Brachial Plexus Injuries

Introduction The nerves which give sensation and control to the upper limb are all connected through the brachial plexus. Most brachial plexus injuries result in severe dysfunction of the arm and hand. In spite of advances in diagnosis and treatment, recovery in the majority of cases is still disappointing. The often catastrophic and permanent paralysis, numbness and pain can have a devastating effect on a patient’s ability to work and enjoy life. Optimum management of these injuries involves; accurate diagnosis, repair or grafting of nerves which may recover, secondary operative treatment to stabilise joints by tendon transfer or arthrodesis, late tendon transfers to improve power, intensive rehabilitation and pain management. When it is clear that an arm and hand will remain numb and flail, amputation will rid the patient of a useless limb and may allow for the use of a prosthetic arm or hand. The trauma surgeon must coordinate investigation and treatment by colleagues expert in imaging, neurophysiology, rehabilitation, pain management, counselling and prosthetics. Patients with these devastating injuries require a great deal of support and encouragement. Operative surgery is of little use unless it is planned as part of a multidisciplinary approach. Anatomy of the Brachial Plexus The anterior grey columns contain the cells of the motor axons which pass via the anterior nerve root to the anterior ramus. These fibres, which are therefore post-ganglionic once they leave the cord, pass via the brachial plexus to the peripheral nerves in the arm and thence to the muscles. Sensory axons pass back up the peripheral nerves, through the brachial plexus, to the anterior ramus where they lie with the motor axons. They then pass into the dorsal nerve root where they are joined by sensory axons from the smaller posterior ramus. They then meet their cell bodies in the dorsal root ganglion where they synapse with pre-ganglionic fibres which pass on through the dorsal nerve root to the cord. A lesion in or beyond the anterior ramus is therefore post-ganglionic: if the nerve root is torn out of the cord, the lesion is pre-ganglionic. The brachial plexus contains contributions from the anterior rami of the 5th, 6th, 7th and 8th cervical and the 1st thoracic nerve roots after they have given segmental supply to the prevertebral and scalene muscles. These nerve roots unite into three trunks; the 5th and 6th cervical form the upper trunk, the 7th cervical forms the middle trunk, the 8th cervical and the 1st thoracic the lower trunk. The trunks are located in the posterior triangle of the neck. They divide into anterior and posterior divisions which lie behind the clavicle. The upper two anterior divisions unite to form the lateral cord, the anterior division of the lower trunk forms the medial cord and all three posterior divisions unite to form the posterior cord. In the axilla the three cords approach the first part of the axillary artery, envelop the second part and give off branches around the third part. The roots lie between the scalene muscles, the trunks in the posterior triangle, the divisions behind the clavicle and the cords in the axilla. Presentation Acute injuries are caused by direct or indirect trauma. Direct trauma occurs in open injuries while indirect trauma usually occurs in closed injuries. The commonest cause of closed trauma in Britain is a fall from a motorcycle. Brachial plexus injuries are more likely in any situation where an unprotected person is flung against something hard. They are more common in patients ejected from cars than in those who remain inside. The injury is usually a closed traction or avulsion of the brachial plexus or it’s roots. If the arm is forced downwards the damage may be confined to

the upper roots or trunks. This will result in paralysis of the muscles of the shoulder girdle with relative sparing of the muscles of the forearm and hand: the hand still works but cannot be placed or held in position. If the arm is forced upwards, the damage may be confined to the lower roots or trunks. This will result in paralysis of the muscles of the forearm and hand with relative sparing of the muscles of the shoulder girdle: the hand can be placed but will not work when it gets there. Closed traction injuries can occur during a difficult delivery, when the baby will be found to have a paralysed arm at birth. Erb described the signs of a high root injury in neonates while Klumpke described those of injuries of the lower roots. Traction injuries can also be iatrogenic. The dangerous “Hippocratic” method of reducing a dislocated shoulder, by placing a foot in the axilla and pulling on the arm, can cause a traction injury as the plexus is stretched over the foot. Kocher’s method is much safer. The more severe traction injuries tend to be associated with fractures or dislocations around the shoulder girdle. The disruption of the bony skeleton allows wider displacement of the arm. Very severe traction injuries of this type are often associated with vascular injuries in the subclavian artery or it’s branches. Penetrating injuries such as those caused by glass, knife or shotgun can produce any combination of injuries to the plexus and surrounding structures. The function of the brachial plexus may be compromised more slowly by pressure from something close by. A growing tumour, such as Pancoast’s, can press on the brachial plexus causing progressive dysfunction. A cervical rib or it’s fibrous analogue can irritate the brachial plexus stretched over it. Radiotherapy can cause fibrosis around the brachial plexus resulting in progressive paralysis and pain.

