Common peroneal nerve palsy due to hematoma at the fibular neck.

Common peroneal nerve palsy is an infrequent pathology mostly related to endogenous or exogenous compression. The exogenous compression is frequently related to trauma: knee fractures or hematoma arisen after a direct blow. Fractures may cause a direct lesion of the nerve; hematoma causes a compression of the nerve at the fibular neck causing pain and functional loss. Lesions of the common peroneal nerve can also be related to total knee arthroplasty. The clinical evaluation is characterized by muscle weakness with or without sensory abnormality. The etiopathogeneses of the compression have to be confirmed by ultrasound or magnetic resonance imaging before the surgical treatment. The purpose of this article is to describe a case of common peroneal nerve palsy due to a posttraumatic hematoma after a sport-related injury. We evaluated this case with dynamic ultrasound with good visualization of the morphology of the lesion and of the compression.