The peroneal nerve, also known as the common fibular nerve, originates as a major division of the larger sciatic nerve. It travels down the back of the thigh before wrapping around the outside of the knee joint, near the head of the fibula bone. This nerve provides motor control to the muscles that lift the foot and toes (dorsiflexion). Additionally, it supplies sensory information from the skin on the outer side of the lower leg and the top surface of the foot. Damage to this nerve disrupts both movement and sensation, leading to a characteristic set of symptoms.
Primary Sensory and Motor Deficits
The most defining symptom of peroneal nerve damage is foot drop, the inability to lift the front part of the foot. This weakness results from the paralysis of the muscles in the leg’s anterior compartment, primarily the tibialis anterior, which are responsible for pulling the foot upward at the ankle. When these muscles cannot contract effectively, the foot remains pointed downward, making it difficult to clear the toes from the ground during walking. The nerve damage also commonly affects the ability to evert the foot, the movement that turns the sole outward. This dual loss of function significantly impairs the foot’s mechanics.
Alongside the motor loss, a distinct sensory deficit is a hallmark of this neuropathy. Patients often experience numbness, or a decreased ability to feel, over the outer portion of the lower leg and the entire top surface of the foot. The sensory loss can sometimes extend into the web space between the first and second toes.
Manifestation in Gait and Movement
The motor weakness of foot drop directly causes observable changes in the way a person walks. The most common compensatory pattern is steppage gait, a high-stepping walk used to prevent the foot from dragging on the ground. To ensure the toes clear the floor, the individual must exaggerate the flexion of the hip and knee, lifting the entire leg higher than normal. This action is a compensation to avoid tripping during the swing phase of the gait cycle.
Another distinctive sign is foot slap, an auditory symptom. With peroneal nerve injury, the weakened dorsiflexor muscles cannot control the descent of the foot after the heel strike. This lack of muscular control causes the forefoot to drop rapidly and forcefully onto the ground. The resulting sound is a noticeable “slap.”
Associated Discomfort and Sensory Changes
While numbness is a primary sensory symptom, peroneal nerve damage can also lead to active forms of discomfort. Paresthesia, commonly described as a feeling of “pins and needles” or tingling, frequently occurs in the same distribution as the numbness—the outer leg and top of the foot. This sensation arises from the abnormal firing of the damaged nerve fibers. A subset of individuals may also experience neuropathic pain, which is often characterized as burning, sharp, or electric-shock-like, and it can be felt along the nerve’s pathway.
Over a longer period, the lack of consistent nerve stimulation to the muscles can result in muscle atrophy. The muscles responsible for lifting the foot and toes may begin to waste away. This thinning or loss of muscle mass, noticeable in the front and outer regions of the lower leg, is a visual sign of chronic motor nerve damage. This muscle wasting can further exacerbate the weakness and functional limitations of foot drop.
Common Causes and Risk Factors
The peroneal nerve is particularly vulnerable to injury due to its superficial location as it wraps around the head and neck of the fibula bone, just below the knee.
External Compression
External compression is a frequent cause of injury, often occurring when sustained pressure is placed directly on the nerve at this site. Prolonged positions such as habitually crossing the legs, extended squatting, or resting the knee against a hard surface can compress the nerve. The application of tight orthopedic devices, such as plaster casts or splints around the lower leg, is another common source of compression-related injury. The pressure exerted by these devices can restrict blood flow and directly crush the nerve against the fibula bone. Additionally, individuals who experience rapid weight loss may lose protective subcutaneous fat, which makes the nerve more susceptible to compression.
Trauma and Medical Procedures
Traumatic incidents involving the knee or lower leg present a high risk for nerve damage. A knee dislocation can stretch or tear the nerve, with up to 40% of patients experiencing this type of injury. Fractures of the fibula bone, especially near its neck, can also directly injure the nerve. Iatrogenic injury, meaning damage caused unintentionally during medical procedures, is a factor in some cases. Surgeries involving the knee or hip, such as a total knee replacement, carry a small but recognized risk of inadvertently stretching or compressing the peroneal nerve.
Systemic Factors
Systemic conditions like diabetes can make the nerve more susceptible to damage and poorer recovery.