The radial nerve (RN) is an upper extremity peripheral nerve. It can be injured or entrapped at many areas along its course.This article will review injuries along the radial nerve proper, the posterior interosseous nerve (PIN), and at the superficial radial sensory nerve (RSN). RN injury can cause weakness in the triceps, wrist and finger extension, and abnormal sensation of the dorsum of the first, second and third digits of the hand.
Etiology can be from trauma, compression, entrapment, or other medical conditions.
- Medical conditions
- Lead intoxication can cause radial palsies
- Mononeuropathy multiplex can be caused by infections, vasculitis, autoimmune diseases, and more.
- The most common traumatic cause is mid-shaft fracture of the humerus. Of course, penetrating injuries at any point along the RN can cause dysfunction.
- Compression and entrapment can be from:
- Compression of the superficial radial sensory nerve at the wrist1
- Supinator muscle entrapment of the posterior interosseous nerve
- Direct pressure on the RN in the spiral groove
- Crutches in the axilla
- Tumors can invade at any point along the nerve.
Epidemiology including risk factors and primary prevention
The RN is the peripheral nerve that is most commonly injured by trauma.
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 Anatomy4
The RN receives innervation from C5-T1 and originates from the posterior cord of the brachial plexus. In the upper arm, the RN branches to the triceps and anconeous, as well as the 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, which is the site for radial tunnel syndrome. The RN supplies the brachioradialis and extensor carpi radialis (ECR) longus before dividing 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 a PIN injury will cause weakness in the extensor muscles of the wrist and fingers.
The RSN goes distally down the anterolateral forearm, becoming more superficial and radial. It has two main branches, the lateral and medial branches, which innervate the dorsal radial aspect of the hand and dorsum of the radial 3.5 digits.6 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)
Handcuff Neuropathy (Cheiralgia paresthetica)
Tightened handcuffs can cause superficial radial neuropathies but also can affect the median and ulnar nerves. The RSN is affected in 78-81% of cases. Symptoms are numbness and paresthesias in the dorsolateral hand. Physical findings of hand edema and wrist abrasions and bruising are common. Follow-up studies indicate that superficial radial neuropathies can be permanent and can produce longstanding dysesthesias.8
This is an entrapment of the RSN at the wrist. In patients with DeQuervain’s tenosynovitis, secondary irritation of the RSN is frequent. It presents with pain, numbness and paresthesias from the radial wrist to the thumb, and complaints of pain over the distal radial forearm. Dysesthesias are common. Symptoms commonly increase with wrist movement. There may be a positive Tinel sign over the RSN, exacerbated with hyperpronation. Physical findings can mimic DeQuervain’s tenosynovitis.
The PIN can become entrapped at the level of the supinator muscle. 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
Supinator entrapment of the PIN can alternatively present without weakness but with forearm aching, similar to a resistant lateral epicondylitis. Maximal tenderness is distal to that in lateral epicondylitis. This is more common with any repetitive elbow motion. Pain can be elicited with resistive supination.9 MRI may show edema and atrophy of the PIN, and electrodiagnostic studies may be normal. Most patients respond to steroid injection, but surgery may be required. 10
Saturday Night Palsy 11
This is the most common etiology of radial neuropathy, secondary to pressure in the spiral groove at the midhumeral level. Common presentation is when an intoxicated person falls asleep with their arm hanging over the back of a chair. This is commonly a neuropraxia with conduction block that usually resolves in up to 6 months time. A similar syndrome can be seen with honeymoon palsy, where overnight pressure from one person’s head compresses the other person’s radial nerve. This patient may present with wrist drop, weakness in supination and elbow flexion, and sensory changes in dorsolateral hand and forearm, with or without elbow extension weakness.
Humeral Shaft Fractures 2
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 optimal. 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.
Radial neuropathy can result from direct pressure in the axilla from a crutch, especially if it is too long. To differentiate it from a distal RN lesion, triceps weakness should be evident.
Newborn Radial Nerve Palsy 3
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 bands.
Specific secondary or associated conditions and complications
There is 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
2. ESSENTIALS OF ASSESSMENT
Symptoms depend upon where the RN is affected:
- Axilla – extension weakness of elbow, wrist, and fingers with radial sensory loss
- Spiral groove – triceps are spared
- PIN – weakness of wrist, and finger extension, but sensory and radial wrist extension sparing
- Wrist – no motor deficits, only RSN involvement
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 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 can find PIN lesions in some cases where electrodiagnostic studies are normal. 20
Supplemental assessment tools
Electrodiagnostics can help localize the lesion and help with prognosis. Electrodiagnostics can help to differentiate a radial neuropathy from possibilities in the differential diagnosis such as C7 radiculopathy or a posterior cord lesion. The compound motor action potential (CMAP) responses on nerve conduction studies (NCS) has been shown to correlate with prognostic outcome. 21
Potential EMG and NCS findings:
- Spiral groove – Conduction block across the spiral groove, decreased extensor indicis proprius (EIP) CMAP, reduced RSN amplitude. Abnormal spontaneous activity and neurogenic findings in the RN distribution excluding the triceps and anconeous.
