- ▪
Potential donors for transfer are those muscles with
- 1
Adequate power to motor the recipient tendon
- 2
Similar tendon excursion to the recipient
- 3
Function synergistic or “in phase” with the recipient
- 1
- ▪
Transfers for radial nerve palsy restore wrist extension, metacarpophalangeal (MCP) joint extension, and thumb extension.
- ▪
Transfers for median nerve palsy restore thumb opposition and interphalangeal (IP) joint flexion.
- ▪
Transfers for ulnar nerve palsy restore thumb adduction, MCP joint flexion, IP joint extension, and index digit abduction.
- ▪
Timing of surgery depends on the achievement of tissue equilibrium.
- ▪
Clinical success requires a multidisciplinary approach to patient care.
Functional deficits resulting from peripheral nerve injuries vary with the particular nerve involved, the location of the lesion, and the extent of concomitant injuries to bone and soft tissue structures. Tendon transfer surgery to restore fundamental wrist and hand function is made possible by the redundancy that exists among the actions of our upper extremity musculature. The development of a surgical plan for tendon transfers involves identifying those muscles that are denervated, evaluating the patient’s functional deficits, and considering which muscles are available for transfer. Potential donors for transfer are those muscles with adequate power to motor the recipient tendon, similar tendon excursion to the recipient, and those with function synergistic or “in phase” with the recipient (i.e., wrist extension and finger flexion, thumb adduction and wrist flexion, finger extension and thumb abduction). Certainly, existing function should not be sacrificed by the harvest of a muscle–tendon unit.
Timing of surgery depends on the achievement of tissue equilibrium. Resolution of wound healing, union of fractures, and mobilization of stiff joints are prerequisites for a well-functioning tendon transfer. Clinical success requires a multidisciplinary approach to patient care including contributions by physicians, nurses, therapists, and electrodiagnosticians. A description of rehabilitation strategies for tendon transfers after peripheral nerve injury can be found in Chapter 59 .
Radial Nerve
Anatomy
The radial nerve is a branch of the posterior cord of the brachial plexus. The first few branches of the radial nerve innervate the triceps. Coursing through the posterior compartment of the arm, the nerve lies immediately adjacent to the posterior humerus for a distance of more than 6 cm. Piercing the lateral intramuscular septum, the radial nerve enters the anterior compartment of the arm approximately 10 cm proximal to the lateral epicondyle. The nerve’s relationship to both the humerus and the stout fibers of the lateral intramuscular septum place it at particular risk in this region for traumatic and iatrogenic injury. Once in the anterior compartment, the radial nerve lies between the brachioradialis (BR) and the brachialis and continues in this interval distally, giving off motor branches to both the BR and extensor carpi radialis longus (ECRL) ( Fig. 58-1 ). Before entering the forearm through the two heads of the supinator, the radial nerve bifurcates into a sensory branch, dorsal radial sensory nerve (DRSN), and a primarily motor branch, the posterior interosseous nerve (PIN). The extensor carpi radialis brevis (ECRB) is variably innervated by either the radial nerve or the PIN (in the majority of cases). The PIN travels through the proximal dorsal forearm innervating the extensor digitorum communis (EDC), extensor carpi ulnaris (ECU), extensor digiti quinti (EDQ), abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and extensor indicis proprius (EIP) before terminating as a sensory nerve to the carpus, lying deep to the tendons of the fourth dorsal extensor compartment.
Physical Examination
The most proximal muscle innervated by the radial nerve is the triceps, and in the majority of cases of a peripheral nerve injury, its function as an elbow extensor is preserved. As illustrated in Figure 58-2 , a radial nerve lesion proximal to the elbow results in loss of function of all the wrist extensor muscles (ECRL, ECRB, and ECU), yielding a wrist drop ( Fig. 58-3 ). Loss of wrist extension results in the inability to generate power grip, which can easily be tested using a dynamometer. EDC function is tested by asking the patient to simultaneously extend the MCP joints of the index through small digits ( Fig. 58-4 ). EIP and extensor digiti minimi function is evaluated by asking the patient to extend the index and small finger MCP joints in isolation. EPL function is assessed by asking the patient to extend all joints of the thumb at the same time. Extensor pollicis brevis (EPB) function is assessed by having the patient extend the thumb MCP joint while keeping the interphalangeal (IP) joint flexed.
