Common peroneal nerve entrapment in an adolescent during a growth spurt: a case report and hypothesis on growth-related vulnerability

Background Common peroneal nerve entrapment at the fibular neck is a well-recognized cause of foot drop, but atraumatic cases in adolescents may be diagnostically challenging. Rapid growth during adolescence may increase local nerve vulnerability through growth-related neuro-musculoskeletal factors, although direct evidence remains limited. Case presentation We report a 16-year-old male who presented with a two-week history of weakness in the left ankle and hallux dorsiflexion without a clear history of trauma, habitual leg crossing, prolonged squatting, tight footwear, systemic disease, or family history of hereditary neuropathy. He had experienced a rapid growth period over the preceding six months, with an increase in height of approximately 6 cm and one shoe size. Physical examination revealed marked weakness of ankle and hallux dorsiflexion, sensory reduction over the lateral leg and dorsum of the foot, and a positive Tinel sign at the fibular neck. High-resolution ultrasonography demonstrated focal enlargement of the left common peroneal nerve at the fibular neck, and electrodiagnostic testing—including fibrillation potentials, motor unit action potentials (MUAPs), and reduced recruitment on needle electromyography of the tibialis anterior—was compatible with focal common peroneal neuropathy. Conservative treatment was unsuccessful. Surgical exploration revealed a discrete, tendon-like fibrous band compressing the nerve at the lower fibular neck; after division of the band, the nerve was fully decompressed. At 14 days postoperatively, dorsiflexion strength and sensory symptoms had improved, and at 3 months, the patient's mother reported continued improvement. Conclusion This case suggests that common peroneal nerve entrapment should be considered in adolescents with atraumatic foot drop; a recent growth spurt may be a potential predisposing factor, although causality cannot be established. Ultrasonography and electrodiagnostic testing may help localize the lesion. Surgical decompression may be effective when symptoms are severe or conservative treatment fails. Because the proposed growth-related vulnerability is inferred from a temporal association in a single case, this report is intended to generate—rather than to prove—a clinically relevant hypothesis that warrants testing in larger, prospective series.