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Am Fam Physician. 2021;103(5):275-285

This clinical content conforms to AAFP criteria for CME.

Author disclosure: No relevant financial affiliations.

Peripheral nerves in the upper extremities are at risk of injury and entrapment because of their superficial nature and length. Injury can result from trauma, anatomic abnormalities, systemic disease, and entrapment. The extent of the injury can range from mild neurapraxia, in which the nerve experiences mild ischemia caused by compression, to severe neurotmesis, in which the nerve has full-thickness damage and full recovery may not occur. Most nerve injuries seen by family physicians will involve neurapraxia, resulting from entrapment along the anatomic course of the nerve. In the upper extremity, the brachial plexus branches into five peripheral nerves, three of which are commonly entrapped at the shoulder, elbow, and wrist. Patients with nerve injury typically present with pain, weakness, and paresthesia. A detailed history and physical examination alone are often enough to identify the injury or entrapment; advanced diagnostic testing with magnetic resonance imaging, ultrasonography, or electrodiagnostic studies can help confirm the clinical diagnosis and is indicated if conservative management is ineffective. Initial treatment is conservative, with surgical options available for refractory injuries or entrapment caused by anatomic abnormality.

Peripheral nerves in the upper extremity are at risk for injury and entrapment. Their long course from the central nervous system through the extremity puts them at risk of compromise at narrow anatomic tunnels and areas of edema and trauma. The brachial plexus branches into five peripheral nerves, three of which are commonly entrapped at the shoulder, elbow, and wrist. Epidemiology data on entrapment neuropathies are sparse. Carpal tunnel syndrome is the most common with a prevalence of 3% in the general population (15% in the workforce).1 Cubital tunnel syndrome is also relatively common, with one U.S. metropolitan area reporting a prevalence of 1.8% to 5.9%.2 Overall prevalence of peripheral neuropathies in the general population is unclear.

Pathophysiology

Mechanisms of nerve injury can include direct pressure, stretch, overuse of a joint, or microtrauma. Prolongation of these injurious mechanisms causes fibrosis, resulting in a larger degree of injury.35 More specifically, nerve injury is divided into three grades of increasing severity: neurapraxia, axonotmesis, and neurotmesis. Neurapraxia is injury that damages the myelin sheath but not the axon. Complete recovery is possible in days to weeks. Axonotmesis extends damage to the axon but preserves the connective tissue framework. This can lead to subsequent degeneration distal to the lesion. Because of the slow rate of axonal regeneration, recovery can take years, with complete recovery often unachievable. Neurotmesis is the total or partial disruption of the entire nerve fiber, including the connective tissue framework. Full clinical recovery is usually not achieved.6,7 How long compression must be present to cause permanent loss of conduction or fibrosis is not well defined in the literature.

History and General Examination

Nerve entrapment should be suspected when limb weakness, pain, or paresthesia is present and not caused by another etiology, such as systemic disease or muscle injury. History should focus on known trauma, time course, aggravating activities, and distribution of symptoms. In the absence of significant trauma, evaluation of range of motion and muscle strength is needed, and inspection, palpation, and neurologic testing of the area should be performed with assessment of the cervical spine.8 Knowledge of myotomes and dermatomes helps localize the specific nerve injured911 (Table 1,10,11 Figure 1,12 and Figure 212 ).

Joint functionCervical rootMusclesNerves
Shoulder abductionC5DeltoidAxillary
Elbow flexionC5, C6BicepsMusculocutaneous
Elbow extensionC7TricepsRadial
Forearm pronationC6, C7Pronator teresMedian
Forearm supinationC6SupinatorRadial
Wrist flexionC7Flexor carpi radialis, flexor carpi ulnarisMedian and ulnar
Wrist extensionC6, C7Extensor carpi radialis brevis, extensor carpi radialis longusRadial
Finger flexionC8Flexor digitorum profundus, flexor digitorum superficialisUlnar and median
Finger extensionC7, C8Extensor digitorum, extensor indicis, extensor digiti minimiRadial (posterior interosseous)
Thumb abductionC7, C8Abductor pollicis longusRadial (posterior interosseous)
Thumb flexionC8, T1Flexor pollicis longusMedian (anterior interosseous)
Finger abduction or adductionT1Intrinsic hand musclesUlnar