- PIN syndrome- Conduction block across the elbow, decreases EIP CMAP, normal RSN amplitude. Abnormal spontaneous activity and neurogenic findings in the PIN distribution.
- Wrist – Normal EMG and NCS except for RSN abnormalities.
3. REHABILITATION MANAGEMENT AND TREATMENTS
Available or current treatment guidelines
Therapy is dependent on the site and cause of the lesion:
With external compression at the spiral groove, conservative management is indicated.
- If no recovery, then 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 – conservative treatment for 6-12 weeks
- Open – 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, repetitive supination of the forearm should be avoided.
- Conservative treatment for 6-12 weeks, then surgery can be considered if no improvement.
- In distal RSN lesions, management is typically conservative.
- Thumb spica splint may help.
- Injections for DeQuervain’s tenosynovitis in Wartenberg Syndrome
- 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 14
Static splinting can have several benefits:
- Stabilizes the wrist
- Improves wrist extension to enhance hand function
- Prevents overstretching of denervated muscles
- Prevents contractures
Dynamic splinting with outriggers
- Simultaneous dynamic thumb and finger extension
- Ineffective in maintaining wrist extension during finger flexion
- Does not fully re-establish the grasp/release pattern
- Consider for RN injury if no recovery
- May allow for finger and thumb extension
- Typical transfers are:
- Pronator teres to ECR longus or brevis
- Flexor carpi ulnaris to extensor digitorum communis
- Flexor carpi radialis to extensor pollicis longus or extensor indicis propius
Patient & family education
Discussing prognosis of nerve lesions 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 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.
4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE
Cutting edge concepts and practice
5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE
Gaps in the evidence-based knowledge
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- Bishop J, Ring D. Management of radial nerve palsy associated with humeral shaft fracture: a decision analysis model. J Hand Surg. 2009;34A: 991-996.
- 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.
- Mahakkanakrauh P, Somsarp V. Dual Innervation of the Brachialis Muscle. Clinical Anatomy. 2002; 15(11):206-9.
- Kishner S , Biundo J. Posterior interosseous neuropathy in rheumatoid arthritis. Journal of Clinical Rheumatology. 1996;2:29-32.
- Arle JE, Zager EL. Surgical treatment of common entrapment neuropathies in the upper limbs. Muscle Nerve. 2000;23:1160-1174.
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- Spinner RJ, Poliakoff MB, Tiel RL. The origin of Saturday night palsy. Neurosurgery. 2002;51:737-741.
- Claessen FM, Peters RM, Verbeek DO, Helfet DL, Ring D. Factors associated with radial nerve palsy after operative treatment of diaphyseal humeral shaft fractures. J Shoulder Elbow Surg. 2015;24(11):e307-11.
- Sadeh M, Gilad R, Dabby R, Blumen SC. Apparent weakness of ulnar-innervated muscles in radial palsy. Neurology. 2004;62(8):1424-1425.
- Colditz JC. Splinting for radial nerve palsy. Journal of Hand Therapy. 1987;Oct-Dec:18-23.
- De Smet L. The DASH questionnaire and score in the evaluation of hand and wrist disorders. Acta Orthop Belg. 2008;74(5):575-81.
- Gummesson C, Ward MM, Atroshi I. The shortened disabilities of the arm, shoulder and hand questionnaire (QuickDASH): validity and reliability based on responses within the full-length DASH. BMC Musculoskelet Disord. 2006;7:44.
- Sear ED, Chung KC. Validity and responsiveness of the Jebsen – Taylor Hand Function Test. J Hand Surg. 2010;35A: 30-37.
- Lee FC, Singh H, Nazarian LN, Ratliff JK. High-resolution ultrasonography in the diagnosis and intraoperative management of peripheral nerve lesions. J Neurosurg. 2011; 114(1): 206-211.
- Dietz AR, Bucelli RC, Pestronk A, Zaidman CM. Nerve ultrasound identifies abnormalities in the posterior interosseous nerve in patients with proximal radial neuropathies. Muscle Nerve. 2016;53(3):379-83.
- Erra C, De Franco P, Granata G, et al. Secondary posterior interosseous nerve lesions associated with humeral fractures. Muscle Nerve. 2016;53(3):375-8.
- Malikowski T, Micklesen PA, Robinson LR. Prognostic values of electrodiagnostic studies in traumatic radial neuropathy. Muscle Nerve. 2007;36:364-367.
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- Freedman M, Helber G, Pothast J, Shahwan TG, Simon J, Sher L. Electrodiagnostic evaluation of compressive nerve injuries of the upper extremities. Orthop Clin North Am. 2012; 43(4):409-416.
Original Version of the Topic
Stephen Kishner, MD and Otono R Silva MD. Radial nerve mononeuropathy. 08/30/2013.
Stephen Kishner, MD
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