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

Abstract

Background: Patients with, or at risk of developing knee osteoarthritis (OA) can acquire the complication of a knee flexion contracture (FC). The prevalence of knee FCs, their severity, and their impact on patients in terms of pain, stiffness and function is unknown. We examined if the presence and severity of knee FC affected these outcomes in patients with, or at risk of, developing knee OA. Methods: Cross-sectional study using the Osteoarthritis Initiative (OAI), a multicenter, prospective cohort of 4,796 participants aged 45 to 79 divided into 3 subcohorts: those with radiographically-established knee OA (n=1390), those at risk of developing knee OA (n=3284), and low-risk non-OA controls (n=122). At study enrollment, knee range of motion was used to categorize FCs as none, mild, moderate or severe. Pain was evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale and the numeric rating scale (NRS). Stiffness was evaluated using the WOMAC stiffness subscale. Function was evaluated using the WOMAC function subscale and 400-meter walk time. Findings: Participants with FC reported worse knee pain, stiffness and function (all p<0.001). Participants with knee OA had worse FC severity-dependent pain, stiffness and function versus those at risk of OA (all p<0.05 for statistical interaction with knee FC severity). Knee FC was associated in a severity-dependent manner with worse WOMAC pain (p<0.001), WOMAC stiffness (p<0.001), and 400-meter completion time (p<0.001) after correcting for subcohort, demographic factors and radiographic severity. Interpretation: Flexion contractures were associated with worse pain, stiffness, and function in people with, or at risk of, knee OA. Flexion contractures may constitute a marker of knee disease severity. Measuring extension should be a routine component of the clinical assessment of the knee joint. Addressing this gap in clinical care may lead to better patient outcomes throughout the spectrum of knee OA. Funding Statement: Funding was provided by the Bruyere Academic Medical Organization Innovation Fund. The funding source had no influence on data analysis, manuscript generation, submission, or any other portion of this report. Declaration of Interests: None declared by the authors. Ethics Approval Statement: The Osteoarthritis Initiative Project was approved by the Institutional Review Board at the OAI Coordinating Center, the University of California at San Francisco.