Handbook of Clinical Neurology, Vol.

201 (3rd series)

Focal Neuropathies
C. Chalk, Editor
https://doi.org/10.1016/B978-0-323-90108-6.00015-6
Copyright © 2024 Elsevier B.V. All rights are reserved, including those for text
and data mining, AI training, and similar technologies.

Chapter 7

Radial neuropathy
COLIN CHALK⁎

Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada

Abstract
Radial neuropathy is the third most common upper limb mononeuropathy after median and ulnar neurop-
athies. Muscle weakness, particularly wrist drop, is the main clinical feature of most cases of radial
neuropathy, and an understanding of the radial nerve’s anatomy generally makes localizing the lesion
straightforward. Electrodiagnosis can help confirm a diagnosis of radial neuropathy and may help with more
precise localization of the lesion. Nerve imaging with ultrasound or magnetic resonance neurography is
increasingly used in diagnosis and is important in patients lacking a history of major arm or shoulder trauma.
Radial neuropathy most often occurs in the setting of trauma, although many other uncommon causes have
been described. With traumatic lesions, the prognosis for recovery is generally good, and for patients with
persistent deficits, rehabilitation and surgical techniques may allow substantial functional improvement.

INTRODUCTION to lateral and lies in direct contact with the posterior sur-
face of the humerus in the spiral groove. Motor branches
The radial nerve shares motor and sensory innervation of
innervating triceps, and two sensory branches, the dorsal
the upper limb below the elbow with the median and
cutaneous nerve of the arm and forearm, leave the
ulnar nerves, and radial nerve lesions often have impor-
main radial nerve trunk very proximally in the arm, well
tant functional impacts. This chapter begins with an
above the spiral groove. The sensory branches provide
account of the anatomy of the radial nerve, followed cutaneous innervation to the dorsal surface of the arm
by a description of clinical features of lesions according
above the elbow and to the dorsal surface of the forearm.
to location. Aspects of electrodiagnostic and imaging
These radial sensory territories lie adjacent to those of
techniques used to evaluate the radial nerve are presented
the medial brachial and medial antebrachial cutaneous
briefly, followed by a survey of etiologies of radial
nerves, and the boundaries of the sensory distributions
neuropathy. The chapter concludes with a consideration
of these nerves are highly variable between individuals.
of issues in the management of patients with radial
Where the radial nerve lies in the spiral groove of the
neuropathies.
humerus, it is relatively poorly protected from external
trauma and is at risk of collateral injury in fractures of
Anatomy
the shaft of the humerus, making this a frequent site of
The radial nerve arises from the posterior cord of the radial nerve injury. Upon leaving spiral groove, the nerve
brachial plexus and carries motor and sensory fibers from crosses the lateral side of the elbow and comes to lie deep
the C5, C6, C7, and C8 nerve roots. On leaving the bra- to brachioradialis. At this point, 1–3 cm distal to the
chial plexus, the nerve dives into the triceps and initially lateral epicondyle, the nerve divides into a third and final
descends on the surface of the triceps medial head. At the sensory branch, the superficial radial nerve (SRN), and
level of the mid-humerus, the nerve passes from medial a terminal motor branch, the posterior interosseous nerve

⁎
Correspondence to: Colin Chalk, MD, CM FRCPC, Department of Neurology and Neurosurgery, McGill University, Montreal
General Hospital, 1650 Cedar Avenue, L7-313, Montreal, QC, H3G 1A4, Canada. Tel: +1-514-934-8059, Fax: +1-514-934-8265,
E-mail: colin.chalk@mcgill.ca
128 C. CHALK
(PIN). The SRN continues down the forearm along the on the dorsal surface of the upper arm, forearm, and
lateral border of brachioradialis and becomes subcutane- dorsolateral surface of the hand. Weakness of elbow,
ous in the middle third of the forearm. At the anatomical wrist, and finger extension is usually obvious, but elbow
snuffbox, it crosses superficial to the tendon of extensor flexion strength is typically relatively normal, even
pollicis longus and divides into medial and lateral with severe weakness of brachioradialis, owing to the
branches. These innervate the dorsolateral aspect of the preservation of biceps brachii function. Demonstrating
hand and proximal parts of the thumb and lateral 2 or involvement of brachioradialis is best accomplished by
3 fingers. Sensory innervation of the dorsum of the flexing the elbow with the forearm pronated and noting
hand and adjacent dorsal digits is shared between the whether there is palpable contraction of the muscle belly.
