bubble_chart Overview

Nerve compression syndrome is one of the bone-fibrous canal and compartment compression syndromes. It occurs when a peripheral nerve is compressed by a bony-fibrous canal or, in rare cases, a fibrous edge, leading to chronic injury and inflammatory reactions that result in abnormal nerve function.

bubble_chart Etiology

The lesions are mostly located in specific anatomical sites, such as osseofibrous canals or key compression points of nerve pathways like inelastic muscle fiber margins and tendinous arches, where the compressed nerves are difficult to avoid or buffer. The disease causes can be summarized into three major categories: ① Intracanal compression: thecal cyst, neurofibroma, chronic inflammatory nerve injury. ② Extracanal compression: osteophytes, bone and joint injuries, ligament injuries. ③ Systemic diseases: rheumatoid arthritis, mucinous edema, obesity, diabetes, hyperthyroidism, Raynaud's disease, pregnancy, etc., which may be associated with nerve compression syndrome.

bubble_chart Pathological Changes

The causative factors of nerve compression disorders are nerve ischemia and mechanical damage. Acute short-term compression can lead to nerve ischemia, obstruction of axoplasmic flow in compressed axons, hypoxia, and edema. Severe and prolonged compression can cause demyelination of nerve fibers, even distal axonal disintegration, and Wallerian degeneration of the myelin sheath. During limb movement, nerve fibers within narrow channels undergo chronic inflammatory injury due to mechanical stimulation, exacerbating the vicious cycle of edema-ischemia. However, the general pathological changes remain at the stage of Seddon's physiological paralysis and grades 1–2 of Sunderland's 5-grade classification. Most cases involve reversible damage.

bubble_chart Clinical Manifestations

1. Pain and paresthesia: Sensory loss or abnormalities may occur according to the dermatome innervated by the nerve.

2. Nighttime aggravation is also known as rest pain.

3. Pain may radiate both proximally and distally, requiring differentiation from double crush syndrome.

4. Muscle atrophy, weakness, and incoordination.

5. Signs of sympathetic nerve involvement: Manifested as disturbances in temperature, color, sweating, and nutrition.

6. Localized tenderness and radiation at the compression site. Tenderness both proximal and distal to the compression site is called the Vallex phenomenon.

7. Tinel’s sign: Light percussion at the compression site causes tenderness and a tingling sensation. In radiculopathy, EMG may show fibrillations and denervation potentials, but generally no slowing of conduction velocity. Peripheral nerve involvement may show slowed conduction velocity and prolonged distal latency. Plain X-rays can only reveal signs of bone hyperplasia or old injuries.

**Nerve Compression Syndromes at Various Sites**

**(1) Carpal Tunnel Syndrome** This condition, also known as delayed median nerve palsy, is caused by compression of the median nerve within the carpal tunnel. The carpal tunnel is located at the base of the palm, with its floor and sides formed by the carpal bones and the transverse carpal ligament spanning above, creating a bony-fibrous canal.

Chronic injury due to prolonged overuse of the hand and wrist is the most common cause, leading to chronic inflammatory changes in the transverse carpal ligament and its enclosed tendons, resulting in canal stenosis. Acute wrist injuries, distal radius fractures, or lunate dislocations may also cause acute or secondary median nerve compression. Certain systemic diseases can increase the volume of the carpal tunnel contents, leading to spontaneous median nerve damage.

The condition predominantly affects individuals aged 30–60, with women five times more likely to be affected than men. It is usually unilateral but can be bilateral. Onset is gradual, with pain, numbness, and swelling in the median nerve distribution, often waking the patient at night and relieved by activity. Sensory abnormalities (hypoesthesia or hypersensitivity) occur in the median nerve territory. Thenar muscle atrophy and thumb clumsiness may develop. Tinel’s sign is positive at the wrist. Extreme wrist flexion for 60 seconds exacerbates paresthesia (Phalen’s test), indicating increased carpal tunnel pressure. Blood pressure cuff inflation above systolic pressure for 30–60 seconds may induce pain in the affected hand. Extreme wrist extension and flexion tests similarly worsen paresthesia and pain. Tenderness and radiating pain are present at the palmar compression site. Median nerve conduction velocity is slowed.

Non-surgical treatments include wrist immobilization in a neutral position and corticosteroid injections into the carpal tunnel. Surgical decompression is required for recurrent or refractory cases. Endoscopic surgery has been reported as an option.

