Harry A. Hoyen
DEFINITION
Radial nerve palsy that is distal to the triceps innervation affects the forearm musculature. A lesion that does not recover results in predictable wrist, finger, and thumb extensor deficits.
ANATOMY
The brachioradialis and forearm extensor musculature originate in the lateral humeral epicondyle and the interosseous membrane (FIG 1A).
Each of the extensor muscles has a relatively flat muscle belly before forming a flat, broad tendon.
The myotendinous junction for the wrist extensors is in the mid-forearm, whereas the myotendinous junction of the finger and wrist extensors is the distal forearm.
The radial nerve arises from the posterior cord of the infraclavicular brachial plexus (FIG 1B). Multiple triceps motor branches are present as the nerve courses in the posterior compartment of the upper arm. The nerve traverses into the anterior compartment through the intramuscular septum. The nerve then lies between the brachialis and brachioradialis before it enters the forearm. The brachioradialis (BR), extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB) are innervated as the nerve divides into the deep radial nerve, the posterior interosseous nerve (PIN), and the superficial radial nerve. The PIN innervates the extrinsic extensors after exiting the supinator musculature.
The motor point for each nerve is fairly consistently located just proximal to the myotendinous junction. In most cases, there is one larger motor branch from the radial nerve or PIN to each muscle.
The sequence of muscle innervation is an important distinction when considering the anatomy of the radial nerve. Whereas some nerves distribute their nerve branches in a tree-like fashion, the radial nerve innervates the extensor musculature in an orderly pattern, from proximal to distal. The proper radial nerve supplies the BR, the ECRL, and occasionally the ECRB. The PIN innervates the ECRB, the extensor digitorum communis (EDC), the extensor carpi ulnaris (ECU), the extensor indicis proprius (EIP), and the extensor pollicis longus (EPL).
FIG 1 • A. Muscles of the forearm. B. Course of the radial nerve.
The order of innervation is important in differentiating a radial nerve injury from a mechanical myotendinous injury or muscle disruption after a forearm laceration.
Understanding the innervation also is helpful while observing and assessing the clinical recovery after radial nerve injury or repair.
PATHOGENESIS
Most radial nerve deficits result from traumatic injuries. Idiopathic and neoplastic etiologies are less common.
Radial nerve injury is most commonly associated with midto distal shaft humerus fractures.1,4,24,25,28
NATURAL HISTORY
The type of traumatic injury is an important predictor of recovery after humerus trauma.
Neurapraxic lesions typically result from low-energy injuries. Recovery can be expected over the course of 3 months. The clinical recovery can be followed by observing the advancing Tinel sign and the reinnervation sequence.
Conditions that persist after 3 months can be further evaluated with electrodiagnostic studies. In the clinical setting of a nonadvancing Tinel sign and electromyographic findings of axonal loss, exploration with intraoperative electrophysiologic testing is warranted. Nerve grafting across the injury is indicated in lesions that do not demonstrate improvement after external neurolysis.18,24,25
Exploration of open and penetrating injuries is recommended. The choice of primary repair or nerve grafting depends on the injury zone. Recent evidence warrants exploration of high-energy injuries, because these lesions have not demonstrated recovery. It is difficult to determine the injury at the acute setting. Interposition nerve graft is often necessary.18
PATIENT HISTORY AND PHYSICAL FINDINGS
A deficit in radial nerve innervation of the extrinsic wrist and finger extensors results in no active wrist, finger, and thumb extension.
The clinical presentation of radial and PIN palsies is differentiated by the fact that the brachioradialis and ECRL are preserved in PIN palsies.
The brachioradialis can be palpated during resisted, neutral position elbow flexion, and the wrist assumes a radial deviated position during attempted active extension.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Electrodiagnostic studies (eg, nerve conduction studies and electromyography) are used initially for assessment and for determining subsequent treatment.
Axonal loss injuries are evident about 4 weeks after the injury; therefore, the initial study is obtained 4 to 6 weeks after the injury.
The electrodiagnostic study also can identify other nerve injuries that were not as evident on the initial evaluation.
Recovery can be followed by clinical examination or with supplemental studies.
A final study is obtained before tendon transfer at 12 to 18 months.
DIFFERENTIAL DIAGNOSIS
Muscle or tendon laceration
Closed myotendinous rupture
Cervical spinal disease
Joint or tendon subluxation (especially if there is lost digital extension)
NONOPERATIVE MANAGEMENT
Splint
Active and passive motion exercises to maintain motion and prevent contracture28
SURGICAL MANAGEMENT
Tendon transfer is the mainstay of treatment. Microvascular repair and nerve graft are discussed in another chapter.
The goal of treatment is independent wrist, finger, and thumb extension with thumb abduction. Donor muscles include the pronator teres (PT), flexor carpi ulnaris (FCU), flexor carpi radialis (FCR), flexor digitorum superficialis (FDS) 3 and 4, and palmaris longus (PL).
