Erb’s palsy is a paralysis of the arm caused by nerve damage during birth. It affects the upper brachial plexus, a network of nerves that runs from the neck to the arm, specifically the nerve roots at the fifth and sixth cervical vertebrae (C5 and C6). These nerves control the muscles of the shoulder, upper arm, and forearm, so when they’re stretched or torn during delivery, the baby loses the ability to move parts of the affected arm. It is one of the most common neurological birth injuries.
What Causes Erb’s Palsy
During a difficult delivery, the baby’s head can be pulled or pushed to one side while the shoulder stays lodged behind the mother’s pubic bone. This stretches the nerves between the neck and shoulder beyond their limits. The condition most often occurs during shoulder dystocia, where the baby’s shoulder gets stuck in the birth canal after the head has already emerged. To free the shoulder, force is sometimes applied that widens the gap between the head and shoulder, damaging the nerve bundle.
Direct compression of the baby’s shoulder against the mother’s pubic bone can also cause injury even without excessive pulling. In rarer cases, the injury happens before delivery. The natural pushing forces of labor, an abnormal position of the baby in the uterus, or structural uterine differences like fibroids or a divided uterus can all contribute.
Risk Factors
Birth weight is the single most significant risk factor. A baby weighing between about 8.8 and 9.9 pounds (4,001 to 4,500 grams) has 2.5 times the risk of an upper brachial plexus injury compared to a normal-weight baby. For babies over 9.9 pounds (4,500 grams), that risk jumps to roughly 21 times higher. Maternal diabetes, which often leads to larger babies, is an indirect contributor.
The method of delivery also matters. Midforceps delivery carries about 18 times the risk, and vacuum extraction about 17 times, compared to unassisted vaginal delivery. Even low forceps triples the risk. Cesarean delivery, by contrast, cuts the risk roughly in half compared to instrumental vaginal delivery.
How It Looks in a Newborn
The most recognizable sign is called the “waiter’s tip” position. The baby’s arm hangs limp at the side, turned inward, with the elbow straight, the forearm rotated palm-down, and the wrist and fingers curled. It looks like a waiter holding their hand out for a tip, hence the name. This posture results from a specific pattern of muscle weakness:
- Shoulder: The baby cannot lift the arm away from the body or rotate it outward because the deltoid and rotator cuff muscles are paralyzed.
- Elbow: The arm stays extended because the biceps and other flexor muscles can’t bend it.
- Forearm and wrist: The hand turns palm-down and the wrist droops because the muscles that rotate the forearm and extend the wrist are weakened.
Grip strength is often preserved, since the muscles controlling the fingers are supplied by lower nerves that remain undamaged. Some babies also lose sensation along the outer part of the upper arm and shoulder. Parents typically notice the injury immediately: the baby moves one arm normally while the other stays still.
How It’s Diagnosed
Doctors usually recognize Erb’s palsy from the physical exam alone. The limp arm and waiter’s tip position at birth are distinctive. To determine the severity and exact location of the nerve damage, specialists use electrodiagnostic testing, which measures how well electrical signals travel through the nerves and whether the muscles respond normally.
These tests distinguish between two main types of injury. In one type, the nerve fiber itself is damaged but the outer sheath remains intact, which generally means the nerve can regrow along its original path. In the more severe type, the nerve is completely disrupted or torn from the spinal cord, which blocks spontaneous healing. The electrical testing provides measurable data on how much function has been lost and helps predict whether recovery will happen on its own.
Recovery and Physical Therapy
Many babies with Erb’s palsy recover significant function, particularly those with milder stretch injuries where the nerve isn’t torn. The first signs of improvement typically appear within the first few months of life as swelling around the nerve resolves and, in some cases, damaged nerve fibers begin to regrow.
Physical therapy and occupational therapy are the foundation of treatment and can begin within the first two weeks of life. A typical early program involves sessions three to five days a week, with therapists gently moving the baby’s arm through its full range of motion to prevent the joints from stiffening. Techniques include passive stretching (moving the arm for the baby), encouraging the baby to use the affected arm during play, taping to support weak muscles, and splinting to keep the wrist and fingers in a functional position. This intensive schedule often continues for the first 18 months, then gradually decreases as function returns.
Parents are taught exercises to do at home between therapy visits. Consistent daily practice, things like guiding the baby to reach for toys with the affected arm or gently stretching the shoulder during diaper changes, plays a major role in the outcome.
When Surgery Is Needed
If a baby shows no improvement in the first three to six months, the nerve damage is likely too severe to heal on its own, and surgery becomes an option. The goal of early nerve surgery is to restore the connection between the brain and the arm muscles before those muscles waste away from disuse. Ideally, nerve procedures are performed within about five months of the injury.
The type of surgery depends on where and how badly the nerve is damaged. For nerves that are torn but not ripped from the spinal cord, surgeons can bridge the gap using a nerve graft, a small section of nerve taken from elsewhere in the body. For nerves that have been pulled from the spinal cord (the most severe injury), a nerve transfer may be performed. In this procedure, a less critical working nerve is rerouted to take over the job of the damaged one.
In older children who still have significant weakness, secondary procedures like tendon or muscle transfers can reposition working muscles to restore specific movements, particularly shoulder rotation and elbow bending. In the most severe cases, a functioning muscle from another part of the body can be transplanted to the arm using microsurgery.
Long-Term Outlook
The range of outcomes is wide. Children with mild injuries often regain full or near-full arm function within the first year. Those with moderate injuries may recover useful movement but retain some weakness, particularly in overhead reaching, outward shoulder rotation, or forearm turning. These limitations can affect activities like throwing a ball, reaching overhead, or turning a doorknob.
In more severe cases, the affected arm may be noticeably thinner and shorter than the other due to muscle wasting and reduced growth stimulation during childhood. The shoulder joint can develop internal rotation contractures, where the arm gets locked in a turned-in position, if the muscles pulling it inward recover while those pulling it outward do not. Over time, this muscle imbalance can reshape the shoulder joint itself, particularly in growing children.
Even children with persistent weakness often develop strong compensatory strategies. Grip strength is frequently excellent because the hand muscles are spared, which means fine motor tasks like writing and using tools remain largely unaffected. Ongoing therapy through childhood helps maximize the functional use of whatever strength returns.