Common Peroneal Nerve Entrapment Neuropathy

Abstract

The common peroneal nerve runs around the fibular head in a shallow subcutaneous layer. It can be externally compressed by the rigid fibula at the bottom and it is fixed by fibrous tissue where it passes through a tunnel composed of the peroneus longus- and soleus muscle, and it is affected by dynamic factors. When the nerve is impaired by external compression, relatively strong paralysis and drop foot may develop. In the presence of impairment due to dynamic factors (idiopathic disease), sensory impairment is the main symptom; motor weakness may be absent or slight. In patients with intermittent numbness and pain elicited by standing and walking, it can be difficult to differentiate between common peroneal nerve neuropathy and lumbar spine disease. Common peroneal nerve conduction studies may not detect common peroneal nerve impairment. Idiopathic disease is not uncommon but may be overlooked; repetitive plantar flexion tests are useful as diagnostic provocation tests. Common peroneal nerve entrapment neuropathy can be treated by less invasive neurolysis under local anesthesia.

Appendix

Supplement 1: Peroneal Nerve Neuropathy Associated with Weight Loss

Common peroneal nerve palsy can be elicited by rapid weight loss [15]. The exact mechanisms are unknown [7]; malnutrition associated with weight loss is not implicated [16]. A loss in adipose tissue around the peroneal head and partial fibrosis may result in peroneal neuropathy [15]. Margulis et al. [17] reported bilateral lower limb peroneal nerve palsy in patients who lost 40 kg of their body weight in the course of a year. While conservative treatment was ineffective, symptom improvement was obtained by nerve decompression around the peroneal head. According to Broekx and Weyns [7], among 200 patients who underwent external neurolysis for foot drop, about half were associated with weight loss primarily after bariatric surgery; the average weight loss in their series was 19.4 kg (range 2–74 kg).

Supplement 2: Fabella Syndrome

The fabella is a sesamoid bone located in the lateral tendon of the gastrocnemius muscle near the knee; 69% of Japanese cadavers harbored a fabella [18]. Although its clinical implications are unknown, it may be of some biomechanical benefit. Patients with a fabella are usually asymptomatic. When its presence elicits pain in the posterolateral knee primarily due to loading or knee extension, a diagnosis of fabella syndrome is made.

The common peroneal nerve passes over and just outside the fabella. When the common peroneal nerve is wide and thin in this area, static and dynamic neuropathy can be observed [18,19,20]. The diagnosis of common peroneal neuropathy secondary to a fabella is based on clinical symptoms. Compression by a fabella is confirmed by electrophysiological-, ultrasound-, and magnetic resonance imaging studies [19, 20]. Treatment is conservative and includes nerve blocks; when these therapies are ineffective, the nerve is decompressed by removal of the fabella.