Utilizing Lateral Sprouting Axons to Reinnervate a Transferred Free Muscle to Enhance Distal Muscle Recovery When Performing High-Level Nerve Repair: Experimental Rat Study

High-level median or ulnar nerve injuries and repairs typically result in suboptimal reinnervation of distal muscles. Functioning free muscle transplantation (FFMT) is increasingly recognized as an effective method to restore function in chronic muscle denervation cases. This study investigates the efficacy of using an additional FFMT, neurotized by lateral sprouting axons from a repaired high-level mixed nerve in the upper limb, to enhance distal hand function.Thirty-five Sprague-Dawley rats were divided into four groups to evaluate the proposed FFMT technique. The infraclavicular median nerve (MN) was transected and repaired in each animal. The nearby musculocutaneous nerve (MCN) was transected, and the terminal nerve after the biceps muscle was divided and embedded into the biceps muscle, creating an FFMT model. The distal stump of the MCN was anchored to the MN, 1.5 mm distal to the MN repair site. Assessments of nerve and muscle function were conducted 4 months postoperatively.Behavioral analysis, along with measurements of biceps muscle weight and tetanic contraction force, indicated significant recovery in the biceps muscle. Histological staining confirmed reinnervation of the MCN from the repaired MN. Additionally, functional examination of the flexor digitorum superficialis muscle revealed no deterioration associated with the repaired MN.The study demonstrates the potentiality of utilizing lateral sprouting axons from a repaired high-level MN to reinnervate an additional FFMT to enhance flexor digitorum superficialis function. The surgical strategy promises recovery of distal muscle function and implies for diverse clinical applications.