The radial nerve (RN) is an upper extremity peripheral nerve and the main nerve to the extensor compartments of the upper extremity. It can be injured at multiple locations along its course. This article will review injuries to the radial nerve proper, and to its main branches, the posterior interosseous nerve (PIN), and the superficial radial sensory nerve (RSN). Depending on the location, RN injury can cause weakness of elbow extension and wrist and finger extension, resulting in wrist drop and grip weakness, as well as abnormal sensation of the posterior and lateral arm, the posterior forearm, and the dorsum of the first, second and third digits of the hand.
Etiology of RN injury includes trauma, compression, entrapment, and various medical conditions that affect the nerves.
Trauma is the most common cause of RN injury. The most common traumatic cause is mid-shaft fracture of the humerus. Prevalence of radial nerve palsies after a fracture of the humeral shaft as determined by systematic review of 21 studies is 11.8%29, with certain locations of humeral shaft fractures more likely to result in radial nerve injury, and with incidence of RN palsy of up to 22% described for Holstein-Lewis humeral shaft fracture.30 Other traumatic injuries at any point along the RN are less common, and cause specific dysfunctions depending on the location of the lesion.
External compression of the nerve has been described from:
- Use of axillary crutches causing proximal RN lesions in the axilla
- Direct pressure on the RN in the upper arm, such as can occur in “Saturday night palsy” or “Honeymoon palsy
- Compression of the superficial radial sensory nerve at the wrist1 also variably termed “Handcuff palsy” or Wartenberg Syndrome31
Entrapment neuropathies can occur along the course of the nerve but are most common in the forearm. These predominately affect the posterior interosseous nerve (PIN).
- The PIN can be entrapped at the lateral intermuscular septum of the arm, termed “Radial tunnel Syndrome”
- Most commonly the PIN can be entrapped at the arcade of Frohse at the supinator muscle, termed “Supinator Syndrome”
- Other focal entrapments are less common
Various medical conditions can result in radial nerve injury
- Lead intoxication historically caused radial palsies, “Saturnine palsy”11
- Infections, vasculitis, autoimmune diseases, and more can cause a nerve condition called Mononeuropathy multiplex, which can affect the radial nerve
- Tumors can invade at any point along the nerve.
Epidemiology including risk factors and primary prevention
The exact prevalence of RN injuries is unknown. Humerus fractures, primarily midshaft, result in a 2-18% occurrence of RN injury.2 Other common etiologies include falls and motor vehicle accidents. No racial or gender predilection has been shown. Newborn radial neuropathy is very rare, occurring with a frequency of 0.4-2.5 per 1,000 births.3
Radial Nerve Anatomy
The RN receives innervation from C5-T1 and originates from the posterior cord of the brachial plexus4. Within the axilla the RN is located posterior to the axillary artery. It then descends into the upper arm where it branches to the triceps and anconeus, and supplies multiple sensory branches supplying the posterior arm and forearm. The RN has potential for injury as it courses down the posterior upper arm and around the posterior humerus, particularly at the midshaft. The RN then courses over the spiral groove of the humerus before it supplies the brachioradialis and extensor carpi radialis (ECR) longus. It then divides into the PIN and the RSN. In 30-50% of population there is a fibrous band at the arcade of Frohse at the proximal head of the of the supinator muscle.5 The PIN emerges from the supinator and can become entrapped at the opening of the supinator muscle as it abuts the arcade or within the supinator itself.
The RSN branches off the main radial nerve at or around the lateral humeral epicondyle below the brachioradialis and progresses distally along the anterolateral forearm, becoming more superficial and radial. It branches into two main branches 5 cm proximal to the radial styloid; the palmar and dorsal branches, which innervate the dorsal radial aspect of the hand and dorsum of the radial 3.5 digits24. This is the site of handcuff neuropathy and Wartenberg syndrome.
There are some variations. The ECR brevis may be supplied by the RN proximal to the PIN, and the brachialis may be supplied by both the radial and musculocutaneous nerves.7
Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)
Saturday Night Palsy/ Honeymooner’s Palsy
Saturday Night Palsy can occur when an intoxicated person falls asleep with their arm hanging over the back of a chair or another firm edge (park bench or table, for example)11. This situation commonly results in a neurapraxic type lesion with conduction block that usually resolves in up to 6 months’ time. A similar syndrome can be seen with Honeymooner’s palsy, where overnight pressure from one person’s head compresses the other person’s radial nerve on the lateral surface of the arm. RN lesions after prolonged non-invasive blood pressure monitoring with a cuff at the upper arm have also been described32. The clinical presentation of these injuries depends on the level at which the radial nerve is compromised. If compression occurs in the axilla, triceps function can be affected. However if compression occurs around the spiral groove, the patient may be more likely to present with variable weakness in elbow flexion, wrist drop, weakness in supination and elbow flexion, and sensory changes in dorsolateral hand and forearm.
