Introduction>
The sciatic nerve is the largest nerve in the human body and primary continuation of the sacral plexus, which contains nerve fibers from L4 - S3. The usual causes of sciatic nerve injury are fractures(Pelvic, Acetabular, Femoral), and the other lesion is intramuscular injection, and neoplasm and laceration, compression(external or internal), ischemia. Sciatic nerve injury casued by hyperstretching is an extremely rare mechanism.
Case report>
An 14-year-old female patient who had performed ballet training presented with left foot drop.
Based on initial physicial examination, strength was grade 4 in the left knee flexion and 1 in the left ankle dorsiflexion and long toe extensor. The sensation was dimished to pinprick and light touch on the left antero-lateral aspect of lower leg. Eighteen days ago she stretched when she practiced ballet. The posture is the act of stretching both legs apart while lying down and is known as the stretching method of the adductor. The electrodiagnostic nerve conduction studies were performed in both lower limbs. The superficial peroneal, sural and deep peroneal sensory nerve action potentials (SNAP) were absent on the left side. The amplitude of compound muscle action potentials (CMAP) of the deep peroneal motor action potential was markedly decreased than the right side. And its motor conduction velocity was also lower than the right side. When compared with the right side, the amplitude of CMAP on the left tibial nerve was less than half. Moving on to the needle elctromyographic examination, left tibialis anterior, peroneus longus, gastrocnemus(medial head), biceps femoris(short head) showed abnormal spontaneous activity. This electrophysiologic study is compatible with left sciatic neuropathy, partial axonal injury (more severely involved peroneal portion than tibial portion). Magnetic resonance imaging (MRI) studies of the lower legs showed signal change at left common peroneal nerve below obturator internus and it was a suspicious finding to sciatic nerve injury. After the diagnosis, she underwent steroid pulse therapy, EST therapy and conservative rehabilitation. Follow up EMG at 4 and 7 months after injury showed an increase in peroneal and tibial CMAP. 13 monts after ionjury, electric potential was induced in the sural sensory nerve and we confirmed that abnormal spontaneous activity disappeared in tibialis anterior and peroneus longus.
Discussion>
Hyperstretching is an extremely rare mechanism of sciatic nerve injury. Most of the previous case reports concerning stretch related injury involved compression and hyperstretching over a long period(ex. lithotomy position for more than 2 hours). Althoug the exact caus is not yet known, when the sciatic nerve in the gluteal region is damaged, the peroneal division is damaged much more frequently than the tibial division, like this case. In this case, we can identify sciatic nerve injury due to excessive stretching of the adductor muscle.
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