A longitudinal study of the effect of sex and age on rate of change in knee cartilage volume in adults.

OBJECTIVE To describe the association between sex, age and rate of change in knee cartilage volume in adults. METHODS A total of 325 subjects (mean age 45 yrs, range 26-61) was measured at baseline and approximately 2 yrs later. Knee cartilage volume and bone size were determined using T1-weighted fat saturation magnetic resonance imaging (MRI). Height, weight, body mass index and radiographic osteoarthritis (ROA) were measured by standard protocols. RESULTS Knee cartilage volume decreased by 1.5-4.2% per annum. In multivariable analysis, females had higher rates of change per annum in knee cartilage volume than males (medial tibia: -3.5%, P < 0.001; lateral tibia: -2.6%, P < 0.001 and patella: -0.8%, P = 0.053). The sex difference first appeared at age 40 and became more marked with increasing age at the medial tibial site only (P = 0.039). Age was significantly associated with annual change in knee cartilage volume at all three sites (beta = -0.06 to -0.12%/yr, all P < 0.05), and these associations were stronger in females. With the exception of the medial site (beta = -0.05/yr, P = 0.117 for ROA exclusion, and beta = -0.06%/yr, P = 0.056 for ROA adjustment), the association with age did not change when subjects with ROA were excluded from analyses or after further adjustment for ROA. CONCLUSIONS Within the age range we studied, knee cartilage volume declines at a faster rate with increasing age. This is partly mediated by ROA at the medial tibial site only. Furthermore, women have substantially higher knee cartilage loss than men, and these sex differences first appear at age 40 and become more marked with increasing age, which has implications for prevention of cartilage loss from middle age.