SRN and the dorsal cutaneous branch of the ulnar nerve. Lesions more distally in the upper arm above the
A cadaveric dissection study of 150 hands found that elbow can be expected to spare the innervation of triceps
the most common innervation pattern was SRN: lateral (so elbow extension will be preserved) and the cutaneous
2½ digits and dorsal ulnar cutaneous: medial 2½ digits, sensory branches supplying the upper arm and forearm.
but with considerable variability. Side-to-side asymme- Most often lesions in the upper arm are at or near the
try of the innervation patterns of the two hands was spiral groove in the mid-humerus. Patients tend to be
frequent (Sulaiman et al., 2015). A recent study using mainly concerned about wrist and finger drops, and
nerve conduction studies found that dual innervation they may be unaware of sensory impairment on the
of the middle finger by both the SRN and the dorsal ulnar dorsolateral hand until this is demonstrated by the exam-
cutaneous nerve occurred in over one third of normal iner. “Weakness of finger extension” is more precisely
subjects (Hemmi et al., 2021). described as weakness of extension at the metacarpopha-
The PIN pierces the supinator, descends along the langeal (MCP) joints. Extension of the interphalangeal
interosseous membrane between the ulna and radius, joints of the fingers by the median- and ulnar-innervated
and gives off branches to the extensors of the wrist and lumbricals will be preserved. This can be demonstrated
digits. The most common order of muscle innervation if the examiner holds the MCP joints in extension and asks
from the radial terminal motor branch are as follows the patient to extend the fingers. However, the extension of
(proximal to distal): brachioradialis, extensor carpi the interphalangeal joint of the thumb, dependent solely
radialis longus, extensor carpi radialis brevis, supinator, on extensor pollicis longus, will be weak. Testing finger
extensor digitorum communis, extensor carpi ulnaris, abduction in the face of a wrist drop may lead the unwary
extensor digitorum minimi, abductor pollicis longus, to conclude that the patient also has an ulnar neuropathy.
extensor pollicis brevis, extensor pollicis longus, and Proper function of the ulnar-innervated interossei requires
extensor indicis proprius (Mazurek and Shin, 2001). the wrist to be in a neutral or extended position, best
There is considerable variability in the origin of the accomplished by supporting the forearm and hand on a flat
more proximal motor branches, with those proximal to surface when testing finger abduction or adduction.
the supinator often arising directly from the main truck Lesions of the PIN produce a pure motor syndrome, as
of the radial nerve rather than the deep terminal branch the sensory branch innervating the dorsolateral hand
(Węgiel et al., 2023). exits at the level of the elbow. Depending on the lesion
In the proximal forearm, the PIN passes through the site, brachioradialis and supinator may be spared, and
radial tunnel, which is formed by the fibrous proximal only the extensors of the wrist and digits are involved.
edge of supinator (“the arcade of Frohse”) and its deep Partial wrist drop with the radial deviation of the hand
head, before it descends further along the interosseous may occur with a lesion of the PIN distal to the branches
membrane. A syndrome of chronic forearm pain, the innervating extensor carpi radialis longus and brevis,
radial tunnel syndrome, has been attributed to a compres- as these muscles will be spared and unopposed by the
sion of the PIN at this site, but the entity is controversial, paralyzed extensor carpi ulnaris. Partial lesions of the
as is discussed further later. PIN may affect digit extension asymmetrically, due to
different degrees of weakness of the individual slips
of extensor digitorum communis and the extensors of
Clinical features
the thumb, index, and little fingers.
