Peripheral nerve injuries

Last updated: November 27, 2023

Summary

Peripheral nerve injuries result from systemic diseases (e.g., diabetes, autoimmune disease) or localized damage (e.g., trauma, compression, tumors) and manifest with neurological deficits distal to the level of the lesion. They occur as isolated neurological conditions or, more commonly, in association with soft tissue, vascular, and/or skeletal damage. Peripheral nerve injury can cause sensory deficits, loss of motor function, or a combination of both. Diagnosis is based on clinical evaluation, imaging techniques (x-ray, CT/MRI), and electrodiagnostic examination (e.g., nerve conduction study, EMG). Observation and conservative treatment (e.g., activity modification, splinting, electrical stimulation) are indicated in most closed injuries, which have a high rate of spontaneous recovery. Patients with open injuries or long disease courses may require surgical treatment. Recovery from peripheral nerve injury is often incomplete and patients may experience chronic pain.

Types of nerve fibers

Nerve fiber overview
Nerve fibers		Myelination	Impulse conduction velocity (m/s)	Afferent fibers	Efferent fibers
A	Aα (Ia, Ib)	Present	100	Ia: primary afferent fibers of the muscle spindle Ib: golgi-tendon organ	α motor neurons
	Aβ (II)		50	Pressure and fine touch sensations Secondary afferent fibers of the muscle spindle	None
	Aγ		20	None	Muscle spindle
	Aδ (III)		15	Somatic pain Temperature sense	Dorsal root fibers
B			7	None	Preganglionic sympathetic fibers
C (IV)		Absent	1	Mechanoreceptors Visceral pain Polymodal	Postganglionic sympathetic fibers

Types of nerve damage

Classification of peripheral nerve injury is useful for determining the prognosis and choosing a treatment strategy.

Neurapraxia

Compression injury causing temporary disruption of nerve conduction
The whole nerve remains structurally intact.
Good prognosis with complete recovery of nerve function

Axonotmesis ^[1]

The axon is damaged but the perineurium and epineurium remain intact.

Leads to central chromatolysis

Definition: the reaction of a neuronal cell body in response to an axonal injury
Function: increase in protein synthesis to help restore the integrity of the damaged axon
Characteristics
- Swelling of the neuronal body
- Dispersion of the Nissl bodies
- Displacement of the nucleus to the periphery

Results in Wallerian degeneration

Definition: an active neuronal degeneration process in response to axonal injury
Function
- To clear axonal debris and prevent scarring
- Facilitate targeted reinnervation and functional recovery of tissues previously innervated by that axon before injury
Characteristics
- Initially retained electrical excitability of axonal membrane distal to the injury, lasting up to 36 hours
- Progressive degeneration of distal segment cytoskeleton with dissolution of axonal membrane
- Degradation of residual myelin sheath by macrophages and Schwann cells
- The proximal stump either stays in place or retracts slightly
- Ultimately, the cell body will sprout regenerative nerve fibers that, ideally, reinnervate the distal tissues.
- Regeneration is significantly more efficient in the peripheral nervous system than in the central nervous system.
- Good chance of at least partial recovery

Neurotmesis ^[1]

Complete nerve transection
Connective sheath damage
The chances of recovery are very poor without surgical repair.

Traumatic neuroma

Benign, painful nodular thickening caused by nerve regeneration at the site of different forms of nerve injury

Axonotmesis Chromatolysis

Nerve injuries in the upper body

Brachial plexus injuries ^[2]^[3]

Brachial plexus injuries: Erb palsy and Klumpke palsy

Erb palsy

Injury to the upper trunk of the brachial plexus (C5–C6)
Etiology
- Excessive lateral flexion of the neck
  - Trauma (e.g., falling on the head and shoulder in a motorcycle accident)
  - Birth injury: excessive lateral traction on the neck during delivery and shoulder dystocia
Clinical features
- Weakness of muscles in the C5 and C6 myotomes → flexed wrist with an extended forearm and internally rotated and adducted arm (waiter's tip posture)
  - Weak biceps brachii, brachialis, and brachioradialis
    - Impaired flexion and supination of the forearm
    - Absent biceps reflex
  - Weak infraspinatus and supraspinatus → impaired external rotation of the arm
  - Weak deltoid and supraspinatus → impaired arm abduction
  - Weak wrist extensors → impaired wrist extension
- Asymmetric Moro reflex in infants (absent or impaired on the affected side)
- Sensory loss in the C5 and C6 dermatomes (thumb and lateral surface of the forearm and arm)
Treatment
- Immobilization in flexion and external rotation with an abduction brace
- Physiotherapy
- Surgery for severe nerve damage or prolonged cases

For weakened muscles in Erb's palsy, imagine BIRDS eating hERBS served by a waiter: Biceps brachii, Infraspinatus, wRist extensors, Deltoid, Supraspinatus, waiter's tip posture.

