Brachial Plexus Causes
Brachial plexus injuries can happen to anyone at any age due to some physical trauma or accident. In infants this type of injury is caused by some kind of difficulty or complication during childbirth. The brachial plexus is the bundle of nerves that controls muscle movement and sensation in the arms. When damaged the arm affected may lose sensation or even movement.
Most infants do not end up with a permanent disability; they typically heal within a few months and have no lasting symptoms. Severe damage can happen in rare cases and this damage may need to be corrected with surgery. As birthing procedures have improved over the last few decades, brachial plexus injuries have decreased in newborns, but they can still be caused by a number of factors.
Brachial Plexus Damage
The brachial plexus nerves are attached at one end to the spinal cord and at the other end to smaller nerves in the arms. They run through the neck, so if the neck gets stretched too much, such as by stretching the head and shoulder in opposite directions, these nerves can become damaged. Damage may range from mild stretching to small tears to larger tears and in the worst cases complete separation from the spinal cord.
The extent of damage dictates how severe the symptoms will be, which include numbness, weakness, loss of sensation, and paralysis. Each of the five nerves of the brachial plexus control different parts of the arm so where the symptoms are seen depends on which nerves have been damaged. For infants that have experienced a brachial plexus injury, most will heal naturally with time, others will need some physical therapy, and a few will need surgery to repair extreme damage.
Large Birth Weight
There are several risk factors for brachial plexus injuries in infants. One of these is a large birth weight. Any way in which the neck gets stretched too far during birth can cause an injury. When the infant is too large to fit easily through the birth canal this stretching can happen to varying degrees. The medical term for a large fetus is large for gestational age, and is considered to be any baby with a birth weight higher than the 90th percentile. The average weight for a baby at birth is seven pounds.
A woman’s doctor should be estimating the birth weight as the pregnancy proceeds. It is not an exact science, but various types of measurements can lead to a relatively accurate estimation of how big the child will be at birth. This helps a doctor decide if a woman will need to have a Cesarean section to avoid complications such as a brachial plexus injury.
Difficult or Obstructed Labor
Another risk factor for a brachial plexus injury is any difficult or prolonged labor. Any time labor becomes a challenge, for whatever reason, and goes on for much longer than normal, there is a risk that a birth injury like brachial plexus damage will occur. This may be from an obstructed birth or simply from mistakes made by the delivery team, including excessive pulling or misuse of instruments.
Shoulder dystocia during delivery is one of the most common causes of a brachial plexus injury. A normal delivery is when the head comes out first, but sometimes the shoulder gets stuck after the head emerges. This is called shoulder dystocia and as the baby is being pushed out the pressure can stretch the brachial plexus to the point of injury. A brachial plexus injury is the most common complication to the baby of a shoulder dystocia during birth. Up to 15 percent of those born with this complication will end up with a brachial plexus injury.
A breech birth is not an ideal way for a baby to be born. A baby should come out head first, but when the buttocks emerge first from the birth canal, it’s called a breech birth, and there is potential for complications. As the infant comes out in this direction, his/her arms are pushed above the head. This makes it more difficult to get the entire body out, and the pressure applied can cause stretching of the brachial plexus nerves. As with a large fetus, a doctor should be able to recognize the risk of breech birth and determine if a Cesarean section (C-section) would be a safer option for the mother and baby.
Mishandling During Birth
Doctors and other caregivers are better trained in delivering babies than ever before, but they can still make mistakes. Those mistakes can lead to birth injuries, including brachial plexus damage. Whether during a difficult birth or a normal birth, the person delivering the baby may pull too hard on an arm or a shoulder and stretch out the baby’s neck. It’s also possible that instruments, like forceps, will be used inappropriately and cause damage to the nerves.
Cesarean Section Birth
A C-section is when a baby is delivered through an incision in the mother’s abdomen, instead of vaginally. When a doctor expects complications or a difficult labor, he or she may determine that a C-section is a safer option. This may be decided in the case of a baby presenting breech who can’t be turned around, or if the baby’s weight is expected to be larger than normal. Having a Cesarean section does not always prevent brachial plexus injuries. It is rare, but they can occur during this procedure.
Other Brachial Plexus Injuries
Birth-related brachial plexus injuries are the most common causes of associated palsies, but they can also be the result of trauma and injury to adults and children. A fall, a car accident, a bullet wound, and even playing contact sports can all lead to the kind of stretching or other trauma that damages the brachial plexus.
For most infants with this type of injury, regardless of the cause, the outlook is good. They will recover completely and heal with time. In some cases, however, the damage is too great to heal naturally, and surgery may be needed. Surgery cannot always correct all the damage, though, and in rare cases a child may live with the signs of brachial plexus injury for the rest of their lives.