Radial neuropathy can result from direct pressure in the axillary region from a variety of reasons, including bullet wounds, lacerations, or direct blunt trauma. Use of crutches in the axilla can also cause direct compression, especially if the crutch is too long. To differentiate it from a distal RN lesion, triceps weakness should be evident.
Humeral Shaft Fractures
With closed fractures, there is a high probability of recovery with observation; however, with open fractures the probability of laceration exceeds 40% and early exploration is optimal2. Iatrogenic nerve injury can also occur during surgical repair of humeral diaphysis fracture.12 Clinical findings will vary depending on the location of the fracture along the humeral shaft.
Spiral Groove Syndrome
Similar to Saturday night palsy, a similar picture can occur after callus formation, or orthopedic hardware. Wrist drop with supination and elbow flexion weakness, and sensory changes in superficial RSN will be seen clinically. Elbow extension will be preserved.
The PIN can become entrapped at the level of the supinator muscle at the arcade of Frohse. This can be related to excessive supination or pronation, and is more common in tennis players, violinists, and swimmers. It presents with painless wrist and finger drop with wrist extension weakness, but radial wrist extension and sensation is spared.
With rheumatoid arthritis (RA), elbow synovitis can compress the PIN. The main differential diagnosis with RA is extensor tendon rupture. Elbow joint steroid injection has a 43% success rate. Early surgical nerve decompression, with or without synovectomy, results in good recovery, even in cases of failed joint injection.8
Radial Tunnel Syndrome
This controversial entrapment neuropathy can occur when the radial nerve or PIN pierces the septum between the brachialis and brachioradialis muscle. Patients can present without weakness but with forearm aching, similar to a resistant lateral epicondylitis. Maximal tenderness may be distal to what occurs in lateral epicondylitis. Pain can be elicited with certain provocative maneuvers like resisted supination, passive pronation, and resisted long finger extension. Typically, there is limited objective data to support diagnosis (EMG can be inconclusive) and diagnosis can be made either clinically or through diagnostic injection. Most patients respond to steroid injection, but if non operative management fails surgical release may be considered. 10
Handcuff Neuropathy (Cheiralgia paresthetica)/ Wartenberg Syndrome
The superficial radial nerve can be injured from a number of causes due to its superficial location in the forearm; in the distal forearm or wrist it can be compressed by tight handcuffs, fractures, lacerations, peripheral IV placements, or wrist watch bands.
In “handcuff neuropathy” tightened handcuffs can cause superficial radial neuropathies but also can affect the median and ulnar nerves due to circumferential pressure. If the RSN is affected only sensory symptoms such as numbness and paresthesias in the dorsolateral hand will be produced. Physical findings of hand edema, wrist abrasions, and bruising are common. Symptoms can typically be reproduced with forearm pronation and ulnar wrist flexion.
The differential of RSN entrapment or damage can include DeQuervain’s tenosynovitis. Physical findings can mimic DeQuervain’s tenosynovitis (and frequently Finkelstein sign can also be positive in patients with Wartenberg Syndrome24). Of note, however, patients with pure tendinitis should have normal sensation over the hand’s dorsum. It is possible for a patient to present with both RSN neuropathy and DeQuervain’s tendonitis; proper diagnosis of RSN neuropathy is recommended however due to risk of symptoms progressing to CRPS/ RSD 25.
Newborn Radial Nerve Palsy
This can be seen with intrauterine compression, iatrogenic injections, blood pressure monitoring, humerus fracture, septic shoulder, congenital constriction bands, as well as no identifiable etiology. Rapid recovery is expected except with constriction bands3.
