Brachial plexus injury

Did You Know?

• Musculocutaneous nerve damage weakens elbow flexors, median nerve damage causes proximal forearm pain, and ulnar nerve paralysis leads to weak grip and finger numbness.
• Most closed infra-clavicular injuries due to shoulder dislocation are managed non-operatively initially, and data show that most fail to recover sensory function but recover some motor function.

Causes

Most brachial plexus lesions result from excessive stretching, rupture where the nerve is torn but not at the spinal cord, or avulsion where the nerve is torn from its attachment at the spinal cord. The nerve roots are often stretched or torn from their origin because the meningeal covering of a nerve root is thinner than the sheath enclosing the nerve. A bony fragment, pseudoaneurysm, hematoma, or callus formation of a fractured clavicle can compress the injured nerve. Direct trauma to the shoulder and neck can crush the plexus between the clavicle and the first rib. Obstetric injuries commonly occur from shoulder dystocia during difficult childbirth, most often during vaginal birth but occasionally during Caesarean section, causing excessive stretch that leads to incomplete sensory or motor function. These injuries are most frequent in young adult males.

Mechanism

Injury to the brachial plexus occurs through two constant mechanisms: traction and heavy impact. Traction involves severe movement that pulls or tensions the nerves. Downward traction, caused by tension on the arm that broadens the angle between neck and shoulder, typically produces lesions of the upper roots and trunk, as seen in motorcycle accidents and sports injuries. Upward traction also broadens the scapulo-humoral angle but tears the T1 and C8 nerves, often resulting from humeral fractures and shoulder dislocations. The brachial plexus comprises the last four cervical nerves (C5-C8) and the first thoracic nerve (T1), which split into trunks, divisions, and cords. The lateral cord gives rise to the musculocutaneous nerve and lateral branch of the median nerve; the medial cord forms the medial branch of the median nerve and the ulnar nerve; the posterior cord yields the axillary and radial nerves.

Diagnosis

The most accurate diagnostic method is operative exploration of the potentially injured segments from the spinal roots to end-organs, evaluated under an operative microscope with or without intraoperative electrical studies. Preoperative imaging is the only way to assess the rootlets and intraforaminal portion of the spinal roots proximal to the dorsal root ganglia, as operative evaluation of this section is difficult and rarely clinically justifiable. The best non-invasive test is magnetic resonance imaging (MRI), which can assess the portion of the plexus that cannot be operatively explored, as well as the cervical cord, post-traumatic soft-tissue changes, and associated injuries. However, conventional MRI has a poor specificity of 72%, meaning a high false-positive rate. Diffusion-weighted imaging, such as diffusion tensor techniques, shows potential clinical utility and can produce 3D reconstructions. Electromyography (EMG) performed weeks or months after injury can indicate muscle denervation but is painful, highly user-dependent, and lacks normal values. Severity is graded using classification systems such as Seddon's, which includes neurapraxia, the mildest form involving interruption of nerve conduction without axon loss.

Treatment

Treatment includes orthosis or splinting, occupational or physical therapy, and sometimes surgery. Many infants improve or recover within six months; those who do not have a poor outlook and require further surgery. The ability to bend the elbow by three months of age indicates probable recovery, and additional wrist movement with thumb and finger extension is an even stronger sign of excellent spontaneous improvement. Gentle range-of-motion exercises performed by parents, along with repeated physician examinations, may suffice for patients with strong recovery indicators. Physical therapy interventions in children can improve range of motion, muscle strength, bone mineral density, and shoulder function. For more serious injuries, surgical options include nerve repairs, nerve replacements, and tumor removal. Psychological problems can hinder rehabilitation due to lack of motivation, so psychological well-being should not be overlooked. Recovery can take many years and depends on the initial diagnosis, injury severity, and type of treatment.