A rodent model of partial muscle re-innervation.

BACKGROUND There is limited appreciation of the risks and benefits of the few salvage treatment options available for inadequate motor function following incomplete spontaneous recovery or surgical repair of major peripheral nerve injuries. The lack of a reliable and economical animal model has hindered laboratory investigation into this difficult clinical problem. We propose a straightforward and reproducible rodent model of partial re-innervation of a hind limb muscle. NEW METHOD Twelve Sprague-Dawley rats underwent identical surgical manipulations: the left tibial nerve was isolated, partially transected (2/3rds), and the remaining intact portion crushed. Eight weeks later, bilateral (1) gastrocnemius (2) soleus and (3) flexor digitorum longus muscles underwent maximal isometric contraction force testing before being excised and weighed. RESULTS Only the gastrocnemius muscles were statistically weaker (p<0.05) in the experimental limb compared with the contralateral (control) limb. There was no difference in muscle weights between experimental and control sides. COMPARISON WITH EXISTING METHODS Our model differs from other published models by: allowing time for compensatory axonal sprouting as would be seen in clinical scenarios, precisely identifying the portion of the tibial nerve to be transected to ensure reproducibility, and achieving temporary but complete denervation by crushing the intact portion of the nerve. CONCLUSIONS Controlled partial transection and crushing of the rodent tibial nerve results in a consistently partially re-innervated and clinically weakened gastrocnemius muscle that can serve as a model in studying incomplete recovery following nerve injury.