Specific secondary or associated conditions and complications
There can be apparent weakness of ulnar-innervated muscles with radial neuropathy in the absence of ulnar nerve injury. The apparent weakness occurs primarily in the interossei and the abductor digiti minimi. These muscles insert on the extensor expansions, and with radial neuropathy there is unopposed traction on these extensor expansions.13
Essentials of Assessment
Symptoms depend upon site of RN injury/ compression:
- Axilla –
- Motor: weakness of all radial innervated muscles, including elbow extension, possibly elbow flexion, wrist extension, and finger extension
- Sensory: decreased sensation over the posterior arm and forearm
- Spiral groove –
- Motor: triceps are spared, however possible elbow flexion weakness, weakness of wrist and finger extension present
- Sensory: may be present in dorsal aspect of hand and posterior forearm
- PIN –
- Motor: weakness of wrist, and finger extension, but radial wrist extension sparing
- Sensory: no sensory deficits
- Wrist –
- Motor: no motor deficits
- Sensory: impaired sensation over the dorsal radial aspect of the hand
Functional impairment to the hand can be significant with radial neuropathy. Inability to extend and stabilize the wrist causes inability to use long flexors adequately in a reciprocal tenodesis action,14 with resulting loss of grip strength, despite normal ulnar and median nerve function. There are many tools to assess hand function, particularly the Disabilities of the Shoulder, Arm, or Hand Questionnaire (DASH)15, its shorter version, QuickDASH16, and the Jebsen Hand Function Test. 17
X-rays of the humerus and elbow may show osseous causes of potential RN compression. Imaging may show callus formation from a fracture, tumors, or osteophytes. MRI studies may show RA of the elbow with effusions and synovitis, as well as tumors or lipomas. Ultrasound may show dynamic causes of compression.18 Ultrasound can show abnormal nerve characteristics, such as increased nerve cross sectional area, and diminished echogenicity and fascicular structure. 19 US may be able to diagnose PIN lesions in some cases where electrodiagnostic studies are normal. 20
Supplemental assessment tools
Electrodiagnostic testing can help localize the lesion and help with prognosis as well as to differentiate a radial neuropathy from other diagnostic possibilities. Common differential diagnoses include: C7 radiculopathy, posterior cord/ plexus lesion, or central causes
Potential EMG and NCS findings:
- Spiral groove –
- Conduction block across the spiral groove if demyelinating lesion, decreased extensor indicis proprius (EIP) CMAP if axonal loss.
- Reduced superficial radial nerve SNAP amplitude.
- Abnormal spontaneous activity and neurogenic findings in the RN distribution excluding the triceps and anconeus.
- PIN syndrome-
- Conduction block across the elbow if demyelinating lesion, decreased EIP CMAP if axonal loss
- Normal superficial radial nerve SNAP amplitude.
- Abnormal spontaneous activity and neurogenic findings in the PIN distribution.
- Wrist –
- Normal CMAP
- Decreased/ abnormal superficial radial SNAP
- Normal EMG findings
Of note, one of the most important nerve conduction studies mentioned above is the radial motor study, which can be obtained by recording over the EIP and stimulating the radial nerve in the forearm, at the elbow, and below the spiral groove 26. However, it should be mentioned that radial motor studies can be technically difficult due to difficulty isolating a CMAP from the EIP as there will likely be volume conduction from nearby radial innervated muscles. There may also be difficulty with accurate distance measurements due to circuitous radial nerve course in the forearm. Thus the value in performing radial motor studies lies in looking for focal conduction block between proximal and distal recording sites or examining relative CMAP amplitude to assess for axonal loss, rather than measuring conduction velocities.
Management and Treatment
Available or current treatment guidelines
Treatment is dependent on the site and cause of the lesion.
In general, prognosis is excellent for spontaneous recovery in the setting of acute trauma or compression without the nerve being severed. Nearly all patients with acute compressive neuropathies have spontaneous resolution with time33. In the setting of radial palsy as a result of humeral shaft fractures, prognosis differs whether fracture is managed operatively or non-operatively. Spontaneous resolution occurs in approximately 95% of radial palsies occurring with non-operatively managed fractures, and 75% in fractures managed operatively.34
- With external compression at the spiral groove, conservative management is indicated.
- If no recovery, then surgical exploration is considered. 22
- If there is neuroma in continuity, then neurolysis or graft is considered.
- Occupational therapy and wrist splinting help in re-establishing functional use of the hand.
- With humeral fracture, fracture needs to be reduced 11,22
- Closed fracture– conservative treatment for 6-12 weeks
- Open fracture– early nerve exploration
- nerve gap – graft or end-to-end repair
- If no recovery is noted within several months, then exploration for the site of compression or transection with possible surgical re-anastomosis may be indicated.
- With PIN Syndrome, treatment can be operative or non-operative
- Rest, activity modification, stretching, splinting, NSAID’s
- Lidocaine/ steroid injections if compressive mass ruled out
- Repetitive supination of the forearm should be avoided.
- Conservative treatment for 6-12 weeks, then surgical decompression can be considered if no improvement, and/ or if a compressive mass identified
- In distal RSN lesions, management is typically conservative.
