Gracilis or semitendinosus myopathy in 18 dogs.

The clinical findings in 18 dogs with gracilis (n = 17) or semitendinosus (n = 1) myopathy are described. Each dog had a similar hind-limb gait abnormality characterized by a shortened stride with a rapid, elastic medial rotation of the paw, internal rotation of the hock and external rotation of the calcaneus [corrected] and internal rotation of the stifle during the mid-to-late swing phase of the stride. Medical management prior to or in lieu of surgery was attempted (n = 8) with no apparent response. Fifteen dogs had one or multiple surgical procedures. Although transection, partial excision, or complete resection of the affected muscle resulted in resolution of lameness following surgery, lameness recurred six weeks to five months (mean, 2.5 months; median, two months) following surgery. Adjunctive medical treatment did not prevent recurrence. Variable replacement of the affected muscle with fibrous connective tissue (predominantly along the caudolateral border of the muscle) was evident grossly, and replacement of myofibers with fibrous connective tissue was confirmed histologically. A definitive etiology could not be established.