Radial nerve lesions and carpal tunnel syndrome

Question 1

Where is the segmental origin of the radial nerve?

Answer 1

There are three posterior divisions of the brachial plexus that form the posterior cord.

The largest and most frequently injured part of both the posterior cord and the brachial plexus is the radial nerve.

The segmental origin is C5-C8 but there is also a sensory component from T1.

Question 2

What is the aetiology of radial nerve lesions?

Answer 2

Radial nerve compression or injury may occur at any point along the course of the nerve.

The most frequent site of compression is the proximal forearm in the area of the supinator muscle and involving the posterior interosseous branch (posterior interosseous nerve syndrome).

Problems may also occur proximally as a result of fractures of the humerus at the junction of the middle and proximal thirds, as well as distally on the radial aspect of the wrist (radial nerve palsy).

Question 3

What are the causes of radial nerve injuries at the axilla?

Answer 3

With features of weak triceps, wrist drop and possibly also median and ulnar nerve involvement. The most common cause is compression.

The radial nerve may be damaged in the axilla by fracture or dislocation of the head of the humerus.

Lesions in or above the axilla result in paralysis and wasting of all the muscles innervated. Clinically, this is manifest as:
The weakness of forearm extension and flexion - triceps and brachioradialis
Wrist drop and finger drop - paralysis of the extensors of the wrist and digits
weakness of the long thumb abductor and extensor muscles
Sensory loss on the dorsum of hand and forearm appropriate to the cutaneous distribution - see radial nerve anatomy

Question 4

What is the Saturday night syndrome?

Answer 4

Saturday night syndrome (so named because it can be acquired by sleeping with the arm over the back of a chair whilst in a drunken stupor, so compressing the plexus):

Is due to compression of the lower part of the brachial plexus. As this is really a brachial plexus injury, the median and ulnar nerves may also be involved.

It may also be compressed by the use of shoulder crutches.

Nerve function usually fully recovers within a few weeks.

Question 5

What are the causes of radial nerve injuries in the upper arm?

Answer 5

In the upper arm (triceps and brachioradialis are often spared):

• May be due to a compression lesion but fracture is the usual cause. Injections given in the arm of small babies can damage the radial nerve.
• As the nerve often passes down in the spiral groove of the humerus, it may be injured with a fracture of the shaft of the humerus.

Question 6

What are the causes of radial nerve injuries at the elbow?

Answer 6

The radial nerve may be entrapped at the elbow at a number of sites but the most common is the proximal border of the tendon of the supinator called the arcade of Frohse.

Check for tenderness over the radial tunnel. There may be pain when the fingers are extended against resistance.

Supination from a pronated position along with flexion of the wrist may reproduce the symptoms.

Question 7

What are the causes of radial nerve injuries at the wrist?

Answer 7

Cause finger drop with a normal wrist and intact sensation.

Causes include fracture of the radius, elbow deformity, soft-tissue masses and compression by the extensor carpi radialis brevis.

Question 8

What are the investigations for radial nerve lesions?

Answer 8

Nerve conduction studies
High contrast US
MRI scan

Question 9

What is the management of radial nerve lesions?

Answer 9

Lesions from compression such as Saturday night syndrome and simple fractures usually recover spontaneously.

General measures to reduce inflammation, such as splints and anti-inflammatory drugs, may be helpful.

Complex trauma needs exploration with a view to surgical repair. Entrapment requires surgical decompression.

Question 10

What is carpal tunnel syndrome?

Answer 10

Carpal tunnel syndrome (CTS) is by far the most common cause of median nerve damage.

The carpal tunnel is an anatomical compartment of the hand; it is bounded on three sides by carpal bones which form an arch, and on the palmar side by the transverse carpal ligament.

Question 11

What is the pathogenesis of CTS?

Answer 11

CTS is caused by compression, entrapment or irritation of the median nerve within the carpal tunnel at the wrist, between the carpal bones and the fibrous flexor retinaculum.

Anything that causes a reduction in the volume or increases the pressure within the compartment may cause CTS.

Rarely, compression of more proximal parts of the nerve can occur at the forearm or elbow. The two significant conditions are pronator teres syndrome and anterior interosseous syndrome.

Question 12

What is the aetiology of CTS?

Answer 12

Most cases of CTS are idiopathic. 
However, it may be associated with:
-Pregnancy.
-Overuse of the hand or wrist.
-Wrist trauma.
-Obesity.
-Hypothyroidism.
-Renal failure.
-Diabetes.
-Inflammatory arthropathy.

Question 13

What are the rarer causes of CTS?

Answer 13

• Post-Colles’ fracture.
• Flexion/extension injury of the wrist.
• Use of walking aids.
• Conditions encroaching on the space within the carpal tunnel (eg, aneurysm, neurofibroma, haemangioma, lipoma, ganglion, xanthoma and gouty tophi).
• Menopause (including surgically induced).
• Inflammatory arthritides of the wrist.
• Acromegaly.
• Renal dialysis.
• Amyloidosis.

