Preoperative Flexion Contracture Does Not Compromise the Outcomes and Survivorship of Medial Fixed Bearing Unicompartmental Knee Arthroplasty

Despite the expanding indications for unicompartmental knee arthroplasty (UKA), the classic indication that limits flexion contracture to <5° in fixed bearing UKA excludes most patients with arthritic knees and has not been challenged in modern literature. This study compared the clinical outcomes between patients with severe flexion contracture and controls undergoing UKA.

Eighty seven medial fixed bearing UKAs performed in patients with severe (≥15°) flexion contracture were matched 1:1 with 87 controls without flexion or recurvatum deformity (−5°<extension<5°) using propensity scores to control for age, sex, BMI, Charlson comorbidity index, ASA class, and baseline patient-reported outcome measures (PROMs). Perioperative outcomes were recorded. Range of motion, Knee Society Score, Oxford Knee Score, SF-36, and patient satisfaction were assessed at 6 months and 2 years. Survivorship was recorded at mean 11.5 ± 3.2 years.

Preoperative knee extension in the control and contracture groups was 0.9° ± 1.9° and 18.0° ± 3.5° (P < .001), respectively, whereas flexion was 122.8° ± 27.9° and 120.6° ± 13.6° (P = .502). The contracture group had poorer Knee Society functional (P = .023) and SF-36 physical score (P = .010) at 6 months. However, there was no difference in PROMs at 2 years. A similar proportion achieved the minimal clinically important difference for each PROM and was satisfied with surgery. Range of motion remained poorer in the contracture group and a higher percentage had residual contractures (P < .001). Ten-year survivorship was 94% and 97% in the control and contracture groups, respectively (P = .145).

Although patients with severe flexion contractures had a poorer range of motion and postoperatively, these patients attained comparable PROMs, satisfaction rates, and mid-term survivorship after UKA.

III, therapeutic study.