The effect of tenotomy and tendon transfers on muscle fiber types in the dog.

Different muscle groups have been shown to have variable muscle-fiber type patterns that may be, in part, due to function and use. In an attempt to identify any changes in fiber composition following surgical alteration of function, eleven beagle dogs had the fibularis longus tendon severed. Four dogs had the tendon reattached 6-24 weeks later. After 6-24 weeks, four dogs had the tendon surgically transferred to the tendon of the tibialis anterior, a functionally different muscle. Three dogs had the tendon immediately transferred to the tendon of the tibialis longus. Biopsies were performed after each procedure to assess fiber changes, and late biopsies were performed in one dog from each group at 27-29 months. Fiber characteristics in the biopsy specimens were identified using histochemical staining. In the first group (tenotomy-reattachment), variable atrophy occurred early but disappeared following reattachment. In the second group (tenotomy and tendon transfer), variable atrophy occurred along with an increased percentage of Type I and Type IIB fibers. Early biopsies performed in the third group (direct transfer) revealed mild Type II hypertrophy. In the late biopsy specimen, an increase of Type I and Type IIB fibers was noted and was similar to the fiber composition of the tibialis anterior to which it was transferred. These findings indicate that muscle-fiber remodeling does occur and that multiple operative procedures are not intrinsically harmful to the muscles. The best evidence from this and previous studies suggests that changes in muscle-fiber type are manifestations of functional adaptation.