Common Nerve Injuries and Entrapment Syndromes of the Upper Extremity

Table 2 summarizes specific physical examination findings and treatment options associated with each nerve.1338

NerveCharacteristicsSensory deficitsMotor deficitsConservative therapySurgical indications
Axillary nerveLateral shoulder region paresthesia, shoulder movement weakness in all planes, difficulty with overhead activitiesLateral shoulderDeltoid, teres minorPhysical therapy, monitoring recovery with serial examination vs. electromyography and nerve conduction studiesNo electrophysiologic improvement after 3 to 4 months of conservative treatment
Long thoracic nerveScapular wingingNoneSerratus anteriorPhysical therapy, avoidance of aggravating activitiesPenetrating trauma resulting in nerve transection, no improvement after 18 to 24 months of conservative treatment
Median nerve at the elbow or forearm anterior interosseous nerve branchNo pain; thumb weakness; unable to make OK sign; if patient is unable to make OK sign but has sensory deficits, consider a proximal median nerve injuryNoneFlexor pollicis longus, flexor digitorum profundusRest, splinting, and observationSpace-occupying lesion, no improvement after 3 to 4 months of conservative treatment
Median nerve at the elbow (pronator syndrome)Aching pain in the proximal volar forearm; palm, thumb, or index finger paresthesiaThumb, index and middle fingers, and radial side of ring fingerVaried but may include weakened grip strengthAvoidance of aggravating activities, rest, trial of NSAIDs, steroid injectionSpace-occupying lesion, no improvement after 3 to 4 months of conservative treatment
Median nerve at the wrist (carpal tunnel syndrome)Pain in the wrist and hand, occasionally radiating to the forearm; paresthesia in the first three digits; weak grip strength due to weakness of thumb abduction and opposition resulting in difficulty with tasks such as opening doors; thenar eminence atrophy in advanced diseaseThumb, index and middle fingers, and radial side of ring fingerAbductor pollicis brevis, first or second lumbricalSplinting, physical therapy, yoga, and acupuncture for the short term
Cochrane review: nocturnal splinting more effective than placebo13
Maximal benefit of conservative treatment typically achieved around 3 months
Steroid injection
Cochrane review: symptomatic improvement for up to one month with steroid injection; more recent studies show up to 10 weeks of improvement and delay of surgery for up to 1 year14
Early surgery: evidence of moderate to severe median nerve damage on electromyography
Significant weakness of grip strength; thenar eminence atrophy; no improvement after 3 to 4 months of conservative treatment
Cochrane review: surgical decompression is better at long-term symptom management than splinting alone; unclear if surgery is better than steroid injection, especially in those with mild symptoms15
Cochrane review: endoscopic and open techniques are equally effective; however, endoscopic recovery is shorter by 8 days16
Radial nerve at the elbow (posterior interosseous nerve)Weakness in finger extension, weakness of ulnar deviation, wrist extension can be maintained (because of sparing of extensor carpi radialis longus), pain is rareNoneExtensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, supinatorRest, activity modification, splinting, stretching, NSAIDs; steroid injection can be therapeutic and diagnosticSignificant motor weakness is present, no improvement after 3 to 4 months of conservative treatment
Radial nerve at the elbow (superficial radial nerve)Pain 3 cm to 4 cm distal to lateral epicondyle, often causes pain at nightLateral forearmNoneRest, activity modification, splinting, stretching, NSAIDs; steroid injection can be therapeutic and diagnosticSurgery rarely required
Radial nerve at the spiral groove (radial neuropathy [Saturday night palsy])Weakness in finger and wrist extension, paresthesia of forearm and handPosterior forearm and dorsal handBrachioradialis (elbow flexion); extensor carpi radialis longus; branches distally include superficial radial nerve and posterior interosseous nerve, which can also be affectedAvoidance of repeat compression, physical therapy nearly 100% effective at 6 months based on small observational study, cock-up splint for normal hand functionFracture of the humerus resulting in nerve compromise