**(2) Ulnar Tunnel Syndrome** Also known as Guyon’s canal syndrome, piso-hamate hiatus syndrome, or Ramsay-Hunt syndrome. The cross-section of the ulnar tunnel is triangular, bounded anteriorly by the superficial transverse carpal ligament, posteriorly by the deep transverse carpal ligament, and medially by the pisiform bone and pisohamate ligament. It contains the ulnar nerve and ulnar artery/vein. Compression of the ulnar nerve here causes ulnar tunnel syndrome.

The most common cause is thecal cysts (28.7%), followed by chronic injury (23.5%) and contusions (10.3%). Other causes include fractures, congenital malformations, and systemic diseases.

Compression of the superficial branch causes sensory disturbances in the ulnar nerve distribution. Deep branch compression leads to intrinsic hand muscle atrophy, weakness, deep aching or burning pain (worse at night), adducted thumb, weak finger abduction/adduction, and clawing of the ring and little fingers. Positive Froment’s and paper grip tests may be observed. Electrophysiological studies show fibrillations on EMG and slowed nerve conduction velocity.

If non-surgical treatments fail, surgical release of Guyon’s canal to fully decompress and mobilize the ulnar nerve is indicated.

(3) Pronator syndrome - Compression of the median nerve at the proximal forearm caused by entrapment between the two heads of the pronator teres muscle. During forearm pronation, the median nerve is lifted by the ulnar head of the pronator teres, making this condition common in individuals who repeatedly perform forceful pronation movements. Initial symptoms include anterior elbow pain that may radiate to the radial three fingers, possible finger flexion weakness, and worsening pain with overuse of the arm. There may be numbness, burning sensations, and objective sensory disturbances in the median nerve distribution area. Tenderness may be present at the upper border of the pronator teres, along with a positive Tinel's sign. Weakness in opposition may occur. Local corticosteroid injections often relieve symptoms, and surgical release of the compressive tendinous arch or fibrous band may be considered if conservative treatment fails.

(4) Anterior Interosseous Nerve Entrapment Syndrome Also known as Kiloh-Nevin syndrome, this condition occurs when the anterior interosseous branch of the median nerve is compressed by the tendinous arch or fibrous band at the upper edge of the flexor digitorum superficialis muscle. Symptoms include pain in the anterior elbow, weakened flexion of the distal interphalangeal joints of the thumb and index finger, and, in cases of complete paralysis of the flexor pollicis longus muscle, a "pinch" sign may be observed. Weakness of the pronator quadratus muscle may be noted during elbow flexion, while hand sensation remains normal, with no paralysis of the intrinsic hand muscles.

(5) Radial Tunnel Syndrome Also referred to as radial arch syndrome, supinator syndrome, or posterior interosseous nerve entrapment, this condition arises from compression of the deep branch of the radial nerve within the radial tunnel by the tendinous arch of the superficial layer of the supinator muscle or the tendinous arch of the extensor carpi radialis brevis muscle. Onset is gradual, with progressive weakness in extending the metacarpophalangeal joints, thumb extension, and thumb abduction, as well as radial deviation during wrist extension due to involvement of the extensor carpi ulnaris muscle while the extensor carpi radialis remains intact. There is no sensory abnormality or pain. A positive middle finger test is characteristic, where pain is elicited along the medial edge of the extensor carpi radialis brevis origin when resisting extension of the metacarpophalangeal joints with the elbow, wrist, and interphalangeal joints extended. Tennis elbow pain typically occurs around the medial epicondyle. Surgical exploration should focus on common compression sites of the posterior interosseous nerve, including the anterior aspect of the radial head, the tendinous arch of the extensor carpi radialis brevis, and the Frohse arcade of the supinator muscle.

(6) Cubital Tunnel Syndrome at the Elbow This condition results from compression of the ulnar nerve within the osseofibrous canal of the cubital tunnel at the elbow. The tunnel is bounded medially by the medial epicondyle, laterally by the olecranon, and floored by the ulnar groove, with a tendinous membrane covering the space between the medial epicondyle and olecranon. Common causes include excessive elbow activity, sequelae of elbow trauma, and congenital deformities. Additionally, elbow joint pain, such as from osteoarthritis, subcutaneous nodules, or rheumatoid arthritis, can also lead to ulnar nerve compression. Onset is gradual, with symptoms including numbness and stabbing pain along the ulnar side of the forearm and hand, particularly in the fourth and fifth fingers. Weakness in flexion of the ring and little fingers, sensory disturbances in the ulnar nerve distribution, intrinsic muscle atrophy, and claw hand deformity (ring and little fingers) may occur. Positive Froment's sign and paper grip test are observed. The ulnar groove may reveal a thickened, tender nerve with a positive Tinel's sign. Electrophysiological studies aid in diagnosis. If non-surgical treatment fails, ulnar nerve transposition or medial epicondylectomy may be considered.