Diagnosis It is important to discover the exact mechanism of injury. In the conscious patient, weakness of one arm is usually obvious. Although it is often difficult in the acutely injured patient, a detailed neurological examination will usually allow one to delineate the extent of the brachial plexus lesion. An accurate record of these initial findings is also useful later. An improvement in the physical signs of a lesion, and the time over which this improvement occurs, may indicate whether it was a neurapraxia, axonotmesis or neurotmesis. A neurapraxia is a “concussion” of a peripheral nerve which usually recovers fully over hours or days. An axonotmesis is the name given to disruption of the axon within an intact enduneurial tube. This recovers over months as the axons grow back down the nerve at the rate of about 1mm a day. The lesion is called a neurotmesis when part or all of the nerve is torn apart or cut through, disrupting all the structural elements. Unless repaired, a neurotmesis will not recover. Even when repaired carefully, the recovery from a neurotmesis is, at best, poor. In the semiconscious patient a lack of spontaneous movement in one arm should make one suspicious of a brachial plexus injury especially if a CT scan has excluded any intracranial cause for a hemiparesis.

Closed injuries in the unconscious patient are the most easily overlooked, but even here there can be useful signs. Denervated skin does not sweat because the sudomotor fibres which control the sweat glands run with the sensory fibres to a particular dermatome. A brachial plexus lesion will disrupt a normal reflex arc. Reflexes should be elicited carefully. The signs of Horner’s syndrome are caused by loss of sympathetic innervation. The pupil is constricted on the affected side and there is loss of sweating on the same side of the head and neck. If the patient is able to open his eyes, unilateral ptosis will be observed. The sympathetic supply to these structures comes from preganglionic fibres which leave the lateral column of grey matter in the spinal cord and pass through the anterior ramus before leaving it in the white rami communicantes to the stellate ganglion. From there the postganglionic sympathetic fibres pass up towards the head. Horner’s syndrome indicates avulsion of the 1st thoracic nerve root. The acutely injured patient should be examined for any other injuries. If the brachial plexus injury is not associated with any other injury, then there is no indication for immediate surgery. The following investigations can then be planned. Myelography is useful for investigating nerve roots injuries. It demonstrates the post-traumatic pseudomeningocoels which form where the roots have been avulsed. The investigation must be delayed for a few weeks to allow the pseudomeningocoels to form. MRI scanning can give earlier information on the nerve roots and it can be combined later with myelography. Nerve conduction studies are not useful initially as they only confirm the neurological deficit found on physical examination. If there has been poor recovery over the first 3 months then nerve conduction studies become more helpful by showing where and whether recovery is occurring. Repeating a full neurological examination at regular intervals is the most useful way of mapping recovery.

Immediate Surgical Treatment Immediate surgical treatment is indicated if the brachial plexus injury is associated with a penetrating injury, vascular injury or bony injury requiring reduction with or without fixation. If the penetrating injury has been caused by something sharp, a knife or glass, it is likely that the nerve lesions will be repairable by end-to-end anastomosis. Each lacerated nerve trunk is repaired with a fine non-absorbable interrupted epineural suture. There is no evidence that a more elaborate repair, such as repair of individual fascicles, confers any advantage. The suture is non-absorbable to induce the minimum tissue reaction in the nerve. The axillary artery lies within the brachial plexus. If a vascular surgeon intends to repair the vessels, it is vital that the nerves are repaired at the same time. Going in later would involve picking the vascular repair off the damaged plexus; a very difficult and dangerous task. In a torn, ragged or massive wound of the kind produced by a gunshot or chainsaw, for instance, a vascular injury in association with the brachial plexus injury is very likely. However there is also likely to be tissue loss. The vascular repair will probably require vein grafts, and, for the reasons just given, the nerves will need to be repaired at the same

