Peroneal nerve palsy caused by popliteal pseudoaneurysm in a child with hereditary multiple exostosis.

A 12-year-old boy with a family history of hereditary multiple exostosis presented with a 3-week history of progressive knee swelling. The clinical examination revealed drop foot and a loss of extension in his right knee. Evaluation with color duplex ultrasonography, computed tomography angiography, and magnetic resonance imaging revealed a popliteal artery pseudoaneurysm associated with exostosis from the distal femur. This patient was diagnosed as having peroneal neuropathy caused by popliteal artery pseudoaneurysm compressing the nerve in the right popliteal fossa. The pseudoaneurysm was repaired primarily, and the exostosis was excised during the operation. Pain and knee contracture resolved after surgery. The patient was then referred to physical therapy for the management of drop foot.