To test the hypothesis that sex-related and joint compartment-related differences in the risk of osteoarthritis (OA) of the knee might be associated with variations in cartilage development, we investigated knee cartilage volume in healthy children.
We studied 92 children who were randomly selected from among students in grades 3-12 of a single school in Hobart, Tasmania (49 boys, 43 girls; age range 9-18 years). Articular cartilage thickness and volume were determined at the patella, medial tibial compartment, and lateral tibial compartment by magnetic resonance imaging (MRI). Sagittal T1-weighted fat-suppressed MRI images were obtained and processed on an independent computer work station.
Males had significantly more knee cartilage than females. Sex accounted for 6-36% of the variation in cartilage thickness and volume, which was statistically significant at all sites. Even after adjustment for age, body mass index, bone area, and physical activity, males had 16-31% higher cartilage volume; this was most marked at the medial tibial site. In addition, lateral tibial thickness was greater than medial tibial thickness (5.9 versus 3.6 mm; P < 0.0001) and lateral tibial volume was greater than medial tibial volume (2,823 versus 2,299 microl; P < 0.0001). Furthermore, physical activity was a significant explanatory factor for cartilage volume at all sites (R2 7-14% depending on site; all P < 0.05). The most consistent activity association was with vigorous activity in the previous 2 weeks (difference between any vigorous activity versus none 22-25% greater; all P < 0.05).
Sex- and joint compartment-related differences in cartilage development may be one explanation for variations in the pattern of knee OA seen in later life. Furthermore, the physical activity associations suggest that cartilage development is amenable to modification.