Reduced muscle radiological density, cross-sectional area, and strength of major hip and knee muscles in 22 patients with hip osteoarthritis

Background Patients with hip osteoarthritis (OA) typically suffer joint pain, and often experience muscular weakness. We hypothesized that substantial atrophy would manifest in multiple muscle groups along the affected limb, resulting in severe muscle dysfunction. Patients and methods We assessed 22 elderly patients with unilateral OA for maximal voluntary isometric strength of hip and knee muscles using a dynamometer that was developed for the purpose. Cross-sectional area (CSA) and radiological density (RD; in Hounsfield units: HU) of hip and knee muscles were assessed using CT. We determined SF-36, HHS, and EQ-5D. Results Hip extension, flexion, adduction, abduction, and knee extension strength were reduced (11- 29%; p < 0.01) in the OA limb relative to the healthy limb. Muscle CSA of hip extensors, flexors, adductors, knee extensors and flexors, but not hip abductors, was reduced (11-19%; p < 0.01) in the OA limb, where RD of all muscle groups except hip flexors was reduced (5-15 HU; p < 0.01). The clinical scores confirmed impairment. Interpretation Major muscles functioning around the hip and knee showed substantial loss of strength and mass, which contributes to the reduced ambulatory capacity of OA patients. Reduced muscle CSA could not fully explain the loss in strength. Infiltration with fat or other non-contractile components, as indicated by a reduced RD, in OA limb muscles was substantial.