Short Notes in Plastic Surgery

June 15, 2018

69. Injuries of the Brachial Plexus

Filed under: Chapter 69 — ravinthatte @ 6:06 am

69. Injuries of the Brachial Plexus

General principles

The word brachial has its root in the Latin word Bracchium to mean an arm the plural of that word is Bracchia. The word plexus refers to the complex arrangement of the nerves which supply the arm both its sensations and the motor power to the muscles that move it. The plexus is formed by the cervical (C) 5678 and thoracic (T) 1 mixed spinal nerve roots formed by the axons of the sensory dorsal root ganglion (DRG) and the motor roots of the anterior horn cells (AHC).

Slide1

The format of this and following chapters

This and the following chapters dealing with injuries to the brachial plexus aim at providing a guide to post-graduate students in Plastic and Orthopaedic and Hand surgery in a practical and readymade format to help them organise their thoughts before appearing for their examinations as well as prior to assisting or undertaking surgery on the brachial plexus. This chapter only describes the general principles as indicated in the title. In the event the material in these chapters is not organised in the traditional manner. The description of the anatomy of how the plexus forms (roots trunks divisions and cords) and the various individual branches emanating from the plexus are dealt with and described as and when specific clinical applications are presented. For example, the next chapter will discuss the treatment for a global palsy where all roots of the plexus are avulsed and the relevant anatomical diagrams will be included for ease of understanding.

Acknowledgements

These chapters would not have been possible but for the enormous help given by Drs. Mukund Thatte and Maksud Devle both academic plastic surgeons from Mumbai, India.

A very brief note on history

The history of the treatment of injuries to the brachial plexus reveals that the progress was extremely slow or almost non-existent till the seventies of the last century. In fact, a pioneer in the field of nerve injuries prior to that period had lamented that the treatment of injuries to the brachial plexus is not likely to see any successful outcomes in the foreseeable future.

The element of avulsion in injuries to the brachial plexus

One of the possible reasons for this pessimism mentioned in the previous paragraph might have been the crucial difference between the injuries to the brachial plexus and the other peripheral nerves. In the brachial plexus there is a possibility of an avulsion of the roots of nerves from the spinal cord prior to their emergence from the bony vertebral column before forming (the brachial) plexus. For all practical purposes at present, this avulsion injury cannot be treated at the site of avulsion by any form of neural repair in the hands of a majority of surgeons in this speciality, though some attempts are now underway to achieve this repair. Injuries causing avulsions of all the nerves C5, 6, 7, 8, T1 which together form the brachial plexus resulting in a flail and insensate limb is called a global palsy and unfortunately constitute more than fifty percent of all injuries in the supraclavicular area. Rarely in post-traumatic injuries all nerves can be lacerated beyond the ganglion and can also lead to a global palsy. An avulsion injury might be also partial involving only some nerve roots and therefore results in a paralysis of only some muscles and loss of sensation in the area of the nerve supply.

Slide2

Nomenclature

Traditionally these avulsion injuries are called ‘pre-ganglionic’ because the sensory roots of the nerves have their ganglia located outside the spinal cord. The motor root however emerges from the grey matter directly. Traditionally the term pre-ganglionic is used for the motor component of the injury as well. The terms supraclavicular and infraclavicular are also frequently used in describing these injuries. Most infraclavicular injuries involve the peripheral parts of the brachial plexus at the level of the cords and the nerves ensuing from the cords to the arm. Post ganglionic injuries can in the supraclavicular areas will involve the trunks and divisions. The terms extraplexal and intra plexal are used to describe the nature of repair. When the injury to the plexus is partial some nerves from the undamaged part of the plexus which can be spared without causing too much morbidity are used to neurotize the damaged nerves. This is an intra-plexal form of repair. When no such intraplexal nerve is available as happens in a global avulsion injury (C5678 T1) nerves which do not form a part of the brachial plexus are used to help in the repair to neurotize the affected nerves of the brachial plexus and this is called an extra-plexal repair. Such extra plexal nerves can also be used to neurotize muscles transferred as a free functioning muscle to restore function (please see paragraph towards the end of this chapter).

The diagnosis

The diagnosis of an avulsion injury leading to a completely flail limb or a partially paralysed arm is made by (1) the history of a high velocity accident in which the shoulder was forced down wards and the head and neck are forced to the opposite side. In a vast majority of cases the injury is caused by a heavy fall from a ‘two-wheeler’ and the injury is “closed” in nature.

Slide3

(2) by total lack of clinical recovery and the electro diagnostic studies of the muscles in the affected limb in three months. In fact, the electro-diagnostic study might show deterioration by an increase in the appearance of spontaneous fibrillation in the affected muscles. (3) by radiological investigations such as the appearance of a pseudo meningocele at the site where the nerve was avulsed.

