The common peroneal nerve is a major division of the sciatic nerve in the lower leg. It travels down the thigh and wraps around the outside of the knee, near the head and neck of the fibula bone. The nerve controls the muscles responsible for dorsiflexion (lifting the foot and toes upward) and foot eversion (turning the sole outward). Damage typically results in foot drop, where the person cannot properly lift the front part of their foot, often leading to a characteristic “slapping” gait. The superficial path of the nerve makes it vulnerable to injury from compression, acute trauma, systemic disease, or medical intervention.
Causes Related to Localized Compression
The common peroneal nerve is highly susceptible to damage from sustained, localized pressure because of its superficial position as it winds around the fibular neck. This vulnerability means that external forces can easily compress the nerve against the underlying bone, leading to a temporary or permanent loss of function.
One of the most common causes of this compression is prolonged positioning, such as habitually crossing the legs tightly or remaining immobilized for an extended time. The pressure placed on the nerve in these positions can restrict blood flow and directly injure the nerve fibers. Similarly, tight splints, casts, or compression bandages applied to the lower leg or knee can inadvertently squeeze the nerve, leading to neuropathy.
Internal sources of localized pressure include space-occupying lesions like intraneural ganglion cysts or benign tumors that slowly grow and compress the nerve against the fibula. Scar tissue formation around the nerve, often following a local injury or surgery, can also entrap the nerve, causing chronic irritation and symptoms.
Damage from Acute Physical Injury
Damage to the peroneal nerve can result from a sudden, high-energy physical event that causes mechanical disruption. Orthopedic injuries around the knee are a major cause of this acute damage, specifically those involving the fibula bone.
Fractures of the fibular neck can directly lacerate or severely stretch the nerve as it wraps around the area. A severe knee dislocation is another high-risk injury due to the stretching forces applied to the nerve.
Direct blunt force trauma, such as a sharp blow to the outside of the knee, can also cause immediate nerve contusion or crushing. In these traumatic cases, the nerve injury is often a primary mechanical disruption, sometimes accompanied by internal bleeding or swelling that creates secondary compression, leading to immediate foot drop and sensory loss.
Underlying Systemic Health Conditions
Peroneal nerve damage can be a manifestation of a widespread disease process affecting the body’s peripheral nervous system, known as systemic neuropathy. Uncontrolled diabetes mellitus is the most frequent metabolic condition to cause this type of nerve damage.
High blood sugar levels over time lead to diabetic neuropathy, which progressively damages the small blood vessels supplying oxygen and nutrients to the nerve fibers. The peroneal nerve, like other long peripheral nerves, is vulnerable to this metabolic distress.
Other systemic conditions include inflammatory disorders, such as vasculitis or chronic inflammatory demyelinating polyneuropathy (CIDP), which compromise the nerve’s structure or blood supply through autoimmune attack. Hereditary neuropathies, such as Charcot-Marie-Tooth disease, also cause progressive nerve degradation, increasing the likelihood of peroneal nerve dysfunction.
Nerve Damage During Medical Procedures
Damage to the peroneal nerve can occur as an unintended complication of medical or surgical intervention, a category known as iatrogenic injury. Orthopedic procedures around the knee and hip carry a specific risk due to the nerve’s anatomical proximity to the surgical field.
Total knee arthroplasty (knee replacement surgery) is a recognized cause. During the operation, the nerve may be stretched, compressed by retractors, or damaged by bone cement or thermal injury. Correction of a significant knee deformity can also place excessive traction on the nerve, causing a stretch injury.
Hip replacement or other major hip surgeries can sometimes lead to peroneal nerve injury, often as a component of a larger sciatic nerve injury. This damage is typically due to patient positioning, retraction, or leg lengthening during the procedure. The prolonged use of a tourniquet to control bleeding during lower limb surgery can also cause temporary or permanent nerve damage due to pressure and restricted blood flow. Improperly administered injections, especially those near the lateral knee or into the lateral thigh, risk direct needle trauma or nerve irritation.