Brachial Plexus

The brachial plexus is a complex network of nerves that originates from the spinal cord and is crucial for the sensory and motor innervation of the upper limb. Formed by the anterior rami of spinal nerves C5 through T1, it traverses from the neck, through the axilla, and into the arm, providing essential nerve supply to the shoulder, arm, forearm, and hand.

Anatomy of the Brachial Plexus

Structure

The brachial plexus is anatomically divided into five main components: roots, trunks, divisions, cords, and terminal branches. This hierarchical organization allows for efficient distribution of nerve fibres:

• Roots: The roots consist of five anterior rami from spinal nerves C5, C6, C7, C8, and T1. These roots converge to form three trunks.
• Trunks: The three trunks are:
  • Superior trunk (C5-C6)
  • Middle trunk (C7)
  • Inferior trunk (C8-T1)

Divisions: Each trunk splits into an anterior and a posterior division, resulting in six divisions in total.

Cords: The divisions regroup to form three cords:

Lateral cord

Medial cord

Posterior cord

Terminal Branches: From these cords emerge five primary terminal branches that innervate various muscles and skin regions:

• Musculocutaneous nerve
• Median nerve
• Ulnar nerve
• Axillary nerve

Radial nerve

Function

The brachial plexus is responsible for both motor control and sensory perception in the upper extremity. It innervates muscles such as the biceps brachii and triceps brachii while also providing sensory input from the skin of the arm and hand. The intricate branching allows for precise control over complex movements and sensations.

Clinical Significance

Injuries to the brachial plexus can lead to significant functional impairments. These injuries are often categorized based on their location:

• Upper Trunk Injuries (Erb’s Palsy): Typically result from trauma that stretches or tears the upper roots (C5-C6). Symptoms may include weakness in shoulder abduction and external rotation.
• Lower Trunk Injuries (Klumpke’s Palsy): Affect the lower roots (C8-T1) and can result in weakness or paralysis of hand muscles, often associated with claw hand deformity.

Causes of Injury

Brachial plexus injuries can occur due to various traumatic events such as:  

• Motor vehicle accidents
• Falls
• Sports injuries
• Difficult childbirth

These injuries can range from mild neuropraxia, which may heal spontaneously, to severe avulsions requiring surgical intervention.

What are the common injuries to the brachial plexus

Common injuries to the brachial plexus can arise from various traumatic events, leading to significant functional impairments in the upper limb. These injuries are categorized based on their mechanism and severity, which can vary widely.

Types of Brachial Plexus Injuries

1. Neuropraxia: This is the mildest form of injury where the nerve is stretched but not torn. It typically results in temporary symptoms such as weakness or numbness, often resolving on its own.
2. Neuroma: In this case, the nerve has torn and healed, but scar tissue forms around it, causing pressure that impairs nerve function.
3. Rupture: A rupture occurs when the nerve is torn but remains attached at the spinal cord. This type of injury can lead to significant loss of function and may require surgical intervention.
4. Avulsion: The most severe form of brachial plexus injury, avulsion occurs when the nerve is completely torn from the spinal cord. This often results in debilitating pain and loss of movement in the affected arm and may necessitate complex surgical repair.

Mechanisms of Injury

Brachial plexus injuries can be caused by various mechanisms:

• Traction Injuries: These occur when the arm is forcefully pulled away from the body, often seen in falls or during contact sports. The head may be pushed away from the shoulder, stretching the nerves.
• Heavy Impact: Injuries can also result from direct trauma, such as a heavy blow to the shoulder or a motor vehicle accident. This impact can cause fractures or dislocations that compress or damage the brachial plexus.
• Obstetric Injuries: During childbirth, excessive pulling on a baby’s head can lead to brachial plexus injuries, commonly referred to as Erb’s Palsy (upper trunk injury) or Klumpke’s Palsy (lower trunk injury). These injuries may affect arm movement and function.

Specific Conditions

• Erb’s Palsy: This condition results from injury to the upper trunk (C5-C6) of the brachial plexus, often leading to weakness in shoulder abduction and external rotation. It is frequently associated with birth injuries or falls onto an outstretched arm.
• Klumpke’s Palsy: Involves damage to the lower trunk (C8-T1) and typically results in weakness of hand muscles and a claw-like hand deformity. This can occur during traumatic events where excessive abduction of the arm happens.