time. Gaps in nerves will need to be filled with grafts too. Unfortunately, the best grafts are peripheral nerves taken from another part of the body. There is a short supply of suitable material. Any nerve which is harvested will leave a permanent deficit. The sural nerve is most commonly used first. This leaves numbness along the outer border of the foot. Very occasionally another limb or part of a limb requires primary amputation at the same time as grafts are needed for the primary treatment of the brachial plexus. In this unusual situation, peripheral nerves may be harvested from the amputated part. The nerve grafts are laid side by side to match the diameter of the nerve in which the gap is to be bridged. Each end of each graft is sutured with interrupted epineural stitches. If there is a bony injury which requires reduction and stabilisation, access to the brachial plexus may be gained while exposing the bone. A displaced fracture of the clavicle should be stabilised if associated with a brachial plexus injury. Access to the brachial plexus can be gained through this traumatic clavicular osteotomy. Why shouldn’t we explore the closed brachial plexus injury which is not associated with any of the concomitant injuries just mentioned? The reason is that even if the whole of the brachial plexus is explored acutely, the nature, site and extent of the injury is often unclear. The damaged nerve trunks are usually found to be in continuity. Severe internal damage may extend over some distance. The only options are to leave alone or excise and graft. Which parts of the damaged nerve trunks should be excised and replaced with graft? It is usually impossible to say in a fresh traction injury. The site and extent of damage-in-continuity can only be assessed later by the degree and type of recovery measured clinically, and by nerve conduction studies. Excision of damaged nerve which might later recover would be a disaster and would waste valuable and scarce nerve graft. When a nerve has been completely divided by a closed traction injury it is usually by an avulsion of the nerve roots from the spinal cord. This lesion cannot be repaired. The injury is preganglionic and will not recover even if the avulsed proximal end is sutured back into the spinal cord. Physiotherapy and Supportive Treatment Over the first few weeks after a closed traction injury of the brachial plexus, much needs to be done. The physiotherapist must endeavour to keep all the joints in the arm and hand fully supple otherwise paralysed parts will quickly become stiff. This stiffness rapidly becomes irreversible and will compromise any later recovery of function. A flail arm will hang limply by the side, and the hand will become oedematous. This oedema will make the hand stiffer. The arm must be elevated when resting or carried in a sling when standing. As the patient becomes aware of his likely poor prognosis he will become anxious and depressed about what the future will hold for his job, leisure and social prospects. The help of a clinical psychologist familiar with these injuries is invaluable. Planning of Late Surgical Treatment Clinical examination repeated every four weeks will demonstrate any recovery. If a preganglionic lesion is suspected, as a result of a Horner’s syndrome for instance, an MRI scan or myelogram can be performed after about four weeks. If nerve root avulsions are found, there will be no recovery of nerve function. If the clinical examination and nerve

conduction studies show progressive recovery then one should wait. If there is no recovery of a particular part of the brachial plexus then this should be explored and grafted after enough time has elapsed for any signs of recovery to begin. Six months is a reasonable time to wait before considering exploration and grafting. In a totally flail limb, one complete peripheral nerve from the arm may be used to graft an extensive length of damage in the parts of the plexus which form other nerves. Deciding what to sacrifice to improve severely reduced function requires experience and care. Tendon or muscle transfers may be used to restore the function of a paralysed muscle group. The principles of tendon transfer must be adhered to. It goes without saying that it is useless to transfer a paralysed muscle. A weak muscle will drop one MRC strength grade when transferred. The transferred muscle should, ideally, be phasic with the one it replaces. In other words one should try to use a muscle which normally contracts at the same time as the one it is to replace or supplement. Flexor carpi ulnaris, for instance, is phasic with the finger extensors. Palpate your own flexor carpi ulnaris as you extend all your fingers strongly. It contracts phasically to stop the finger extensors from pulling the wrist into extension. The transferred tendon must have a similar excursion to the tendon it is supplementing or replacing. It must not be forced to go round too sharp a bend. Detaching it from it’s proper insertion should not reduce function more than the transfer will gain. Almost every muscle and tendon in the arm has been used in a reported successful transfer. Here are two examples: if the insertion of trapezius is detached from the acromion with a block of attached bone which is inserted into a groove cut in the outer aspect if the surgical neck of the humerus, the accessory nerve then supplies a muscle which abducts the shoulder; if the insertion of pectoralis major is detached and sutured to the proximal end of the biceps tendon, the elbow is now flexed by a muscle supplied by the lateral and medial pectoral nerves. As these nerves come off the plexus between the trunks and anterior divisions, the transfer is only suitable for lesions of the cords or the posterior divisions. Nerve transfers can improve function. The distal end of a functioning nerve is anastamosed to the proximal end of a nerve which has lost its proximal connection. Intercostal nerves can be used for transfers. Stability of the upper limb can be improved by fusing one or more flail joints. The pectoralis major transfer just described only works well with a stable shoulder. If the shoulder is unstable as a result of weakness of the shoulder muscles, the transfer must be combined with a shoulder fusion. A fused shoulder allows the patient to control the position of the humerus with the shoulder girdle muscles. Fusion of the wrist helps to stabilise the hand in the absence of wrist flexor or extensors. This fusion also allows a functioning wrist flexor or extensor to be used as a transfer for improving hand function. The combination of fusions and transfers suitable for each patient will depend on their exact deficit and functional needs. Shoulder fusion combined with an elbow flexion transfer can restore useful function in a proximal brachial plexus lesion where the hand is spared. Brachial plexus lesions often result in chronic pain with parasthesia in the limb, sometimes combined with phantom pain. Patients with these problems are often helped by visits to a specialised pain clinic where drug therapy can be combined with nerve block injections and psychological support with pain management strategies. Prosthetics

