Transient Peroneal Nerve Palsies From Injuries Placed in Traction Splints WILLIAM M. MIHALKO, MD, PHD, BERNARD ROHRBACHER, MD, BRIAN McGRATH, MD Two patients thought to have distal femur fractures presented to the emergency department (ED) of a level 1 trauma center with traction splints applied to their lower extremities. Both patients had varying degrees of peroneal nerve palsies. Neither patient sustained a fracture, but both had a lateral collateral ligament injury and one an associated anterior cruciate ligament tear. One patient had a sensory and motor block, while the other had loss of sensation on the dorsum of his foot. After removal of the traction splint both regained peroneal nerve function within 6 hours. Although assessment of ligamentous knee injuries are not a priority in the trauma setting, clinicians should be aware of this possible complication in a patient with a lateral soft tissue injury to the knee who is placed in a traction splint that is not indicated for immobilization of this type of injury. (Am J Emerg Med 1999;17:160-162. Copyright © 1999 by W.B. Saunders Company) The peroneal nerve is a relatively superficial structure that passes over the neck of the fibula. The nerve courses posteriorly down the thigh, then laterally behind the head of the fibula, before dividing into superficial and deep branches anterior to the proximal shaft of the fibula. Its location and surrounding anatomic structures make it susceptible to injury by direct trauma, traction, or a varus force applied to the lower leg. These scenarios have been reported in the postoperative setting,a-3 after lower extremity trauma involv- ing traction or varus forces, 4-9 and from simple inversion ankle injuries. 1° The peroneal nerve is more susceptible to traction types of injuries than any other nerve in the lower extremity because the fibular head and neck act as a fulcrum on the nerve at its lateral most juncture (Figure 1A). Traction applied to the lower extremity will tend to realign the tibia and the femur in a straight line from an anatomic 6 ° of valgus. As the fibular head is directed laterally, it acts as a hard tissue fulcrum against the nerve. If lateral supporting structures are compro- mised then the amount of force the fibular head will have on the nerve can be drastically increased as the tibia and femur act as long lever arms and the knee joint is allowed to open laterally (Figure 1B). The peroneal nerve at this juncture is thus at risk for damage to nutrient vessels or direct damage to axis nerve fibers. 11 Normally, the laminated architecture and the elastic properties of the nerve will serve as an initial defense From Department of Orthopaedic Surgery, State University of New York at Buffalo, Buffalo, NY. Manuscript received July 31, 1997, returned September 10, 1997; revision received September 21,1997, accepted October 2, 1997. Address reprint requests to Dr McGrath, Suite B2, Buffalo General Hospital, 100 High St, Buffalo, NY 14203. Key Words: Peroneal nerve, knee, ligament, nerve palsy, traction splint. Copyright @ 1999 by W.B. Saunders Company 0735-6757/99/1702-0014510.00/(3 160 mechanism to this type of traction force. Once the stretch on the nerve is excessive, however, then the microvascular supply of the nerve is compromised and microhematomas may form. After this point shearing of the nerve sheath may commence along with herniation of the nerve, causing formation of a pseudoneuroma. If the traction force contin- ues in an excessive magnitude then the nerve fibers may begin to rupture. One of the first extensive case reports of peroneal nerve palsies was written by Platt and Lond in 1941.9 Nine cases of different severities of peroneal nerve injuries with varying degrees of mechanisms, treatments, and outcomes were discussed. Since that time, many types of injuries to the peroneal nerve have been documented in the literature, ranging from traumatic 5-7,9 to iatrogenic, 1-3,~2 but transient injuries from traction immobilization in the trauma setting, to our knowledge, have not been reported. This article is a case report of two patients treated in the emergency department (ED) of a regional level 1 trauma center over a 2-month period of time. Both patients pre- sented initially with traction splints on their lower extremi- ties and varying degrees of peroneal nerve palsies. When the traction splints were removed both patients recovered func- tion of their peroneal nerve within 6 hours. This report serves as a reference for the mechanism behind this type of peroneal nerve palsy and also as a reminder that a traction splint may be detrimental if used for the wrong indications. CASE REPORTS Patient 1 A 25-year-old man was struck by a passing motorist while unlocking his driver's side door. He was transported without a traction splint, but upon arrival at 3:50 AMthe trauma team applied a Thomas traction splint to his right lower extremity because of lower thigh swelling and pain suspected to be secondary to a distal femur fracture. The emergency medical technicians (EMTs) re- ported that the patient was moving all extremities at the scene and was neurovascularly intact during transport. After initial evaluation and treatment in the trauma room the patient was sent for computed tomography (CT) of the head and plain radiographs of his face and right lower extremity. The traction splint was left in place. By the time the patient arrived in the ED radiology department, he was unable to dorsiflex his foot, extend his big toe, or feel sensation on the dorsum of his right foot. Radiographic examination of his lower extremity was normal, and an orthopedic consultation was requested for right knee pain and associated peroneal nerve palsy. On examination the patient had a large right knee effusion with tenderness over the lateral epicondyle of his femur and fibular head. There was a grade III lateral collateral ligament injury on the right with a positive Lachman test and no posterior instability detected. There was no valgus laxity noted and the patient had a