No abstract

The medial belly of the gastrocnemius and the extensor digitorum longus muscles of rats were tenotomized. One day following tenotomy, the mean sarcomere length of the fast medial gastrocnemius was 1.8 microns, a value comparable to that of tenotomized slow soleus. The mean sarcomere length of the tenotomized extensor digitorum longus, however, was 2.0 microns, a figure which differed significantly from the values obtained for both the soleus and the gastrocnemius. Histological preparations showed the presence of central core degeneration in slow fatigue-resistant fibers of the tenotomized gastrocnemius comparable to that seen in the soleus. No changes were found in the fibers of the tenotomized extensor digitorum longus. The fact that central core lesions were produced in the fibers of soleus and medial gastrocnemius but not in the extensor digitorum longus may be related to the lesser reduction in sarcomere length following tenotomy of the latter muscle.

No abstract

Tenotomy of the proximal and distal tendons of the soleus muscle of female Wistar rats was performed and sarcomeric length and muscle fascicle length measured. On the first postoperative day muscle bellies were found shortened and their sarcomeric length considerably reduced. Four weeks following tenotomy, although the muscle bellies remained shortened, sarcomeric length was comparable with that of control muscles. Measurement of muscle fascicle lengths at this time showed that those of experimental muscles were nearly 50% less than those of control muscles. It was concluded from these experiments that a reduction of the number of sarcomeres in series had occurred, thus compensating for the reduced length of the muscle belly.

The soleus muscle of the rat undergoes degenerative changes after tenotomy. The effects are maximal one week postoperatively, after which follows a period of recovery. Muscle histology eventually returns to normal six week after tenotomy. Recovery is effected by means of peripheral myofibril splitting and de novo synthesis of myofibrils within the central portion of the fiber.