Title: Median (FCR / FDS) to Radial (PIN / ECRB) Nerve Transfer.
Published: 7/14/2011, Updated: 7/19/2011.

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

The median to radial nerve transfer was first performed in a unique radial nerve palsy patient.  This first patient had a proximal injury associated with a humeral head fracture and lost radial nerve function. In this case, tendon transfers were contraindicated due to coexisting complex regional pain syndrome and associated stiffness. In addition, nerve grafting was contraindicated due to proximal level of injury and advanced age. Excellent results following the median to radial nerve transfer in this single patient have allowed the expansion of indications such that nerve transfers are an alternative to tendon transfers and nerve grafting. The median to radial nerve transfer utilizes the following specific nerve branches for transfer: (1) flexor carpi radialis to the posterior interosseous nerve and (2) flexor digitorum superficialis to the extensor carpi radialis brevis. The median nerve branches are “pre-dissected” and no interfascicular dissection is required during this procedure. At our institution, we combine this with an end-to-side tendon transfer of pronator teres to extensor carpi radialis brevis as long as there is no significant stiffness for early recovery of wrist extension. Early motor re-education shortens the time of recovery, with reinnervation of radial nerve muscles usually noted by nine months.

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  Figure 12 – Supinator and Radial Nerve 231.1 KB
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  Figure 13 – Recipient Radial Nerve 255.0 KB
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  Figure 14 – Donor and Recipient Nerves 300.4 KB
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  Figure 15 – PIN and Supinator Nerve 233.8 KB

• Superficial head of pronator teres to extensor carpi radialis brevis tendon transfer.
• Lateral antebrachial cutaneous to superficial branch of radial sensory nerve transfer.

Incision Description:

• Lazy S incision in the proximal forearm extending to the mid-forearm.
• If the tendon transfer is included, the incision is extended further distal.

Surgical Steps:
Exposure and Dissection:

1. A lazy-S incision in the proximal forearm extending to the mid-forearm for the nerve transfer and more distally if the tendon transfer is performed.
2. Dissection to identify and protect the cephalic vein and the adjacent lateral antebrachial cutaneous nerve.
3. Identify the superficial head of the pronator teres tendon which is lateral/radial to the vessels and medial/ulnar to the radial sensory nerve.

Pronator Teres Step-lengthening or Tendon Transfer:

4. If just the median to radial nerve transfer is performed (without tendon transfer), then step-lengthen the tendon of the superficial head of the pronator teres to gain exposure to the median nerve in the proximal forearm. If a simultaneous pronator teres (PT) to extensor carpi radialis brevis (ECRB) tendon transfer is performed, then completely elevate the tendon of the PT distally to gain access to the median nerve in the proximal forearm. To gain adequate length of PT, the dissection is extended to include a strip of distal radius periosteum, which is kept in continuity with the distal insertion of the PT. The periosteum is elevated from distal to proximal using a freer elevator and then the PT is elevated as well.

Identification of Donor Median Nerve:

5. Identify the median nerve in the proximal portion of the incision. The nerve is medial/ ulnar to the radial vessels. 
6. Release and reflect the deep head of the pronator teres.
7. Divide the tendinous leading edge of the flexor digitorum superficialis.
8. If using a tourniquet, quickly use a nerve stimulator and identify the branches of the median nerve:

• Anterior interosseous nerve (AIN) - is the only nerve coming off on the radial or lateral side of the median nerve.
• Pronator teres nerve branch - is the most superficial branch of the median nerve.  It comes off very proximally and lies on top of the main median nerve.
• Flexor carpi radialis (FCR) and palmaris longus (PL) nerve branch - is located branching from the ulnar side of the median nerve and deep.
• Flexor digitorum superficialis (FDS) nerve branches – two branches exists, proximal and distal. These come off distal to the FCR/PL branch also on the medial/ulnar aspect of the nerve.  Electrical stimulation along the ulnar aspect of the remaining main median nerve will let you know whether there is still a residual distal FDS branch that hasn’t yet bifurcated from the main median nerve. 

9. After using the nerve stimulator to confirm the function and identification of the donor median nerves, make a drawing or tag these branches loosely with a vessel loop so that if you lose the ability to do intraoperative stimulation (due to tourniquet-induced neurapraxia), you’ll know exactly what the various branches are.
10. The donor branches of choice are to FDS and FCR.  These can be very easily separated away from the main median nerve. In fact, they have already branched from the main median nerve. These donor branches are already  “predissected”. 

