Fibrotic myopathy of the semitendinosus muscle in a cat.

Fibrotic myopathy of the semitendinosus muscle causing a progressive mechanical right hind limb lameness in a cat was treated with a Z-plasty lengthening procedure of the affected muscle. Lameness resolved after surgery; however, recurrence of gait abnormality began 2 weeks later. One year after surgery, the cat's gait was abnormal; this had little effect on ambulation. Histologic examination of biopsy specimens taken from the affected muscle at surgery revealed complete replacement of myofibers with dense fibrous connective tissue. Etiopathogenesis was not determined.