Elimination of Preoperative Flexion Contracture as a Contraindication for Unicompartmental Knee Arthroplasty

Introduction: Unicompartmental knee arthroplasty (UKA) is an effective alternative to total knee arthroplasty (TKA) for the management of unicondylar osteoarthritis. Historical contraindications limit patients' eligibility for UKA. However, recent reports have suggested that some contraindications may not be absolute. This study evaluates preoperative flexion contracture with regard to UKA. Methods: This study was a retrospective review of 53 patients with preoperative flexion contracture between 11 degrees and 20 degrees who underwent fixed-bearing UKA and a matched cohort of 53 patients who underwent cruciate-retaining TKA. Results: Preoperatively, the average flexion contracture was 13.8 degrees in the UKA group and 14.1 degrees in the TKA group (P = 0.42). Mean preoperative motion was greater in the patients treated with UKA (106 degrees) than in those treated with TKA (97 degrees; P < 0.001). Postoperatively, patients who underwent UKA had greater motion than patients who underwent TKA had (121 degrees versus 113 degrees; P < 0.01). Residual flexion contracture was greater in the UKA group (4.1 degrees) than in the TKA group (2.1 degrees; P = 0.02). The two groups demonstrated similar improvements in Knee Society clinical scores (P = 0.32). However, patients treated with UKA demonstrated higher Knee Society functional scores, compared with patients treated with TKA (86 versus 75; P = 0.03). Discussion: Although residual flexion contracture was worse after UKA, this group had similar clinical improvement, greater postoperative motion, and greater function scores, compared with the matched TKA group. Preoperative flexion contracture >5 degrees may not be an absolute contraindication to UKA. Conclusion: The contraindications to UKA regarding flexion contracture may not be as absolute as previously thought. Larger, prospective studies are needed to generalize these findings to a wider population.