Erb’s palsy is a nerve injury that affects a newborn’s arm, caused by damage to a bundle of nerves near the neck and shoulder during birth. It occurs in roughly 1 to 2.5 out of every 1,000 live births, making it one of the more common birth injuries. Most cases affect only the upper arm and shoulder, though more severe forms can involve the entire arm and hand.
Which Nerves Are Involved
The injury targets the brachial plexus, a network of nerves that runs from the spinal cord in the neck, through the shoulder, and down into the arm. These nerves control all movement and sensation in the arm, from the shoulder down to the fingertips. In classic Erb’s palsy, the damage hits the upper portion of this network, specifically the nerve roots that exit the spine at the fifth and sixth cervical vertebrae (C5 and C6). These two roots control the muscles responsible for lifting the arm at the shoulder, rotating it outward, and bending the elbow.
When the injury extends to a third nerve root (C7), it also affects the ability to straighten the elbow and wrist. In the most severe cases, all five nerve roots feeding the arm are damaged, resulting in a completely limp arm with no movement or sensation. A classification system developed by the surgeon Alain Narakas groups these injuries into four categories: upper Erb’s (C5-C6 only), extended Erb’s (adding C7), total palsy (all roots), and total palsy with Horner’s syndrome, where damage also affects nerves to the eye, causing a drooping eyelid on the same side.
How It Happens During Birth
Erb’s palsy occurs when the baby’s head and neck are stretched away from the shoulder during delivery. This most often happens during shoulder dystocia, a complication where the baby’s head delivers but one shoulder gets caught behind the mother’s pubic bone. The pulling force needed to free the shoulder can overstretch the brachial plexus nerves on that side.
Several factors increase the risk. Larger-than-average babies (a condition called macrosomia) are more likely to experience shoulder dystocia. Prolonged or difficult labor, breech deliveries, and the use of vacuum or forceps extraction also raise the likelihood. Maternal diabetes, which tends to produce larger babies, is another contributing factor. The injury can range from a mild stretch that bruises the nerves to a complete tear or avulsion where the nerve root is pulled away from the spinal cord entirely.
What It Looks Like in a Newborn
The hallmark sign is a characteristic arm position sometimes called the “waiter’s tip” posture. The affected arm hangs limply at the baby’s side, rotated inward with the elbow straight and the wrist flexed. It looks as though the baby is holding their palm out behind them, waiting for a tip. The baby can’t lift the arm, bend the elbow, or rotate the forearm palm-up on the injured side.
Parents and doctors also notice that the baby’s startle reflex (the Moro reflex, where both arms fling outward when the baby feels unsupported) is absent or incomplete on the affected side. In milder cases, the baby may have some weak movement at the shoulder or elbow but clearly favors the other arm. In total palsy, the entire arm is flaccid with no grip strength, and the baby may not respond to touch on that arm at all.
How Severity Is Assessed
Doctors use standardized scoring systems to track the injury over the first weeks and months. The Active Movement Scale measures how well the baby can move each joint, grading muscle function from no contraction at all to full movement against gravity. This scale is useful from birth onward. A separate scoring tool called the Toronto Test Score becomes reliable starting at three months and helps predict which babies will need surgery: a score below 3.5 at three months suggests the injury is severe enough that surgical repair may be necessary.
The three-month checkup is considered the most critical milestone. Doctors look specifically for two things: whether the baby can bend the elbow (biceps function) and whether the baby can lift the arm at the shoulder (deltoid function). If neither of these movements has returned by three months, the injury is unlikely to resolve on its own.
Physical Therapy and Early Treatment
Physical therapy and occupational therapy should begin within the first few weeks of life. In one documented case, therapy started as early as 11 days after birth. The initial focus is on maintaining flexibility in joints that the baby can’t actively move, since unused joints stiffen quickly in a growing infant.
Parents are taught to perform gentle passive movements on the affected arm several times a day. These typically include rotating the shoulder outward, lifting the arm overhead, bending and straightening the elbow, turning the forearm palm-up, and extending the wrist and fingers. A common regimen involves 10 repetitions of each movement, repeated four to five times throughout the day. The goal isn’t to force the arm but to keep joints mobile so they’re ready when nerve function returns.
Positioning the arm correctly during rest matters too. Parents learn to keep the affected arm gently rotated outward using a light bandage or small weight, which prevents the shoulder from developing inward contractures. One specialized approach called the Sup-ER protocol uses a small splint worn about 22 hours a day that holds the forearm and shoulder in an outward-rotated position. This splint can be started as early as six weeks of age and aims to preserve normal shoulder joint development while waiting for nerve recovery.
When Surgery Becomes Necessary
Most babies with mild Erb’s palsy recover significant function without surgery, particularly those in the upper (Narakas I) category. But for babies who show no biceps function by three months, or no ability to lift the arm against gravity by six months, surgical repair offers the best chance of meaningful recovery.
Surgery is typically performed between four and six months of age. Earlier intervention, before six months, is associated with better outcomes because nerves regenerate more effectively in younger tissue. Waiting beyond 18 months reduces the potential for nerve regrowth and increases the risk of complications.
The type of surgery depends on what the surgeon finds. During the operation, electrical testing reveals how much signal is getting through the damaged nerve segment. If more than half the signal passes through, simply freeing the nerve from scar tissue may be enough. When less than half gets through, the surgeon performs nerve transfers or grafts. These procedures reroute healthy, less critical nerves to take over the functions of damaged ones. For example, a nerve that controls part of the chest muscle can be redirected to power elbow bending, or a small branch from an intact nerve in the forearm can be transferred to restore biceps function. For children between ages two and five who still lack the ability to rotate the shoulder outward, tendon transfer surgery can redirect existing muscles to fill that gap.
Recovery Timeline and Outlook
The severity of the initial injury is the strongest predictor of long-term outcome. Babies with upper Erb’s palsy (C5-C6 only) who show early signs of recovery in the first few weeks generally do well, with many regaining full or near-full arm function within the first year. Those with extended Erb’s palsy (involving C7) take longer and may retain some weakness in elbow extension or wrist control.
Children with total palsy face a longer recovery with more residual limitations. Even with surgery, they may not regain full hand function, though meaningful improvements in shoulder and elbow movement are common after nerve repair. For babies with Horner’s syndrome alongside total palsy, the prognosis is the most guarded, as the nerve damage extends to the deepest roots of the plexus.
Long-term complications can develop as the child grows, particularly when the nerve injury is moderate to severe. The most common issue is a shoulder joint that doesn’t develop symmetrically, since imbalanced muscle pull during growth can reshape the ball-and-socket joint. Contractures (permanent tightening of muscles or tendons) can limit range of motion if passive stretching isn’t maintained consistently through childhood. Some children develop a noticeable size difference between their arms, with the affected side being slightly shorter and thinner due to reduced nerve input during growth years. Ongoing occupational therapy through childhood helps maximize function and address these secondary changes as they emerge.