Erb palsy (waiter's tip posture) Waiter's tip deformity in Erb palsy

Klumpke palsy

Injury to the lower trunk of the brachial plexus (C8–T1)
Etiology
- Hyperabduction of the arm
  - Trauma (e.g., breaking a fall by grabbing a branch)
  - Birth injury: excessive upward traction on the arm during delivery
- Compression of the lower trunk of brachial plexus (subacute to chronic onset)
  - Pancoast tumor
  - Cervical rib
Clinical features
- Weakness of intrinsic hand muscles (thenar, hypothenar, lumbricals, interossei) → total claw hand (persistent flexion of the interphalangeal joints and extension of the metacarpophalangeal joints in the hand)
- Preganglionic Horner syndrome if injury occurs proximal to the white ramus communicans
- Decreased peripheral pulses if subclavian vessels are compressed by a Pancoast tumor or cervical rib (see “Thoracic outlet syndrome”)
- Absent grasp reflex in infants
- Sensory loss in the C8 and T1 dermatomes (little finger and medial surface of the forearm and arm)
Treatment
- Splinting the hand to correct the claw hand
- Physiotherapy
- Surgery for severe nerve damage

Brachial plexus Klumpke palsy Brachial plexus: interactive 3D Tour

Peripheral nerve injuries in the upper extremity

Distal nerve lesions are more likely to cause claw deformities (e.g., ulnar claw or median claw) because they result in a loss of lumbrical function with intact extrinsic flexors
In proximal nerve lesions, hand distortions (e.g., pope's blessing) are only visible when the patient tries to flex the fingers or make a fist.

Overview of peripheral nerve injuries in the upper extremity
Injured nerve	Nerve roots	Common causes	Motor deficits	Sensory deficits
Axillary nerve injury	C5–C6	Anterior shoulder dislocation Fracture of surgical neck of the humerus Iatrogenic (e.g., shoulder reconstruction procedures, rotator cuff surgery, osteosynthesis of humeral fractures) Compression due to mass in the axilla (e.g., nodular fasciitis, schwannoma)	Paralysis of the deltoid muscle → impaired arm abduction (> 15°) Paralysis of the teres minor muscle → impaired external rotation of the arm Muscle atrophy: flattened deltoid	Lower part of the deltoid region and lateral arm
Musculocutaneous nerve injury	C5–C7	Trauma Upper trunk compression (e.g., Erb palsy)	Paralysis of brachialis and coracobrachialis muscles → impaired elbow flexion Paralysis of biceps brachii → impaired forearm supination Reduced biceps reflex (C5–C6)	Lateral forearm, from the elbow to the base of the thumb
Radial nerve injury	C5–T1	Compression of the radial nerve (most common) within the axilla Crutch palsy Saturday night palsy Mid-arm: midshaft fracture of the humerus Wrist Radial fracture Wearing tight bracelets or handcuffs Repeated supination/pronation (e.g., screwing movements)	Axillary injury: impaired forearm extension at elbow, wrist drop Mid-arm injury: wrist drop ↓ Grip strength: Maximal flexion can only be achieved when the wrist is extended.	Dorsal arm and forearm Hand: dorsal aspect of the thumb, index, and the middle fingers
Median nerve injury	C5–T1	Proximal injury: supracondylar fracture of humerus Distal injury Carpal tunnel compression Wrist laceration (suicide attempt) Pronator teres syndrome: compression of the median nerve between the humeral and ulnar heads of the pronator teres	Atrophy of thenar muscles Impaired flexion of wrist, thumb, index, and middle finger Proximal injury (above the anterior interosseus nerve origin) Hand of benediction (when trying to make a fist) Ulnar deviation upon wrist flexion Distal injury (below the anterior interosseus nerve origin): median claw (when extending the fingers) Deep injury to the wrist or forearm impairing the thenar muscles' functions: ape hand Positive pinch sign in anterior interosseus nerve syndrome	Proximal injury Thenar eminence Palmar aspect of thumb, index and middle fingers, lateral ring finger Distal injury: same as proximal injury
Recurrent branch of median nerve injury	C5–T1	Superficial palm laceration	Ape hand Atrophy of thenar muscles: impaired flexion, abduction, and opposition of the thumb	No sensory deficits
Ulnar nerve injury	C8–T1	Proximal injury Fracture of medial epicondyle of the humerus (funny bone) Cubital tunnel syndrome Distal injury Ulnar tunnel syndrome (from cycling, ganglion cysts) Hook of hamate fracture (typically from falling on an outstretched hand)	Ulnar claw (mainly in distal nerve injuries) Wartenberg sign Froment sign Proximal injury Radial wrist deviation when flexing Inability to flex the ring finger and little finger Impaired flexion of wrist and medial fingers Impaired adduction/abduction of fingers (interossei muscles) Impaired lumbrical muscle action of the little finger and ring finger	Palmar and dorsal aspects of the little finger, medial half of ring finger, and hypothenar eminence

