Knee Flexion Contractures Are Associated with Worse Pain, Stiffness, and Function in Patients with Knee Osteoarthritis: Data from the Osteoarthritis Initiative

Background Patients with or at risk of developing knee osteoarthritis (OA) can acquire a knee flexion contracture (FC). The prevalence, severity, and association of knee FC on OA outcomes such as pain, stiffness, and function are not well described and clinical scales may omit measuring joint range of motion. Objective (1) To determine if the presence and severity of a knee FC was associated with worse joint pain, stiffness and/or function and (2) to determine if this association was present in participants with or at risk of knee OA. Methods Following a detailed standardized protocol, maximum knee extension was obtained from the baseline physical examination data using a goniometer with the fulcrum over the knee joint line, the upper arm directed towards the greater trochanter and the lower arm directed towards the lateral malleolus. Design Cross-sectional, using the Osteoarthritis Initiative database. Setting and Participants Baseline cross-sectional data collected from a prospective outpatient cohort study, recruiting from four academic health care centers in the United States. Three subcohorts were included: those at-risk of OA (n = 5995 knees), those with radiographic OA (n = 2610 knees), and controls (n = 62 knees). Main Outcome Measures We categorized knee FCs as none, mild, moderate, or severe. Pain scales included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale and numeric pain rating scale; stiffness, the WOMAC stiffness subscale; and function, the WOMAC function subscale and 400-m walk time. Results Participants with FC reported overall worse pain, stiffness, and function compared to those without FC in a severity-dependent manner. OA participants' scores showed between 1.8- and 11.0-fold mean relative worsening versus at-risk participants (P < .05 for all). Knee FC was independently associated in a severity-dependent manner with all outcomes (P < .01). Conclusions Knee FCs were associated with worse pain, stiffness, and function in a severity-dependent manner in a population with or at risk of knee OA. There was an interaction between OA subcohort and FC severity (P-for-interaction <.01 for all WOMAC outcomes). Evaluation of the longitudinal effects of contracture on OA and at-risk patient outcomes is necessary.