Objective

To identify the independent relation of synovitis with incident radiographic knee osteoarthritis (OA) after adjusting for other structural factors known to cause synovitis.

Design

We examined MRIs from knees that developed incident radiographic OA from the Multicenter Osteoarthritis Study (MOST) and compared these case knees with controls that did not develop OA. We examined baseline MRIs for knees developing OA at any time up to 84 months follow-up. We scored lesions in cartilage, meniscus, bone marrow and synovitis. Synovitis scores were summed (0-9) across three regions, suprapatellar, infrapatellar and intercondylar region, each of which was scored 0-3. After bivariate analyses examining each factor's association with incidence, we carried out multivariable regression analyses adjusting for age, sex, BMI, alignment and cartilage and meniscal damage.

Results

We studied 239 case and 731 control knees. In bivariate analyses, cartilage lesions, meniscal damage, synovitis and bone marrow lesions were all risk factors for OA. After multivariable analyses, synovitis was associated with incident OA. A higher synovitis score increased the risk of incident OA (adjusted OR per unit increase 1.1; (95% CI 1.0, 1.2, P = .02)), but increased risk was associated only with synovitis scores of ≥3 (adjusted OR 1.6; 95% CI 1.2, 2.1, P = .003).

Conclusions

Synovitis, especially when there is a substantial volume within the knee, is an independent cause of OA.

Objective

To determine the effect of physical activity on knee osteoarthritis (OA) development in persons without knee injury and according to knee alignment.

Design

We combined data from Multicenter Osteoarthritis (MOST) and Osteoarthritis Initiative (OAI), studies of persons with or at high risk of OA. Subjects had long limb and repeated posteroanterior knee radiographs and completed the physical activity survey for the elderly (PASE). We studied persons without radiographic OA and excluded knees with major injury and without long limb films. We followed subjects 30 months (in MOST) and 48 months (in OAI) for one of two incident outcomes: (1) symptomatic tibiofemoral OA (radiographic OA and knee pain), or (2) tibiofemoral narrowing. 'Active' persons were those with PASE score in the highest quartile by gender. We examined risk of OA in active group using logistic regression adjusting for age, gender, body mass index (BMI), Western Ontario and McMaster Arthritis Index (WOMAC) pain score, Kellgren and Lawrence (KL) grade (0 or 1), and study of origin. We also analyzed knees from malaligned and neutrally aligned limbs.

Results

The combined sample comprised 2,073 subjects (3,542 knees) with mean age 61 years. The cumulative incidence of symptomatic tibiofemoral OA was 1.12% in the active group vs 1.82% in the others (odds ratio (OR) among active group 0.6, 95% confidence interval (CI) 0.3, 1.3). Joint space narrowing occurred in 3.41% of knees in the active group vs 4.04% in the others (OR among active group 0.9 (95% CI 0.5, 1.5)). Results did not differ by alignment status.

Conclusions

Physical activity in the highest quartile did not affect the risk of developing OA.