Sensory innervation areas of the peripheral nerves (arm, ventral view) Clinical features of axillary nerve injury Radial nerve neuropathy Thenar atrophy secondary to median nerve injury Proximal and distal median nerve lesions Ulnar nerve neuropathy

Peripheral nerve injuries in the cervicothoracic region

Overview of peripheral nerve injuries in the cervicothoracic region
Injured nerve	Nerve roots	Innervated muscles	Common causes	Motor deficits
Phrenic nerve injury	C3–C5	Diaphragm	See “Phrenic nerve paralysis.”	Elevation of the diaphragm on the side of the phrenic nerve lesion → ↓ pulmonary and cardiac function
Suprascapular nerve injury	C4–C6	Infraspinatus and supraspinatus	Compression Entrapment of the nerve within the suprascapular notch Paralabral ganglion cyst Thickening and/or bony ossification of the overlying superior transverse scapular ligament Major or repetitive trauma	Limited adduction, abduction, and external rotation of the arm Shoulder instability (due to paralysis of rotator cuff muscles)
Dorsal scapular nerve injury	C5	Rhomboid major, rhomboid minor, levator scapulae	Isolated injury is uncommon Usually accompanies injury to the scalene muscles	Lateral winging of the scapula
Long thoracic nerve injury	C5–C7	Serratus anterior	Axillary surgery (e.g., lymph node dissection during mastectomy) Stab wounds Carrying a heavy backpack for a long time	Winged scapula: medial scapula protrudes from the thorax Impaired abduction of the arm beyond 90°
Thoracodorsal nerve injury	C6–C8	Latissimus dorsi, teres major	Surgery in the inferior part of the axilla or on scapular lymph nodes	Latissimus dorsi: limited shoulder retraction, impaired adduction, and internal rotation of the arm Teres major: limited internal rotation and adduction of the arm

Diaphragm innervation: "C3, 4, 5 keep the diaphragm alive."

Medial winging of the scapula

Phrenic nerve paralysis

Anatomical course of the nerve
- Originates as a branch from the cervical plexus of C3–C5
- Passes ventrally on the anterior scalene muscle before descending into the chest wall
- Runs between pleura and pericardium accompanied by pericardiacophrenic artery and vein
- Supplies motor innervation of the diaphragm and sensory innervation of the pericardium, parietal pleura (mediastinal and diaphragmatic part), and peritoneum
Etiology
- Unilateral
  - Trauma
  - Iatrogenic (e.g., cardiac surgery)
  - Compression (e.g., malignancy)
- Bilateral
  - Motor neuron diseases (e.g., amyotrophic lateral sclerosis)
  - Neuropathies (e.g., Guillain-Barré syndrome, post-polio syndrome)
  - Cervical spine surgery
  - Trauma
  - Tumor
Clinical features
- Unilateral paralysis
  - Often asymptomatic
  - Exertional dyspnea possible
- Bilateral paralysis: severe dyspnea
Diagnostics
- Unilateral phrenic nerve paralysis
  - Auscultation
    - Decreased respiratory movement
    - Dull on percussion
  - CXR
    - Ipsilateral diaphragmatic elevation
    - Possibly mediastinal shift
    - Compression atelectasis
  - Fluoroscopy: paradoxical elevation of the paralyzed hemidiaphragm on respiration or on asking the patient to sniff (sniff test)
- Bilateral phrenic nerve paralysis
  - Spirometry: decreased vital capacity
  - Diaphragmatic electromyography
Treatment
- Mechanical ventilation may be required.
- Possible implantation of a diaphragmatic pacemaker