In contrast to a high radial nerve palsy (also known as palsy of the radial nerve proper), a lesion distal to the elbow will involve only those muscles innervated by the PIN (see Fig. 58-2 ). Clinically, examination of the patient with low radial nerve palsy demonstrates wrist radial deviation during active extension because of maintenance of ECRL function and loss of ECU function.
After initial evaluation and diagnosis of radial nerve palsy, it is recommended that the patient be fitted for a radial nerve orthosis. Traditional outrigger orthoses or newer lower profile orthoses along with an appropriate home exercise program prevent the development of wrist and MCP joint contractures and can considerably enhance function ( Figs. 58-5 and 58-6 ). The reader is referred to Chapter 45 for more detail regarding orthotic fabrication for the nerve-injured hand. During subsequent visits, serial physical examinations of a patient with radial nerve palsy is an important tool for monitoring recovery, guiding treatment, and managing patient expectations.
Despite the limited functional consequence of a loss of BR activity after a radial nerve injury, evaluation of this muscle for signs of reinnervation is extremely important in the weeks and months after injury. Because the BR is the first muscle innervated by the radial nerve in the anterior compartment of the arm, reinnervation of the BR implies nerve conduction distal to the site of the lesion. Once motor function of the brachioradialis is restored, it is likely that wrist and MCP joint extension will soon follow.
Timing of Tendon Transfers
The preferred timing of tendon transfers for a radial nerve palsy falls into one of two categories: early transfers done to act as an “internal orthosis” or later transfers to restore function when recovery is deemed unlikely. Early transfers are performed within weeks of nerve injury and usually consist of a single tendon transfer for wrist extension. This transfer for wrist extension allows power grip by placing the finger and thumb flexors at a biomechanical advantage. Release of finger opening is accomplished by wrist flexion and the associated tenodesis effect of the long finger extensor tendons. The preferred timing of late transfers varies widely among authors, with intervals ranging between 6 and 18 months.
The expected time to recovery of any peripheral nerve lesion can be calculated based on the work of Seddon ( Table 58-1 ). Neurapraxias tend to recover within 3 to 4 weeks after injury as remyelination occurs promptly. In contrast, an axonotmesis injury involves Wallerian degeneration and implies incomplete and slow regeneration. Assuming a rate of nerve regrowth of 1 mm/day, the expected time to clinically detect return of function can be estimated based on the distance between the nerve lesion and the site of innervation of the BR. Therefore, it is reasonable to expect that a radial nerve lesion occurring at the mid-shaft of the humerus would take at least 6 months to recover. Delaying tendon transfers until that time seems reasonable to allow sufficient time for nerve recovery. During this time, a radial nerve orthosis will enhance function and should be prescribed.
| Type | Definition | Outcome |
|---|---|---|
| Neurapraxia | Interruption of nerve conduction; some segmental demyelination; axon continuity intact | Reversible |
| Axonotmesis | Axon continuity disrupted; neural tube intact | Wallerian degeneration; incomplete recovery |
| Neurotmesis | Complete disruption of nerve continuity; loss of axons and neural tubes | No spontaneous recovery; surgery required |
Radial Nerve Tendon Transfers
In an isolated high radial nerve injury, muscle–tendon units innervated by the median and ulnar nerve are possible donors. Given the preserved function of both the wrist flexors (i.e., flexor carpi radialis [FCR] and flexor carpi ulnaris [FCU]) and both pronators (pronator teres [PT] and pronator quadratus), there are several available options. Classic transfers for radial nerve palsy include the Brand, Jones, and modified Boyes , transfers. Among these transfers is the common use of the PT to ECRB and the palmaris longus (PL) to EPL. The preferred choice of a motor to reanimate the EDC varies with each author. In low radial nerve palsy, a transfer for wrist extension is not required because ECRL function is preserved.