The clinical features of radial neuropathy are determined Lesions of the radial nerve at the wrist affect the
by the site of the lesion. Lesions at the nerve’s origin from terminal cutaneous branch and produce sensory impair-
the posterior cord of the brachial plexus are uncommon ment only. Classically the area involved includes the
and generally occur in the setting of major trauma to the dorsolateral surface of the hand and lateral two or three
upper arm or shoulder. The result is weakness of triceps, digits to the level of the PIP joints, but there is consider-
brachioradialis, supinator, and the entire extensor com- able variability. Dual innervation of the middle finger by
partment of the forearm, along with sensory impairment branches from the radial and ulnar nerves appears to be
 RADIAL NEUROPATHY 129
common (Hemmi et al., 2021). The sensory impairment arm, and the next radial-innervated muscle, usually bra-
generally has little functional impact, although in some chioradialis, just proximal to the elbow. Consequently,
patients, associated neuropathic pain, hyperpathia, or the most common site of radial nerve compression, in
allodynia can be troublesome. the spiral groove of the humerus, can usually be localized
confidently because triceps is spared and brachioradialis
is abnormal.
Electrodiagnosis and imaging
The limitations of electrodiagnostic testing for
The anatomy of the radial nerve makes routine motor and localization in radial neuropathies provide an opportu-
sensory nerve conduction studies more difficult techni- nity for the use of imaging techniques. A summary of
cally than is the case with the neighboring median and studies of imaging of the radial nerve can be found
ulnar nerves. As the nerve is placed relatively deep in in Chapter 2 of this volume. There are few studies
the forearm and upper arm through much of its course, directly comparing electrodiagnosis with imaging in
sites for stimulation in which supramaximal stimulation the evaluation of radial neuropathies. One study reported
for motor nerve conduction studies can reliably be 26 patients with radial neuropathies who had both elec-
achieved are limited. A second problem is the lack of trodiagnostic studies and ultrasonography performed at
an easily accessible small muscle that will produce a the same center (Dietz et al., 2016). In 7 patients, both
well-formed, sharply contoured compound muscle were normal. In the remaining 19, the authors concluded
action potential. The usual compromise is to stimulate that ultrasonography augmented electrodiagnostic find-
the nerve in the proximal forearm and just above the ings in 16. In 2 patients, a nerve tumor was found. In
elbow and to use either the extensor digitorum communis 6 others, ultrasonography showed distinct enlargement
or extensor indicis proprius as the recording site (Kimura of the PIN, separate from enlargement in the main
2013; Preston and Shapiro, 2020). Because the usual two radial nerve truck; the significance of this finding is
stimulation sites are close together, and the nerve is still uncertain. There have also been reports of “hourglass-
placed relatively deep, determining the motor conduction like constrictions” observed by ultrasound in the proxi-
velocity is less reliable than with the median and ulnar mal radial nerve in patients presenting with nontraumatic
nerves. Volume conduction may also make it difficult wrist drop (Qi et al., 2021; Bae et al., 2022). The constric-
to clearly define the onset of the compound muscle action tions have been attributed to a local inflammatory
potential. In addition, identifying whether changes in process leading to edema and structural change in the
compound muscle action potential amplitude between nerve, but good pathological studies are lacking. Some
the proximal and distal stimulation are due to technical advocate surgical procedures such as neurolysis for
factors or true conduction block can be challenging. “hourglass constrictions,” but there are no controlled
Stimulation of the nerve more proximally in the arm studies to support using such techniques.
