Common Entrapment Syndromes

Nerve entrapment syndromes are a group of conditions in which peripheral nerves are damaged, through compression or repeated trauma. This session will look at the three most common nerve entrapment syndromes:

• Median nerve at the wrist (carpal tunnel syndrome)
• Ulnar nerve at the wrist (Guyon’s canal) and elbow
• Radial nerve in the forearm

The pathological process is similar in each case. Therefore, the general principles of treatment are similar.

These general principles will be considered first. Each nerve specific syndrome will then be reviewed, the anatomy described and specific treatments discussed.

Suprascapular nerve, lateral femoral cutaneous nerve (meralgia paraesthesia) and tibial nerve at the ankle (tarsal tunnel syndrome) will be examined in the Learning Zone session on Uncommon Entrapment Syndromes.

Nerve entrapment syndromes are caused by chronic injury to a nerve as it travels through a bony or ligamentous tunnel. Repetitive compression, rubbing or sliding of the nerve within the canal, or against a bony prominence, results in chronic injury to the nerve. Immobilisation of the affected area with a splint can reduce this form of damage.

Entrapment neuropathies can also be caused by systemic disorders such as rheumatoid arthritis, pregnancy, acromegaly or hypothyroidism.

Repetitive injury to a nerve may result in ischaemia, oedema and damage to the myelin sheath of the nerve.

Focal segmental demyelination at the site of compression is the key patho-physiological feature of all nerve entrapment syndromes.

Complete recovery of function after surgical decompression reflects re-myelination of the injured nerve. Incomplete recovery in more chronic and severe cases of entrapment is due to Wallerian degeneration of the axons and permanent fibrotic changes in the neuromuscular junction, which prevent re-innervation and restoration of function.

The symptoms of nerve entrapment syndromes are dependent on the nerve involved, but some generalisation can be made.

The symptoms can be identified as irritative symptoms (pain, paresthesia), which affect sensory nerves and follow a temporal sequence. If these symptoms are not treated, ablative symptoms follow (numbness – sensory nerves, weakness and atrophy – motor nerves), and may be irreversible.

In some mixed sensory and motor nerves, for example the median nerve, the signs of sympathetic dystrophy may also feature in chronic cases. These symptoms include:

• Dry, thin, hairless skin
• Ridged, thickened, crackly nails
• Recurrent skin ulcerations

The initial management involves:

• Analgesia
• Reducing the aggravating movement (splinting or change of activity)

If this fails, surgical decompression may be required.

An example is shown of splinting the affected area to reduce movement.

Carpal Tunnel Syndrome

What is the incidence of carpal tunnel syndrome (CTS) in any one year?

What type of neuropathy is involved in this condition?

Who suffers the greatest incidence of this condition. Men or women?

Does the incidence of this condition lessen or increase with age?

Patients typically complain of intermittent pins and needles or a burning pain in the median nerve distribution of the hand.

Pain is generally worse at night than during the day, and may be relieved if the patient shakes their hands.

CTS normally affects at least two of a combination of the thumb, index finger and middle finger on the palmar surface of the hand.

Symptoms affecting the ring and little fingers, wrist pain and radiation of pain proximal to the wrist may occur, but are uncommon.

CTS is unlikely if there are no symptoms present in any of the first three digits.

Symptoms are usually bilateral and progressive with an insidious onset.

In the later stages of the disease, an aching sensation may radiate to the forearm and elbow.

The image illustrates the dermatomal distribution of sensory changes in CTS. The blue area indicates the area of sensory loss.

Risk Factors

A number of risk factors are associated with a predisposition to CTS.

Compression of tunnel walls	Rheumatoid arthritis,Trauma e.g. Colles fracture,Acromegaly,Subluxation of the wrist.
Internal tunnel compression	Myxoedema,Oedema after repetitive movements,Fluid retention in pregnancy,Chronic proliferative synovitis.
Changes in the median nerve	Peripheral neuropathy,Diabetes mellitus.

Examination

A number of clinical signs are useful for confirming the diagnosis of CTS.

Thumb abduction

On routine examination, finding weakness on thumb abduction is common. Weakness of resisted thumb abduction, i.e. movement of the thumb at right angles to the palm, is helpful in establishing the diagnosis of CTS.

Ulnar Nerve Entrapment

How common a condition is ulnar nerve entrapment?

Ulnar nerve entrapment is the second most common entrapment neuropathy.

Where does ulnar nerve entrapment most commonly occur?

