Achilles tendon injury. Plantar flexion strength and structure of the soleus muscle after surgical repair.

Bilateral needle biopsy specimens obtained from the soleus muscles of nine male subjects one year or more after surgical repair of Achilles tendon rupture were studied by light microscopy and enzyme histochemistry. Static and dynamic plantar flexion torques were also recorded. Although all subjects were symptomless, the soleus muscle of the injured leg in five was characterized by varying degrees of primary myopathy but only in two cases did this coincide with marked hypotrophy of the calf muscles and decrease of plantar flexion strengths. Myopathy precipitated by immobilization may persist on account of active insufficiency and early pain inhibition. The relevance of objective strength assessment is emphasized.