and the axilla is feasible but generally requires a stimulus It seems likely that ultrasound and magnetic reso-
intensity that patients may not tolerate. The radial nance neurography will become more widely used as
sensory nerve conduction study is technically easier, as equipment and trained personnel become more widely
the terminal radial sensory branch is superficial along available. In patients who develop radial neuropathies
the lateral aspect of the wrist and can easily be stimulated without a clear history of trauma, the threshold for
and recorded. Cho et al. described techniques for sepa- obtaining imaging studies should be low, because the
rately recording sensory nerve action potentials from yield of identifying focal structural lesions with imaging
the medial and lateral branches of the superficial radial is relatively high. In general, ultrasound is at a disadvan-
nerve, arguing that the stimulation of the main trunk tage when a nerve is deeply placed, as is the case with the
alone may miss abnormalities if the medial or lateral radial nerve for much of its course, and magnetic reso-
branches are affected in isolation (Cho et al., 2016). nance neurography is probably the preferable imaging
Generally speaking, the technical factors noted above modality if both are available.
mean that normal values for radial motor nerve conduc-
tion parameters have been more difficult to establish than
Etiologies
with the median and ulnar nerves, and that interpreting
the results in an individual patient relies much more Many etiologies for radial neuropathy have been
on comparison between the affected and normal sides. described. These can be organized into three broad
On the other hand, because the radial nerve innervates groups: (1) etiologies that reflect sites of vulnerability
a dozen muscles, needle electromyography can often due to the nerve’s anatomical relations; (2) etiologies that
be helpful for localization in radial neuropathies. In have been described affecting the radial nerve, but to
particular, there is a long distance between the radial which any mixed nerve may be susceptible; and (3) poly-
innervations of triceps, which is very proximal in the neuropathies that have a predilection to present with
130 C. CHALK
radial nerve territory deficits (and in which further inves- are generally mainly concerned about the wrist and finger
tigation or time demonstrates that the patient’s problem drop and may be unaware of any sensory impairment.
is not confined to the radial nerve). Humerus fracture: The proximity of the radial nerve
to the humerus makes it susceptible to injury in patients
with humerus fractures. About one tenth of patients with
Radial neuropathies in anatomically
humerus fractures have an associated radial neuropathy,
vulnerable sites
with fractures of the mid or distal third of the shaft
Unlike the median and ulnar nerves, the radial is gener- accounting for the majority (Shao et al., 2005, Ilyas
ally well protected by muscle and other soft tissues as it et al., 2020). In addition, iatrogenic radial neuropathy
descends from its origin down the arm. Consequently, related to surgical repair of humerus fractures is esti-
compression injuries of the radial nerve are less often mated to occur in 4% of patients undergoing surgery
seen in day-to-day practice than those of the median (Wang et al., 2009). Most radial neuropathies in the set-
nerve (in the carpal tunnel) or the ulnar nerve (at the ting of closed humerus fractures will improve spontane-
elbow). There are three sites where the radial nerve is ously. Electrodiagnostic studies can provide some guide
relatively vulnerable to injury: in the axilla; in the upper to prognosis. One study found that in patients with a
arm, where the nerve is closely related to the spiral radial compound muscle action potential (CMAP) ampli-
groove of the humerus; and at the wrist, where the termi- tude at least 10% of normal, spontaneous recovery
nal sensory branch lies superficially on the dorsolateral occurred in over 80%. On the other hand, no recordable
surface of the wrist. radial CMAP and no motor unit potential recruitment in
Radial neuropathy in the axilla: At its point of origin brachioradialis 3–6 months posttrauma were predictive
from the posterior cord of the brachial plexus, the radial of a poor outcome (Malikowski et al., 2007). In patients
nerve lies deep and is well protected. Injuries at this site with radial neuropathy associated with humerus fracture
are uncommon and generally occur only in the setting of in whom the status of the nerve is unknown, exploration
high-velocity trauma or missile wounds to the shoulder may be indicated. However, given the high rate of
or proximal arm. However, as the nerve traverses the spontaneous recovery, a period of expectant observation
axilla before descending on the medial head of triceps, is advisable. Controlled studies are lacking, but meta-
it is relatively superficial and is potentially at risk of analysis of retrospective studies suggests that explora-
compression injury. Bilateral radial nerve compression tion should be delayed at least 2 but not more than
in the axilla due to prolonged use of or improperly fitted 6 months in patients who show no clinical or electrodiag-
crutches has been long recognized (Rudin and Levine, nostic signs of recovery (Shao et al., 2005). A more
1951), but there are few good descriptions in the last half recent systematic review of retrospective studies found
century (Poddar et al., 1993). The incidence is unknown. that exploration within 3 weeks of injury was associated
Once recognized and crutch use is discontinued, recov- with recovery in almost 90% and concluded that
ery generally ensues. Crutch paralysis should be prevent- early exploration should be routinely considered (Ilyas
able by ensuring that crutches fit properly, so that the et al., 2020).