Although each of the three sets of transfers have been used by the authors, the preferred transfers for radial nerve palsy are the PT to ECRB, PL to the rerouted EPL, and FCR to EDC. The rationale for this last choice is the preservation of the FCU, which is an important contributor to power tasks, such as wielding a hammer. Preservation of this ulnar-sided flexor also helps to balance the radial deviation caused by the tendon transfers to the ECRB. This is particularly important in the case of low radial nerve palsy with an intact ECRL. Harvest of the FCU is also more time-consuming compared with the FCR. The FCU has muscle and fascial attachments along the entire ulna that must be freed to maximize its excursion. If the FCR is chosen for the EDC motor, a single utilitarian curvilinear radial-sided incision can be used to perform all the transfers.
In our experience, transfer of the flexor digitorum superficialis (FDS), either through the interosseous membrane or around the ulnar border of the forearm to the EDC, is more prone to fail. Difficulties with rehabilitation to activate this “out-of-phase” transfer (i.e., learning to fire a finger flexor as an extensor) and the development of adhesions after interosseous transfer are common.
Surgical Technique in Brief
The FCR and PL are readily accessible beneath the full-thickness volar forearm flap. Branches of the radial sensory nerve and the radial artery are identified and protected. Dorsal dissection allows exposure of the PT tendon, located beneath the BR musculotendinous junction deep to the emerging radial sensory nerve. The PT tendon is harvested with a strip of periosteum to augment its coaptation to the ECRB tendon ( Fig. 58-7 , online). Further elevation of the dorsal skin flap exposes the ECRB, EPL, and EDC within the second, third, and fourth dorsal compartments, respectively. The PL is released from its insertion into the palmar fascia and mobilized toward the freed EPL tendon. The EPL must be transposed from the third compartment toward the PL. This transposition provides better thumb extension and eliminates the thumb adduction vector of the EPL.
Tendon transfers of the thumb and finger extensors are performed before transfers about the wrist. This sequence allows the surgeon to judge sufficient tension using wrist motion. The EPL tendon is woven into the PL, and the FCR is woven into the EDC using a tendon braider ( Fig. 58-8 , online). Tension is adjusted until wrist flexion of 30 degrees produces adequate thumb and finger extension via tenodesis and wrist extension allows passive finger flexion into the palm. Once digital extension transfers are completed, the PT is woven into the ECRB. Tension is adjusted until a 30-degree extension resting posture of the wrist is achieved. All Pulvertaft tendon passes are secured with braided, nonabsorbable suture. Once skin flaps are closed, the extremity is positioned with the wrist in 30 degrees of extension, the MCP joints in full extension, and the thumb abducted with the IP joint in extension.
Rehabilitation of radial nerve tendon transfers is the subject of the next chapter. In general, tendon transfers for radial nerve palsy lead to improved ability to pick up and release objects ( Fig. 58-9 ).
Median Nerve
Anatomy
The median nerve arises from the lateral and medial cords of the brachial plexus and has contributions from the C5, C6, C7, C8, and T1 spinal nerve roots. The median nerve travels distally into the arm lateral to the brachial artery and medial to the biceps brachii. In the mid to distal one third of the arm, the median nerve crosses anterior to the brachial artery and comes to lie medially to the artery as it approaches the antecubital fossa, where it lies deep to the lacertus fibrosus.
The median nerve enters the forearm between the two heads of the PT. In the proximal forearm, motor branches arise to innervate the flexor–pronator musculature including the PT, PL, FDS, and FCR ( Fig. 58-10 ). The anterior interosseous nerve (AIN) originates from the median nerve between 5 and 8 cm distal to the medial epicondyle and provides motor branches to the index and long flexor digitorum profundus (FDP) tendons, the flexor pollicis longus (FPL), and the pronator quadratus. Like the PIN, the terminal branch of the AIN is a carpal sensory branch.
