Nerve palsies associated with humerus fractures typically involve the radial nerve. Involvement of the median nerve has also been reported, but is quite uncommon [2
]. When this occurs, it is most commonly seen in children who sustain supracondylar humeral fractures.
Nerve injuries that are treated with either primary repair or nerve graft regenerate at 1 mm/day or 1 inch/month [20
]. Although there is no time limit to sensory reinnervation, target muscles must be reinnervated within 12–18 months to have meaningful recovery. After this time, an insufficient number of motor end plates remain for adequate function to be restored. Nerve transfers have been described to restore function in peripheral nerve injuries. This treatment modality is advantageous over direct repair or grafting of proximal injuries because it shortens the distance for nerve regeneration to the target muscle. This in essence converts a proximal or high level injury to a low level injury [25
]. Decreasing the distance for reinnervation with a distal nerve transfer will shorten the time frame for nerve regeneration and allow recovery of motor function.
In the patient described above, the lack of motor unit potentials on electrodiagnostic studies 5 months after injury suggest that meaningful recovery of motor function without surgical intervention was unlikely. The proximal location of her nerve injury also suggested that even with resection of the damaged segment and interpositional nerve grafting, nerve regeneration would not occur within the 18-month time limit for adequate return of motor function. However, by using nerve transfer to reinnervate closer to the target muscle, we successfully restored function to her native pronator teres and AIN innervated muscles.
The anatomy allowing the transfer procedure has been well described. Specifically, the nerve branches to the pronator teres are the most proximal branches of the median nerve in the forearm. The pronator teres nerve most commonly branches 0.4–2.3 cm below the median epicondyle and typically has two main branches to its muscle belly [23
]. The anatomy of the radial nerve branches distal to the brachioradialis occurs in a predictable pattern. The supinator and the ECRB are innervated distal to the ECRL. We have noted that the supinator branch exits the main trunk of the radial nerve posteriorly. The ECRB branch has been noted to come off variably from either the posterior interosseous nerve (PIN), the superficial branch of the radial nerve, or the radial nerve prior to its bifurcation [1
Although the donor and recipient nerve branches are relatively close, one caveat for success with nerve transfers in the upper extremity includes creating a tension-free coaptation between the donor and recipient nerves. One principle that we have stressed in the operating theater has been to divide the nerves: “donor distal and recipient proximal.” This is accomplished by neurolysing the recipient nerves proximally off of their main trunk and dissecting the donor nerve distally toward their target muscle. This allows enough length to perform the necessary transfers in a tension-free manner and permits early range of motion.
Pronation is important in many activities of daily living including eating, dressing, and writing. Loss of pronation results in compensatory activities such as contralateral trunk flexion combined with arm abduction. The supinated posture severely limits arm and hand function.
Restoration of pronation through tendon transfers has been described for the obstetrical brachial plexus patient. Use in acquired deficits of the adult population to restore pronation has not been reported. In this case, we report the successful use of ECRB branch of the radial nerve to reinnervate pronator teres in the context of a proximal median nerve injury. Pronator function returned at 4 months postprocedure.
Similarly, we have previously described transfer of a redundant motor branch to the FDS to the pronator teres branch in two patients with rare cases of isolated loss of pronation [23
]. Reinnervation was seen at 4 and 8 months, respectively.
We also were able to reinnervate the AIN through transfer of the supinator branch of the radial nerve with return of function at 8 months postprocedure. Transfer of the supinator branch does not preclude future tendon transfer to the AIN innervated muscles should motor function be inadequate with nerve transfers. Though our patient had excellent return of power in her reinnervated muscles, residual stiffness in her thumb interphalangeal joint and index finger distal interphalangeal joint limited our results. However, donor nerves were obtained from redundant radial nerve functions making donor site deficits minimal.
In summary, we propose a novel method to restore motor function after a complete high median nerve injury that uses expendable donor nerves and should be considered in the armamentarium of the peripheral nerve and hand surgeon.