patient takes weight mostly on the hands, and a minimum Other causes: Injury to the radial nerve (mainly the
of pressure is exerted against the axilla. Alternatively, posterior interosseous branch) can occur in elbow
Canadian crutches can be prescribed to avoid compres- arthroscopy, particularly with anterolateral portal place-
sion injuries in the axilla, although these may lead to ment (Mercer et al., 2015). In one retrospective series of
PIN compression (Genç et al., 2003). 473 patients, 5 radial nerve injuries were observed,
Radial neuropathy in the upper arm: Compression but these were all transient (Kelly et al., 2001). Other
injuries: In the classical “Saturday night palsy,” an intox- rare causes of radial nerve injury in the upper arm have
icated individual falls asleep with the arm dangling over been described, including compression by prolonged use
the back of a chair, compressing the radial nerve against of automatic BP cuff machines during labor (Bickler
the humerus as it travels in the spiral groove and wakes et al., 1990) or surgery (Lin et al., 2001), with a compres-
with a wrist drop. Elbow extension and sensation in the sion garment for lymphedema (Rhee et al., 2019), as a
upper arm and forearm are spared, as the respective complication of cardiovascular interventions performed
motor and sensory branches leave the main nerve truck via cannulation of the radial artery (Jang et al., 2018),
proximal to the spiral groove. Depending on the severity or in softball pitchers using the “windmill” technique
of the compression, varying degrees of weakness of (Sinson et al., 1994). Compression of the radial nerve
thumb and finger extension (at the metacarpophalangeal in the upper arm can occur in neonates in the setting of
joints), wrist extension, forearm supination, and bra- prolonged or difficult labor. These radial neuropathies
chioradialis will be found, along with sensory impair- generally have a good prognosis and are important to
ment on the dorsolateral surface of the hand. Patients distinguish from obstetrical brachial plexus injuries, in
 RADIAL NEUROPATHY 131
which outcomes are often poor (Hayman et al., 1999, nerve (SRN) lies superficial to the tendon of extensor
Alsubhi et al., 2011). pollicis longus and is vulnerable to compression or other
Posterior interosseous nerve (PIN): Many authors trauma. The resulting radial nerve syndrome (sometimes
consider that the PIN commences when the deep terminal called Wartenberg’s syndrome) is purely sensory, and
branch of the radial nerve emerges from the supinator the affected area involves the dorsolateral surface of the
muscle and thus make a distinction between lesions of hand, sometimes extending onto the proximal phalanges
the PIN and the more proximal portion of the deep of the thumb and lateral three fingers. There is often a clear
terminal branch. Defined in this way, lesions of the history of a traumatic event immediately before the onset
PIN spare extensor carpi radialis longus and brevis and of the sensory symptoms (e.g., in a personal example, a
result in weakness of digit extension, but not wrist drop. hand being jammed against a doorframe while transport-
As the PIN carries no cutaneous sensory fibers, lesions ing a heavy sofa). Musculoskeletal pain from the injury
produce a pure motor syndrome. Posterior interosseous may preoccupy the patient at first, overshadowing the
neuropathies are uncommon complications of fractures radial sensory impairment. “Handcuff neuropathy,” due
of the proximal radius or radial head (Sudhahar and to compression of the SRN by tight handcuffs, is often
Patel, 2004; Yoshida and Tsuchida, 2018) and can be associated with intoxication or forcible restraint (Stone
complications associated with external elbow fixation and Laureno, 1991). The SRN can also be compressed
devices used for the repair of complex or unstable elbow by a watchstrap or by a tight plaster cast or dressing
fractures (Trigo et al., 2017) or open repairs of proximal (Lanzetta and Foucher, 1993) or injured during intrave-
radial fractures (Perretta et al., 2016). Nontraumatic or nous catheter insertion in the “intern’s vein” (the tributary
“spontaneous” PIN lesions have been long recognized. of the cephalic vein that is often prominent on the dorso-
In some patients with “spontaneous” posterior inteross- lateral aspect of the distal radius) (Kvarstein and Jorum,
eous neuropathy, pain in the upper arm or shoulder at 2010). Based on a cadaveric dissection study, Vialle
onset and gradual spontaneous recovery have led to suggested the latter injury can be avoided if the vein is
the idea that these may be variants of acute brachial entered at least 12 cm proximal to the radial styloid process
plexopathy (Parsonage Turner syndrome). As noted (Vialle et al., 2001).
