Radial Nerve and Tendon Transfers - Overview

Tendon transfers involve using of a functional muscle tendon unit to replace a lost function. This loss of function can be due to a peripheral nerve injury, spinal cord injury, stroke, traumatic brain injury, cerebral palsy, or any other cause. The more closely the tendon to be transferred resembles the nonfunctioning muscle tendon unit, the more likely it will be successful. Several basic principles should be considered prior to beginning the transfer and all these variables play an important role in determining the most optimal transfer.

I. Basic Principles 

A. Correction of Contracture: All joints should be supple with full passive motion prior to tendon transfer, as postoperative active motion will not be greater than preoperative passive motion. If the joint does not have full passive motion, this is corrected prior to tendon transfer by contracture release. 

B. Tissue Equilibrium: The optimal time should not be until the scars are mature, the joints are supple, and the edema has resolved. Every effort should be made to place the transfers in healthy tissue, even if this means performing a different transfer. When a bed of healthy tissue is not present, consideration should be given to resurfacing with vascularized fasciocutaneous flaps prior to tendon transfer. 

C. Straight Line of Pull: The most efficient tendon transfer is one that passes in a straight-line from its origin to the site of insertion. 

D. One Tendon—One Function: It is obvious that a tendon cannot be used for two different functions (digital flexion and extension), but the effectiveness of the transfer is reduced when trying to provide two similar functions (digital extension and thumb extension), as the transfer will only effectively move the joint to which it is most tightly attached. 

E. Strength: The tendon chosen for transfer must have adequate strength to perform its new function. A muscle loses roughly one grade of strength following the transfer, ie, a muscle graded at 5/5 might decrease to 4+/5 following the transfer. As a general rule, muscles that have been denervated and have subsequently recovered are not good donor muscles. In order to successfully perform tendon transfers, an understanding of the relative strengths of the muscles in the forearm and hand should be obtained (Table 17a-1). When choosing a muscle to transfer, one would prefer to have a muscle of the same or greater strength as the donor.

F. Amplitude of Motion

1. It is difficult for a muscle to replace one with a greater excursion. By rough estimation, tendons that insert at the wrist level have 30 mm of total excursion, the digital extensors have 50 mm of excursion, and the digital flexors have 70 mm of excursion (Table 17a-2).

2. It can also be stated that muscles attaching at the wrist have ∼30 mm excursion, muscles attaching around the metacarpophalangeal (MP) joints have 50 mm of excursion, and muscles attaching nearer the finger tips have ∼70 mm of excursion. These are general rules and the specific excursions are slightly different for the flexor pollicis longus (FPL) and the flexor digitorum superficialis (FDS) tendons.

3. To increase the amplitude of a given muscle, a transfer can incorporate more than one joint to allow the tenodesis effect to augment amplitude. This occurs when a wrist flexor is transferred to a digital extensor. The wrist flexor has an amplitude ∼30 mm, but this can be used to restore motion in a muscle, which normally has 50 mm excursion by flexing the wrist and allowing the digital extension to be augmented through tenodesis. 

G. Synergy: A transfer will be more effective and easier for the patient to use if the action of the transferred muscle is synergistic to the one it is replacing. Because wrist extension is synergistic with digital flexion and wrist flexion with digital extension, these reciprocal actions are to be kept in mind when performing a transfer. 

H. Expendable Donor: The transfer of a tendon should not result in loss of a function. Therefore, at least one wrist flexor and extensor should be maintained. 

I. Arthrodesis: It is generally best to avoid arthrodesis to stabilize a joint as patients can use a mobile joint to their advantage, even if there is limited voluntary control of the joint. For example, a patient with a supple wrist may have minimal wrist control, but can supinate the forearm, allowing for wrist extension through gravity and attendant digital flexion via tenodesis to help with grasp.

II. Classification: Peripheral nerve injuries are generally classified as high (elbow level) or low (wrist level). They are also classified as single nerve injuries or combined (more than one) nerve injuries.

III. Operative Technique: When performing a tendon transfer, the functional tendon is repaired to the nonfunctional tendon using a strong weave to connect the tendons and decrease the chance for separation of the two tendons. This is commonly completed with three Pulvertaft weaves, in which one tendon is passed through the substance of the second tendon, interlocking the tendons and securing them to each other, creating a strong repair. The tension is set tight to allow for some slight postoperative stretch, as it is rare to create a transfer that is too tight. The postoperative program varies, depending on the type of transfer, but generally involves a period of 3-weeks immobilization, followed by active and passive mobilization.

