Functional and morphometric evaluation of end-to-side neurorrhaphy for muscle reinnervation

This study was undertaken to quantify the effect of motor collateral sprout ing in an end-to-side repair model allotting end organ contact. Besides doc umentation of the functional outcome of muscle reinnervation by end-to-side neurorrhaphy, this experimental work was performed to determine possible d owngrading effects to the donor nerve at end organ level. In 24 female New Zealand White rabbits, the motor nerve branch to the rectus femoris muscle of the right hindlimb was dissected, cut, and sutured end-to-side to the mo tor branch to the vastus medialis muscle after clearing an epineural window . The 24 rabbits were divided into two groups of 12 each, with the second g roup receiving additional crush injury of the vastus branch. After a period of 8 months, maximum tetanic tension in the reinnervated rectus femoris an d the vastus medialis muscles was determined. The contralateral healthy sid e sen ed as control. The reinnervated rectus femoris muscle showed an average maximum tetanic fo rce of 24.9 N (control 26.2 N, p = 0.7827), and the donor vastus medialis m uscle 11.0 N (control 7.3 N, p = 0.0223). There were no statistically signi ficant differences between the two experimental groups (P = 0.9914). The av erage number of regenerated myelinated nerve fibers in the rectus femoris m otor branch was 1185 +/- 342 (control, 806 +/- 166), and the meal? diameter was 4.6 +/- 0.6 mu m (control, 9.4 +/- 1.0 mu m). In the motor branch to t he vastus medialis muscle, the mean fiber number proximal to the coaptation site was 1227 (+/-441), and decreased distal to the coaptation site to 795 (+/-270). The average difference of axon counts in the donor nerve proxima l to distal regarding the repair site Tvas 483.7 +/- 264.2. In the contrala teral motor branch to the vastus medialis muscle, 540 (+/-175) myelinated n erve fibers were counted. In nearly all cross-section specimens of the moto r branch to the vastus medialis muscle, altered nerve fibers could be ident ified in one fascicle distal and proximal to the repair site. The results show a relevant functional reinnervation by end-to-side neurorr haphy without functional impairment of the donor muscle. It seems to be evi dent that most axons in the attached segment were derived from collateral s prouts. Nonetheless, the present study confirms that end-to-side neurorrhap hy is a reliable method of reconstruction for damaged nerves, which should be applied clinically in a more extended manner.