The interaction between physical activity and amount of baseline knee cartilage.

OBJECTIVES Conflicting reports of the effect of physical activity on knee cartilage may be due to the heterogeneity of populations examined and, in particular, the underlying health of the knee joint. This study examined the influence of recreational and occupational physical activity on cartilage volume loss. METHODS A total of 250 participants with no significant musculoskeletal disease were recruited. A gender-specific median cartilage volume split was used to define people in the lowest and highest 50% of baseline cartilage volume. Baseline recreational and occupational activity was examined by questionnaire, while cartilage volume was assessed by MRI at baseline and 2.4 years later. RESULTS Significant interactions were demonstrable between physical activity and cartilage volume loss based on stratification of baseline cartilage volume (all P ⩽ 0.03). There was a dose-response relationship between frequently performed baseline occupational activities and medial cartilage volume loss in both the low (B = 0.2% per annum, 95% CI: 0.0, 0.04% per annum) and high (B = -0.2% per annum, 95% CI: -0.4, 0.0% per annum) baseline cartilage volume groups (P = 0.001 for interaction). Individuals with low baseline cartilage volume who were active in their occupation and/or recreational activity had greater medial cartilage volume loss than their more inactive counterparts (2.4% per annum vs 1.5% per annum, P = 0.02). CONCLUSION Whereas people with less baseline cartilage volume are more at risk of structural knee damage with either heavy occupational or recreational workloads or both, individuals with high baseline cartilage volume may advantageously modify their risk for knee OA by participating in more frequent occupational physical activities.