American Society for Peripheral Nerve

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Electrophysiologic outcomes of AIN end to side transfer for severe cubital tunnel syndrome; Preliminary results
Matthew WT Curran, MD1; Akiko Hachisuka, MD, PhD.2; Adil Ladak, MD, MSc3; Michael J Morhart, MD, M.Sc1; Jaret L. Olson, MD1; K. Ming Chan, MD2; (1)Division of Plastic and Reconstructive Surgery, University of Alberta, Edmonton, AB, Canada, (2)Division of Physical Medicine and Rehabilitation, University of Alberta, Edmonton, AB, Canada, (3)Division of Plastic Surgery, University of Alberta, Edmonton, AB, Canada

Introduction: Cubital tunnel syndrome is the second most common compression neuropathy. In severe cases, functional outcomes following surgical decompression of the cubital tunnel are poor. This in large part is due to the substantial distance between the site of injury and the target hand muscles. To circumvent that challenge, an end to side (ETS) nerve transfer to the ulnar nerve using a branch of the anterior interosseous nerve to the pronator quadratus muscle has gained increasing popularity. However, whether the donor motor axons are able to grow through the coaptation to the target muscles is unknown. The purpose of this study was to determine the relative contributions of the AIN and the ulnar nerve to the motor recovery.

Methods: In a prospective series of cubital tunnel patients with severe axonal loss, decompression of ulnar nerve at the cubital tunnel and an end to side transfer AIN to the deep motor branch of the ulnar nerve was completed. To evaluate the contributions of the AIN and the ulnar nerve to the hypothenar muscle, motor nerve conduction studies and motor unit number estimation (MUNE) were done before surgery and at 3, 6 and 12 months following surgery. The results were analyzed using non-parametric statistical techniques.

Results: Of the 10 patients enrolled, 7 had a minimum of 6 months follow-up with a median period of 8 {6-12 [median(IQR)}. Patients were all male with a median age of 69 (57-74). There was no evidence of axonal growth from the AIN to the hypothenar muscles in any of the patients. MUNE at the last follow-up [11(6-111) remained unchanged from baseline [12(7-22); p=0.61].

Conclusions: There is no electrophysiologic evidence of axons crossing from the AIN following an end to side transfer. All motor axons innervating the hypothenar muscles originate from the ulnar nerve.

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