- Thumb spica splinting trial
- Rest, activity modification, stretching, splinting, NSAID’s
- In radial tunnel syndrome, prolonged conservative treatment is indicated. If pain does not resolve after 12 weeks, surgery may be considered. 9
Splinting for radial nerve palsy
Many types of splints have been described for patients with radial nerve palsy:
Splinting can be static, dynamic, or a combination of both14. Goal is to maintain range of motion, prevent contracture of all joints of the wrist and hand (especially thumb-index web, all digits at the metacarpal phalangeal/ MCP joint), and assist with function as nerve recovery occurs.
- Can be volar, dorsal, or circumferential
- Volar cock up wrist splint
- Stabilizes the wrist. Consider for higher radial nerve injury that requires more wrist support
- Improves wrist extension to enhance hand function
- Overstretching of denervated muscles
- Overpowering of wrist extensors by flexors
- Limits flexion of fingers
- Prevents use of palmar sensation
Dynamic splinting with outriggers
- Dynamic outriggers extend the fingers and thumb with energy storing materials such as elastic, springs, or spring wire, while still allowing for active flexion
- Simultaneous dynamic thumb and finger extension
- Ineffective in maintaining wrist extension during finger flexion
- Can be cumbersome
- Some studies suggest users do not fully re-establish the grasp/release pattern14
Surgical Management and Treatment
Nerve Repair and Grafting
- Indications for early surgical exploration vary, but typically include: open fractures, penetrating trauma, iatrogenic injury, vascular injury, progressive deficits
- Late surgical exploration is a common strategy for persistent palsies and studies have shown good outcomes with repair, neurolysis, or grafting as far as 3 months after injury
- Repair should be performed tension-free
- Nerve grafting can also be used for residual gap management if distance is too great to overcome by direct epineural repair without tension.
- Consider for RN injury if no recovery
- May allow for restoration of wrist, finger, and thumb extension if performed successfully
- Ideal prerequisites for successful tendon transfers can include (elucidated by Jones, Brand Boyes, Steindler, Bunnell, and others27):
- Supple joints with full range of motion
- Adequate donor tendon strength and excursion
- Intact donor muscle innervation
- Typical transfers are:
- Pronator teres transfer is favored to improve wrist extension
- Can transfer to ECR longus or brevis
- Debate over which transfers provide the best finger and thumb extension
- Flexor Carpi Ulnaris vs Flexor Carpi Radialis vs Flexor Digitorum Superficialis
- Can transfer to extensor digitorum communis to improve finger extension
- Palmaris Longus vs Flexor carpi radialis vs Flexor Digitorum Superficialis
- Can transfer to extensor pollicis longus or extensor indicis propius to improve thumb and index finger extension
- Flexor Carpi Ulnaris vs Flexor Carpi Radialis vs Flexor Digitorum Superficialis
- Pronator teres transfer is favored to improve wrist extension
Patient & family education
Discussing prognosis of nerve lesion may help manage patient expectations and improve patient satisfaction. This conversation can help patients and their families to prepare strategies for daily living while preventing further comorbidities. For example, with PIN lesions, discussion of avoidance of repetitive supination of the forearm is recommended.
Outcome and prognosis depend on the type of injury.
Neurapraxia: normal function is regained in the majority of cases, usually in 2-8 weeks.
Axonotmesis: recovery will generally take longer, but recovery is excellent in most cases. Recovery can be by axon regrowth or sprouting.23 Regrowth, if it occurs, happens at a rate of about 1 mm per day.
Neurotmesis: with discontinuity of the axon and surrounding connective tissue there is poor recovery, even with surgical repair.
Cutting Edge/ Emerging and Unique Concepts and Practice
Gaps in the Evidence- Based Knowledge
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- Hayman M, Roland EH, Hill A. Newborn radial nerve palsy: report of four cases and review of published reports. Pediatric Neurology. 1999;21(3): 648-651.
- Jacobson JA, Fessell DP, Da Gama Lobo L, Yang LJ. Entrapment neuropathies I: upper limb (carpal tunnel excluded). Seminars in Musculoskeletal Radiology. 2010;14(5): 473-486.
- Missankov AA, Sehgal AK, Mennen U. Variations of the posterior interosseous nerve. Journal of Hand Surgery (Br). 2000;25B(3):281-282.
- Cappellari AM, Bona AR, Lukasova K. Electrophysiological study of medial and lateral branches of the superficial radial nerve. Muscle Nerve. 2013;47:105-107.
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Original Version of the Topic
Stephen Kishner, MD, Otono R Silva MD. Radial nerve mononeuropathy. 8/30/2013.
Previous Revision(s) of the Topic
Stephen Kishner, MD. Radial nerve mononeuropathy. 3/27/2017.
Gabrielle Nguyen, MD
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