Abstract ID: A37
Abstract Title: A case of distal peroneal nerve palsy with misinterpretation of EMG results.
Poster Type: Either
ABSTRACT BODY
Introduction: After post-operative nerve palsy, EMG is most commonly required to determine the type, the severity and the localisation of nerve injury (1). We present here a case in which interpretation of EMG is difficult and misleading.
Case report: October 11, a 42 y/o motorist male, 70 Kg, 180 cm had his left foot crushed in a collision with a car. It resulted in a displaced comminuted fracture of calcaneus, a severe soft tissue defect of medial aspect of the heel and nearly cut posterior tibial nerve.
October 28, an open reduction and internal fixation with K-wire and external fixation. Post operative pain was huge and unsuccessfully treated by maximal multimodal IV medication. Morphine side effects were becoming critical (itching, sedation, nausea and vomiting).
October 29, a continuous sciatic nerve block was proposed and accepted after discussion with the patient about possible technical difficulty and risk. The block was performed by a senior experienced anaesthesiologist using the lateral midfemoral approach and a stimulating catheter. Contractions of gastrocnemius were stimulated and accepted. 15 mL lidocaine 2% with epinephrine and 15 mL ropivacaine 0.75% were administered through the catheter followed by its connection to a PCA pump containing ropivacaine 0.2%. A complete relief of the pain occurred within 15 minutes. The patient was happy.
November 2nd, the catheter was removed. The patient was admitted in another surgical unit and underwent a wound reconstruction with transfer of abdominal flap on the foot. The two periods' tourniquet placed around the thigh lasted for 60 and 45 minutes. On November 29, an EMG was ordered by the surgeon who had found a couple weeks before a complete hallux paralysis and a sensory loss on peroneal nerve distribution below the fibular neck. The EMG found a normal conduction velocity 40 m/s and decreased amplitude on the peroneal nerve. The tibial nerve was not tested. Presence of fibrillations on tibialis anterior, extensor muscles and medial gastrocnemius concurred to an axonal denervation of the sciatic nerve perhaps secondary to regional technique performed above the popliteal fossa. On December 6, the Senior anaesthesiologist re-examined the patient. He found a Hoffmann-Tinel sign on dorsal aspect of the ankle and on the fibular neck, a normal sensory test of the calves and Achilles' tendon, normal contractions of the tibialis anterior and the gastrocnemius and visible movements of the four other toes. A needle-EMG on the biceps femoris was then ordered. It showed normal insertional and spontaneous activity, normal recruitment. This excludes any nerve injury above the popliteal fossa (1). A CT-scan of the lower limbs was ordered. Surprisingly, an important atrophy of all the muscles of the left lower limb was found. No visible lesion was noted at the puncture site situated at the mid-thigh.
Discussion: In this case, the hallux paralysis was certainly caused by a conjunction of trauma and multiple surgeries on the calcaneus. The peroneal nerve paresis at the fibular neck was perhaps caused by nerve compression due to the leg positioning for 5 hours' reconstruction surgery. The muscular atrophy caused by 8 weeks' immobilisation was perhaps another cause as it is reported in emaciated patients (2). This atrophy might result in muscular fibrillations (2). This case shows how easy the anaesthesiologist is rendered responsible by the smoking gun in his hand (1). It belongs to the anesthesiologist alone to prove that the bullet is not responsible of casualties.
1. Funicane BT, ed. Complications of regional anesthesia. Philadelphia: Churchill-Livingstone; 1999: 271-91.
2. Osselton JW, ed. Clinical Neurophysiology: EMG, Nerve Condution and Evoked Potentials. 1st ed. Cambridge: Butterworth-Heinemann; 1995: 156-208.
ATTACHED FILES
Reg Anesth Pain Med 2004; 29(2):A37