Radial nerve

Most frequently injured nerve in the upper extremity, most commonly associated with humeral shaft fractures. All open injuries require exploration, whereas most closed injuries can usually be observed. Rarely, a neuritis or tumour of the radial nerve at levels as high as the brachial plexus will present with radial nerve palsy.
Fractures of the humerus may result in a closed radial nerve injury that is typically observed for a period of 3 months before surgical exploration. Idiopathic causes of radial nerve paralysis can be treated conservatively after treatable causes such as tumours have been excluded.

Anatomy

Brachial plexus, posterior cord, from C5, C6, C7, C8, and T1

Dorsal to the axillary artery and vein, abutting the shaft of the humerus near the spiral groove, separated from the bone by a thin layer of the medial head of the triceps. It then runs posterolaterally, in proximity to the deep brachial artery beneath the lateral head of the triceps, traveling along the anterior surface of the lateral intermuscular septum.

The radial nerve gives off branches to the extensor carpi radialis longus and brachioradialis as it enters the antebrachial fossa between the biceps and brachialis medially and the brachioradialis laterally. As it passes over the elbow joint, it divides into a terminal motor and sensory branch at the level of the radiocapitellar joint, but the exact site may vary by as much as 5 cm. The motor branch is the posterior interosseous (or deep radial) nerve, and the sensory branch is the superficial radial nerve.

The superficial branch of the radial nerve runs into the forearm under the brachioradialis before innervating the radial aspects of the dorsal wrist and hand. The posterior interosseous nerve travels a short distance over the radiohumeral joint, passing dorsolaterally around the radial head before entering the substance of the supinator. The nerve then winds around the neck of the radius to travel on the dorsal surface of the interosseous membrane.

The posterior interosseous nerve supplies the majority of forearm and hand extensors (including the extensor carpi radialis brevis, supinator, extensor digitorum communis, extensor digiti quinti, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis proprius), with the exception of the extensor carpi radialis longus and brachioradialis. The normal course of the posterior interosseous nerve is through the supinator brevis muscle. Two anomalous courses of the nerve have been described. One anomaly occurs in substance of the supinator, and the other involves a branch traveling superficial to the supinator brevis.

For a more detailed account read Mazurek

Cause of Radial Nerve Palsy

Injury may occur anywhere along the course of the radial nerve, from the brachial plexus to the hand, resulting in a similar clinical presentation regardless of the cause. Nontraumatic radial nerve palsy is rare. The cause of spontaneous paralysis of the posterior interosseous nerve or the radial nerve is often unknown. Nevertheless, acute nerve paralysis requires investigation to rule out treatable causes of the disease such as neuritis, tumors, or compression. Neuritis, for example, is usually associated with several weeks of severe pain.

Orthopaedic injury

12% of humeral shaft fractures are complicated by a radial nerve paralysis. Spontaneous recovery within 8 to 16 weeks has been reported in over 70% In particular, spiral fractures of the distal shaft of the humerus with varus angulation (Holstein Lewis fracture) Radial nerve paralysis associated with dislocation of the radial head is believed to result from traction on the nerve within the substance of the supinator, the paralysis is usually transient. Monteggia fractures may be complicated by a radial nerve palsy at the level of the posterior interosseous nerve. Most postoperative radial nerve paralysis results from traction during exposure.

Tumour and Inflammation

Compression due to either a benign or malignant tumour. Lipomas are the most common tumors reported in the literature to cause radial nerve palsy. Radial nerve palsy may also result from nerve tumors.

Anatomic compressions

The radial nerve can be compressed at multiple points along its course. At the elbow, it can be compressed by the fibrous bands proximal to the radial tunnel, the vascular leash of Henry (the radial recurrent artery), the tendinous margin of the extensor carpi radialis brevis, and the arcade of Frohse (the tendinous superficial head of the supinator). Posterior interosseous nerve syndrome is a radial nerve paralysis that is believed to result from compression of the deep branch of the radial nerve at the level of the arcade of Frohse. Spinner noted that radial nerve paralysis resulted from a narrowing at the leading edge of the superficial head of the supinator. Triceps compression - reports of transient palsies of the radial nerve after strenuous muscle activity have been attributed to compression of the nerve by the lateral head of the triceps muscle.

Open Wounds

Following sharp division, the clinical results after primary repair have been good to fair in most instances, if the nerve is explored early and repaired without tension.

Post operative

The treatment of postoperative radial nerve palsy requires a great deal of consideration. A previous surgical scar or an exploration of the arm without the aid of a tourniquet often prevents a clear identification of nerves during dissections. Radial nerve paralysis may occur as the result of a traction injury or compressive neuropraxia after surgery. A thorough and honest reflection by the surgeon is required when a radial nerve paralysis is noted after surgery. If there is any chance that the nerve may have been severed or partially transected, immediate re-exploration is indicated to ensure the best clinical outcome.

