Injury to the brachial plexus due to birth trauma is a condition that affects the delicate network of nerves controlling movement and sensation in a newborn’s arm, shoulder, and hand, occurring in approximately one to three out of every thousand births worldwide.
Epidemiology
Brachial plexus birth injury happens when the complex bundle of nerves that runs from the spinal cord in the neck down into the shoulder, arm, and hand becomes damaged during the delivery process. This injury affects roughly one to three babies in every thousand births, making it one of the more commonly recognized birth-related nerve injuries that healthcare providers encounter in newborn care.[1][3]
The condition does not appear to favor one gender over another significantly, and it typically affects only one arm rather than both. In the vast majority of cases, the injury involves just a single limb, though the severity and specific nerves affected can vary widely from one infant to another. Because of improved obstetric care and greater use of cesarean delivery when difficult births are anticipated, the incidence has decreased somewhat compared to previous decades, though the injury still occurs regularly across all healthcare settings.[7]
Around 70 to 80 percent of children who experience this type of birth injury recover fully without permanent damage. However, children who do not show substantial improvement within the first three months of life are more likely to experience some lasting impairment, which most commonly affects the shoulder, elbow, or forearm. This means that while many families will see their baby return to normal function, a significant minority will need ongoing care and intervention.[4]
Causes
The root cause of brachial plexus birth injury lies in mechanical stress applied to the delicate nerve fibers during the process of childbirth. The brachial plexus—the name given to this network of five nerves that branch off from the spinal cord at the neck—can become stretched, compressed, or even torn when excessive force is placed on the baby’s head, neck, and shoulders during delivery.[1]
During delivery, particularly when complications arise, the baby’s neck may be stretched to one side as the shoulders attempt to pass through the birth canal. This stretching increases the angle between the baby’s neck and shoulder, putting enormous tension on the nerve bundle. In some cases, the infant’s head and neck are pulled toward one side as the shoulders navigate the birth canal or surgical incision. In other instances, the shoulders themselves may be stretched, or the baby’s arm may be pulled during a head-first delivery. When a baby is delivered in a breech position, with the feet or buttocks emerging first, pressure on the raised arms can also damage these nerves.[2][7]
The severity of the injury depends on how much force was involved and which specific nerves were affected. In the mildest cases, the nerves are simply stretched but not torn—a condition called neurapraxia. This type of injury often heals on its own within the first three months of the baby’s life. More serious injuries involve a rupture, where the nerve is actually torn but not at the point where it attaches to the spine. The most severe injuries, called avulsions, occur when the nerve roots are completely torn away from the spinal cord itself. Avulsion injuries cannot be directly repaired and often require surgical replacement of damaged tissue through nerve transfers.[1]
Risk Factors
Several factors increase the likelihood that a baby will experience brachial plexus injury during birth. One of the most significant risk factors is a difficult delivery, particularly one complicated by shoulder dystocia—a situation where the baby’s shoulder becomes stuck behind the mother’s pelvic bone after the head has already been delivered. This complication requires the medical team to perform specific maneuvers to free the shoulder, and these maneuvers can place significant stress on the brachial plexus nerves.[4][7]
Babies who are larger than average are at increased risk. This includes infants who weigh eight pounds or more at birth, as well as those born to mothers with gestational diabetes, which often results in larger babies. The combination of a large baby and a smaller birth canal creates mechanical challenges during delivery that can lead to nerve injury.[2][7]
Breech deliveries, where the baby emerges bottom-first or feet-first rather than head-first, also carry elevated risk for brachial plexus injury. The abnormal positioning during delivery can result in unusual pressures on the baby’s arms and shoulders. Similarly, prolonged labor that lasts many hours can increase the likelihood of injury, as both mother and baby become fatigued and complications become more probable.[2]
Maternal factors also play a role. Maternal obesity can make delivery more challenging and increase the risk of shoulder dystocia and associated nerve damage. Additionally, mothers who have previously given birth to a child with brachial plexus injury appear to have a higher risk of the condition recurring in subsequent pregnancies, though the reasons for this pattern are not entirely clear.[7]
Symptoms
The signs of brachial plexus birth injury are usually visible immediately after birth or within the first few days of a baby’s life. The most obvious symptom is that the affected arm shows reduced or completely absent movement compared to the other arm. Parents and healthcare providers may notice that the baby is not moving one arm at all, or that movement is significantly weaker on one side. The arm may hang limply at the baby’s side or be positioned in an unusual way, sometimes bent toward the body.[2][7]
When doctors examine the newborn, they will check for the Moro reflex, also known as the startle response. This is a natural reflex where a baby throws back their head, extends the arms and legs, and then pulls them back in when startled. In babies with brachial plexus injury, this reflex will be absent or significantly diminished on the affected side. The affected arm may appear to flop when the infant is moved or rolled from side to side.[2][7]
