Motor unit properties of nerve-intact extensor digitorum longus muscle grafts in young and old rats

Impaired reinnervation has been implicated as the cause of the threefold di sparity in the recovery of maximum force (P-0)of standard muscle grafts in old compared with young rats. The specific, null hypothesis of this study i s that compared with age-matched control extensor digitorum longus (EDL) mu scles, nerve-intact EDL muscle grafts in young and old rats show no evidenc e of an age-related impairment in reinnervation. Nerve-intact grafts were p erformed in 3-month-old and 23-month-old rats and were evaluated 60 days po stoperatively. Compared with age-matched control EDL muscles, nerve-intact grafts in young and old rats showed no difference in muscle mass or motor u nit numbers. The mean motor unit P-0 for nerve-intact graft muscles in both age groups was significantly lower than that of age-matched control muscle s. These data support our hypothesis that if axons are allowed to regenerat e in an endoneurial environment, there is no evidence of an age-related imp airment in muscle reinnervation.