Muscle regeneration following segmental necrosis in tenotomized muscle fibers.

The aim of this study was to determine how the new myotendinous junctions were re-established at the proximal and distal ends of the soleus muscle after tenotomy. Both proximal and distal tendons of the soleus muscle in mature female rats were severed. The animals were killed and the soleus muscles were removed and prepared for light and electron microscopic examination 1, 3, 5, 7, 14, 21, 28, and 42 days after the operation. It was found that segmental fiber destruction followed by removal by macrophages occurred at the ends of the soleus muscle fibers. This resulted in the liberation and myogenic activation of satellite cells. By 3 days after tenotomy the fusion of myoblasts to form myotubes could be seen. The myotubes developed within the original basal lamina and reattached to the surviving non-necrotic segments and grew in both length and width so that by 6 weeks postoperation, normal myotendinous junctions had been reformed. This study is the first to show that re-establishment of the myotendinous junction following tenotomy is accomplished by regeneration of the necrotic ends of the tenotomized fibers.