Functional outcomes of ulnar nerve neurotization by anterior interosseous nerve in high level injury

Background: The ulnar nerve injury induce sever hand malfunction due to intrinsic muscle paralysis. The ulnar nerve repair in proximal area (high ulnar nerve injury) seldom leads to intrinsic muscle function because of long distance of nerve return. Therefore, the best techniques to restore intrinsic hand function in patient with high ulnar nerve injury is distal nerve transfer to minimize the regeneration time and distance. Objective: The aim of this study is to describe the surgical results obtained with the transfer of the motor branch of the anterior interosseous nerve destined to the pronator quadrates muscle to the motor division of the ulnar nerve (the deep branch of ulnar nerve). Methods: It is a retrospective study of thirty elderly patients with high ulnar nerve injury underwent a transfer of distal branch of anterior interosseous nerve to deep branch of ulnar nerve, and end to end suture of the ulnar nerve at the site of injury in Sohag microsurgery unit. Results: The mean postoperative follow-up period was 22 months (range from 12 to 38 months). At the fi nal follow-up, twenty-seven (90%) patients showed good results according to the Highet-Zachary scheme (M3 or M4, S3+, and negative Froment’s sign). The other three patient (10%) showed a poor result (M1, S2, positive Froment’s sign). Conclusion: This technique of transfer of distal branch of anterior interosseous nerve to deep motor branch of ulnar nerve and primary repair of ulnar nerve at site of injury is effective for motor and sensory recovery of distal ulnar innervated side of the hand.


Introduction
The ulnar nerve injury induce sever hand malfunction due to intrinsic muscle paralysis. The ulnar nerve repair in in proximal area (high ulnar nerve injury) seldom leads to intrinsic muscle function because of long distance of nerve recovery. Therefore, the best techniques to restore intrinsic hand function in patient with high ulnar nerve injury is distal nerve transfer to minimize the regeneration time and distance [1,2]. Injuries of the ulnar nerve can be classifi ed as high or low. Low injuries take place distal to the origins of the motor branches of the fl exor carpi ulnaris and ring and little fi nger fl exor digitorum profundus muscles. Although the strength of the extrinsic hand muscles is not infl uenced, sensation is lost on the ulnar border of the hand and in the ring and little fi ngers, and the ulnar-innervated intrinsic muscles lose their function. Consequently, this shows through a weakened thumb pinch, claw deformity, loss of the normal pattern of fi nger fl exion, and signifi cant loss of hand dexterity and strength. High injuries occur above the aforementioned place ( Figure 1). Here, loss of active ring fi nger fl exion, little distal interphalangeal joint fl exion, and wrist fl exion compound the fi ndings; paradoxically, however, the claw deformity has a tendency to be less severe [3].
Despite meticulous microsurgical repair, the prognosis of an injury of the ulnar nerve at a level above the elbow is usually considered poor in terms of potential for motor recovery of the distal muscle of the hand. A special nerve transfer technique was developed as a surgical alternative for these cases aiming to approximate the donor axons to the recipient muscles of the Citation: Noaman

Material and methods
It is a retrospective study of thirty elderly patients with

Surgical technique
The procedure was performed under general anesthesia, with tourniquet infl ation of the affected upper limb. In order to ascertain the absence of nerve function at the level of the wrist, electrical stimulation of the ulnar nerve was performed before any intraneural dissection, and thus avoiding that  Tables 1,2 In patients with good results, the average static two-point discrimination was 7 mm (range from 6 to 8 mm) and the moving two-point discrimination was 6 mm (range from 5 to 6 mm). The grip and pinch strength in patients with good results

Discussion
There are many series reporting that high ulnar nerve lesions above the level of the elbow often have a poor prognosis. This is attributed to the fact that the ulnar nerve is a mixed nerve that carries both sensory and motor fi bers and even with the most meticulous repair under the microscope, some cross innervations show poor sensory and motor recovery. Also, the long distance between the site of lesion and the innervated intrinsic muscles of the hand made it take long time to reach the motor end plate. During this long period, the denervated intrinsic muscles will undergo irreversible atrophic changes.
Gaul [4] reported that adults with high ulnar nerve lesions never recovered acceptable function. Vastamäki, et al. [5] concluded that a satisfactory result cannot be expected if the level of injury is more than 60 cm from the tip of the middle fi nger (i.e., high ulnar nerve lesions). Taha and Taha [6] reported that tendon transfer was needed in 72% of patients with high ulnar nerve lesions. Ruijs, et al. [7] reported the meta-analysis of 23 articles including the individual data for 623 median or ulnar nerve injuries. In ulnar nerve injuries, the chance of motor recovery was 71% lower than that in median nerve injuries. Secer, et al. [8]

Motor
Number   Pfaeffl e, et al. [9] observed that all patients with high-level ulnar nerve lesions required tendon transfer because the motor recovery is usually poor.

Sensoryc
In this study, the terminal branch of the AIN supplying pronator quadrates muscle was transferred to the motor branch of the ulnar nerve. From the anatomical point of view, the width, and the number of myelinated fi bers of both nerves are similar (the pronator quadratus branch of the median nerve was 1.5 ± 0.4 mm in diameter, with 866 ± 144 nerve fi bers).
The deep branch of ulnar nerve was 2.1 ± 0.4 mm in diameter, with 1318 ± 120 nerve fi bers [6,9,10]. Direct coaptation is performed without the need for nerve grafting. The functional loss is minimal after denervation of pronator quadrates as the pronator teres can compensate. All these advantages make this procedure a good option to restore the motor function of irreparable high ulnar nerve lesions. There are many options to restore the sensory function of high ulnar nerve injuries by distal nerve transfer from the median nerve or by end-to-side repair to the median nerve.
In our report, primary repair of the ulnar nerve at the site of injury to restore sensory recovery.
Ozkan, et al. [12] described end-to-end transfer of the ulnar digital nerve of the index or long fi nger to the ulnar digital nerve of the small fi nger. They reported good sensory recovery in most cases. The disadvantage of this technique is that it decreased the sensory area in the same hand. Brown, et al. [13] described end-to-end transfer of the third common palmar digital nerve of median nerve to the volar sensory component of ulnar nerve and end-to-side re-innervation of the ulnar dorsal cutaneous branch to the remaining median sensory trunk. The sensory recovery was acceptable in their work.
Many authors described end-to-side suture of the sensory ulnar nerve component to the third common palmar digital nerve of the median nerve in the palm or to the trunk of the median nerve in the distal forearm with variable results. The advantage of this technique is that no additional sensory loss occurred [14][15][16].
To our knowledge, only a few publications have used the same technique of distal neurotization of high ulnar nerve lesions using the AIN and the primary repair of the ulnar nerve at the level of injury to restore the motor and sensory function of the ulnar nerve. This report clarifi ed the indications, the advantages, and disadvantages, and showed satisfactory results.

Conclusion
This technique of transfer of distal branch of anterior interosseous nerve to deep motor branch of ulnar nerve and primary repair of ulnar nerve at site of injury is effective for motor and sensory recovery of distal ulnar innervated side of the hand.