Question 14

What is the presentation of CTS?

Answer 14

CTS is characterised by tingling, numbness, or pain in the distribution of the median nerve (the thumb, index, and middle fingers, and medial half the ring finger on the palmar aspect) that is often worse at night and causes awakening.

The affected hand may be hung out of the bed at odd angles to try to revive it. Pain may become more persistent, and may radiate to the forearm, elbow, arm and even the shoulder.

Weakness may be noted in hand grip and opposition of the thumb. There may also be some muscle wasting of the thenar eminence in more severe cases.

Question 15

What are the signs seen in CTS?

Answer 15

Positive Phalen test: flexing the wrist for 60 seconds causes pain or paraesthesia in the median nerve distribution.

Positive Tinel’s sign: tapping lightly over the median nerve at the wrist causes a distal paraesthesia in the median nerve distribution.

Positive carpal tunnel compression test: pressure over the proximal edge of the carpal ligament (proximal wrist crease) with thumbs causes paraesthesia to develop or increase in the median nerve distribution.

Question 16

What are the differentials for CTS?

Answer 16

Other median nerve compression syndromes 
Cervical radiculopathy 
Shoulder bursitis 
Thoracic outlet syndrome 
TIA
Tendonitis 
Fibrositis 
Lateral epicondylitis 
Pronator syndrome
Anterior interosseous syndrome

Question 17

What is pronator syndrome?

Answer 17

This is compression of the median nerve where it passes between the two heads of the pronator teres, causing pain in the wrist and forearm and weakness of the thenar muscles.

Question 18

What is the anterior interosseous syndrome?

Answer 18

Compression mainly of the motor nerve, most commonly caused by the tendinous origin of the deep head of the pronator teres, causing difficulty moving the index and middle fingers.

Question 19

What are the investigations for CTS?

Answer 19

Investigations are useful in patients whose clinical features yield a high index of suspicion for CTS but who fail to respond to first-line treatment.

Electroneurography (ENG) - this is the gold-standard investigation for CTS. The median nerve is stimulated proximal to the carpal ligament and compound muscle action potential is picked up over the thenar eminence.

Electromyography (EMG) - this is useful in some cases but is not as sensitive as ENG.

Ultrasonography - this is being used increasingly as a confirmatory test. It is obviously relatively cheap, quick and non-invasive.

MRI scan - this can be used as an alternative to ultrasonography and when electrophysiological studies are ambiguous. CTS can be classified into three groups according to the nerve T2 signal and the flattening ratio at the hook of hamate level: Group 1 - high and oval; Group 2 - high and flat; Group 3 - low and flat.

Question 20

What is the management of CTS?

Answer 20

Conservative management may be successful for early or mild disease or where advanced disease is associated with minimal symptoms. If non-operative strategies fail, open carpal tunnel decompression provides good results and high levels of reported satisfaction for most patients

Corticosteroids:
-Local steroid injections are widely used for diagnostic and therapeutic purposes in the management of CTS.

Surgery

Physiotherapy

Question 21

What are the general measures of the management of CTS?

Answer 21

Explain that the symptoms may resolve within six months. This is most likely to occur in young people (less than 30 years of age) if the symptoms are unilateral and of short duration, and in women in whom fluid retention due to pregnancy is the precipitating factor.

Splints are often beneficial

Advise minimisation of activities that exacerbate symptoms

Consider referring patients when the diagnosis is uncertain or where treatments have failed to work after three months.

Question 22

What are the surgical treatment options for the management of CTS?

Answer 22

Surgical treatment consists of the release of the nerve by cutting the transverse carpal ligament. This can be done either with an open approach or endoscopically.

Although surgery usually produces good outcomes, it has disadvantages, which are mainly surgery-related pain, hand weakness, and complications from surgery.

Ultra-minimally invasive sonographically guided carpal tunnel release is a relatively new technique that preserves the superficial anatomy and diminishes the damage of a surgical approach.

Question 23

What is involved in the rehabilitation after surgery for CTS?

Answer 23

Rehabilitation after surgery- These include immobilisation using a wrist orthosis, dressings, exercise, controlled cold therapy, ice therapy, multimodal hand rehabilitation, laser therapy, electrical modalities, scar desensitisation and arnica.

Question 24

What is the role of physiotherapy in the management of CTS?

Answer 24

Stretching the wrist to help increase blood flow, therefore promoting healing.

Simple exercises, such as wrist bend, wrist lift and wrist flex, help improve the patient’s strength and flexibility.

Nerve glide exercises to improve the mobility of the median nerve.

However, some exercises may exacerbate a patient’s symptoms.

Question 25

What is the prognosis of CTS?

Answer 25

Symptoms can resolve within six months in about one-third of persons, particularly younger patients.

A poor prognosis is often associated with bilateral symptoms and a positive Phalen test.

However, the severity of symptoms and signs often doesn’t correlate well with the extent of nerve compression.