Can an Injured Ulnar Nerve be used as a Neurotizer for Distal Nerve Transfer?
Chieh-Han John Tzou, MD1, Johnny Chuieng - Yi Lu, MD2
1Division of Plastic & Reconstructive Surgery, Department of Surgery, Medical University of Vienna, Austria, Vienna, Austria; 2Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital, Taoyuan, Taiwan and David Chwei-Chin Chuang, MD, Department of Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital, Taoyuan, Taiwan
Purpose of Study In nerve transfers, a physiologically active nerve with low morbidity is intentionally divided and transferred to a more important but irreparably denervated target. Distal nerve transfer, away from the site of injury, is performed distal to the supra- & infraclavicular fossa and close to the neuromuscular junction. This is an efficient strategy to treat brachial plexus injury with a quick rehabilitation. We investigate (1) whether a partially injured nerve can be used as a neurotizer for transfer? and(2) what degree of damage to the nerve can still be useful? Methodology Forty Sprague–Dawley rats were randomized into four groups, where UN(Ulnar-Nerve) were coapted to MCN(Musculocutaneous-Nerve) after different injuries: Group A: no injuries-positive control, GroupB: UN is partially cut 25%; GroupC: cut 50% and GroupD: cut 75% and. The left ulnar nerve (neurotizer) and the musculocutaneous nerve (target nerve) were exposed and identified in the upper arm and axilla. The injured UN was resected as distally as possible, then transferred and coapted tension-free with the distal stump of the resected musculocutaneous nerve end-to-end with 11-0 sutures. After a 12 week recovery, we measured muscle weight, electrophysiological study of the biceps muscle (EMG & muscle contraction force measurement) and axon counts of the ulnar and musculocutaneous nerve. Results Muscle weight measurements showed that Group C(50%cut) and D(75%cut) had the lightest muscle weight (28 g). Statistically significant differences (p<0.001) were seen between Group A(control,38g) and all experimental groups(B=30g, C&D=28g). Electromyography(EMG) measurements of the biceps muscles showed similar trends, where the control group (4.97mv) was significantly (p=0.003) larger than D(75%) 3.76mV and Group C(50% ) was 3.89mV. Muscle tetanus contraction force measurements showed statistically significant (p=0.001) differences between the control (48.79g) and all experimental groups, Group D(75%), 34.64g, Group C(50%) and D(25%) 37.44g and 41.13g, respectively. Histomorphologic analysis showed that number of nerve fibers in a normal ulnar nerve as 1498±245. Significant differences were present comparing the fiber numbers of Group D(75%, 450±120) with Group C (50%, 950±253) (p=0.05) and Group B (25%, 1123±198) (p=0.02). Conclusion Injured nerves can still be used as neurotizer although outcome was direct proportional with the degree of injury. Significant permanent injury was sustained on the donor ulnar nerve when injury occurred to >50% of the nerve, resulting in poor functional outcome.
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