The association between objectively measured physical activity and knee structural change using MRI

Objectives This study describes the longitudinal association between objectively assessed physical activity (PA) and knee structural change measured using MRI. Methods 405 community-dwelling adults aged 51-81 years were measured at baseline and approximately 2.7 years later. MRI of the right knee at baseline and follow-up was performed to evaluate bone marrow lesions (BMLs), meniscal pathology, cartilage defects, and cartilage volume. PA was assessed at baseline by pedometer (steps/day). Results Doing >= 10 000 steps/day was associated with BML increases (RR 1.97, 95% CI 1.19 to 3.27, p=0.009). Participants doing >= 10 000 steps/day had a 1.52 times (95% CI 1.05 to 2.20, p=0.027) greater risk of increasing meniscal pathology score, which increased to 2.49 (95% CI 1.05 to 3.93, p=0.002) in those with adverse meniscal pathology at baseline. Doing >= 10 000 steps/day was associated with a greater risk of increasing cartilage defect score in those with prevalent BMLs at baseline (RR 1.36, 95% CI 1.03 to 1.69, p=0.013). Steps/day was protective against volume loss in those with more baseline cartilage volume but led to increased cartilage loss in those with less baseline cartilage volume. (p=0.046 for interaction). Conclusions PA was deleteriously associated with knee structural change, especially in those with pre-existing knee structural abnormalities. This suggests individuals with knee abnormalities should avoid doing >= 10 000 steps/day. Alternatives to weight-bearing activity may be needed in order to maintain PA levels required for other aspects of health.