Timing of surgical intervention is controversial. Conventional surgical recommendations are to proceed after the patient has reached a documented clinical and electromyographic plateau of useful radial nerve regeneration. This typically occurs 1 year after the nerve lesion.25
Tendon transfer primarily for wrist extension may be performed early, at the same setting as nerve surgery, to improve function and minimize brace reliance as the nerve regenerates.
Preoperative Planning
Prerequisites
MHC grade 4+ or 5 median or ulnar nerve–innervated donor musculature
Maintained passive motion in wrist and finger extension with no contracture
Controlled systemic disease processes
Positioning
The patient is positioned supine with arm table support and a tourniquet.
Approach
Three general exposures are used:
Radial incision with volar exposure for FCR and PT and dorsal exposure for the ECRB and ECRL
Distal, dorsal incision for EDC exposure
Individual approaches for harvest of the FCU, FCR, and FDS
The ideal tendon transfer tension is based on the individual muscle properties. In general, the optimal tension is established at the peak of the length–tension curve for the donor muscle, while the wrist and fingers are maintained in the ideal position. Because this donor muscle position is difficult to determine intraoperatively without specialized equipment, this point reasonably corresponds to the midpoint of the passive muscle excursion. The ideal joint position for each transfer is discussed with the individual transfers.
TECHNIQUES
WRIST EXTENSION RESTORATION THROUGH PT TO ECRL AND ECRB 2,8,27
Make a longitudinal radial incision over the midshaft of the radius.
This allows exposure of the PT and the wrist extensors through a single incision.
Identify and expose the PT volarly while protecting the radial artery and superficial radial nerve (TECH FIG 1A).
Extend the pronator insertion by harvesting a strip of periosteum distally (TECH FIG 1B).
Release the proximal muscle to improve its excursion (TECH FIG 1C).
Develop the dorsal subcutaneous flap and identify the ECRB and ECRL.
Deliver the PT dorsally, deep to the brachioradialis (TECH FIG 1D).
Perform a Pulver-Taft weave into the ECRL and ECRB, and then secure the transfer with 2-0 or 3-0 nonabsorbable braided suture (TECH FIG 1E,F).
TECH FIG 1 • A. The PT is harvested through the volar-radial approach. The superficial radial nerve seen here is protected during the exposure between the FCR and BR or between the BR and ECRL. B.The PT tendon can be extended by carefully fashioning a distal periosteal sleeve. C. Muscle excursion can be improved by releasing the PT proximally. D. The tendon is transferred deep to the BR. E,F. The PT is then woven through the ECRL and ECRB tendons.
FINGER EXTENSION THROUGH FCU TO EDC TRANSFER 7,16,19,20
Make a distal, volar longitudinal incision to expose the FCU insertion at the pisiform (TECH FIG 2A).
Extend the exposure proximal to a point 8 cm from the humeral insertion and release the FCU periosteal attachments as necessary to improve excursion (TECH FIG 2B).
Identify the ulnar neurovascular structures.
Develop a broad subcutaneous dorsal flap to improve the ECU line of pull to the EDC (TECH FIG 2C). The ECU may be placed beneath the most superficial subcutaneous fascial layer.
TECH FIG 2 • A. The FCU is exposed through the volar-ulnar exposure. B. The FCU tendon is mobilized from its ulnar periosteal origin. C. Tissues are released to create a broad subcutaneous tunnel to transfer the tendon to the dorsal forearm. D,E. The bulky transferred tendon seen here is split and thinned to facilitate the transfer and attachment. F. The tendon is sewn using a Pulvertaft weave.
Trim distal muscle and, if necessary, the tendon to enable passage of tendon into the EDC (TECH FIG 2D,E).
Make a dorsal longitudinal incision 5 to 7 cm long in the retinaculum of the distal forearm.
Release the proximal extensor retinaculum to permit excursion after transfer.
Perform a single or double weave into the EDC tendons. Locate the point of insertion into each slip that recreates the normal finger cascade (TECH FIG 2F).
The final transfer tension is set with the metacarpophalangeal joints in full extension while the wrist is in 30 degrees of extension.
Secure finger extensor transfers with 3-0 or 4-0 nonabsorbable braided sutures.
FINGER EXTENSION THROUGH FCR TO EDC TRANSFER 7,9,12
Use volar radial exposure to identify the radial artery and the FCR (TECH FIG 3A).
Incise the FCR sheath and transect the tendon while maintaining the wrist in flexion.
Two different passage techniques may be chosen.
In the first, a subcutaneous tunnel to the dorsal incision (similar to the FCU transfer) is developed (TECH FIG 3B,C), and the FCR is passed beneath the superficial radial nerve to the EDC.
In the second, the FDS and median nerve are retracted ulnarly to identify the anterior interosseous nerve and the interosseous membrane proximal to the pronator quadratus (TECH FIG 3D–F), and the FCR tendon is passed volar-to-dorsal through an enlarged opening in the IOM (TECH FIG 3G,H).
Be cautious of the anterior interosseous nerve.
Do not violate the central band.
Tension, weave, and suture into EDC, as with FCU transfer (TECH FIG 3I,J).
