Partially irreversible paresis of the deep peroneal nerve caused by osteocartilaginous exostosis of the fibula without affecting the tibialis anterior muscle

Dysfunction of the lower limb's muscles can cause severe impairment and immobilisation of the patient. As one of the leg's major motor and sensory nerves, the deep peroneal nerve (synonym: deep fibular nerve) plays a very important role in muscle innervation in the lower extremities. We report the case of a 19-year-old female patient, who suffered from a brace-like exostosis 6-cm underneath her left fibular head causing a partially irreversible paresis of her deep peroneal nerve. This nerve damage resulted in complete atrophy of her extensor digitorum longus and extensor hallucis longus muscle, and in painful sensory disturbance at her left shin and first web space. The tibialis anterior muscle stayed intact because its motor branch left the deep peroneal nerve proximal to the nerve lesion. Diagnosis was first verified 6 years after the onset of symptoms by a magnetic resonance imaging (MRI) scan of her complete left lower leg. Subsequently, the patient was operated on in our clinic, where a neurolysis was performed and the 4-cm-long osteocartilaginous exostosis was removed. Paralysis was already irreversible but sensibility returned completely after neurolysis. The presented case shows that an osteocartilaginous exostosis can be the cause for partial deep peroneal nerve paresis. If this disorder is diagnosed at an early stage, nerve damage is reversible. Typical for an exostosis is its first appearance during the juvenile growth phase.