CASE REPORT Neuritis ossificans of the common peroneal nerve: a case report Dionysios Trigkilidas & Surjit Lidder & David Delaney & Rob C. Pollock & Asif Saifuddin Received: 16 May 2009 / Revised: 14 July 2009 / Accepted: 15 July 2009 # ISS 2009 Abstract Neuritis ossificans is an extremely rare reactive process affecting peripheral nerves, which can be challeng- ing to diagnose and treat. Magnetic resonance imaging (MRI) is an excellent imaging modality for these lesions, showing inflammatory reaction around the nerve. Only a few cases have been previously reported, and all of the patients underwent surgical resection. In this article we report the first case of neuritis ossificans affecting the common peroneal nerve, treated non-operatively, and we review the literature. Keywords Neuritis . Ossificans . Common peroneal nerve . Magnetic resonance imaging . Myositis Introduction Neuritis ossificans is an extremely rare reactive process affecting peripheral nerves. In the few cases reported, all patients presented with pain and paraesthesia along the particular nerve distribution. The aetiology of the condition is unknown, with none of the previously reported patients identifying a history of trauma. Histologically, these lesions are characterised by zonal architecture [1] similar to that found in myositis ossificans. Case report A 32-year-old woman presented with a 4-week history of pain over the lateral aspect of her right knee. The pain was constant, shooting in nature, present at night and resistant to simple analgesics. There was no history of trauma or metabolic disease. She was unable to bear weight due to the pain and maintained her knee at 30° flexion for comfort. On palpation there was tenderness along the course of the common peroneal nerve and an indistinct palpable lump over the fibular head. She had a positive Tinel’ s sign and decreased sensation on the lateral aspect of the right leg, foot and big toe. Ankle dorsiflexion and eversion were 4/5 motor strength on the Medical Research Council (MRC) scale. Initial radiographs were unremarkable. Magnetic reso- nance imaging (MRI) showed a well-defined 23 mm× 15 mm×15 mm lesion with partially calcified margins closely related to the common peroneal nerve with surrounding soft tissue oedema and swelling of the nerve proximal and distal to the lesion (Figs. 1a–c). Computed tomography (CT) confirmed the presence of peripheral D. Trigkilidas : S. Lidder : R. C. Pollock The London Sarcoma Unit, Royal National Orthopaedic Hospital NHS Trust, Stanmore, UK D. Delaney Department of Pathology, Royal National Orthopaedic Hospital NHS Trust, Stanmore, UK A. Saifuddin Department of Radiology, Royal National Orthopaedic Hospital NHS Trust, Stanmore, UK D. Trigkilidas (*) 103 Linden Gardens, Enfield, Middlesex EN1 4DY, UK e-mail: diotrigkilidas@hotmail.com Skeletal Radiol DOI 10.1007/s00256-009-0766-y