Association of Knee Flexion Contracture with Radiographic Disease Worsening in Persons with or at High Risk for Knee OA

Purpose: Knee flexion contracture (FC), the inability to fully straighten the knee, is commonly seen in persons with knee OA. History of knee injury or surgery and knee OA disease activity may cause joint capsular shortening, synovial thickening/scarring, hamstrings tightness, and articular structural changes of osteophyte formation, resulting in loss of knee extension motion. In theory, inability to fully extend the knee during weight bearing activities concentrates joint compression forces over a smaller contact area and may potentially accelerate articular tissue degradation. It is unclear if presence of FC is associated with subsequent radiographic disease worsening, accounting for baseline disease severity and prior knee injury or surgery. Understanding the independent role of FC in knee OA disease course will inform prevention and treatment of knee OA. We sought to determine the association of baseline knee FC with subsequent disease worsening in persons with or at high risk for knee OA followed up to 10 years. Methods: The OAI (Osteoarthritis Initiative) is a prospective, observational cohort study of persons with or at high risk for knee OA. At study enrollment, knee range of motion was measured using a goniometer. We categorized motion as hyperextension (<0°), normal extension (0°), mild FC (1-4°), and moderate/severe FC (≥ 5°), separately for the right and left knees. Bilateral knee radiographic disease severity by Kellgren/Lawrence (KL) grade was assessed centrally by 2 experts, blinded to each other’s reading and all other data, at baseline and follow-up visits over up to 10 years. OAI participants whose index knee had baseline KL grade 0-3 and at least 1 follow-up KL grade reading were included in the analysis. The index knee was the knee with worse baseline KL grade or the right knee if KL grade was the same in both knees. Radiographic disease worsening was defined as the first occurrence of KL grade increase after baseline in the index knee. Baseline covariates included index knee injury (ever injured the knee badly enough to limit ability to walk for at least 2 days) and knee surgery (ever had knee surgery or arthroscopy). Follow-up time for persons without an outcome occurrence (radiographic worsening) was right censored at the last visit where the outcome was assessed. Persons with an outcome contributed follow-up time from the last time without the outcome until the outcome was first documented. We used Cox proportional hazards regression models accounting for interval and right censoring to examine the association of baseline FC categories with radiographic disease worsening, unadjusted and adjusted for age, sex, BMI, knee injury, knee surgery, index knee baseline KL grade, and contralateral baseline KL grade. Results are reported as hazard ratios (HRs) and 95% confidence intervals (CIs). Results: Among 3940 OAI participants [age: mean 61.1 years (SD, 9.1), BMI: 28.6 kg/m2 (4.8), 59.2% women], 32.9% had hyperextension, 35.8% normal extension, 19.0% mild FC, and 12.3% moderate/severe FC. As shown in Figure 1, those with moderate/severe FC had a significantly higher cumulative hazard than those with normal knee extension over up to 10-year follow-up. In the fully adjusted model (Table 1, Model B), persons with moderate/severe FC had a hazard ratio of 1.42 (95% confidence interval, 1.13-1.79) compared to those with normal extension. Conclusions: After accounting for baseline disease severity, knee injury, and knee surgery, presence of ≥ 5° knee flexion contracture was associated with an increased risk of subsequent radiographic disease worsening by 42% in persons with or at high risk for knee OA. Given that knee flexion contracture can be managed by stretch, joint mobilization, and movement training, health care providers may consider incorporating knee range of motion measurement in routine knee OA care to identify those at risk for disease progression and initiate timely intervention.View Large Image Figure ViewerDownload Hi-res image Download (PPT)