Association between hip muscle cross-sectional area and hip pain and function in individuals with mild-to-moderate hip osteoarthritis: a cross-sectional study.

BACKGROUND: To examine the associations between hip muscle cross-sectional area and hip pain and function in community-based individuals with mild-to-moderate hip osteoarthritis. METHODS: This study included 27 participants with mild-to-moderate hip osteoarthritis. Cross-sectional area of hip muscles, including psoas major, rectus femoris, gluteus maximus, gluteus medius and minimus, adductor longus and magnus, obturator internus, and obturator externus, were measured from magnetic resonance images. Hip pain and function were evaluated using the Hip Disability and Osteoarthritis Outcome Score (HOOS) categorised into 5 subscales: pain, symptoms, activity of daily living, sport and recreation function, and hip-related quality of life (for each subscale 0 representing extreme problems and 100 representing no problems). RESULTS: Mean age of the 27 participants was 63.2 (SD 7.6) years and 66.7% (n = 18) were female. After adjusting for age and gender, greater cross-sectional area of adductor longus and magnus was associated with a higher HOOS score in quality of life (regression coefficient 1.4, 95% confidence interval (CI) 0.2-2.7, p = 0.02), activity of daily living (regression coefficient 1.3, 95% CI 0.1-2.6, p = 0.04) and sport and recreation function (regression coefficient 1.6, 95% CI 0.1-3.0, p = 0.04). There was a trend towards an association between greater cross-sectional area of psoas major and a higher quality of life score (regression coefficient 3.6, 95% CI - 0.5 to 7.7, p = 0.08). The cross-sectional area of hip muscles was not significantly associated with HOOS pain or symptom score. CONCLUSION: Greater cross-sectional area of hip adductors was associated with better function and quality of life in individuals with mild-to-moderate hip osteoarthritis. Greater cross-sectional area of hip flexors might be associated with better quality of life. These findings, while need to be confirmed in longitudinal studies, suggest that targeting the hip adductor and flexor muscles may improve function and quality of life in those with mild-to-moderate hip osteoarthritis.