Radial nerve at the wrist (handcuff neuropathy)Pain and paresthesia of the hand; if motor findings are present, consider a higher radial nerve lesionDorsal radial handNoneEliminate external compression, steroid injectionSurgery rarely required, no improvement after 3 to 4 months of conservative treatment
Spinal accessory nerveWeakness in shoulder abduction (> 180 degrees), scapular wingingNoneTrapezius (shoulder shrug) and sternocleidomastoidPhysical therapy, avoidance of aggravating activitiesPenetrating trauma resulting in nerve transection, no improvement after 18 to 24 months of conservative treatment
Various nerves at brachial plexus levelTransient paresthesia and weakness from neck or shoulder traveling down the armVaried based on affected nervesVaried based on affected nervesRest, physical therapy, pain controlEvidence of anatomic abnormalities (foraminal stenosis) predisposing to repeat injury
Suprascapular nerveWeakness in shoulder flexion, abduction, external rotationSensory to shoulder jointSupraspinatus (shoulder abduction) and infraspinatus (external rotation of the shoulder)Physical therapy to maintain range of motion, activity modification to limit overhead activitiesEarly surgery for space-occupying lesion (i.e., ganglion cyst)
Systematic review of 21 studies (275 athletes) showed lower patient-reported pain as tracked by visual analog scale and a return to sport of 92% of athletes17
Ulnar nerve at the elbow (cubital tunnel syndrome)Pain, paresthesia, numbness in the fourth and fifth digits; weakness in finger abduction, thumb abduction, and thumb-index pincer; positive Tinel sign at the cubital tunnel; weak wrist flexion not due to the median nerve innervation of flexor carpi radialis and flexor digitorum superficialis, which compensate for loss of flexor carpi ulnarisHypothenar eminence, fifth finger, and ulnar side of fourth fingerIntrinsic hand muscles, flexor carpi ulnarisActivity modification, NSAIDs, elbow pads, physical therapy, night splinting in 45 degrees of extension with neutral forearm, steroid injectionNo improvement after 3 to 4 months of conservative treatment
Most common procedures are surgical decompression or nerve transposition; in one Cochrane review they were equally effective18
Ulnar nerve at the wrist (cyclist's palsy)Atrophy of intrinsic hand muscles (hypothenar, lumbrical, interosseous); pain, paresthesia, numbness of the hand; positive Froment sign (Figure 6; https://www.youtube.com/watch?v=WnTVWnTFymA)Hypothenar eminence, fifth finger, and ulnar side of fourth fingerIntrinsic hand muscles (grip strength)Patient education, activity modification, padding on handlebars, splinting, physical therapy, and NSAIDs; steroid injection not indicated because causes are usually related to structural or mechanical abnormality; drain ganglion cyst if this is the causeManagement of anatomic cause (e.g., ganglion cyst, lipoma, hook of hamate fracture), no improvement after 2 to 4 months of conservative treatment
Postsurgical splinting and rehabilitation recommended
Typical return to work in 6 to 8 weeks

SHOULDER AND ARM

Brachial Plexus. Brachial plexus injury is commonly associated with contact sports. Known as a stinger, this injury causes transient paresthesia and weakness radiating from the neck in the distribution of the injured nerve root. Proposed mechanisms are traction, compression, or direct trauma to the brachial plexus or cervical nerve root (e.g., leading with the shoulder during a tackle in football).20 The most common distribution is the C5 and C6 myotomes and dermatomes. Following a first episode, return to play is acceptable when there is complete resolution of symptoms and cervical spine injury has been excluded.32,39 Persistent or recurrent stingers prompt additional evaluation for cervical stenosis or other bony abnormalities.32

Axillary Nerve. The axillary nerve is vulnerable as it passes around the humerus and through the quadrilateral space of the posterior shoulder. Shoulder dislocations, repetitive use injuries, humeral neck fractures, and local pressure (e.g., from crutches) are mechanisms of injury.19 Damage to the axillary nerve results in paresthesia or pain of the lateral shoulder and weakness in shoulder external rotation, extension, abduction, and forward flexion.

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