Knee flexion contractures in patients with osteoarthritis: clinical features and histologic characterization of the posterior capsule.

Objective: To (1) identify demographic and clinical factors associated with knee flexion contracture (KFlC) in the setting of osteoarthritis (OA) and (2) histologically compare the posterior knee capsule of patients with OA with and without KFlC.

Design: Cross-sectional study.

Setting: Primary care, including private and institutional practice.

Patients: Thirteen patients with primary OA and KFlC and 8 patients with primary OA without KFlC.

Methods: We compared the KFlC and non-KFlC groups to identify demographic and clinical factors associated with KFlC. We examined the histology of the posterior knee capsules of 9 patients with KFlC and 6 without.

Main Outcome Measurements: Patient demographic and clinical factors. For histology we measured the proportional composition of collagenous, adipose, and synovial tissues; fibroblast and adipocyte cellularity; and synovial thickness.

Results: Patients with contracture had longer duration of OA, reduced flexion of the surgical knee, and reduced extension of the contralateral knee (P = .04, <.01, and <.01 respectively). Histologically, there was a greater proportion of collagenous tissue and a lower proportion of adipose and synovial tissues in the contracture group than in the noncontracture group; however, the differences were not statistically significant. Cellularity was similar between the 2 groups.

Conclusions: Longer duration of knee OA, reduced surgical knee flexion, and reduced contralateral, nonsurgical knee extension were associated with KFlC in the OA knee undergoing total arthroplasty. Monitoring bilateral knee range of motion in patients with longer-duration OA could allow earlier intervention, reducing functional loss. Capsular tissue composition analysis may indicate a fibrotic disease process. Further research in which a larger sample size is used will help clarify these novel findings.