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Title: Reverse End-to-side Anterior Interosseous to Ulnar Motor Nerve Transfer.
Published: 3/2/2011, Updated: 4/6/2011.

Author(s): Susan E. Mackinnon MD, Andrew Yee BS.
Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, St. Louis, MO.

The anterior interosseous to ulnar motor nerve transfer was first performed by Mackinnon SE in April of 1991 in a patient with a complete high ulnar nerve injury. Since then, the procedure has been used by our institution to recover some intrinsic function in patients with otherwise irreparable ulnar nerve injuries. However, there is a much larger population of patients with the varied ulnar intrinsic function: (1) patients with some, but not normal ulnar intrinsic function, (2) patients with good, but not certain likelihood of some intrinsic recovery with a more distal ulnar nerve repair, and (3) patients with high ulnar nerve injury, but have a martin-Gruber component to their ulnar intrinsic function. This larger population pool of patients, with indications that do not fall under the anterior interosseous to ulnar motor end-to-end nerve transfer, could utilize an augmentation of some ulnar nerve function with additional motor fibers. The anterior interosseous nerve (AIN) is also the donor nerve choice for augmentation of ulnar nerve intrinsic function. Rather than an end-to-end (ETE) nerve transfer with the AIN, a reverse end-to-side (RETS) nerve transfer is completed. That is, the end of the donor AIN is coaptated to the side of the recipient motor fascicular group of the ulnar nerve through an epineural window. This allows for the “supercharge” of the ulnar motor component. The RETS anterior interosseous to ulnar motor nerve transfer was first performed by our institution in August of 2009 and found, a year later, excellent recovery of ulnar nerve intrinsic function in a patient with recurrent cubital tunnel syndrome. The RETS procedure was performed after completing a rat experimental study, which definitively showed motor axons regenerating into a denervated nerve in a RETS fashion. This study was originally designed as a potential negative study, but surprisingly found equal transversing nerve fibers in the RETS coaptation when compared to an ETE coaptation. Since the experimental study, our institution has found many clinical situations where the RETS procedure has been an excellent addition to the surgical management of patients with ulnar intrinsic weakness.

Figures and Videos

Standard Version 

Extended Version 

Surgical Tutorial – Reverse End-to-side Anterior Interosseous to Ulnar Motor Nerve Transfer. The donor anterior interosseous nerve (AIN) is transferred to the side of the recipient ulnar motor fascicular group within the distal forearm to preserve ulnar nerve motor intrinsics. Guyon's canal release is a required part and is completed prior to this procedure. Specific to this case, a revision ulnar nerve transposition was completed proximally. This procedure is a variation of the end-to-end AIN to ulnar motor nerve transfer. The extended version includes both the Guyon's canal release and the reverse end-to-side nerve transfer.

Surgical Techniques

PROCEDURE: Reverse End-to-side Anterior Interosseous to Ulnar Motor Nerve Transfer.

Donor Nerve: Pronator quadratus branch of the anterior interosseous nerve.
Recipient Nerve: Motor fascicular component of the ulnar nerve (deep motor branch).
Nerve Coaptation: Reverse end-to-side.

Incision Description:
  • Incision is marked ulnar to the thenar crease and comes across the wrist in a Brunner’s fashion and carried proximal to the wrist on the forearm for about 12cm.
  • Hand incision is an exposure for Guyon’s release and decompression of the deep motor branch.
  • Forearm incision is an exposure for reverse end-to-side anterior interosseous to ulnar motor nerve transfer.
Surgical Steps:
Exposure and Dissection:
1. Incise skin and dissect through subcutaneous tissue.
Guyon’s Canal Release and Decompression of Deep Motor Branch of Ulnar Nerve:
2. The ulnar nerve is decompressed through Guyon’s canal using the following six steps:
A. Open Guyon’s canal.
B. Release the thickened antebrachial fascia just proximal to Guyon’s canal.
C. Sweep the neurovascular bundle medially.
D. Palpate the hook of the hamate.
E. Observe the hypothenar muscles and fascia and identify the proximal free border of the hypothenar fascia ulnar to the hook of the hamate.
F. Decompress the deep motor branch by dividing the attachment of the hypothenar muscles by staying close to the hook of the hamate.
Reverse End-to-side Anterior Interosseous to Ulnar Motor Nerve Transfer:
3. Follow the ulnar nerve proximally into the forearm and identify the branch point of the dorsal cutaneous branch of the ulnar nerve.
4. Retract all of the flexor tendons radially to identify the pronator quadratus.
5. Identify the neurovascular bundle of the distal anterior interosseous nerve as it enters the pronator quadratus.
6. Divide the anterior interosseous nerve in the mid-portion of the pronator quadratus to the point it begins to branch.
7. Transect the anterior interosseous nerve distal where it begins to branch and transpose the nerve towards the ulnar nerve to determine the location of the revere end-to-side (RETS) coaptation and neurolysis. This will insure that no tension will be found on the coaptation and unnecessary neurolysis. The location of the RETS coaptation is usually between 6-9cm proximal to the wrist crease.
8. Using micro-pickups, tap across the main ulnar nerve to drop into the cleavage pain between the sensory and motor component of the ulnar nerve.
9. Identify the motor fascicular group as it comes around the hook of the hamate. With your eyes, visually neurolyse the motor fascicular group proximally to assure that the appropriate motor fascicular component is identified within the ulnar nerve.
10. The motor component of the ulnar nerve in the forearm lies between the sensory dorsal cutaneous branch of ulnar nerve and the sensory fascicular group. The motor fascicular group is slightly smaller than the main sensory fascicular group of the ulnar nerve.
11. Open the perineurium of the motor fascicular group of the ulnar nerve in order to facilitate the RETS micro-neurosurgical repair. Do not make an injury or neuroectomy into the recipient endoneurium. Just open the epineurium and perineurium.
12. Check for tension on the nerve repair by moving the hand, fore, and arm through the full range-of-motion. If tension is found on the repair, move the repair more proximally. The RETS nerve transfer requires a tension-free repair.


1. Brown JM, Yee A, Mackinnon SE. Distal median to ulnar nerve transfers to restore ulnar motor and sensory function within the hand: technical nuances. Neurosurgery. 2009;65(5):966-77.

2. Novak CB, Mackinnon SE. Distal anterior interosseous nerve transfer to the deep motor branch of the ulnar nerve for reconstruction of high ulnar nerve injuries. J Reconstr Microsurg. 2002;18(6):459-64.