(7) Suprascapular Nerve Entrapment Syndrome This condition is caused by compression of the suprascapular nerve at the scapular notch near the lateral superior angle of the scapula. The notch is bordered laterally by the base of the coracoid process, with the transverse ligament spanning above it to form an osseofibrous canal. Occupations requiring prolonged, excessive shoulder activity predispose individuals to this condition. Symptoms include persistent dull shoulder pain radiating to the neck and interscapular region, exacerbated by shoulder movement. Weakness in shoulder abduction and external rotation may occur, with atrophy of the supraspinatus and infraspinatus muscles but typically no local tenderness.

(8) Piriformis Syndrome The sciatic nerve usually passes anteriorly and inferiorly to the piriformis muscle, exiting through the infrapiriform foramen between the lower edge of the piriformis and the superior gemellus muscle. Compression at this site leads to piriformis syndrome. The primary cause is acute or chronic injury to the piriformis muscle. Patients report buttock pain and paresthesia radiating to the posterior thigh. Deep tenderness over the piriformis muscle may be found, and resisted abduction and external rotation of the hip can reproduce the pain and reveal weakness. Passive hip flexion, adduction, and internal rotation worsen the pain.

(9) Lateral Femoral Cutaneous Nerve Entrapment Syndrome This condition occurs when the lateral femoral cutaneous nerve is compressed within the osseofibrous canal formed between the anterior superior iliac spine (ASIS) and the two layers of the inguinal ligament. Symptoms include burning pain, numbness, and hypersensitivity in the nerve's distribution, with possible reduced touch, pain, and temperature sensation. Tenderness and radiating pain may be present anterior and medial to the ASIS, exacerbated by hip hyperextension. No motor deficits are observed.

(10) Common Peroneal Nerve Entrapment Syndrome This condition is caused by the entrapment of the common peroneal nerve in the osseofibrous tunnel at the fibular neck. Injury and external compression are common disease causes, manifesting as pain and numbness in the foot and lateral lower leg. Motor impairments include weakness or inability to dorsiflex the ankle, extend the toes, and weak or absent eversion. Sensory disturbances may occur in the lateral lower leg and lateral foot. Tenderness and Tinel's sign may be present at the fibular neck.

The compression of the superficial peroneal nerve's cutaneous branch at the exit of the deep fascia in the distal lower leg is another potential entrapment point of this syndrome. Injury and overly tight footwear or socks can lead to this condition, which manifests only as pain and paresthesia in the nerve's innervated area.

(11) Tarsal Tunnel Syndrome The tibial posterior nerve is compressed within the osseofibrous tunnel formed by the flexor retinaculum and the calcaneus at the medial malleolus (to be decocted later), leading to this condition. Chronic injury caused by overuse of the foot is a common disease cause. Patients complain of intermittent stabbing pain, burning pain, or numbness in the sole or heel, which worsens with prolonged standing or walking. Night pain is frequent and may wake the patient. Tenderness and Tinel's sign may be present at the medial malleolus (to be decocted later). Weakness in metatarsophalangeal joint flexion may occur, and a tourniquet inflation test can induce foot pain.

(12) Entrapment Syndrome of the Common Plantar Digital Nerve This condition is also known as Morton's disease or Morton's metatarsalgia. It may result from the entrapment of the plantar digital nerve between adjacent metatarsal heads, the deep intermetatarsal ligament, and the metatarsal tendon membrane. The disease cause is often chronic injury due to prolonged standing or cumulative walking. Patients report paroxysmal burning pain beneath the metatarsal heads, most commonly affecting the third and fourth toes. Pain worsens with walking and standing and improves with rest and removing shoes. Transverse compression of the metatarsal heads can reproduce the pain in the affected space. Non-surgical treatment involves wearing loose, flat-soled soft shoes and supporting the flattened transverse arch. Traditional surgery involves excision of the painful neuroma, while recent reports indicate excellent outcomes from transection of the deep intermetatarsal ligament.

bubble_chart Treatment Measures

Non-surgical treatment involves local immobilization, corticosteroid injections, and NSAID administration to reduce the inflammatory response of entrapment lesions and alleviate symptoms. However, this disease is a slowly progressive condition and rarely resolves spontaneously. Generally, surgical incision of the osseofibrous tunnel is required to decompress and release the nerve. Care should be taken to avoid rough surgical maneuvers that could further
injure the nerve.