The common peroneal nerve is a major nerve that travels down the leg, providing both movement and sensation to the lower limb. This nerve is particularly vulnerable to injury where it winds around the head of the fibula, just below the knee. Its primary function is to control the muscles responsible for lifting the foot and toes upward, a movement known as dorsiflexion. Damage to this nerve results in a condition called “foot drop,” characterized by the inability to properly clear the foot while walking.
External Pressure on the Nerve
The superficial location of the common peroneal nerve near the fibular head makes it highly susceptible to mechanical force or sustained external pressure. This compression is one of the most frequent causes of nerve damage, often occurring when the nerve is physically squeezed against the underlying bone. Prolonged or habitual positioning that puts pressure on the outside of the knee can lead to a compressive neuropathy, such as sitting with the legs crossed for extended periods.
Other forms of sustained pressure, such as extended squatting or kneeling, also endanger the nerve by forcing it against the bone. Individuals who are immobilized for long periods, perhaps due to intoxication, deep sleep, or prolonged hospital stays, may unknowingly place their leg in an awkward position that compresses the nerve. This sustained pressure restricts blood flow and physically deforms the nerve tissue, leading to temporary or permanent dysfunction.
Restrictive medical devices are another common source of external pressure. A cast, splint, or tight compression bandage applied to the lower leg, especially if improperly fitted or tightened after swelling subsides, can exert excessive force on the nerve. This iatrogenic, or medically-induced, compression can lead to nerve injury that presents shortly after the device is applied or adjusted. The nerve is compressed against the fibular head, which lacks the protective muscle and fat layers found elsewhere in the leg.
Physical Injuries and Surgical Complications
Acute physical trauma to the knee or lower leg can directly injure the common peroneal nerve, leading to sudden and significant damage. Direct blunt force or a sharp object impacting the outside of the knee can sever or severely bruise the nerve. Traumatic dislocations of the knee joint pose a particularly high risk, with common peroneal nerve injury occurring in up to 40% of acute cases.
Fractures involving the fibula or tibia also carry a risk of nerve damage, either from the initial break or from sharp bone fragments lacerating the nerve. The nerve can also be injured by a severe stretching force, or traction, often associated with a forceful ankle or knee injury.
Damage can also occur as a complication of invasive medical procedures, a phenomenon known as iatrogenic injury. The common peroneal nerve is at risk during certain orthopedic surgeries, including total knee arthroplasty and hip replacement surgery. The damage may result from the nerve being stretched during joint manipulation, compressed by surgical instruments, or inadvertently cut during the procedure.
Underlying Health Conditions
Peroneal nerve damage can also arise from systemic diseases or internal growths that affect the nerve without external force. Metabolic disorders are a frequent internal cause, with Diabetes Mellitus being the most common systemic disease leading to a peripheral neuropathy. High blood sugar levels over time can damage the small blood vessels supplying the nerve, leading to reduced blood flow and nerve fiber degradation.
Inflammatory conditions can also cause damage by triggering an immune response that attacks the nerve tissue itself or the blood vessels supplying it. Conditions such as vasculitis or Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) can lead to inflammation and swelling of the nerve, resulting in dysfunction. These processes cause damage from within, making the nerve more vulnerable even to minor compression.
In some cases, space-occupying lesions can internally compress the nerve as it travels down the leg. Tumors or cysts, such as a ganglion cyst or a nerve sheath tumor, can grow near the nerve and exert pressure, leading to a progressive neuropathy.
Exposure to certain toxins, including heavy metals or excessive alcohol use, can cause a generalized peripheral neuropathy that manifests focally in the common peroneal nerve. Additionally, significant, rapid weight loss can remove the protective subcutaneous fat padding around the fibular head, making the nerve more vulnerable to external compression injuries.