Successful intramuscular neurotization is dependent on the denervation period. A histomorphological study of the gracilis muscle in rats

To characterize the extent to which reinnervation potential depends on the duration of denervation, intramuscular neurotization of the gracilis muscle was performed either immediately or 2, 4, 6, and 8 weeks after transection of the obturator nerve. For neurotization, the sciatic nerve was split into three fascicle groups and fixed intramuscularly. Muscle morphology after 6 weeks of regeneration was identified with anti-myosin immunohistochemistry and NADH staining. Newly formed motor endplates were characterized using acetylcholinesterase staining and electron microscopy. Wet muscle weight ratio indicated the functional state of synapses. Depending on the denervation period, three levels of regenerative outcome were evident. Best results were seen after immediate neurotization or after 2 weeks of denervation. Regeneration, although at a significantly lower level, also occurred after denervation periods of 4 and 6 weeks. Regeneration following neurotization after 8 weeks of denervation was negligible. Quantity and quality of motor endplate formation depended on the denervation period. Thus, in special clinical situations intramuscular neurotization within a distinct time window provides a good reconstructive option.