It can occur anywhere along its length but it is most common at the elbow (cubital tunnel syndrome).

Where can damage to the motor component of the ulnar nerve manifest itself?

Damage to the motor component of the ulnar nerve can cause loss of the intrinsic muscle function in the hand.

Wrist Anatomy

The second most common area for compression is in the Guyon’s canal at the wrist. The image shows the position of the ulnar nerve at the wrist and into the hand through the Guyon’s canal.

Wrist

Depending on the site of compression, the patient may demonstrate motor, sensory or a mixed picture.

Yellow: zone 1

Proximal to bifurcation of the ulnar nerve, compression causes a mixed loss. This is commonly caused by a fractured hook of hamate or a ganglion.

Green: zone 2

Motor branch after bifurcation, compression causes loss of motor supply to muscles innervated by ulnar nerve in the hand. A fracture of the hook of hamate is the most common cause.

Blue: zone 3

Sensory branch after bifurcation, compression causes sensory loss to hypothenar eminence (the little finger and lateral side of ring finger). The most common causes are an aneurysm of the ulnar artery, thrombosis and synovial inflammation.

Elbow Anatomy

Posner (1998) described five areas of potential compression at the elbow; but the epicondylar groove and cubital tunnel are the most common areas. The compression may be caused by a congenitally shallow epicondylar groove, post trauma, tumours, infections and arthritic spurs.

The ulnar nerve runs behind the elbow on the inside of the arm. The humerus has a groove on the back where the nerve lies. Here the nerve can be felt as the ‘funny bone’.

Clinical Presentation – Elbow Specific

Ulnar nerve compression at the elbow may be post-traumatic or non-traumatic in origin. The trauma may be a single event, but is more commonly due to mild repetitive injuries. Those cases of non-traumatic origin are often associated with employment that requires repeated elbow flexion and/or extension, or resting on the elbows for prolonged periods of time.

Spontaneous subluxation of the ulnar nerve out of the cubital tunnel may also occur, aggravating symptoms of entrapment because of the rubbing action exerted by the bony surfaces.

Clinical Presentation – Wrist and Elbow Combination

Symptoms may vary from mild transient paraesthesia to severe intrinsic muscle atrophy. Pain may be in the elbow, or wrist, and may radiate to the hand or shoulder.

In mixed nerve involvement, numbness usually precedes motor loss.

Early muscle weakness may cause difficulty in opening bottles or doors, or early fatigue in repetitive moments, and may be painless.

Examination

Dorsal sensation to the ring and little finger is preserved in wrist entrapment, but not in elbow entrapment because the dorsal cutaneous branch of the ulnar nerve leaves the ulnar nerve about 9cm proximal to the wrist. Intrinsic muscle function is tested by asking the patient to cross the index and middle fingers. Other tests include:

Froment’s sign

Weakness of adductor pollicis can be demonstrated by eliciting Froment’s sign when grasping a piece of paper. The flexor pollicis longus (FPL Median) is used causing the thumb to flex because adduction is insufficient.

Ulnar claw

In lesions of the ulnar nerve below the mid-forearm, a claw hand is produced. In lesions above the mid-forearm, clawing does not occur because the long flexors to these fingers are also denervated (Ulnar paradox, shown above).

Differential Diagnosis

Differential diagnoses for these conditions include:

• Cervical disc disease
• Brachial plexus abnormalities, thoracic outlet syndrome, pancoast tumour
• Elbow abnormalities, epicondylitis
• Infections, tumours, diabetes mellitus, hypothyroidism, rheumatoid diseases and alcoholism
• Wrist fractures
• Ulnar artery aneurysms or thrombosis at the wrist

Investigations

Investigations take the form of:

Imaging studies

Radiographs of the elbow and wrist are mandatory in ulnar nerve compression because entrapment of the ulnar nerve may occur at more than one level.

Radiographs of the elbow may reveal abnormal anatomy such as a valgus deformity, bone spurs or bone fragments, a shallow olecranon groove, osteochondromas and destructive lesions (for example tumours, infections and abnormal calcifications).

Radiographs of the wrist may reveal fractures of the hook of the hamate, dislocations of the wrist bones and, to a lesser extent, soft tissue masses and calcifications.

Magnetic resonance imaging (MRI) is not usually necessary unless delineation of soft tissue masses, or visualisation of swelling or other abnormalities in the nerve, is desired.

