Longitudinal changes in intermuscular fat volume and quadriceps muscle volume in the thighs of women with knee osteoarthritis.

OBJECTIVE: To quantify rates of change in quadriceps muscle (QM) and intermuscular fat (IMF) volumes over 2 years in women in the Osteoarthritis Initiative (OAI) study and examine group differences between those with radiographic osteoarthritis (ROA) and those without ROA. METHODS: The OAI database was queried for women ≥50 years of age in the incident and progression cohorts with and without ROA at baseline. Midthigh magnetic resonance imaging scans (15 contiguous slices, 5 mm slice thickness) of eligible women were randomly selected and anonymized. Image pairs were registered. QM and IMF were segmented in the 12 most proximal matching slices with the segmenter blinded to image time point. Age-adjusted differences in QM and IMF volume changes between groups were tested using analysis of covariance. RESULTS: Forty-one women without ROA (mean ± SD age 60.7 ± 7.6 years) and 45 women with ROA (mean ± SD age 64.5 ± 6.7 years) were included. Mean ± SD QM and IMF volume changes in the non-ROA group were -4.1 ± 11.1 cm(3) and 3.4 ± 7.1 cm(3), respectively, and -5.4 ± 13.5 cm(3) and 3.1 ± 7.4 cm(3) in the ROA group, respectively. Age-adjusted between-group differences in QM and IMF changes were not significant (P > 0.05). CONCLUSION: Two-year changes in QM and IMF volumes appear consistent with aging and do not seem to be related to OA status. Direct comparison with a control cohort without OA risk factors could confirm this. Since group assignment was based on baseline data, there may have been women in the non-ROA group who developed ROA over followup, resulting in some overlap between groups.