Efficacy of End-to-Side Nerve Transfer for Patients With Severe Cubital Tunnel Syndrome

Introduction Peripheral nerve trauma especially through compressive injury is very common. Of these, ulnar neuropathy at the elbow is the second most prevalent. In severe cases, functional outcomes even with surgery are often poor. Principle reasons being that the ulnar nerve innervates a large number of intrinsic hand muscles. At an average of 350 mm from the site of injury to the target muscles, the distance is very long, Although peripheral nerve fibres have the ability to regenerate, it is very slow at only 1 mm/day. That would translate to a year for the regenerating fibres to reach the hand. With the favorable condition in the distal stump and target muscles to regrowth rapidly declining over time, few axons will successfully reach target. Therefore, alternative methods of surgical treatments are being sought to circumvent this major hurdle.

Rationale and purpose One potentially promising alternative is through distal nerve transfer by using a terminal branch of the anterior interosseous nerve (AIN) to the pronator quadratus muscle and coapt it to the ulnar nerve close to the wrist. That would greatly shorten the distance to target by 200 mm or more. By approximating the end of the AIN donor stump to the side of the ulnar nerve through an eipneurial window (termed reverse end to side or RETS) transfer, it allows preservation of the integrity of the ulnar nerve fibres thus providing a conduit for the regenerating native axons to reach the hand. While this concept is theoretically appealing and has gained increasing popularity in clinical practice, a crucial question of central importance remains answered: Can the AIN donor axons indeed breach the ulnar nerve trunk and reinnervate the hand muscles? Aside from testing the central premise of RETS, it would be important to know the exact magnitude of reinnervation that can be achieved from the donor nerve through this procedure.

With the above rationale in mind, the objective of this proposal is to test the hypothesis that reinnervation of ulnar intrinsic hand muscles by the AIN can be achieved through the RETS procedure. This will be done through quantifying the amount of innervation by the AIN donor nerve to the ulnar intrinsic hand muscles using motor unit number estimation, a non-invasive electrophysiological technique. The investigators will also evaluate whether there is an associated improvement in hand function following the procedure.

Experimental protocol Subjects For this study, the investigators aim to recruit a prospective series of 60 patients with severe cubital tunnel syndrome causing marked motor axonal loss.

Primary outcome measures Motor unit number estimations of native axons in the ulnar nerve innervation the intrinsic hand muscles compared to those from the AIN.