The baby’s grip strength may also be affected, depending on which nerves were damaged and how severely. Some infants will have a noticeably weaker grip on the injured side. The arm may be held straight at the elbow and pressed against the body. In some cases, numbness is present, though this is harder to detect in newborns than weakness or lack of movement.[7]
The specific symptoms depend on which part of the brachial plexus was injured. The most common type, called Erb’s palsy, involves the upper portion of the nerve network and typically causes weakness in the muscles of the shoulder and the biceps. This accounts for roughly 45 percent of all brachial plexus birth injuries. Children with Erb’s palsy may not be able to move their shoulder properly but may still be able to move their fingers.[4][5]
In more severe cases involving all five nerves of the brachial plexus, called total plexus involvement, children may have no movement at all in the shoulder, arm, or hand. This type represents roughly 20 to 30 percent of brachial plexus injuries. Another variant, called Klumpke’s palsy, affects the lower portion of the nerve network and primarily impacts the muscles of the hand, though this type almost never occurs in babies or young children.[1]
Sometimes, a more severe injury is signaled by the presence of Horner’s syndrome, which occurs in roughly 10 to 20 percent of cases. This condition involves a drooping eyelid, a smaller pupil in one eye, and diminished sweat production on part of the face on the affected side. The presence of Horner’s syndrome usually indicates that the nerve injury is associated with an avulsion and may involve damage to the nerve controlling the diaphragm, which can cause breathing difficulties.[1]
Prevention
Preventing brachial plexus birth injury is challenging because the condition often results from unpredictable complications during delivery. However, certain measures can reduce risk. The most important preventive strategy involves careful monitoring of pregnancy and identification of risk factors before labor begins. When doctors know that a baby is particularly large, that the mother has gestational diabetes, or that other risk factors are present, they can plan the delivery more carefully and consider interventions such as cesarean section if vaginal delivery appears likely to be complicated.[7]
During labor and delivery, healthcare providers trained in managing shoulder dystocia can reduce the force applied to the baby’s neck and shoulders when complications arise. Specific maneuvers and positioning techniques exist to help free a stuck shoulder without placing excessive tension on the brachial plexus. Proper training and quick recognition of developing problems are essential components of prevention.[4]
Despite best efforts, it is not always possible to prevent brachial plexus birth injury. Some cases occur even with excellent prenatal care and skilled obstetric management. Taking steps to avoid difficult delivery whenever possible remains the primary approach to reducing risk, but families should understand that not all injuries can be anticipated or prevented.[7]
Pathophysiology
Understanding what happens inside the body during a brachial plexus birth injury helps explain both the symptoms and the recovery process. The brachial plexus consists of five nerve roots labeled C5, C6, C7, C8, and T1, named according to the vertebrae in the neck where they exit the spinal cord. These five roots intertwine and branch to form the complex network that ultimately gives rise to all the nerves controlling the arm, hand, and fingers. Each nerve has specific functions, some controlling muscle movement and others carrying sensory information like touch and temperature from the hand back to the brain.[1]
When injury occurs, the type and extent of nerve damage determine what functions are affected. In a stretch injury, the nerve fibers are pulled but remain intact. This “shocks” the nerve temporarily, disrupting its ability to transmit signals properly. Because the nerve structure itself is not destroyed, these injuries often heal on their own as the nerve recovers its normal function over weeks to months.[5]
More severe injuries involve actual tearing of nerve tissue. When the nerve is torn but the injury occurs away from the spinal cord, it is called a rupture. Ruptured nerves cannot heal on their own and typically require surgical repair to restore function. The most devastating injuries are avulsions, where the nerve root is completely torn away from the spinal cord itself. Because the injury occurs at the spinal cord level, direct surgical repair is impossible. Instead, surgeons must use nerve transfer techniques, taking functioning nerves from other parts of the body and redirecting them to supply the affected muscles.[1]
The pathophysiology also explains why early intervention matters. When muscles are not receiving proper nerve signals, they begin to weaken and waste away through a process called atrophy. Additionally, joints that are not moved through their full range of motion can develop contractures, where the soft tissues around the joint become tight and stiff, limiting movement even after nerve function returns. This is why physical therapy and range-of-motion exercises are started early, even before the nerves have had time to heal, to maintain muscle and joint health while recovery progresses.[4][8]
Nerve healing is a slow process. When nerves regenerate after injury, they do so at a rate of roughly one millimeter per day. This means that recovery can take months or even years, depending on how far the nerve must regrow to reach the muscles it controls. The distance from the neck to the hand explains why recovery of hand function often takes much longer than recovery of shoulder function in children with brachial plexus injuries.[8]