Editorial: Peripheral nerve injury

Abstract

Neurosurgeons who treat patients with peripheral nerve injuries face the challenge of deciding if and when to operate. This is especially true when the mechanism of injury is stretch. The most challenging cases are brachial plexus injuries in which the functional loss is disabling and the distance from the site of injury to the denervated muscles is far. The standard approach is to monitor patients for approximately 3 months before making a decision to operate or to continue waiting. As the average rate of nerve recovery is approximately 1 inch per month, it is rare for patients with these injuries to show signs of recovery even in cases that eventually have good outcomes without surgical repair. However, because there is a time limit on when a repair can be done based on progressive internal nerve scarring, the surgeon reduces the potential outcome of repair by waiting until spontaneous recovery is precluded. In cases of nerve root avulsion at the spinal cord level, there is no chance for spontaneous recovery, making other approaches more advisable. Surgeons have been using nerve transfer procedures for decades;1,2 a common early approach was the intercostal to musculocutaneous nerve (MCN) transfer. Functional outcomes were quite variable for these approaches, with many patients achieving only a minimal ability to flex the elbow. More recently, several investigators have reported better outcomes with nerve transfers involving the use of small motor branches or individual fascicles dissected from a parent nerve. The most common approach was initially reported by Oberlin and colleagues,3 in which a single fascicle from the ulnar nerve destined to innervate a portion of the flexor carpi ulnaris muscle is anastomosed to the biceps motor branch of the MCN. The advantages of this approach are that the surgical site is separated from the area of trauma and the distance from the new anastomosis to the muscle is short. Initial reports by Oberlin and others were encouraging. However, only when the “new and improved” technique of a double transfer involving both ulnar and median nerve motor fascicles emerged did investigators indicate that elbow flexion was frequently inadequate with the single nerve transfer. The problem for surgeons who are not involved in developing these procedures is that only when a new technique emerges is there a critical appraisal of the prior technique. Nevertheless, such techniques are extremely important as tools to help patients with these disabling injuries. The article by Ray et al.4 describes a double transfer technique in a series of patients who suffered brachial plexus injuries involving the upper trunk. These authors have convincingly shown that this approach provided useful restoration of elbow flexion in well-selected patients and resulted in minimal or no new neurological deficits. As mentioned in their report, many peripheral nerve surgeons combine additional transfers in order to restore function in other muscles denervated by upper trunk injuries. The more common of these are spinal accessory nerve transfers to suprascapular nerves and radial nerve fascicles (triceps) to axillary nerves. The common thread is to identify a portion of a functioning nerve that is functionally redundant and transfer it to a damaged motor nerve close to its innervated muscle. This offers many advantages to more traditional nerve injury repair including the use of nerves that are not injured, elimination of sensory fascicles in the recipient nerve that would reduce the yield of motor fibers, and potentially decreased time to recovery by making the transfer close to the denervated muscle. Surgeons have also been using nerve transfers to restore motor function in other parts of the body, including those of the lower extremities, as reported by Spiliopoulos and Williams.5 In this case report, a femoral nerve motor branch is transferred to a motor branch of the adductor muscle in the thigh. The reverse approach, transfer of an obturator motor fascicle to restore quadriceps motor function, has also been used. Very few large studies have utilized these procedures, and those that have tend to minimize any negative effects. In addition, surgeons have been slow to report results for transfers that typically fail (for example, transfers to the anterior tibial region for foot drop). For this reason, single case reports must be considered as very preliminary evidence of efficacy and must be followed by careful prospective studies before surgeons adopt the procedures. The work of Spiliopoulos and Williams will require reports from larger series with careful monitoring of outcomes to aid surgeons in deciding whether this approach is useful. The advantages of nerve transfer over the exploration of injured nerves are clear when there is no chance for spontaneous recovery. In cases in which the stretch injury is far from the innervated muscle, it is not always obvious Editorial See the corresponding articles in this issue, pp 1520–1533.