Elevation of the left hemidiaphragm from phrenic nerve paralysis 1/2

Nerve injuries in the lower body

Overview of nerve injuries in the lower body
Injured nerve	Nerve roots	Common causes	Motor deficits	Sensory deficits
Iliohypogastric nerve injury	T12–L1	Iatrogenic injury during abdominal open surgery	Impaired contraction of lower parts of transversus abdominis and internal oblique	Lateral hip Suprapubic region In iatrogenic injury: burning or tingling sensation radiating to regions innervated by the injured nerve
Genitofemoral nerve injury	L1–L2	Iatrogenic injury during abdominal laparoscopic surgery	Paralysis of cremaster (↓ cremasteric reflex)	Anterior scrotum/labia majora Upper anterior and medial thigh (lateral femoral triangle, caudal of inguinal ligament)
Lateral femoral cutaneous nerve injury (meralgia paresthetica)	L2–L3	Compression at the level of the inguinal ligament, caused by: Increased intraabdominal pressure (e.g., pregnancy, uterine fibroids, obesity, ascites) External compression (from, e.g., tight belts, pants, or compression dressings, trauma to the anterior superior iliac spine) Local compression (due to, e.g., tumors, muscle compression from prolonged sitting or standing, hematomas) Pelvic surgery	None	Meralgia paresthetica: pain and paresthesias on the lateral surface of the anterior thigh Can be improved by wearing looser clothing and/or losing weight
Femoral nerve injury	L2–L4	Diabetic lumbosacral plexopathy Direct injury (e.g., pelvic fracture, knife injuries, gunshots) Iatrogenic: pelvic, abdominal, or spinal surgery; femoral line placement Prolonged pressure on the nerve: psoas hematoma, aortic or iliac aneurysms, or tumors	Paralysis of iliopsoas, pectineus, rectus femoris, and sartorius muscles → impaired hip flexion Paralysis of quadriceps femoris muscle → impaired knee extension and decreased patellar tendon reflex	Pain in the inguinal region (pain relieves during external rotation and flexion of the hip) Anterior cutaneous branches: anteromedial thigh Saphenous nerve lesion: medial lower leg, knee (e.g., infrapatellar pain), medial edge of the foot
Obturator nerve injury	L2–L4	Pelvic surgery Internal compression (e.g, due to thickened obturator fascia, tumors, obturator hernias) External compression (e.g., due to pelvic ring fractures)	Paralysis of hip adductors (adductor longus, adductor brevis, adductor magnus, obturator externus, gracilis, pectineus)	Howship-Romberg sign: pain and paresthesia over the inner aspect of the thigh
Superior gluteal nerve injury	L4–S1	Iatrogenic injury from intramuscular injection in the upper medial gluteal region	Paralysis of gluteus medius and minimus, tensor fascia lata → impaired hip abduction Positive Trendelenburg sign: lateral pelvic drop towards the opposite (healthy) side	None
Common peroneal nerve injury	L4–S2	Superficial peroneal nerve: stretch trauma (e.g., ankle sprains), fascial defects Fracture of the fibular head Compression: tight casts, sitting cross-legged, lithotomy position during surgery ^[4]	Superficial peroneal nerve: paralysis of peroneus longus and peroneus brevis → impaired eversion of the foot Deep peroneal nerve: paralysis of foot and toe extensors (dorsiflexors) (e.g., tibialis anterior), leading to: Foot drop Steppage gait	Superficial peroneal nerve: lateral surface of the lower leg, dorsum of the feet and toes, except for the space between the first and second toe Deep peroneal nerve: area between the first and second toes (flip-flop zone)
Sciatic nerve injury	L4–S3	Herniated lumbar disc Posterior hip dislocation Iatrogenic (misplaced intragluteal injection) Direct trauma (gun and/or stab wounds) Total hip arthroplasty ^[5]	Paralysis of hamstring muscles (semimembranosus, semitendinosus, biceps femoris) and adductor magnus → impaired knee flexion and hip adduction Sciatic nerve splits into tibial nerve and common peroneal nerve → motor deficits of muscles innervated by these nerves	Lower leg and foot
Tibial nerve injury		Trauma of the knee or leg (e.g., tibial fracture) Baker cyst (causes proximal lesion) Tarsal tunnel syndrome (causes lesion of the posterior tibial nerve)	Paralysis of biceps femoris (long head) Paralysis of foot flexors (e.g., triceps surae) → inability to stand on or curl toes and to invert foot Proximal lesions: eversion of the foot at rest	Sensory loss over sole of the foot (See “Morton neuroma” for more information.)
Sural nerve injury		Achilles tendon rupture Entrapment neuropathy (e.g., crural fascia thickening) Ganglion lipomas	None	Posterolateral side of the lower leg Lateral border of the foot Small area under the heel
Inferior gluteal nerve injury	L5–S2	Posterior hip dislocation	Paralysis of gluteus maximus → impaired thigh extension Difficulty standing up from a sitting position and climbing stairs Backward lurching gait: an abnormal gait in which the trunk tilts backward while walking during the heel strike phase of the limb with the weak hip extensor Forward pelvic tilt	None

