Surgery carries a risk of unintended injury to the peripheral nervous system. This damage is known as a peripheral nerve injury (PNI), which involves harm to the nerves outside the brain and spinal cord. While medical teams take significant precautions, PNI is a known, though relatively rare, potential outcome of surgical procedures. The resulting loss of nerve function can manifest as temporary or permanent changes in sensation or movement.
How Nerves Are Injured During Surgery
Nerve injuries during surgery occur through several physical mechanisms related to the surgical environment and tissue manipulation.
One common cause is direct mechanical compression, which happens when a nerve is pressed against a hard surface for a prolonged period, such as during patient positioning. Blood pressure cuffs, tourniquets, or surrounding swelling and hematoma formation after the procedure can also exert damaging pressure.
Another mechanism involves traction, or the stretching of the nerve, which occurs when a surgeon pulls or retracts tissue to gain access to the surgical site. Excessive stretching can damage the internal structure of the nerve, particularly in procedures like joint replacement or fracture repair. In more direct trauma, a nerve can suffer a laceration or complete transection from accidental contact with a scalpel, needle, or other sharp surgical instrument during incision or dissection.
Finally, nerves are susceptible to thermal injury from heat sources. Electrocautery devices, which use electrical current to stop bleeding, can generate heat that damages nearby nerve tissue. The chemical reaction during the polymerization of bone cement in certain orthopedic procedures also releases heat. These forces lead to different degrees of structural damage, which dictates the potential for recovery.
Understanding Levels of Nerve Damage
The severity of a peripheral nerve injury is classified using systems like Seddon’s, which defines three degrees of damage that impact the prognosis. The mildest form is Neuropraxia, involving a temporary loss of nerve function due to a block in signal conduction. The nerve structure remains intact, and recovery is typically complete within weeks to a few months.
A more severe injury is Axonotmesis, where the axon is damaged, but the protective outer sheath remains intact. This requires the axon to regenerate, a slow process, but the preserved sheath guides the regrowth, making functional recovery possible.
The most severe classification is Neurotmesis, which represents a complete physical severance or destruction of the entire nerve trunk, including the axon and surrounding connective tissue. Neurotmesis means the nerve ends are completely separated, making spontaneous regeneration highly unlikely without intervention. While Neuropraxia often resolves on its own, Neurotmesis typically requires surgical repair to bridge the gap and allow regeneration.
Identifying Postoperative Symptoms
The first indication of a nerve injury is usually noticeable changes in sensation or movement once the effects of anesthesia wear off. Common sensory symptoms include numbness (a complete loss of feeling) or paresthesia (a tingling or “pins and needles” sensation). Patients may also report dysesthesia, which is an unpleasant burning or electric shock sensation.
Damage to motor nerves leads to changes in muscle function, including weakness, difficulty moving a limb, or localized paralysis. For example, a patient might experience difficulty lifting their foot (foot drop) or struggle with fine motor control in their hands.
Pain is another symptom, often presenting as sharp, shooting, or severe chronic pain that follows the nerve’s distribution. It is important to immediately report any of these signs—especially severe pain or a complete loss of movement—to the medical team. Early diagnosis improves the ultimate outcome.
Pathways to Healing and Recovery
Recovery from nerve damage is a slow and gradual process, determined by the severity of the initial injury. For mild injuries like Neuropraxia, function typically returns completely within a few weeks to three months as the temporary conduction block resolves. Injuries involving axonal damage, such as Axonotmesis, rely on the physical regeneration of the nerve fiber.
Peripheral nerves regenerate at an average rate of approximately one millimeter per day (about one inch per month). Recovery time is proportional to the distance the nerve must regrow from the injury site to its target. An injury in the shoulder, for instance, could take many months to reach the hand.
Treatment involves modalities designed to support this slow process. Physical therapy is essential for maintaining muscle tone and joint mobility while the nerve reconnects. Medications are also used for pain management, particularly for neuropathic symptoms.
If non-surgical management does not result in improvement after several months, or if the nerve was completely severed, a second surgery may be necessary. This procedure may involve nerve grafting, using a segment of a sensory nerve to bridge the gap, or a direct repair to reconnect the severed ends.