Fixed Flexion Deformity After Unicompartmental Knee Arthroplasty: How Much Is Too Much

BackgroundThe detrimental impact of postoperative fixed flexion deformity (FFD) after unicompartmental knee arthroplasty (UKA) is manifold. This study aims to define the amount of postoperative FFD that is clinically relevant after UKA.MethodsBetween 2005 and 2012, 803 patients who underwent a primary UKA at a tertiary hospital were prospectively followed up. They were categorized into 3 groups based on the amount of postoperative FFD: (1) 0° (control); (2) 1°-10° (mild FFD); and (3) >10° (severe FFD).ResultsThere were 26 patients (3%) with severe FFD at 2 years after UKA. The Knee Society Function Score and Knee Score in the severe FFD group were 10 ± 4 and 10 ± 2 points lower than in the control group, respectively (P = .017 and P = .001). Similarly, the Oxford Knee Score and Physical Component Score in the severe FFD group was 5 ± 1 and 7 ± 2 points lower than in the control group, respectively (P = .033 and P < .001).ConclusionThis study suggests that postoperative FFD of >10° after UKA is associated with significantly poorer functional outcomes.