Other Causes

Tourniquet
Injection injuries
“Saturday night palsy.” due to pressure after sleeping with arm over chair or hard object.
Patients who develop a spontaneous neuropathy may also have a susceptibility to other compressive neuropathies (i.e., hereditary neuropatthy). Radial mononeuritis has also been related to alcohol, lead, arsenic, typhoid, and serum sickness.

Clinical Evaluation

Sensory loss

Dorsal surface of the proximal half of the thumb, index, and middle fingers and is usually limited to a small, triangular area on the dorsum of the first and second metacarpal webspaces.

Motor deficit

Wrist drop, loss of wrist and finger extension. Radial nerve injuries usually result in a decrease in power grip and pinch primarily related to the loss of wrist extension.

Level of lesion

Distinguish from lesions affecting the nerve roots (C5 through T1) or the brachial plexus.
Loss of the anconeus muscle is not clinically noticeable after proximal radial nerve paralysis.
Loss of triceps function reflects an injury at the level of the brachial plexus.
If the brachioradialis or extensor carpi radialis longus are not functional, then the injury is most likely at the level of the humeral shaft.
Pure Posterior interosseous nerve palsy presents with radial deviation of the wrist with dorsiflexion because of the preservation of the extensor carpi radialis longus. These patients are usually unable to extend their fingers or thumb at the metacarpophalangeal joints, and they have no sensory deficit because the superficial radial nerve is preserved.

Diagnostic Studies

History and a physical examination are often all that is needed to determine the level of injury and the suspected cause of radial nerve paralysis.

Radiographs should be obtained if a fracture, dislocation, or foreign body is suspected.

Magnetic resonance imaging should be obtained if a mass is suspected at any level along the course of the radial nerve.
All patients experiencing neural compromise after penetrating injury in proximity to nerves should be explored without the need for preoperative electrodiagnostic studies.

Standard electrodiagnostic studies will, however, help to determine the level of injury or its distribution if the physical examination is unclear. Patients with nerve paralysis that persists beyond 6 to 8 weeks should be examined with electrodiagnostic studies. By 12 weeks, motor unit potentials will be present and will help to differentiate between recoverable injures and those that will require surgery.

Classification

To Classify injuries you need to answer these questions

Open or Closed - It is important to make a distinction between open and closed injuries because the management is quite different.
Level of injury? - High injury:above the level of insertion of the pectoralis major muscle to the humerus Intermediate injury when it occurs between the insertion of the pectoralis muscle and the terminal branches of the radial nerve. Low injury when it involves the posterior interosseous nerve.
Acute, Chronic, Associated trauma/ injury

In general, all nerve injuries can be classified as first- through sixth-degree injury.

First degree - neurapraxia, segmental demylination without loss of nerve continuity or Wallerian degeneration.
Second degree - axonotmesis, injury to the axon, but intact endoneurial tissue and Schwann cell tubes.
Third degree - additional injury to the endoneurium, but the perineurium remains intact.
Fourth degree - neuroma in continuity with complete scar block of nerve function.
Fifth degree - transected nerve.
Sixth degree - combination of any of the above injuries

Management Options

It is important while waiting for treatment or recovery to splint the the wrist in slight extension and maintain function with physiotherapy.

Open injuries - EXPLORE

If the nerve is in continuity at the time of the exploration, it is treated as a closed injury. If the radial nerve has been sharply transected, but there is adequate nerve length and minimal soft-tissue injury, then it should be repaired primarily. The proximal and distal extent of the transected or injured nerve can be more clearly delineated if the surgery is delayed for 3 weeks. Nevertheless, it may be quite difficult to explore a nerve safely after a delay because of the progression of the surgical scar. Before 3 weeks, the extent of nerve injury can be determined with intraoperative electrodiagnostic studies and microscopic examination.

Closed injuries

Surgical exploration is indicated only when transection of the radial nerve is suspected, as might be the case after a comminuted humeral fracture or if it develops after closed manipulation. Radial palsy following closed intramedullary nailing is often due to a neuropraxia and should recover spontaneously If a radial nerve transection is not suspected, then the patient should be observed closely for a period of 3 months. Fortunately, most closed radial nerve palsies are associated with either a neurapraxia or a second- or third-degree injury that usually recovers spontaneously with time. A Tinel sign can be used to follow the progressive recovery of the nerve along its anatomic course in both second- and third-degree injuries.

Patients who do not demonstrate clinical evidence of recovery within 2 to 3 months of observation or after a negative surgical exploration should undergo electrodiagnostic evaluation.
Electrodiagnostic studies will help to determine the level and extent of the radial nerve injury. High, intermediate, or low radial nerve injuries should be explored, compression points should be released, and the nerve should be repaired or reconstructed when conservative management fails. The level of the nerve injury can be further delineated by an intraoperative, nerve-to-nerve study, as mentioned earlier. Because the motor endplates are not out of reach for regenerating axons, patients with low and intermediate radial nerve injuries repaired primarily or grafted at 3 to 4 months have an excellent prognosis. Conversely, the axons have a long distance to travel after a high radial nerve injury. This has resulted in the recommendation for tendon or nerve transfer after high injuries that fail to recover within 3 months. Also, patients with complete loss of radial nerve function following neuritis or whose treatment has been significantly delayed should be considered for tendon or nerve transfer.