Differences between tibial nerve and peroneal nerve injuries: TIPPED
• Tibial → impaired foot Inversion and Plantarflexion
• Peroneal → impaired foot Eversion and Dorsiflexion

Innervation of the lower extremity (ventral view) Innervation areas of the peripheral nerves (leg, ventral view) Osteofascial compartments of the leg Trendelenburg and Duchenne signs

Diagnostics

The diagnosis of peripheral nerve injuries is based on a thorough clinical history, neurological examination, and, in some cases, diagnostic tests (e.g., x-ray if fracture is suspected).

Imaging
- Plain x-ray: detection of compression or transection due to dislocated bone or fracture segments
- CT/MRI: evaluation of causes like nerve tumors, avulsions, and focal soft tissue pathologies
Electrodiagnostic studies: detect and grade nerve injury, nerve compression, and identify early stages of recovery
- Electroneurography (nerve conduction study): analysis of a muscle's electrical activity in response to stimulation of its supplying nerve
- Needle electromyography (EMG)

Management

Conservative treatment ^[6]

Expectant management (e.g., closed injuries of the nerve with a high rate of spontaneous recovery)
Activity modification (e.g., avoid sports or activities that increase the likelihood of further nerve injury)
Splinting ^[7]
- Prevents stiffness and contractures of joints
- Supports residual nerve functionality and reinnervation
Physiotherapy
Electrical stimulation: supports the regeneration of the proximal axons and reinnervation of the denervated muscles after surgical nerve repair ^[8]
Analgesia
- Nonopioid analgesics (e.g., NSAIDs)
- Infiltration with local anesthetics
Drug therapy
- Treatment of chronic neuropathic pain following peripheral nerve injury (e.g., gabapentin) ^[9]
- Used in combination with surgical treatment to enhance remyelination and motor regeneration (e.g., lithium) ^[10]

Surgical repair

Indications
- Open, non-contaminated, sharp injuries and concomitant vascular injuries → immediate surgical exploration and repair
- Open, contaminated injuries and postreduction palsy → early surgical exploration and repair (within 3 weeks)
- Patients without clinical or electromyographic signs of spontaneous recovery → delayed surgical exploration and repair (within 3 months)
Procedures
- Nerve repair (neurorrhaphy): reconstruction of nerve continuity
- Nerve transfer: an intact healthy nerve is redirected towards a denervated nerve in order to restore the innervation of its target organ
- Tendon transfer: a tendon from a sufficiently powerful muscle is redirected towards another tendon in order to restore its motion and function

References

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Stewart JD. Foot drop: where, why and what to do?. Pract Neurol.. 2008; 8 (3): p.158-169.doi: 10.1136/jnnp.2008.149393 . | Open in Read by QxMD
Yeremeyeva E, Kline DG, Kim DH. Iatrogenic sciatic nerve injuries at buttock and thigh levels: the Louisiana State University experience review. Neurosurgery. 2009; 65 (4 Suppl): p.A63-66.doi: 10.1227/01.NEU.0000346265.17661.1E . | Open in Read by QxMD
John P. Rossiter, Alan C. Jackson. Pathology. Elsevier ; 2013: p. 351-386
Akuthota V, Herring SA . Nerve and Vascular Injuries in Sports Medicine. Springer Science & Business Media ; 2009
Jacobs MA, Austin N, Austin NM . Splinting the Hand and Upper Extremity: Principles and Process. Lippincott Williams & Wilkins ; 2003
Haastert-Talini K, Grothe C. Electrical stimulation for promoting peripheral nerve regeneration. Int Rev Neurobiol. 2013; 109: p.111-124.doi: 10.1016/B978-0-12-420045-6.00005-5 . | Open in Read by QxMD
Griggs RB, Bardo MT, Taylor BK. Gabapentin alleviates affective pain after traumatic nerve injury. Neuroreport. 2015; 26 (9): p.522-527.
Fang XY, Zhang WM, Zhang CF et al. Lithium accelerates functional motor recovery by improving remyelination of regenerating axons following ventral root avulsion and reimplantation. Neuroscience. 2016; 329: p.213-225.doi: 10.1016/j.neuroscience.2016.05.010 . | Open in Read by QxMD

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