The brachial plexus is a network of nerves that conduct signals from the spinal cord to the shoulder, arm and hand. Just like a train switching yard, the plexus redirects the small nerve fibres that arise from the spinal cord into the large nerves, where they can travel in a protective membrane; this means that damage that occurs to the nerves arising from the plexus, or to the plexus itself, can have far-reaching consequences for the brain, but function to the limb is only moderately impaired. If we didn’t have these ‘junction boxes’, then the consequences for the brain would be less severe, but the limb would drastically lose function, as an entire muscle group would lose connection to the brain.
Causes of Brachial Plexus Lesions
Brachial plexus injuries may arise from several causes, including sports, high-velocity motor vehicle accidents, especially in motorcyclists, and also from birth injuries. Injury from a direct blow to the lateral side of the scapula is also possible. The severity of nerve injuries may vary from a mild stretch to the nerve root tearing away from the spinal cord (avulsion).
Types of Brachial Plexus Lesions
Brachial plexus lesions can be divided into three types:
1. Upper Brachial Plexus Injury
This occurs from excessive lateral neck flexion away from the shoulder. Most commonly, forceps delivery or falling on the neck at an angle causes upper plexus lesions leading to Erb's palsy. This type of injury produces a very characteristic sign called Waiter's Tip Deformity due to loss of the lateral rotators of the shoulder, arm flexors, and hand extensor muscles.
2. Complete Brachial Plexus Injury
Less frequently, the whole brachial plexus can be affected. The entire limb is flaccid and paralysed.
3. Lower Brachial Plexus Injury
Most infrequently, a sudden upward pulling on an abducted arm (as when someone breaks a fall by grasping a tree branch) will produce a lower brachial plexus lesion, in which the eighth cervical (C8) and first thoracic (T1) nerves are injured "either before or after they have joined to form the lower trunk. The subsequent paralysis affects, principally, the intrinsic muscles of the hand and the flexors of the wrist and fingers". This results in a form of paralysis known as Klumpke's paralysis.
Classification of Brachial Plexus Injury
This is the mildest form of nerve injury. It involves an interruption of the nerve conduction, but the nerve fibre is still healthy.
The nerve fibre is damaged, but the covering of the nerve is not; this means that the nerve fibre can regrow down the tube, without having to bypass scar tissue.
This is the most severe form of nerve injury, in which the nerve fibre is completely disrupted by contusion, traction or laceration, and the internal support fibres of the nerve are also affected. Regrowth of the nerve is hampered by the presence of scar tissue, and by cross-connectivity, where nerves are reconnected to the wrong ‘circuits’.
This is the most severe form of nerve injury, where the nerve sheath itself is disrupted. This requires delicate microsurgery, with unpredictable recovery rates.
Expert preventative healthcare
Dr Paul Masters
Dip Hum Sci (Chiro), LCSP, BSc (Comp Ther), MSc (Chiro), DC
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