Neurorrhaphy and Nerve Grafting

Nerve grafting is indicated if the nerve defect is large or there is significant tension on the repair.Good results have been noted in 80 percent of patients that required radial nerve grafts.

Tendon Transfers

Most authors agree that tendon transfers provide good results if nerve reconstruction fails in patients with radial nerve palsy. Tendon transfer is recommended if there are no signs of radial nerve recovery within 1 year.
Currently, there is continued disagreement on the best combination of tendon transfers to use in treating patients with radial nerve paralysis. The level of the radial nerve injury and a patient’s overall function and anatomy often dictate the best surgical option available. Most authors agree that the extensor carpi radialis brevis and longus should be reconstructed using the pronator teres tendon. The extensor digitorum communis can be reconstructed using the flexor digitorum superficialis (III), the flexor carpi ulnaris, or the flexor carpi radialis. The rerouted extensor pollicis longus can be reconstructed using the palmaris longus or the flexor digitorum superficialis (IV), and, in some cases, the abductor pollicis longus and extensor pollicis brevis can be reconstructed with the flexor carpi radialis. Lowe et al prefer to use the pronator teres to the extensor carpi radialis brevis, the flexor carpi ulnaris to the extensor digitorum communis, and the palmaris longus rerouted to the extensor pollicis longus (when available); otherwise, we use the flexor digitorum superficialis.

In the 1970s, Bevin 80 advocated early tendon transfer in radial nerve transection. He reported an average recovery time from nerve repair to be 7.5 months, with 66 percent of patients achieving good or excellent function. In the tendon transfer group, all patients noted good to excellent results in 8 weeks. The pronator teres was transferred to the extensor carpi radialis longus and brevis, the palmaris longus was transferred to the thumb extensors and long abductor (when present), and the flexor carpi ulnaris was transferred to the common digital extensors. When the palmaris longus was not present, the thumb extensors and abductor were motored by the flexor carpi ulnaris as well. However, it was difficult to fully determine from Bevin’s article the approximate level of the radial nerve injury in the patients reviewed.

Burkhalter also advocated early tendon transfer because he believed the transfer acts both as a substitute during regrowth of the nerve or when lesions are irreparable and also as a helper during reinnervation. In a recent article, Kruft et al. reported that irreversible radial nerve paralysis should be treated with early tendon transfer. They reported 43 patients who underwent tendon transfer, with 38 patients ultimately returning to their original jobs. The authors qualified their results by stating that tendon transfers “never fully replace an intact radial nerve for the purpose of controlling the hand.”

Elton and Omer observed that patients with radial nerve paralysis treated by tendon transfer often experienced extensor tightness, which prevented simultaneous flexion of the wrist and fingers. Barton described this as a “rather unnatural movement, seldom needed in ordinary life.” Several authors have thought that the greatest functional loss after radial nerve palsy was not the loss of finger extension, but instead the loss of power grip, which cannot be easily recreated with standard tendon transfers. As such, it is important to fully examine alternative approaches to treating radial nerve palsy to decrease the long-term morbidity associated with tendon transfers that clinically often appear “unnatural.”

Nerve Transfer

In 1948, Lurje described the use of nerve transfers for severe brachial plexus injuries when other options were not available.

Currently, nerve transfers are typically performed under limited circumstances such as brachial plexus avulsions, when no other options are available.
The median nerve has a limited number of anatomic variations in the forearm; therefore, it provides several dependable sources for nerve transfer to the distal radial nerve. Nerve transfers in patients with radial nerve paralysis may provide a useful alternative to tendon transfers in patients with delayed presentation or high proximal nerve injuries or in situations of complete loss of nerve function however additional experience with this technique is needed before definitive recommendations regarding its indications and use can be made.

References

Lowe, James B. III, M.D.. Sen, Subhro K. M.D.. Mackinnon, Susan E. M.D.. Current Approach to Radial Nerve Paralysis. Plastic & Reconstructive Surgery. 110(4):1099-1113, September 15, 2002.

Mazurek, Michael T. MD. Shin, Alexander Y. MD. Upper Extremity Peripheral Nerve Anatomy: Current Concepts and Applications. Clinical Orthopaedics & Related Research. 1(383):7-20, February 2001.

Ristic, Sasha MD. Strauch, Robert J. MD. Rosenwasser, Melvin P. MD. The Assessment and Treatment of Nerve Dysfunction After Trauma Around the Elbow. Clinical Orthopaedics & Related Research. (370):138-153, January 2000.