Introduction There is a paucity of data examining the effects of weight change on knee joint structures and symptoms. This study examined the effect of weight change on change in knee cartilage volume and symptoms in an obese cohort.

Methods 112 obese subjects (Body Mass Index ≥30 kg/m²) were recruited from various community sources to examine the effect of obesity on musculoskeletal health. Tibial cartilage volume, determined by MRI, and knee symptoms, determined by the Western Ontario and McMaster Osteoarthritis Index (WOMAC) were collected at baseline and an average of 2.3 years later.

Results Percentage weight change was associated with change in medial tibial cartilage volume (β −1.2 mm³, 95% CI −2.3 to −0.1 mm³, p=0.03) that was consistent throughout the spectrum of weight loss through to mild weight gain. Percentage weight change was not associated with change in the lateral tibial (p=0.93) or patella (p=0.32) cartilage volumes. Percentage weight change was associated with change in all WOMAC subscales (all p≤0.01): pain (β −1.8 mm, 95% CI −3.2 to −0.4 mm), stiffness (β −1.6 mm, 95% CI −2.5 to −0.7 mm) and function (β −6.9 mm, 95% CI −11.6 to −2.1 mm).

Conclusions The linearity of effect implies that weight loss is associated with reduced medial cartilage volume loss and improved knee symptoms, while weight gain is associated with increased medial cartilage volume loss and worse knee symptoms. These results suggest that in obese people, small amounts of weight change may have the potential for a disease modifying effect on both knee joint structure and symptoms. While weight loss is an important primary management strategy in obese individuals, avoidance of further weight gain should also be a clinical goal.