Introduction

The peroneal nerve is a nerve that is essential for the function of your lower leg. Nerves help you feel things and move muscles, but the peroneal nerve plays a vital role in helping you walk.¹ This nerve is a bit more vulnerable than other nerves. That’s because it wraps around the fibular head, a bone on the outside aspect of your knee. Due to its location, it is a bit more exposed. Injury to this nerve can result in numbness, tingling, pain, and weakness in the leg. More concerningly, it can cause an issue known as “foot drop”, where a patient has a problem lifting their foot, making it difficult to stand or walk without significant help or compensation.¹
Injury to the peroneal nerve happens when there is compression along the outside of the knee.  The most common times this occurs are with people who frequently cross their legs at the knee, those with a cast that is too tight over the peroneal nerve, or individuals on bed rest for various reasons. Some people who may be more prone to developing peroneal nerve injury include, but are not limited to, those with a lower body mass, anorexia, arthritis, diabetes, or a history of a knee or ankle injury.¹ Common knee injuries that can result in a peroneal nerve injury include knee fractures, dislocations, or fibula fractures at the knee or ankle level.¹

Anatomy of the peroneal nerve

The peroneal nerve comes from the sciatic nerve, which is commonly referred to in the setting of sciatica or lumbar radiculopathy. The peroneal nerve controls and activates the lower extremity.² The superficial peroneal nerve tells the muscles in the foot to move in eversion. It allows sensation outside the leg and on the top of the foot.  On the other hand, the deep peroneal nerve will enable you to move the foot and toes upward and provide sensation in the webspace between the first and second toes. 

The peroneal nerve is responsible for motor and sensory functions, which help you feel and move your lower leg. Some of the main tasks of the peroneal nerve include dorsiflexion, or flexing the foot up, extension of the great toe, and eversion of the ankle.²

The peroneal nerve is most vulnerable along the lateral aspect of the knee and lower leg, where it wraps around the fibular neck. This region is prone to compression, with a cast or leg crossing, but is also in a vulnerable place in the setting of trauma.  For example, studies have shown that about 40% of patients with a dislocation of the knee also suffer from a peroneal nerve injury.²

Common causes of compression

Tight casts or braces 

When the plaster of a cast is tight or lacks padding, it can cause compression of the lateral aspect of the knee, potentially resulting in a peroneal nerve injury.³ A cast around the ankle that ends just below the knee has the most risk of compressing the peroneal nerve.⁴ Sometimes it's not just improper casting; in some cases, patients will experience so much swelling that what may have been initially an appropriate cast suddenly becomes too tight and causes compression of the peroneal nerve. 

Prolonged leg crossing

Prolonged or habitual episodes of crossing the legs can result in lateral pressure on the outside of the knee, leading to compression of the peroneal nerve.³ Just like leg crossing, long periods of kneeling, maybe occupational or participating in an activity you don’t do often, such as picking strawberries, can cause a compression of this nerve, resulting in foot drop.⁴ 

Poor positioning in bedridden patients 

Patients who are hospitalised or immobilised, or unable to adjust their positioning, may be prone to a peroneal nerve injury due to compression of the peroneal nerve over the lateral aspect of the knee.³ In all of these situations, individuals who are very thin, or suffering from anorexia, or those with autoimmune conditions or diabetes may be more prone to this type of injury than others.³

Clinical presentation

Gate changes, motor, and sensory symptoms  

A foot drop is one of the most common symptoms of a peroneal nerve injury.  It can cause you to walk differently, very noticeably, causing the patient to lift one knee much higher than the other to ambulate forward. Other symptoms include, but aren’t limited to, difficulty moving the foot or toes, numbness, tingling, and pain in the shin or top of the foot.¹

Diagnosis

First, a healthcare provider may examine you. During this examination, they may notice foot drop, weakness with moving the foot up or rolling it out to the side, or numbness and tingling in specific areas innervated by the peroneal nerve. 

Imaging options to diagnose this condition include CT scans, ultrasounds, or a special type of MRI called a Magnetic Resonance Neurography. An electromyogram also examines how muscles contract when the nerve is stimulated. Ultimately, a nerve conduction study reveals how nerves transmit electrical impulses.¹

Management and treatment

Ultimately, treatment is determined by several factors, primarily by where the nerve is damaged or pinched and the severity of the injury.¹ If the healthcare provider cannot determine this based on physical exam, further diagnostic imaging or testing may be necessary to determine the severity of injury. 

If the injury is caused by a too-tight cast or the habit of crossing your legs, the first step in treatment would be removing the triggering event, whether that involves removing the cast, loosening it, or retraining the patient to avoid habits that trigger this type of injury. 

If the injury is caused by or worsened by improper gait, one option may be to use splints, orthotics, or braces to help correct the patient's gait. This, combined with physical therapy and gait training, can yield significant overall results for the patient.¹

Finally, in cases where conservative treatments do not work or the injury is severe enough, some patients may need to be evaluated to see if they would be good candidates for surgery. The provider will relieve nerve pressure and/or repair the nerve during these surgeries. Sometimes, the surgeon may need to harvest tissue from another source to replace or supplement a severely injured nerve.¹

Prevention

Fortunately, there are many ways to help prevent a peroneal nerve injury. Proper padding and careful casting can prevent nerve compression in the first place. In a hospital setting, healthcare staff must encourage regular repositioning for immobilised patients or may have difficulty adjusting themselves. Finally, spreading awareness about this condition and its causes is essential to help people adapt their lifestyles, such as avoiding sitting with their knees crossed. As always, it is crucial to seek immediate medical attention if you develop numbness or an injury to the lower leg at any point.

Conclusion

Compression of the peroneal nerve can be prevented with proper patient education, casting, and training of healthcare personnel. The key to treating this condition appropriately is early recognition and prevention.  Teaching patients and healthcare providers simple habits can help prevent avoidable conditions. By being aware of the anatomy of the lower leg and particularly vulnerable areas, such as the fibular neck, we can avoid injury to these areas.  As always, it is essential to consult a healthcare provider if you or a loved one believes an injury to the peroneal nerve may affect them.