Achilles tendon injury. II. Structure of tenotomized rabbit crural muscles after primary and delayed tendon suture.

This investigation was designed to study the long-term effects of surgical treatment, as recommended and followed in clinical practice, on the fine structure of rabbit crural muscles after Achilles tenotomy. Two main results were made: (A) Even after 12 weeks of mobilization a number of morphological changes were found, especially in the soleus muscles. These abnormalities were similar to those found in human soleus muscles after surgically treated Achilles tendon rupture. (B) There were a large number of small heavily stained (for myofibrillar ATPase at pH 9.4) fibres in the experimental soleus muscles, such that the normal ratio of fibre types was reversed. This was apparent if tendon suture had been performed after a delay of 3 weeks. The results suggested that as a consequence of the de- and regenerative events, induced by immobilization or tenotomy plus immobilization, a number of new fibres had been formed. Some of these were so short that they were out of reach of nerve terminals and remained non-innervated. Furthermore, from the point of view of clinical practice, the extensive long-term effects of suture delay make themselves manifest not until at least a delay of one week.