Characteristics of the gluteus medius muscle in an asymptomatic patient with radiographic signs of coxarthrosis.

This case study describes the micromorphology and some biochemical features of gluteus medius muscle in a 79-year-old woman with radiographic signs of coxarthrosis but with no clinical symptoms who initially was admitted in the orthopaedic emergency service with a non-displaced subcapital fracture of the femoral neck due to a domestic accident (fall). The X-ray of the hip showed some characteristic features of coxarthrosis, classified grade 2 of the Kellgren criteria. After informed consent, it was decided to carry out the functional evaluation according to the indexes of Lequesne and WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) and to take a biopsy of the gluteus medius muscle for microscopical examination and myosin heavy chain isoform identification during hip replacement surgery. For the Lequesne Index (score 0-24), the total score was 0, and for the WOMAC (score 0-96), the total score was also 0, both speaking in favour of full joint and muscle function. All the structural features observed in muscle were considered not to have any pathological relevance. The composition of the myosin heavy chains in the gluteus medius muscle was 48% MHC I, 41% MHC IIa, and 11% MHC IIx. The muscle characteristics do not support earlier concepts about muscle weakness as a predisposing factor for osteoarthritis. It is moreover concluded that the diagnosis should rather consider clinical symptoms than radiographic signs of osteoarthritis.