A brachial plexus injury is damage to the network of nerves that runs from your neck down into your arm, controlling all movement and sensation from your shoulder to your fingertips. These injuries range from a mild stretch that heals on its own to a complete tear from the spinal cord that requires surgery. About 70% of cases in adults are caused by motorcycle or bicycle accidents, while in newborns the injury occurs in roughly 1.5 out of every 1,000 births.
The Nerves Involved
The brachial plexus is formed by five nerve roots that exit the spinal cord in your neck, labeled C5 through T1. These roots weave together and eventually branch into five major nerves, each responsible for a different part of your arm. The musculocutaneous nerve bends your elbow. The axillary nerve lifts and rotates your shoulder. The median nerve moves your forearm and parts of your hand. The radial nerve controls muscles throughout the upper arm, elbow, and hand. The ulnar nerve handles fine finger movements.
Because all five nerves originate from this single bundle, an injury in the neck or shoulder area can knock out function across multiple parts of the arm at once. Which nerves are damaged, and where along the bundle the damage occurs, determines exactly what you lose.
How These Injuries Happen
In adults, the most common cause is high-speed trauma. Motorcycle and bicycle crashes account for about 70% of brachial plexus injuries, typically when the head and shoulder are forced apart violently, stretching or tearing the nerves. Contact sports, falls, and any forceful impact that separates the neck from the shoulder can also cause damage. The underlying mechanisms include direct pressure, traction (pulling), compression, and stretch-induced loss of blood flow to the nerve.
In newborns, the injury usually happens during a difficult delivery, particularly when the baby’s shoulder gets stuck behind the mother’s pubic bone (shoulder dystocia). The pulling force needed to free the baby can stretch or tear the brachial plexus.
Types of Injury, From Mild to Severe
Brachial plexus injuries fall into four categories based on how badly the nerve is damaged:
- Neuropraxia (stretch): The nerve is pulled or strained but not torn. This is the mildest form and often heals without surgery.
- Constriction: The nerve is pinched or squeezed, sometimes by surrounding tissue or bone.
- Rupture: The nerve is torn in half. It will not heal on its own and typically requires surgical repair.
- Avulsion: The nerve root is ripped completely away from the spinal cord. This is the most severe type and the hardest to treat, since the nerve can’t simply be reattached at its origin.
Scar tissue can also form around a disrupted nerve, creating what’s called a neuroma. This mass of scar tissue blocks nerve signals and can cause pain, sometimes requiring its own surgical treatment.
Erb’s Palsy vs. Klumpke’s Palsy
Doctors classify brachial plexus injuries partly by which nerve roots are affected. When the upper roots (C5 and C6) are damaged, it’s called Erb’s palsy. This causes numbness and paralysis in the shoulder and upper arm. A classic sign is the “waiter’s tip” position, where the arm hangs at the side with the wrist turned inward. Erb’s palsy is the more common pattern in newborns.
When the lower roots (C8 and T1) are damaged, it’s called Klumpke’s palsy. This affects the wrist and hand, causing loss of sensation and paralysis in the fingers. Klumpke’s palsy is less common but can be especially disabling because it compromises the fine motor control you need for gripping, writing, and everyday hand use.
In severe accidents, all five roots can be damaged simultaneously, leaving the entire arm paralyzed and numb.
Signs That Point to a Serious Injury
The hallmark symptoms are weakness, numbness, or complete loss of movement in part or all of the arm. You might feel a burning or electric shock sensation shooting down the arm at the moment of injury. In milder cases, the arm may feel heavy or tingly but still function. In severe cases, the arm hangs limp.
One important red flag is a condition called Horner syndrome, where the pupil on the injured side becomes smaller and the eyelid droops. This signals that the lowest nerve roots near the spinal cord are involved, which often means an avulsion has occurred. If this sign appears alongside arm weakness, the injury is likely severe.
How It’s Diagnosed
After a physical exam testing strength and sensation throughout the arm, doctors typically order imaging and electrical nerve testing. MRI can show whether nerve roots have been torn or pulled from the spinal cord. Nerve conduction studies and electromyography (EMG) measure how well electrical signals travel through the nerves and whether the muscles they supply are still receiving input.
There’s a common belief that you need to wait two to three weeks after the injury before EMG gives reliable results. While it’s true that the full extent of nerve degeneration can take one to four weeks to develop, a skilled specialist can detect significant nerve damage almost immediately by looking at how motor units recruit during the test. Early testing can still provide useful information, even if a repeat test later gives a more complete picture.
Treatment Options
Mild stretch injuries (neuropraxia) often recover on their own over weeks to months. Physical therapy during this period keeps joints flexible and prevents muscles from wasting while the nerve heals.
For more severe injuries, surgery becomes necessary. The optimal window is three to six months after the injury. Waiting longer reduces the chances of a good outcome because muscles that go too long without nerve input eventually lose their ability to respond, even if the nerve is repaired.
Nerve Transfer vs. Nerve Grafting
The two main surgical approaches are nerve grafting and nerve transfer. In a nerve graft, a less important nerve is harvested from elsewhere in the body and used to bridge the gap in the damaged nerve. In a nerve transfer, a working but less critical nerve near the injury site is rerouted to take over the job of the damaged one.
For upper brachial plexus injuries (C5-C6), international data strongly favors nerve transfers. In pooled studies, 83% of patients who received nerve transfers regained strong elbow flexion, compared to 56% of patients who received nerve grafts. For shoulder function, patients who received dual nerve transfers (rerouting two donor nerves instead of one) achieved an average shoulder abduction of 122 degrees, while nerve graft patients averaged only 50 degrees. That’s the difference between raising your arm overhead and barely lifting it to the side.
What Recovery Looks Like
Nerves regrow at roughly one millimeter per day, or about one inch per month. That rate is essentially fixed, so recovery timelines depend heavily on how far the signal needs to travel from the repair site to the target muscle. An injury repaired near the neck might take a year or more before the hand shows improvement, simply because of the distance involved.
Recovery isn’t just about nerve regrowth. Intensive physical and occupational therapy plays a major role in retraining the brain to use muscles that may now be wired differently, especially after a nerve transfer. Progress tends to be gradual. Early signs include tingling in previously numb areas, followed by flickers of muscle movement that slowly build in strength over months. Full recovery can take two to three years in some cases, and the final result depends on the severity of the original injury, how quickly surgery was performed, and how consistently rehabilitation is maintained.
Not everyone regains full function. Avulsion injuries, in particular, carry the most guarded outlook. But advances in nerve transfer techniques have significantly improved outcomes for upper plexus injuries over the past two decades, giving many patients meaningful use of their arm even after devastating trauma.