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
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.