Timing of Repair
The commonly seen closed injuries are initially managed conservatively. Some of them are neuropraxic injuries and recover in few weeks time. Other injuries should be observed up to 10 to 12 weeks for spontaneous recovery. During this period passive range of joints is maintained. After one month of injury an electromyography and CT myelography / MR myelography is performed. Patients with clinical (flail and anaesthetic limb, Horner’s sign, severe deafferentation pain) and radiological evidence of root avulsions( pseudomeningoceles) can be operated at this time. Other patients should be followed for another 6 to 8 weeks for neurological recovery. If there is no recovery, surgery should not be delayed further as results of surgery deteriorate with passage of time. If partial recovery has occurred, exploration and reconstruction of the nerves that are not recovering is indicated. Management of missile injury of the brachial plexus differs considerably from the traction injuries. The tissues are crushed and burnt from a direct contact with the missile and stretched via temporary cavitation. Wounds are heavily contaminated with virulent organisms.These injuries are better treated as delayed repair if there is little or no recovery.
Surgical techniques: Exposure of brachial plexus
Exploration of plexus is done under general anesthesia through a reverse C shaped incision with its horizontal limb about 1 cm above and parallel to the clavicle and the vertical extension along the posterior border of the sternocleidomastoid muscle. The supraclavicular pad of fat is reflected downwards and laterally from the posterior border of sternocleidomastoid muscle. The inferior belly of omohyoid muscle is divided and plexal elements are identified in the space between the anterior and middle scalene muscles. Their absence suggested root avulsions.
The suprascapular nerve is located along the lateral aspect of the upper trunk. Often its proximal end is involved in the upper trunk neuroma. In severe traction injuries suprascapular nerve is retracted distally and might be located in the retro- or infraclavicular region. The spinal accessory nerve is located, once the deep fascia is incised along the anterior border of the trapezius muscle. The phrenic nerve is located on the anterior surface of scalenus anterior muscle and identified by its vertical course and contractions of diaphragm on electrical stimulation. It is dissected distally and then divided and moved laterally for transfer. Infraclavicular plexus is explored through an incision in the deltopecteral groove with its distal extension in the inner aspect of the arm. Exposure of the cords and their terminal branches usually need the division of pectoralis major and minor muscles.
Surgical techniques: Nerve related procedures
1. Direct nerve repair – A direct nerve repair without nerve grafts is possible in only sharply transected injuries (stab and iatrogenic injuries) provided the proximal and distal ends can be approximated without the tension. In more common traction injuries nerve ends are retracted apart and a direct coaptation is not feasible.
2. Nerve grafting – Nerve grafting is the predominant technique employed in brachial plexus repair. Nerve grafts are required in traction injuries to bridge the nerve defects once the neuromas are resected. The commonly used donor nerves are the sural nerve, medial cutaneous nerve of the forearm, lateral cutaneous nerve of the forearm and ipsilateral ulnar nerve as a pedicled vascularized nerve graft in lower root avulsions.
The nerve graft should be 20% longer than the length of the nerve defect. Vascuarized nerve grafts may be more suitable in a scarred bed and at reconstructing large nerve defects. In global brachial plexus with C8 and T1 root avulsions, pedicled vascularized ulnar nerve has been used for a contralateral C7 root transfer to the median nerve.
3. Nerve transfers– Nerve transfer or nerve bypass procedure involves transfer of a functional but less important nerve to the distal injured nerve usually within a period of 6 to 9 months after the injury. Nerve transfers are performed for repair of severe brachial plexus injury in which the proximal spinal nerve roots have been avulsed from the spinal cord. The use of nerve transfers has been a major advance in the field of brachial plexus reconstruction with many different donor nerves being used to restore the desired function.
In partial brachial plexus injuries, both extraplexal and intraplexal nerve transfers, result in good functional outcomes. An important aspect in nerve transfer is to reinnervate the target muscle close to its motor end plates. This reduces the denervation period and functional gains are superior when compared to proximal nerve transfer.
In extraplexal neurotization a non brachial plexus component nerve is transferred to an injured nerve. One of the most commonly performed extraplexal nerve transfer is between the spinal accessory nerve and the suprascapular nerve. This restores useful degree of shoulder abduction and external rotation by reinnervating the supraspinatous and infraspinatous muscles. A simultaneous transfer to the axillary nerve yields much better results in shoulder abduction and is best achieved following a nerve transfer between the triceps branch of radial nerve and the axillary nerve.
Donor nerves in restoration of elbow flexion include ulnar and or median nerve fascicles , medial pectoral nerve , intercostal nerves , phrenic nerve , thoracodorsal nerve, and spinal accessory nerve . An intercostal nerve contains no more than 500 motor fibers , hence at least two or three intercostals nerves (T3, T4 and T5) are transferred to the musculocutaneous nerve. Chuang et al and Gu et al have popularized the transfer of phrenic nerve to musculocutaneous nerve (either directly or with a sural nerve graft).Phrenic nerve to spinal accessory nerve transfer has the disadvantage of requiring a long nerve graft to reach the musculocutaneous nerve . In the exposure of intercostals nerves a semicircular incision is extended from axilla to the chest along the infraareolar region. In restoration of elbow flexion, the deep central branches of the third, fourth and fifth intercostals nerves are dissected up to the costochondral junction and transferred laterally to the musculocutaneous nerve.
Fascicular nerve transfers (ulnar and median)– A longitudinal incision is made along the anteromedial aspect of upper arm. The musculocutaneous nerve is identified after it has traversed the coracobrachialis muscle. In its distal course the musculocutaneous nerve gives off its motor branches to the biceps and brachialis muscles. A longitudinal epineurotomy is made in the ulnar nerve at the level of the biceps motor branch and an isolated fascicle of the ulnar nerve is sutured end to end to the biceps motor branch. In a similar fashion a fascicle of the median nerve is coapted with the motor branch to the brachialis muscle.