Introduction: Exercise therapy is effective in improving symptoms of knee osteoarthritis, but its effect on structural change remains unclear.
Purpose: To describe the associations between physical activity and structural changes of the knee joint as assessed by magnetic resonance imaging (MRI) in adult male and female subjects.
Methods: A convenience sample of 325 subjects (mean age 45 yr, range 26-61) was measured at baseline and approximately 2 yr later. Measures of physical activity included questionnaire items, physical work capacity (PWC170), and lower-limb muscle strength. Knee cartilage volume, tibial plateau area, and cartilage defect score (0-4) were determined using T1-weighted fat saturation MRI.
Results: Lower-limb muscle strength at baseline was positively associated with both percent-per-year changes in total cartilage volume (r = 0.13) and lateral and total tibial plateau area (r = 0.15 and 0.17) but not other sites. Change in muscle strength was negatively associated with annual changes in lateral and total tibial plateau area (r = −0.13 and −0.17). In females only, PWC170 at baseline was negatively associated with percent-per-year changes in lateral and total cartilage volume (r = −0.16 and −0.17) and positively for lateral and total tibial plateau area (r = 0.18 and 0.16). Conversely, change in PWC170 was positively associated with changes in cartilage volume at all sites (r = 0.24-0.26). For all associations, P < 0.05.
Conclusions: Overall, these associations were modest in magnitude, but they suggest that knee cartilage volume and tibial plateau area are dynamic structures that can respond to physical stimuli. Greater muscle strength and endurance fitness, especially in women, may be protective against cartilage loss, but it also may result in a maladaptive enlargement of subchondral bone in both sexes, suggesting that physical activity may have both good and bad effects on the knee.