Specimens of vastus medialis muscle from 78 patients with end-stage OA of the knee undergoing total joint arthroplasty were examined histopathologically in one study by Kink B et al in 2007.
1) The study revealed all muscle specimens exhibited atrophy of type 2 fibers. In 32% of the patients, atrophy of type 1 fibers was also noted. Selective atrophy of type 2 fibers might reflect pain-related immobilization of a limb. 68% of the specimens was interpreted as possibly resulting from pain-associated disuse.
2) Changes such as neurogenic muscular atrophy, muscle fiber degeneration, and regeneration might contribute as cofactors in the development or progression of OA.
3) Soft tissue changes indicating long-term disease, such as calcification, fibrosis, and lipomatosis, were frequently observed (in 69%, 71%, and 94% of the patients, respectively).
4) This study also revealed a significant association between degenerative muscle changes and the presence of a varus deviation of the leg axis.