 21.0-61.0).
Radiological assessment of the tibiofemoral valgus (TFV) angle for revision patients was compared with an age and sex matched control group. In the revision group, average TFV angle was +1.5 pre-operatively and +6.1 post-operatively with an average change of +4.6. In the control group average TFV angle was -0.4 pre-operatively and +4.3 post-operatively with an average change of +4.7.
Conclusion
Our UKR patients with early failure requiring revision were far more likely to be female (p=0.0012) whilst age and BMI were similar between groups. Although the change in TFV 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.
