The common peroneal nerve, also known as the common fibular nerve, branches from the larger sciatic nerve. It wraps around the neck of the fibula bone just below the knee, making it particularly vulnerable to injury due to its superficial location. Its primary function is motor control of the muscles that lift the foot and toes upward, a movement called dorsiflexion. Damage to the peroneal nerve typically results in a condition known as “foot drop,” where the inability to lift the foot causes a characteristic high-stepping or “slapping” gait.
External Pressure and Acute Trauma
The most frequent cause of peroneal nerve damage involves direct mechanical injury or prolonged external compression. Because the nerve is situated so close to the skin and bone at the fibular head, it lacks the protective padding of soft tissue found elsewhere. Acute damage can result from a direct blow to the outer side of the knee or a laceration near the fibular neck.
More complex traumatic injuries also pose a significant risk, particularly severe knee dislocations or fractures of the proximal fibula. In these cases, the nerve can be stretched excessively or compressed by displaced bone fragments or surrounding swelling. For example, a severe knee dislocation can injure the common peroneal nerve in up to 40% of patients.
Chronic, sustained pressure on the nerve is another common mechanism of injury, often without a major traumatic event. Habitually crossing the legs applies direct, focused pressure to the nerve as it rests against the fibular head, which is one of the most frequent non-traumatic causes of dysfunction. Other forms of prolonged compression include wearing tight casts, braces, or high boots that constrict the area, or remaining immobile in an awkward position for an extended period, such as during prolonged deep sleep or intoxication.
Underlying Health Conditions and Systemic Factors
Peroneal nerve damage can also arise from systemic diseases or internal growths that compromise nerve health or space. Diabetes mellitus is a prominent systemic factor, as long-term poor blood sugar control leads to diabetic neuropathy. This condition weakens peripheral nerves, making them more susceptible to injury and compression at common entrapment sites like the fibular head.
Inflammatory conditions, such as vasculitis, can indirectly harm the peroneal nerve by reducing its blood supply. Peripheral nerves have a sparse vascular network, making them vulnerable to ischemia, or restricted blood flow, caused by inflammation or disease affecting the small vessels. This lack of oxygen and nutrients can damage the nerve fibers.
Internal growths near the knee joint are another source of damage, as they create a space-occupying lesion that compresses the nerve. Ganglion cysts, which are non-cancerous, fluid-filled sacs often originating from the nearby tibiofibular joint, can expand and slowly squeeze the peroneal nerve. Similarly, benign tumors, such as lipomas or neurofibromas, can exert pressure on the nerve as they grow in the vicinity of the fibular neck. Finally, genetic conditions like Charcot-Marie-Tooth disease cause a progressive, generalized nerve weakness that often manifests significantly in the peroneal nerve, leading to chronic weakness and foot drop.
Injury Related to Medical Procedures
Damage to the peroneal nerve can occur inadvertently as a complication of various medical treatments, a phenomenon known as iatrogenic injury. Orthopedic surgeries, particularly total knee replacement (TKA) and total hip arthroplasty (THA), carry a small but documented risk of nerve injury.
In TKA, the nerve is at risk of being stretched or compressed, especially when correcting a severe valgus (knock-kneed) deformity. The incidence of common peroneal nerve palsy after TKA is generally low, ranging from 0.12% to 0.4%.
During THA, the common peroneal nerve is susceptible to injury due to traction, compression, or stretching, particularly in procedures involving leg lengthening or revision surgery. The nerve can also be compressed by improper retractor placement or by the patient’s positioning on the operating table. Prolonged surgical procedures require specific attention to patient positioning, as sustained pressure on the fibular head against a hard surface can lead to compression injury, even in the absence of direct surgical manipulation.