Specific nerve injuries

Brachial plexus lesions

Damage to the brachial plexus is caused by:

traction as a result of violent displacement of the shoulder girdle and cervical spine;

open, penetrating injuries by knife or missile;

operation in the area (for example, for removal of lymph nodes);

malignant infiltration at the base of the neck, for example Pancoast syndrome.

Traction injury is particularly associated with road traffic accidents to motorcyclists. Any component of the plexus (Fig. 34.5) can sustain any grade of injury (neurapraxia, axonotmesis, neurotmesis). In addition, nerve roots may be avulsed from the spinal cord (preganglionic injury). According to the degree of injury the paralysis varies from a completely flail and useless arm and hand to paralysis of groups of muscles and anaesthesia according to the roots affected. Injuries are usually divided into:

       supraclavicular;

       infraclavicular,

although it is possible for there to be damage both above and below the clavicle.

The most common pattern of injury to the supraclavicular plexus is a lesion of the CS and C6 roots and upper trunk (Erb—Duchenne palsy). There is loss of shoulder abduction and external rotation, elbow flexion and forearm supination. Sensation is absent on the outer aspect of the arm and hand. Klumpke described a lesion of the lower roots, but this is rare on its own. Injuries to all of the roots are more common.

Management of traction injuries

It is important to establish the mechanism of injury as nerve ruptures are more likely after high-energy trauma. The nerves affected can largely be deduced from careful clinical examination. Signs of preganglionic injury include:

Hornet’s syndrome;

paralysis of the thoracoscapular muscles (innervated by branches near the roots);

swelling in the posterior triangle of the neck;

severe pain in the anaesthetic arm.

Investigation 

     Includes radiographs of the chest and cervical spine to look for vertebral or rib fractures and to assess phrenic nerve function. In cases of supraclavicular injury myelography, preferably combined with computerised topographic (CT) scanning, or MRI gives useful additional infor­mation on the integrity of the roots before surgery (Fig. 34.6). Neurophysiological assessment is not usually helpful until 2—3 weeks after injury.

  Severe traction injuries to the brachial plexus have a devastating effect on the limb and the outlook is often poor. Careful management is therefore important to maximise recovery. If clinical examination reveals complete absence of function of any part of the plexus and the injury was caused by high-energy trauma, then exploration of the brachial plexus is indicated as soon as the general condition of the patient allows. Therefore, transfer to a specialist unit should be arranged as soon as possible. If early surgery is not possible then every effort should be made to operate by 3 months from injury, as the results of repair are undoubtedly worse with increasing delay. At operation the damage to the plexus is carefully documented and nerve grafting is carried out for nerve ruptures. Until recently, repair of avulsed roots was not thought to be possible, but some recovery has now been obtained after repair of ventral (motor) roots within the spinal canal. Alternatively, nerve transfers are performed to restore the most important functions of avulsed roots as far as possible.

Stab wounds

Any sharp injury to the brachial plexus should be explored as soon as possible and repaired using nerve grafts.

Obstetric brachial plexus palsy

Injury to the brachial plexus can result from traction on the shoulder girdle during birth. The upper roots are most com­monly affected (Erb—Duchenne palsy). The prognosis is good with conservative management in most cases. Physiotherapy is necessary to prevent joint contractures, particularly of the shoulder. The prognosis is improved by surgery to the brachial plexus in approximately 10 per cent of cases. Indications for operation are:

  failure to regain elbow flexion by 3—6 months;

  complete paralysis of the limb.

Branches of the brachial plexus

Axillary or circumflex nerve

This is most commonly injured in association with disloca­tion of the shoulder joint. The deltoid muscle is paralysed and there is a patch of anaesthesia over the outer side of the arm. The majority of cases recovers spontaneously, but rup­ture of the nerve does sometimes occur and then recovery is only possible if nerve grafting is carried out.

The long thoracic nerve

The long thoracic nerve to serratus anterior (nerve of Bell) may be injured by operations on the breast or chest wall, or is occasionally involved in neuropathies. Paralysis of serratus anterior results in ‘winging’ of the scapula and difficulty in elevating the arm above a right angle (Fig. 34.7).