TECH FIG 3 • A. The FCR is identified and the tendon mobilized through a volar–radial exposure. B,C. A radial subcutaneous tunnel is developed, and the FCR tendon is passed deep to the radial sensory nerve, emerging dorsally. Alternatively, the FCR tendon may be passed through the IOM. D,E. The AIN is identified and protected. F. The IOM is exposed just proximal to the pronator. G,H. The FCR is transferred through the window in the IOM to the dorsal forearm quadratus. I,J. The transfer is secured with 3-0 nonabsorbable suture.
THUMB EXTENSION THROUGH PL TO EPL 2,17,21
Identify the palmaris longus at the wrist crease through the same incision described for exposure of the FCR (TECH FIG 4A).
Dissect and divide the proximal fascial bands to facilitate harvest (TECH FIG 4B).
Develop a subcutaneous tunnel to the dorsal thumb below the cutaneous nerves.
The EPL may be addressed in either of two ways:
Release the EPL from the third compartment to facilitate transfer location. This technique permits the muscle–tendon connection to remain intact if radial nerve recovery is possible (TECH FIG 4C).
Divide the EPL proximally (only if recovery is not possible) and perform the transfer in a more volar location. The thumb extension vector is improved with the transfer in this location.
Set the tension at the level of the thumb metacarpal with the wrist in neutral and close to maximum tension on the PL and EPL (TECH FIG 4D,E).
Secure the weave with 3-0 or 4-0 nonabsorbable braided suture.
TECH FIG 4 • A. This approach was combined with a FCR–EDC transfer with identification of the PL through the same exposure. B. Adhesions are released allowing tendon mobilization. C. The EPL is left intact, transposed volarly, and prepared for transfer at the level of the thumb metacarpal. D,E. The Pulvertaft weave is initiated and completed once proper tension is set.
MODICATION: FINGER EXTENSION AND THUMB ABDUCTION THROUGH LONG FINGER FDS TO EIP/EPL; RING FINGER FDS TO LONG, RING, AND SMALL EDC; AND PL TO ABDUCTOR POLLICIS LONGUS 5,9
Perform oblique palmar incisions to harvest the FDS of the long and ring fingers.
Include both slips for transfer.
Suture the remaining distal tendon to the volar plate or soft tissue to prevent proximal interphalangeal hyperextension.
Use the volar incision to retrieve the FDS tendons and to harvest the PL.
Precisely expose the interosseous membrane (IOM) and make preparations for tendon transfer as discussed in the preceding section.
Perform a dorsal incision and exposure similar to that detailed in the preceding section. Transfer the two FDS tendons dorsally through the IOM.
The long finger FDS is transferred to the EIP and the EPL. The ring finger FDS is transferred to the long, ring, and small EDC tendons.
Set tension at the wrist at 30 degrees and at the MP joint at full extension.
Secure the transfer with 3-0 or 4-0 suture.
The PL is harvested as detailed for the EPL transfer.
The radial subcutaneous route also is used to transfer the PL to the abductor pollicis longus (APL), proximal to the retinaculum.
The location of this transfer is slightly more proximal to the PL than the EPL transfer due to the length available for the APL.
Set tension in near-full thumb abduction at wrist 30 degrees; secure with 3-0 or 4-0 suture.
FINGER EXTENSION AND THUMB ABDUCTION THROUGH FCU TO EDC AND EPL, AND PL TO APL
Although one donor muscle is not typically transferred to two recipients,3 an FCU transfer to the EPL and EDC has been described. This may be combined with a wrist extension transfer.
The technique is similar to that discussed for the FCU to EDC transfer along the ulnar subcutaneous route. The tension is such that the thumb and index metacarpal are parallel.
POSTOPERATIVE CARE
Postoperative splint with wrist at 30 to 40 degrees and MP joints in 0 to 10 degrees of hyperextension
Proximal and distal interphalangeal active and passive motion at 3 to 5 days
Static immobilization for 3 weeks, then tenodesis motions with activation of wrist extension transfer
Integration of finger and thumb active extension as wrist motion improves
The most difficult motion to obtain is independent finger extension with the wrist in the extended position.
Passive wrist flexion exercises are determined by the recovery of wrist flexion after splint removal. The arc of flexion can be expected to be less than the preoperative level.
A dynamic splint may be applied so that finger extension may begin at 1 week postoperative. An articulated splint may be used to permit dynamic wrist motion, but the patient must be very adept and have a clear understanding of the therapy regimen.23,28
OUTCOMES
Wrist extension of 40 to 50 degrees (80% M4), wrist flexion 20 to 40 degrees
Finger extension: at wrist neutral, 0 to 10 degrees flexion; at wrist in 30 degrees of extension, 0 to 30 degrees
Functional scores: 80% excellent to good21 ; no reported disabilities of the arm, shoulder, or hand
COMPLICATIONS
If transfer adhesions occur, the therapy can be modified according to postoperative course. Tenolysis should be delayed until at least 9 to 12 months after surgery.
Transfer attenuation
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