later, there are also numerous case reports of focal The diagnosis of a superficial radial neuropathy is
neoplastic and other mass lesions of the radial nerve that usually clear on clinical grounds. Nerve conduction stud-
present as apparently “spontaneous” wrist or finger drop, ies showing an absent SRN sensory nerve action poten-
and imaging studies, preferably magnetic resonance tial or a reduced amplitude compared to the unaffected
neurography, should be part of the standard investigation side can support the diagnosis. The diagnostic yield of
of a patient with a “spontaneous” posterior interosseous electrodiagnosis may be increased if separate conduction
neuropathy. studies of the medial and lateral branches of the SRN are
A more difficult related problem is the so-called performed (Cho et al., 2016). The SRN can be visualized
radial tunnel syndrome (RTS). This syndrome of chronic by nerve ultrasonography, and this may provide insight
lateral forearm pain has long been controversial, and an into cases lacking a clear history of trauma (Visser,
excellent overview of the history of RTS is provided by 2009). Most patients with SRN improve spontaneously
Stewart (2010). A recent review (Ang et al., 2023) points once the cause is corrected, although exploration and
out that the literature on RTS is complicated by inconsis- neurolysis may be indicated occasionally (Lanzetta and
tent terminology (e.g., RTS vs. “resistant tennis elbow”), Foucher, 1993).
disagreement about diagnostic criteria (e.g., is evidence
of PIN dysfunction needed for the diagnosis?), and a lack
Etiologies not specific to the radial nerve
of controlled studies of treatment. In most accounts of
RTS, the compression of the PIN by the proximal edge In most patients with radial neuropathy, a clear traumatic
of the supinator muscle (the arcade of Frohse), a vascular or mechanical cause can be identified. In those in whom a
loop (the loop of Henry), or hypertrophic forearm clear cause is not apparent, or when the deficit develops
muscles is posited to be the cause of chronic pain in insidiously over weeks to months, a focal lesion that
the forearm, and surgical exploration of the region is might affect any mixed somatic nerve should be consid-
advised. However, clinical or electrophysiological signs ered. Some recently reported examples affecting the
of PIN dysfunction are rarely found, and it seems likely radial nerve include metastatic adenocarcinoma (Liu
that the large majority of patients with RTS should not and Li, 2023), leprosy (Kumar et al., 2018), ganglion cyst
be considered to have a radial neuropathy. (Park et al., 2021), and intraneural leiomyoma (Lee et al.,
Radial neuropathy at the wrist: On the lateral surface of 2020). When there are clinical findings and electrodiag-
the wrist, the terminal sensory branch or superficial radial nostic evidence of a radial neuropathy, but a traumatic or
132 C. CHALK
mechanical cause is not evident, imaging of the nerve fitting and adjustment by a hand therapist, but measures
should be performed. Magnetic resonance neurography such as the 9-hole peg test show better hand function com-
is probably preferable to ultrasound, given that the radial pared to static splints (Cantero-T
ellez et al., 2020).
nerve lies deep in the arm for much of its course.
