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Brachial Plexus Birth Palsy: Definition and Mechanisms of Injury:

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Brachial Plexus Birth Palsy: What is it and why does it occur?

BPBP is the partial or total paralysis (diminished movement) of the upper extremity due to a stretching of the brachial plexus nerves during delivery (Figure 2). The stretching of the nerve occurs at birth, resulting in a rupture or avulsion in the spinal cord.


Figure 2. In a difficult delivery, the baby's shoulder sits in the maternal pelvis (1.Pubis 2.Sacrum). The handling of the newborn stretches the brachial plexus nerves, ultimately resulting in a brachial plexus injury. (Figure 3. brachial plexus nerves).

Brachial plexus anatomy and types of paralysis

The brachial plexus is composed of the union of nerves from the spinal cord, converging in the cervical spine. Nerves carry electrical signals from the brain to control muscle movement and sensitivity. Thus, brachial plexus originates in the neck, passes beneath the clavicle and its roots are distributed in the upper extremity muscles and skin (Figure 3).



Figure 3. The brachial plexus nerves originate in the neck and reach the arm, by passing below the clavicle. 1. Cervical spine 2.Clavicle 3.Brachial plexus nerves


  • The brachial plexus is composed of four cervical nerve roots (C5-C8) and the first thoracic nerve root (T1). The anatomy and function of the brachial plexus is very complex but we can simplify it. The more number of roots are injured, the more number of movements will be affected at birth, worsening the prognosis.
  • The union of C5 and C6 forms the upper trunk, thus enabling the shoulder motion, elbow flexion and forearm supination (rotating the palm upward). Its lesion results in the high C5-C6 palsy or Erb's palsy. The newborn is unable to move the shoulder, the elbow is extended and the forearm pronated (palm down) (Figure 4).


Figure 4. Erb's palsy: the arm is close to the chest, the elbow is extended and the palm turned down. The upper trunk of the brachial plexus is injured.



  • The C7 root continues as the middle trunk, allowing the extension of the elbow, wrist and fingers. Its lesion is associated with the upper trunk injury, resulting in the high C5-C7 palsy or extended Erb's palsy. The newborn is unable to extend the elbow and wrist.


Figure 5. Extended Erb's palsy: the wrist is down. The upper and middle trunks of the brachial plexus are injured.


  • The binding of C8 and T1 roots forms the lower trunk, thus enabling flexion of the wrist and fingers and the performance of fine motor hand movements. Its lesion is associated with C5-C7 injury and is called total brachial plexus birth palsy. The upper extremity is completely flaccid. This injury carries the worst prognosis (Figure 6).


Figure 6. Total brachial plexus palsy: the entire limb is flaccid due to a loss of innervation of all muscles. The entire brachial plexus is injured.

What is a nerve? What happens when it is injured? How does it regenerate?

The nerve is an enclosed, cable-like bundle of axons (Figure 7). The axons conduct electricity, originating from the neuron in the spinal cord level and connecting it to muscles, enabling muscle contraction. Each root of the plexus has about 10,000 axons.


Figure 7. The nerve is wrapped in layers of connective tissue (1,3,4), allowing the projection of the axons to the muscles, enabling muscle contraction.


When a nerve is broken (rupture), nerve regeneration capacity varies according to the degree of rupture of the casing. The more disruption of the nerve sheath, the lesser capacity for regeneration. When a nerve is torn off the spinal cord (avulsion), regeneration is impossible.

Nerve regeneration (growth of axons within its casing) has a speed of 1 mm per day. Thus, during regeneration, the farther the muscle distance from the neck, the longer we will have to wait until reinnervation takes place enabling muscle contractility. Sequentially, the shoulder will move first followed by the elbow and the hand.

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