Slide4

The M.R.I. is considered the most appropriate for this purpose. See above (4) A C.T. myelogram is the other option to identify the herniation of the meninges where the nerves have been avulsed. (5) a plain radiograph of the area which shows fractures of the bony vertebral column at the suspected site of avulsion can also indirectly contribute in the diagnosis of injuries to the nerves at the spinal level. Plain X-rays can also diagnose fractures involving the shoulder and other joints in the arm as also a raised diaphragm indicating Phrenic nerve injury and this will influence the treatment undertaken in the surgical rehabilitation of the affected arm. A tentative period of three months is mentioned above as a general consensus.  Reconstructive procedures are usually begun at this time. However in a confirmed (by MRI and electrophysiology) five root avulsion injury with no progress it can start earlier.

Basic principle in the treatment of avulsion injuries of all roots of the brachial plexus

Because no recovery is possible in the avulsed nerves these injuries will require to be treated by bringing in extra-plexal tissue for example a transfer or rerouting of an unaffected nerve in the vicinity, the sacrifice of which will not cause any gross morbidity due to the loss of power in the muscle which it supplied originally or cause unacceptable area of anaesthesia after its sacrifice. As an alternative a vascularised muscle as a free flap can be brought in which can be neurotised by an unaffected extra-plexal local nerve. This muscle is used to re-establish the most desired action or actions that the surgeon feels are crucial in the rehabilitation of the patient. More than one muscle might be used in stages to achieve the desired result at different joints. The conditions mentioned in the earlier description while using a nerve alone and the possible morbidities that it may cause apply here as well (details of such procedures will be given in later chapters for ease of understanding).

Injuries to the plexus with open wounds

As opposed to the above where the final diagnosis must wait, in cases of open injuries caused during accidents or resulting from attacks by sharp instruments the decision to repair the damaged nerves outside the bony canal is easier. If the patient is stable or is rendered stable after the treatment of life saving injuries the wound can be explored thoroughly, the lacerated nerves can be identified and repaired after vascular reconstruction is performed if required.  Repair of torn muscles can be undertaken simultaneously. Here too the surgeon is helpless in repairing avulsions of the nerves from the spinal cord though perhaps reconstructive surgery can begin early in such cases because the diagnosis is made on the table. If the patient is unstable, the injuries to the nerves are mapped, torn ends of the nerves can be approximated with radio opaque vascular clips to prevent retraction and the patient can be explored early by what is called a ‘subacute exploration’. Traditionally gunshot injuries as well as penetrating punctured wounds are treated more conservatively to allow a clearer picture to emerge regarding the exact damage caused to the brachial plexus.

Injuries to the nerves of the brachial plexus which do not include an element of avulsion.

In addition to avulsion injuries there are three other types of closed injuries that the nerves can suffer outside of the bony spinal column. They are based on the classification described by Seddon originally described for other peripheral nerves. Slide14 In the severest form the traction injury can tear the nerve and the nerve loses its continuity. This is called neurotemesis.

The stretch injury can also disrupt a nerve by tearing the axons without losing its apparent continuity because of the sheaths that envelope the nerve can be fully or partially intact. This in the Seddon’s classification is called axonotemesis. Sunderland classified this type of injury further by stating that the damage to the investing layers of a nerve played a part in the severity of the effects of axonotemesis. Slide15 The investing layers are (1) endoneurium which covers the individual axon (2) perineurium which encloses a group of axons or fascicles (3) and the epineurium which invests a group of fascicles or a nerve. In the Sunderland classification axonal damage with an intact endoneurium has the best chances of recovery. Then on, the successive damage to the endoneurium as well as damage to the perineurium delays the recovery of the nerve proportionately.

 

Slide5

Slide6

Slide7

Slide8

The nature of recovery in axonotemesis might be patchy and the surgeon usually waits for some months before ultimately deciding to reconstruct the nerve or to undertake reanimation of the affected muscles by way of plexal constituents when elements within the plexus are available and can be used without significant morbidity or by extraplexal sources by the principle explained in the cases of pan-plexal avulsion. The element of devascularisation of the nerve in closed injuries is difficult to judge. The Sunderland’s classification of axonotemesis is sound but the recovery of the nerve must be evaluated by way of clinical and electro-diagnostic methods. However, at the time of surgical exploration the Sunderland classification can come to the rescue of the surgeon by the examination of the nerve under magnification allowing him to choose the nature of surgery depending upon which investing layers are damaged. A neuroma at the site of the injury will need a linear epineural incision to expose the neuroma’s interior to find out if the whole or any part of the nerve is in continuity. Intra operative electrical stimulation of the nerve and its effect on the muscles that the nerve supplies in the form of contraction help a great deal in the diagnosis of the state of the nerve. Depending on the findings of these observations a repair can be performed after ascertaining the integrity of the investing layers of the nerve.