MEDICATION FOR NEUROPATHIC PAIN
Polyneuropathy presenting with Sensory impairment produced by radial nerve lesions is
radial neuropathy not extensive and generally has little or no functional
The possibility that a patient who presents with a wrist impact. Some patients with superficial radial nerve
drop may in fact have a polyneuropathy rather than a lesions experience neuropathic pain in addition to sen-
process isolated to the radial nerve should be borne in sory impairment, and treatments for neuropathic pain
mind. Perhaps the most frequent entity to consider is such as gabapentinoids, tricyclics, or topical vapocoolant
multifocal motor neuropathy (MMN), in which wrist preparations may be helpful.
or finger extensor weakness, often unilateral, is the
presenting feature in up to one third of patients (Slee SURGICAL EXPLORATION
et al., 2007). MMN was not widely recognized until
As noted earlier, because the radial nerve is well pro-
the 1990s, and it is possible that some of the patients
tected through most of its course, minor or unappreciated
with “idiopathic” posterior interosseous neuropathies
repetitive trauma is unlikely to be the cause of radial
reported in older literature in fact had MMN (Stewart
neuropathy. Thus, radial neuropathy developing in the
2010). Unilateral wrist drop as the presenting feature
absence of an obvious history of trauma should raise
of multifocal acquired demyelinating sensory and motor
the suspicion of a focal mass lesion, and the clinician
polyneuropathy (MADSAM or Lewis-Sumner syn-
should have a low threshold to request imaging studies.
drome) has been reported (Zwicker et al., 2022).
Unclear imaging findings may in turn lead to a need for
Unexpectedly severe or persistent wrist drop occurring
surgical exploration to secure a diagnosis.
after seemingly trivial episodes of trauma or compression
The question of whether surgical exploration is
may sometimes prove to be the presenting episode
indicated in patients with radial neuropathy in the setting
of hereditary neuropathy with liability to pressure palsies
of humerus fractures is a common dilemma. If the frac-
(HNPP) due to a deletion of the PMP-22 gene (Attarian
ture requires open reduction, the surgeon will generally
et al., 2020). Evidence of mild generalized slowing of
be able to assess if the radial nerve is in continuity at
nerve conduction velocities can be a clue to the presence
the time of the surgery. If the fracture can be managed
of HNPP. Onset with wrist drop (typically bilateral)
by closed reduction, the status of the nerve is unknown,
is characteristic of polyneuropathy due to acute lead
and imaging is often of limited value. If there is no
intoxication (Thomson and Parry, 2006), and porphyric
clinical evidence of function distal to the lesion, EMG
neuropathy presenting with bilateral radial neuropathy
may sometimes demonstrate that the patient can still
has been described (King et al., 2002).
activate a few motor unit potentials, implying that the
nerve is at least partly in continuity. Even in patients
Management who lack clinical or electrodiagnostic evidence of pre-
ORTHOSES served distal function acutely, the prognosis for recovery
of function is still good (Shao et al., 2005), and watchful
A wrist drop produces an important impairment of hand waiting is advisable. Prospective studies of the optimal
function and affects essentially all object-handling tasks duration of waiting are lacking; retrospective studies
because of loss of grip strength and wrist stability. suggest at least 2 but not more than 6 months, although
A persistent wrist drop may also lead to the shortening some data suggest that earlier exploration is associated
of the unopposed flexor muscles and reduced mobility with better outcomes (Ilyas et al., 2020).
or even contracture of the wrist. An orthotic device can
help prevent contracture, and by stabilizing the wrist in
NERVE GRAFTING AND TENDON OR NERVE TRANSFERS
its functional neutral position, an orthosis can improve
hand function. The simplest orthosis, a static splint, is rigid Weakness of finger and especially wrist extension is the
and holds the wrist in a neutral position. More sophisticated principle source of long-term disability in most patients
variants, so-called dynamic splints, also suspend the with radial neuropathy, because the resulting impairment
proximal phalanges of the fingers with springs or elastics of grip strength and wrist stability affects all object-
and hold the thumb in partial extension and abduction. handling tasks. Proximal radial neuropathies, in which
Dynamic splints are more expensive and require careful there is also weakness of elbow extension, are less
 RADIAL NEUROPATHY 133
common and typically occur in the context of major Bae D, Kang S, An J (2022). Spontaneous radial nerve palsy
trauma, with other disabling musculoskeletal injuries. showing torsion in the radial nerve trunk and edema in
Several surgical techniques may be considered to the posterior interosseous nerve. Acta Neurol Belg 122:
improve wrist and finger extension in patients with radial 1077–1079.
