Retained blackthorn causing peroneal tendonitis: a case report.

We present the first reported case of peroneal tenosynovitis secondary to a retained blackthorn in a patient with a 4 months history of persistent pain and swelling around her lateral malleolus following a penetrating injury. Ultrasonography reported considerable subcutaneous fluid but no identifiable foreign body. Magnetic resonance imaging confirmed peroneal sheath synovitis with a possible retained foreign body posteriorly. Surgical exploration revealed marked synovitis and chronic inflammation of the peroneal sheath with the tip of a blackthorn deep to peroneus longus. This case illustrates the many ways in which penetrating blackthorn injuries may present. In particular it highlights the need for a high index of suspicion for retained foreign material and the need for further imaging and surgical exploration when symptoms do not resolve.