INTRODUCTION: The purpose of this study was to determine if intraoperative electromyography (EMG) is a good predictor of neurolysis results on an injured peripheral nerve.

METHOD: 15 SD male rats, 250-300g each, were used. In each rat, the right and left peroneal nerves were exposed, and electromyography was performed. The stimulation site was on the peroneal nerve 3mm distal to its origin from the sciatic nerve. Muscle action potentials were recorded by 2 monopolar needles inserted in the extensor digitorum longus (EDL) muscle belly.

On the right side (control) the intact nerve was stimulated, followed by stimulation of the same nerve after opening of the epineurium, then the perineurium. Muscle action potential amplitudes were recorded at each level.

On the left side the peroneal nerve was crushed by one 5-inch needle holder to a width of 3mm, at a point 6mm distal to its origin from the sciatic nerve. It remained clamped for one minute and was then released. After three months, external neurolysis was performed on the crushed segment of the nerve, extending beyond the area of the injury both proximally and distally. Electromyography was performed before and after the neurolysis, following the same procedure as on the right side. After an additional 2-month survival time, a final EMG study was performed.

RESULTS: 1. On the right side (control), the mean muscle action potential amplitudes (AMP) were 20.6mV at the intact nerve, as compared to 22.1 mV within the opened epineurium, and 22.0 mV within the opened perineurium. The difference among these amplitudes was not statistically significant (P>0.5). 2. On the left side, the mean muscle action potential amplitude at the crushed nerve before neurolysis was 12.34 mV; after neurolysis, it was 18.49 mV, and the difference was statistically significant (p<0.05). 3. 13/15 (87%) had better muscle action potential amplitudes after neurolysis than before, while only 2/15 (13%) had worse. 4. The mean muscle action potential amplitudes two months after neurolysis showed a mild decrease, but this was not statistically significant.

CONCLUSIONS: 1. The muscle action potential amplitudes (AMP) in the normal nerve were not affected by opening either the epineurium or the perineurium. 2. In crushed nerves that need external neurolysis, muscle action potential amplitudes improved in 87% of the cases. 3. Intraoperative electromyography can predict neurolysis results.