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
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
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
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
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.
Last updated
19/08/2004
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