Neuromuscular dysfunction after surgical treatment of oral cancer.

Surgical treatment of oral cancer usually includes radical dissection of the neck, in which the sternocleidomastoid muscle is sacrificed. In modified neck dissection the accessory nerve is spared, but may be severed by e.g. manipulation. The facial nerve may also be severed by traction or distension. We have done an electromyographic study of 35 patients, 20 men and 15 women, aged from 21 to 92 yrs, 6 to 176 months after oral cancer operation. EMG findings of the upper trapezius muscle were normal in only six of 32 patients who had had a radical or upper neck dissection, although the accessory nerve had been identified and spared during surgery. The surgeons' evaluation of the risk to the facial nerve was in good correlation to EMG findings, both the orbicularis oris and the mentalis muscle were better preserved, if the risk was considered minor. The loss of motor units in voluntary contraction and the nerve latencies to the muscles were in good correlation to many factors from the spectral analysis of the EMG, e.g. to the root mean square (RMS), to the mean rectified value (MRV), to the mean amplitude and to the number of turns. The accessory nerve is easily damaged, and the injury is often not noted during neck dissection. Significant problems may also arise with lesions of the facial nerve. Quantitative EMG analysis may add to sensitivity of the postoperative EMG studies.