Muscular changes in osteoarthritis of the hip and knee.

Muscular abnormalities in the patients with degenerative osteoarthritis were examined histologically and histochemically. Enzyme stainings for DPNH-tetrazolium reductase and myosin ATP-ase at pH 10.4 and 4.6 were performed on 26 vastus lateralis biopsies from the patients with osteoarthritis of the knee and 21 gluteus medius specimens from those with osteoarthritis of the hip. All specimens were obtained at surgery. The patients were all female with their ages ranging from 40 to 74 years. Control specimens were obtained from 16 fractured females with absence of arthritis. Type 2 fiber atrophy and internal derangement of fibers were found in both osteoarthritic and control muscles, but were more frequently seen in the vastus lateralis of the patients with osteoarthritis of the knee. Abnormal mosaic patterns of fiber types, such as fiber type grouping and grouped atrophy of type 2 fibers, were frequently found in the vastus lateralis of the patients with osteoarthritis of the knee (73.1%), and less frequently in that of controls (6.3%). However, abnormal mosaic patterns were not found in the gluteus medius obtained from either osteoarthritic patients or control subjects. Abnormal changes in mosaic pattern of fiber types in the vastus lateralis of osteoarthritis of the knee may suggest associated motor neuron dysfunction; the abnormality was not observed in the gluteus medius specimens of the patients with osteoarthritis of the hip, for which a different background in neurological factors may be involved.