The flail, insensate and painful arm is the worst outcome of a complete brachial plexus lesion. Supporting the limb with a brace can be helpful provided the shoulder has been fused. If elbow control can be gained with a tendon transfer, a wrist fusion can support the hand in an acceptable cosmetic position. Alternatively a below-elbow amputation can allow the use of a better cosmetic prosthesis, provided elbow control exists or has been restored. Some patients still prefer to opt for trans-humeral amputation of the arm. Although with a transfer or fusion to control the shoulder it is possible to use a prosthesis, most patients tend not to. The purpose of the arm is to place the hand for sensory input and function. The pain, parasthesia and sensitivity of the limb can make the wearing of a prosthesis uncomfortable. The purely cosmetic advantage of an artificial hand is often outweighed by the nuisance of it. Complex electro-pneumatic robotic limbs have been developed but these still fail on the sensory side. Even when very accurate movement and placement of the artificial hand can be achieved, a “blind” hand is not worth placing accurately. Trauma surgeons sometimes consider brachial plexus injuries unrewarding to treat. If the final results are sometimes rather disappointing this does not make these severely incapacitated patients less worthy of our best efforts. The best results of treatment are usually less spectacular than in many other types of limb injury, but the maximum possible return to function should still always be the aim.

Further Reading

1.

Gray’s Anatomy. Descriptive and Applied. Thirty-Fourth Edition Edition. Ed D.V.Davies. Longmans, 1972.

2.

Aids to Examination of the Peripheral Nervous System. Medical Research Council Memorandum No. 45. Her Majesty’s Stationary Office,

London, 1975.

3.

Anatomic Variations in the Upper Extremity. Tountas, C.P., Bergman, R.A., Churchill Livinstone, London, 1993.

4.

Lesions of the Brachial Plexus, Including Thoracic Outlet Syndrome. AAOS instructional course lectures. Vol 26, C.V.Mosby, St. Louis,

1977.

5.

Treatment of the Flail Arm. Yeoman, P.M., Seddon, H.J., J.Bone Joint Surg 43B:493-500, 1961.

6.

Tonkin M, Eckersley J, Gschwind C. The Surgical Treatment of Brachial Plexus Injuries. Aust. N.Z. J. Surg. 66: 29-33, 1996.

7.

Carlstedt T, Grane P, Hallin R, Noren G. Return of Function after Spinal Cord Implantation of Avulsed Nerve Roots. Lancet. 346(8986):

1323-5, 1995.

8.

Oxford handbook of Clinical Specialties. Third Edition. Collier J, Longmore J, Harvey J. 724: Oxford University Press. 1991.

9.

Sherburn E, Kaplan S, Kaufman B, Noetzel M, Park T. Outcome of Surgically Treated Birth-Related Brachial Plexus Injuries in Twenty

Cases. Pediatric Neurosurgery. 27: 19-27, 1997.