Natural history of knee cartilage defects and factors affecting change.

BACKGROUND Knee cartilage defects may play an important role in early osteoarthritis, but little is known about their natural history. METHODS Knee cartilage defect score (range, 0-4), cartilage volume, and bone surface area were determined using T1-weighted fat-saturated magnetic resonance imaging in 325 subjects (mean age, 45 years) at baseline and 2 years later. RESULTS Thirty-three percent of the subjects had a worsening (>or=1-point increase) and 37% of the subjects had an improvement (>or=1-point decrease) in cartilage defect score in any knee compartment during 2.3 years. A worsening in cartilage defect score was significantly associated with female sex (odds ratio [OR], 3.09 and 3.64 in the medial and lateral tibiofemoral compartments) and baseline factors, including age (OR, 1.05 per year in the medial tibiofemoral compartment), body mass index (OR, 1.08 in the lateral tibiofemoral compartment), tibiofemoral osteophytes (OR, 6.22 and 6.04 per grade), tibial bone area (OR, 1.24 and 2.07 per square centimeter), and cartilage volume (OR, 2.91 and 1.71 per milliliter in the medial tibiofemoral and patellar compartments). An improvement in cartilage defect score had similar but reversed associations with these factors (except for sex), including a decrease in body mass index (OR, 1.23 in the medial tibiofemoral compartment). CONCLUSIONS Knee cartilage defects are variable, and changes are associated with female sex, age, and body mass index. Increases are associated with baseline cartilage volume, bone size, and osteophytes, suggesting a role for these in the pathogenesis of cartilage defects. Interventions such as weight loss may improve knee cartilage defects.