Bertelli J, Ghizoni M (2016). Results of nerve grafting in
neuropathies (El Madhoun and Midha, 2016). A variety
radial nerve injuries occurring proximal to the humerus,
of tendon transfer procedures have been devised, the
including those within the posterior cord. J Neurosurg
choice depending on the nature of the patient’s deficit 124: 179–185.
and the preference of the surgeon (to improve wrist Bickler P, Schapera A, Bainton C (1990). Acute radial nerve
extension, tendon of pronator teres to extensor carpi injury from use of an automatic blood pressure monitor.
radial brevis; for finger extension, flexor carpi radialis Anesthesiology 73: 186–188.
to extensor digitorum communis; for thumb extension, Cantero-T
ellez R, Villafañe J, Garcia-Orza S et al. (2020).
palmaris longus to extensor pollicis longus). An alterna- Analyzing the functional effects of dynamic and static
tive approach, gaining popularity in the last two decades, splints after radial nerve injury. Hand Surg Rehabil 39:
is nerve transfer, in which fascicles from a healthy motor 564–567.
nerve are grafted to a motor branch of the injured nerve, Cho N, Kim K, Park B et al. (2016). Superficial radial
sensory neuropathy: medial and lateral branch injury.
distal to the site of injury, and close to the denervated
Muscle Nerve 53: 690–693.
muscles. For radial neuropathy, the transfer of median
Dietz A, Bucelli R, Pestronk A et al. (2016). Nerve ultrasound
nerve fascicles from flexor carpi radialis to the PIN has identifies abnormalities in the posterior interosseous nerve
the potential to improve function in several denervated in patients with proximal radial neuropathies. Muscle
muscles. For proximal radial nerve lesions in which there Nerve 53: 379–383.
is also triceps weakness, nerve grafting with sural nerve El Madhoun T, Midha R (2016). Editorial: radial nerve.
can often restore reasonable elbow extension (Bertelli J Neurosurg 124: 175–178.
and Ghizoni, 2016). For a more detailed account of Genç H, Levento glu A, G€uney F et al. (2003). Posterior inter-
nerve grafting and tendon and nerve transfers in radial osseous nerve syndrome caused by the use of a Canadian
and other mononeuropathies, the reader is referred to crutch. Muscle Nerve 28: 386–387.
Chapter 14 of this volume. Hayman M, Roland E, Hill A (1999). Newborn radial nerve
palsy: report of four cases and review of published reports.
Pediatr Neurol 21: 648–651.
Hemmi S, Kurokawa K, Nagai T et al. (2021). Anatomical
CONCLUSIONS
variations of the superficial branch of the radial nerve
The lesion in a patient with a radial neuropathy can and the dorsal branch of the ulnar nerve: a detailed
usually be localized by an understanding of the nerve’s electrophysiological study. Muscle Nerve 63: 913–918.
anatomy alone, sometimes supplemented by information Ilyas A, Mangan J, Graham J (2020). Radial nerve palsy recov-
from electrodiagnostic testing or imaging. In most ery with fractures of the humerus: an updated systematic
review. J Am Acad Orthop Surg 28: e263–e269.
patients with radial neuropathy, there is a clear history
Jang A, Yu J, Oh P et al. (2018). Radial motor nerve palsy fol-
of trauma, but in patients without antecedent trauma,
lowing transradial coronary intervention. Circ Cardiovasc
or insidious onset and progression, imaging studies, Interv 11: e007203.
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