Diagnostic procedures

Electromyography tests and nerve conduction studies are indicated to confirm the area of entrapment, document the extent of the pathology and detect, or rule out, the possibility of double crush syndrome (compression of nerve in more than one place).

In addition, Tinel’s and Phalen’s tests can also be used:

Fig 1: Tinel’s test	Fig 2: Phalens test

 

Treatment and Prognosis

Conservative treatments are most successful when paraesthesia is transient and caused by malposition of the elbow or blunt trauma.

NSAIDS also are useful adjuncts to relieve nerve irritation.

Conservative treatment should be carried out for 6-12 weeks, depending on patient response.

Indications for surgery

Surgery may be indicated where there is:

• No improvement in presenting symptoms after 6-12 weeks of conservative treatment
• Progressive palsy or paralysis
• Clinical evidence of a long-standing lesion (e.g. muscle wasting, clawing of the fourth and fifth digits)

Surgical therapy

Surgical therapy of ulnar nerve entrapment depends on the site of compression. Surgical therapy at the elbow can be either decompression in situ, or decompression with anterior transposition.

Prognosis

With appropriate decompression performed in a timely manner, the result should be a return to normal function.

If decompression in situ is performed appropriately, return to normal function is almost immediate.

With transposition of the nerve following decompression, postoperative immobilisation and the rehabilitative process, three to six months may pass before normal function is achieved.

Radial Nerve Compression

How common a condition is radial nerve compression?

Radial nerve compression is the least common of the nerve entrapment syndromes of the major nerves in the upper limb.

Where does radial nerve compression most commonly occur?

Radial nerve compression or injury may occur at any point along the anatomic course of the nerve. The most frequent site of compression is in the proximal forearm, in the area of the supinator muscle, and involves the posterior interosseous branch.

What else can also damage this nerve?

Fractures at the junction of the proximal and middle thirds of the humerus and on the radial aspect of the wrist may also damage the nerve.

Radial Nerve Injuries: Radial Nerve Palsy

Radial nerve palsy in the arm is most commonly caused by a fracture of the humerus and may occur acutely at the time of the injury, secondary to fractaure manipulation or from a healing callus.

Radial nerve palsy is characterised by palsy or paralysis of all extensors of the wrist and digits, as well as the forearm supinators. Very proximal lesions also may affect the triceps. Numbness occurs on the dorsoradial aspect of the hand and the dorsal aspect of the radial 3½ digits.

Initially, a period of medical management is required for 6-12 weeks to allow swelling and the palsy to subside. If a palsy develops after a closed manipulation, a further gentle manipulation is carried out.

Open exploration is indicated if there is no relief of the palsy, or if it is felt that the nerve may be entrapped between the fracture fragments. In an open fracture of the humerus with an associated palsy, exploration of the nerve at the time of debridement, as well as possible fixation, is the treatment of choice.

The x-ray shows a fracture of the humerus.

Radial Nerve Injuries: Posterior Interosseous Nerve Syndrome

After emerging from under the supinator, the radial nerve may be compressed before it bifurcates into medial and lateral branches. This can cause a complete paralysis of wrist extension.

If compression occurs after the nerve bifurcates the patient will complain of weakness of the wrist and finger extensors.

Attempts at active wrist extension result in weak dorsoradial deviation because extensor carpi radialis is supplied by the radial nerve proximal to the bifurcation.

The image illustrates the route of the radial nerve in the elbow.

Investigations

Investigations take the form of:

Radiographs

In suspected entrapment of the radial nerve in the arm, radiographs are required to detect, or rule out, a fracture, healing callus or tumours as the cause of entrapment.

MRI

MRI is useful in detecting tumours such as lipomas and ganglions, as well as aneurysms and rheumatoid synovitis.

Diagnostic procedures

EMGs help to locate the site of injury and help the clinician monitor the nerve recovery over time.

EMGs may not be positive for 3-6 weeks following injury.

Treatment and Prognosis

The treatments and prognosis are outlined as follows:

Medical therapy

A period of immobilisation and NSAIDs may diminish swelling and improve symptoms. In addition, functional splints help prevent contracture, and improve function, as signs of nerve healing follow.

Surgical therapy

Surgical therapy is indicated if there is failure to respond to medical management within 6-12 weeks, unless it is caused by:

• Closed manipulation, where a re-manipulation is indicated. If there is no recovery, proceed to open exploration of the nerve
• Open fracture, where the nerve is explored at the time of debridement

Prognosis

Outcome and prognosis depend on the degree of injury.

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