Slide9

In the third category the axons suffer a temporary loss of function and do not suffer any significant cellular damage. The effects of this condition wane off rapidly. This condition is called neuropraxia in the Seddon classification. The stretching force in this condition is not very severe as revealed by the history and observation for a few hours will show recovery in the patient’s condition.

A paradox

One very important difference in the loss of the function of the muscles as opposed to loss of sensations following avulsion injuries to the brachial plexus needs to be noted. The sensory neuron cell bodies (dorsal root ganglion) of the sensory axons lie outside the spinal cord and therefore even though the sensory roots are avulsed from the spinal cord the ganglionic cell bodies remain intact and therefore Wallenerian degeneration does not extend beyond the ganglion in the affected sensory nerve roots. As a result, though the arm is insensate investigation such as sensory nerve action potential (SNAP) denoting the speed of the sensory electrical impulse remains normal because the ganglion is intact confirming that the injury is in the nature of an avulsion proximal to the ganglion (Pre-ganglionic). This paradox does not occur on the motor side where the Wallenerian degeneration proceeds up to the motor neurons in the spinal cord. Here the electromyogram will show fibrillation at rest and inadequate response to direct stimulation of the muscles and or attempted voluntary contraction as the muscle is paralysed and later degenerates following the loss of its nerve supply.

 

Advances in the treatment of injuries to the brachial plexus 

The progress in the treatment for the effects caused by the injuries to the brachial plexus gathered speed in the seventies of the last century owing to the ‘die hard’ attitude of the surgeons and the development of optical instruments which allowed great magnification of the parts being operated on. The development of fibreoptic light which was brighter less traumatic and could be carried by cables helped a great deal in this effort. Simultaneously fine surgical instruments and micro-sutures came to be developed. On this background Millesi first described (1977) the possibility of repairing fascicles instead of co-opting the cut ends of the whole of the nerve arbitrarily. Slide16 This fascicular repair was applied to the repair of the fascicles of a damaged nerve as well as when a nerve graft was co-opted to repair a gap in the nerve. The same principle of fascicular repair could be used when a cut end of an intact nerve was used as a new conduit to re-neurotise an affected nerve in its distal part or at the time of re-neurotisation of a free muscle transfer.

Slide10

In recent times the repair of nerves has been undertaken with the help of biological tissue adhesives after orienting the cut ends in their normal axis. The tissue adhesive can also be used to bind the cable grafts in bundles.

Common extra-plexal tissue used in the treatment for rehabilitation of injuries to the brachial plexus.

The following nerves can be utilised as extra plexal donors. (1) The spinal accessory cranial nerve (2) The Phrenic nerve (3) The cervical nerves (4) The intercostal nerves (5) The C7 nerve root from the opposite side. (7) The hypoglossal nerve has also been used. If these nerves are found to be not long enough to target the recipient nerve then the repair is accomplished with the help of nerve grafts between the above extraplexal nerve and the recipient nerve damaged in its proximal part.

Source of Nerve Grafts

The two most frequently used nerves to harvest nerve grafts are the sural nerve in the lower leg and the radial cutaneous nerve in the forearm (for the course and approach to harvesting of the radial cutaneous nerve please see the previous chapter on ‘compressive neuropathy of the radial nerve).

Slide11

Both cause only a little morbidity after their harvest. In addition the medial cutaneous nerve of the arm as well as the medial cutaneous of the forearm can be harvested for the purpose of obtaining nerve grafts and also result in very little morbidity. Typically these are all used in a total palsy. In partial injuries the Sural is favoured.

Slide12

Though not extraplexal the ulnar nerve has also been used as a graft. It can also be used as a vascularised graft both pedicled as well as by way of a free microvascular transfer. The sacrifice of the paralysed ulnar nerve is a compromise to achieve rehabilitation in areas supplied by the median nerve.

Free functioning muscle transfer (FFMT)

In global or pan-plexal palsies in order to make the paralysed arm functional at multiple levels, the shoulder the elbow the wrist and the fingers; one or two FFM transfers are undertaken because neurotization by way of extra plexal nerves, for example for the shoulder, does not suffice for all the other areas mentioned. The commonest muscle used for this purpose is the Gracilis muscle which is strong but not bulky and has a long tendon and its harvest leads to a scar which is hidden on the medial side of the thigh.

Slide13

Results

Generally speaking the results of surgery in the treatment of injuries to the brachial plexus by whatever cause are better in children than adults. Treatment in adults above the age of fifty are generally poor though treatment can be undertaken after counselling and advise. The results are generally speaking superior when treatment is begun within three to six months of the injury irrespective of the nature of the injury.

 

 

Advertisements

Create a free website or blog at WordPress.com.