IV. Peripheral Nerve
A. Radial Nerve Palsy

1. Radial nerve palsy can be divided into high and low injuries. A high radial nerve palsy involves the radial nerve proper, whereas the low palsy involves the posterior interosseous nerve (PIN) (both of these are near the level of the elbow).

2. The importance in the difference in high and low radial nerve palsies is in the presence or absence of active wrist extension. The radial nerve proper will innervate the brachioradialis (BR), extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB) prior to dividing into the PIN and the radial sensory nerve and thus, a patient with the high radial nerve palsy will lack wrist extension, thumb extension, and digital extension. 

3. With radial nerve injuries, three functions are lost and must be replaced:
a. Thumb extension
b. Finger extension
c. In high nerve palsies, wrist extension.

4. Low radial nerve transfers

a. Thumb extension
Digital extension

PL—extensor pollicis longus (EPL) 
Brand—flexor carpi radialis (FCR)–EDC
Jones—flexor carpi ulnaris (FCU)–EDC
Modified Boyes—FDS ring–EDC

b. Each of these transfers for digital extension can be used successfully. The disadvantage of the FCU transfer lies in sacrificing the strongest wrist flexor and its importance in hammering or the “dart throwing” motion. The disadvantage in the FDS ring transfer is the lack of synergism and although EDC excursion is best replicated by the FDS transfer, it is more difficult for the patient to retrain a muscle traditionally used for digital flexion to provide digital extension. 5. High radial nerve transfers (in addition to the low radial nerve transfers) a. Wrist extension—Pronator teres (PT)–ECRB b. Pronator teres is almost always used to restore wrist extension and is transferred to the most central radial wrist extensor—ECRB.

TABLE 17a-1: Relative strength of muscles available for transfer BR and FCU

Relative strength = 2
Wrist extensors (ECRB, ECRL, ECU), digital flexors (FPL, FDS, FDP), PT, and FCR

Relative strength = 1
Digital extensors (EDC, EIP, EDQ) Relative strength = 0.5 Notes: ECU, extensor carpi ulnaris; EDC, extensor digitorum communis;

1. This classification does not include the shoulder. It is a guide to the forearm and hand only. Determination of patient suitability for posterior deltoid-to-triceps transfer or biceps-to-triceps transfer is considered separately. 
2. The need for triceps reconstruction is stated separately. It may be required to make BR transfers function properly (see text). 
3. There is a sensory component to the classification. Afferent input is recorded using the method described by Moberg and precedes the motor classification. Both ocular and cutaneous input should be documented. When vision is the only afferent available, the designation is “Oculo” (abbreviated O). Assuming there is 10 mm or less two-point discrimination in the thumb and index finger, the correct classification would be Cu, indicating that the patient has adequate cutaneous sensibility. If two-point discrimination is >10 mm (meaning inadequate cutaneous sensibility), the designation O would precede the motor group (eg, O2). 
4. Motor grouping assumes that all listed muscles are grade 4 (MRC) or better and a new muscle is added for each group; for example, a group 3 patient will have BR, ECRL, and ECRB rated at least grade 4 (MRC).

Source: Reprinted with permission from McDowell CL, Moberg EA, House JH. The Second International Conference on Surgical Rehabilitation of the Upper Limb in Tetraplegia (Quadriplegia). J Hand Surg Am. 1986;11:604–608.

TABLE 17a-2: Excursion muscles available for transfer Wrist extensors and flexors

30 mm excursion (ECRL, ECRB, ECU, FCR, FCU)
Digital extensors

50 mm excursion (EDC, EIP, EDQ, EPL)
Digital flexors

70 mm excursion (FDP)

Key Articles

Peljovich A, Ratner JA, Marino J. Update of the physiology and biomechanics of tendon transfer surgery. J Hand Surg Am. 2010;35(8):1365–1369. 

Ratner JA, Peljovich A, Kozin SH. Update on tendon transfers for peripheral nerve injuries. J Hand Surg Am. 2010;35(8):1371–1381.

Radial Nerve Learning Module