Identification of Recipient Radial Nerve:

11. To find the radial nerve, move lateral/radial and expose the radial sensory nerve. This can be followed more proximally to bring you to the radial nerve proper in the region of the arcade of Frohse. This is just distal to the elbow. Next, identify the nerve to the ECRB. This is much smaller than the radial sensory nerve and is located just radial to the radial sensory nerve. To gain exposure, divide the overlying crossing vessels with ligature or clips.
12. Then transversely release the fascial/tendinous leading edge of the ECRB. This is done by lifting the ECRB and cutting transversely at the undersurface of the muscle. Obviously, the entire muscle is not divided, just the tendinous leading edge at the undersurface of this muscle. This will also relieve compression off the underlying nerve.
13. Once the ECRB tendinous leading edge has been divided, you will see the superficial head of the supinator.  This is quite deep within the wound directly overlying the bony structures.  Decompress the posterior interosseous nerve along its course through the supinator as well.
14. Follow the posterior interosseous nerve more proximally and dissect it free to get length for your transfer.
15. Remember to divide donor distal, recipient proximal. Follow your recipient radial nerve branches proximally to gain length as noted.  Electrically stimulate the recipient motor component of the radial nerve (PIN, ECRB) to confirm that there is no function before dividing the branches.

Median (FCR / FDS) to Radial (PIN / ECRB) Nerve Transfer:

16. Divide the recipient posterior interosseous nerve and the nerve to the ECRB proximally. Use long down curve retractors and aggressive retraction to gain exposure and divide these nerve branches just proximal to the elbow crease level.
17. If you’re going to do a sensory nerve transfer of lateral antebrachial cutaneous nerve to radial sensory nerve, then divide the radial sensory at this level as well. If you’re not, then you can leave the radial sensory nerve intact. 
18. Bring the posterior interosseous nerve and the nerve to the ECRB over towards the median nerve. You’ll find that there is a posterior branch off the posterior interosseous nerve, which is the nerve to the supinator. Neurolyze this free from the posterior interosseous nerve and exclude it from the nerve transfer.  Don’t waste valuable motor fibers on reinnervating supination, which is provided by the biceps brachii muscle.
19. Divide the donor FDS branch distally. You’ll probably just need one. Bring it over towards the nerve to the ECRB. This is usually a very appropriate size match as the nerve to the ECRB is small.
20. Divide the nerve to the FCR distally. Neurolyse the fascicle to the palmaris longus away from the nerve to the FCR prior to dividing it so that you can use this as a fallback for a palmaris longus to extensor pollicis longus tendon transfer if this nerve transfer fails.
21. Bring the donor FCR nerve over towards the recipient PIN.
22. Make sure there is absolutely no tension on your nerve transfers and separate the two nerve transfers so there is no crossover and mixing of antagonistic donor and recipient fibers. 
23. It will be your choice to do the repair with the tourniquet inflated or deflated. However, get hemostasis and do the repair.  If you are running out of tourniquet time, then deflate the tourniquet. Otherwise, consider doing the repair with tourniquet up as there is less bleeding from vasa nervorum and visualization is improved.  The microsurgical repair is done with 9-0 microsuture and fibrin glue to reinforce with an OR microscope.

Superficial Head of Pronator Teres to Extensor Carpi Radialis Brevis Tendon Transfer:

24. If simultaneous tendon transfer is being done, proceed with your end-to-side fish-weave tendon transfer of the tendon of the superficial head of the PT to the ECRB brevis tendon, keeping the wrist extended.
25. We inject and place a Marcaine pain pump for peri-operative pain control. A superficial drain is placed away from the nerve repairs.

Post-operative Management:

26. If a tendon transfer has been performed, then we immobilize the elbow at 90 degrees of flexion, the forearm in pronation and the wrist extended to protect the tendon transfer for two weeks. Then we free the elbow, but keep the wrist extended for another two weeks.
27. If just the nerve transfer has been done, then we immobilize the elbow for 7-10 days, and then start gentle range of motion and nerve gliding. 
28. Motor re-education starts within the first post-operative month with our hand therapist educating the patient as to the donor recipient movements on their normal hand and encouraging these maneuvers on the reconstructed hand to facilitate early motor re-education.

Related References:

1. Brown JM, Tung TH, Mackinnon SE. Median to radial nerve transfer to restore wrist and finger extension: technical nuances. Neurosurg. 2010 Mar;66(3 Suppl Operative):75-83.

2. Ray WZ, Mackinnon SE. Clinical outcomes following median to radial nerve transfers. J Hand Surg Am. 2011 Feb;36(2):201-8.