Radial nerve

This nerve is most commonly injured in the radial groove in association with fracture of the shaft of the humerus or as a result of pressure, as in ‘Saturday night’ palsy due to falling into a heavy sleep with the arm over the sharp back of a chair. Clinical features include:

  motor paralysis of brachioradialis, the wrist extensors and extensor digitorum. It should be remembered that extension of the interphalangeal joints will still be present if the hand is supported because of the action of the lumbricals and interossei, which are inserted into the extensor expansions. In higher lesions the triceps will also be affected;

  sensory loss of sensation over the dorsum of the thumb and the first web space. In higher lesions sensation is also lost on the dorsum of the forearm (Fig. 34.8).

Recovery of the radial nerve is usually good either after conservative management or repair, if appropriate. If not, then good results can be obtained by tendon transfer.

Median nerve

The median nerve is classically injured at the elbow or wrist. Injuries at the elbow are due to fractures of the distal humerus or dislocation of the elbow joint. Clinical features include:

motor paralysis of the pronators of the forearm and flexors of the wrist and fingers, with the exception of the flexor carpi ulnaris and the medial part of the flexor digitorum profundus. The index finger and thumb cannot be flexed at the interphalangeal joints, but flexion of the other fingers is performed by the portion of the flexor digitorum profundus which is supplied by the ulnar nerve. The thenar muscles are paralysed with resulting loss of abduction and opposition of the thumb;

sensory sensation is lost over the palmar aspect of the thumb, index, middle and the radial half of the ring fingers, as well as part of the palm.

Damage to the median nerve at the wrist is comparatively common as a result of lacerations, fractures of the distal -radius or compression in the carpal canal. Clinical features include paralysis of the thenar muscles and loss of sensation on the palmar aspect of the radial three and a half fingers (Fig. 34.9).

Ulnar nerve

The ulnar nerve is most commonly damaged by lacerations in the forearm or entrapment as it passes behind the medial epicondyle of the humerus, in which case decompression or anterior transposition may be indicated.

Clinical features include:

motor paralysis of the small muscles of the hand, with the exception of the thenar muscles and lateral two lum­bricals. The patient is unable to abduct and adduct the fingers, or indeed grip a piece of paper between them (Fig. 34.10). Weakness of flexion of the metacarpophalangeal joints and extension of the interphalangeal joints result in a claw-type deformity. If the patient pinches a piece of paper between the thumb and the index finger the distal phalanx of the thumb assumes a flexed position, as weak­ness of the adductor pollicis permits over-action of flexor pollicis longus (Froment’s sign, Fig. 34.11). In longer standing cases, muscle wasting will be evident in the interosseus spaces and along the medial border of the hand. Lesions proximal to the elbow also cause paralysis of the flexor carpi ulnaris and medial half of the flexor digitorum profundus;

sensory sensation is lost on the medial one and a half fingers (Fig. 34.12).

Lower limb nerves

Sciatic nerve

The sciatic nerve is occasionally injured by wounds, fractures of the pelvis, posterior dislocation of the hip, operation for hip replacement or tumours. The prognosis for recovery is poor, particularly in proximal injuries. If the lesion is above the origin of branches to the hamstrings, the following features will be present:

motor the flexors of the knee are paralysed, but some degree of flexion is possible owing to the action of the sartorius and gracilis muscles. Complete paralysis exists below the knee, and the pull of gravity therefore causes foot drop;

sensory complete loss below the knee, with the exception of the skin supplied by the saphenous nerve, i.e. the medial border of the foot;

causalgia may complicate partial lesions.

Common peroneal (lateral popliteal) nerve

Partial lesions of the sciatic nerve affect the peroneal division much more frequently than the tibial division. The common peroneal nerve itself is quite sensitive to injury by fractures or dislocations around the knee, pressure from plasters o splints and operations around the knee. Complete lesions will cause:

  motor complete paralysis of the extensor muscles of the ankle and toes and the peroneal muscles, with resulting foot drop and tendency to inversion of the ankle;

sensory anaesthesia of the dorsum of the foot and toes.

The prognosis depends on the severity of injury, but is poor even after repair for neurotmesis. Function may be improved by tendon transfer at the ankle.

Femoral nerve

The femoral nerve is occasionally injured by stab wounds or operations on the groin. Paralysis of the quadriceps results. The prognosis is good if a laceration of the nerve is repaired early.