A technique for diagnosing the individual patterns of innervation of the trapezius muscle prior to neck dissection.

Based on the techniques of regional anaesthesia, a method for simulating the effects of radical neck dissection on the innervation of the trapezius muscle by selectively and reversibly blocking the accessory nerve and its superficial cervical anastomoses, was developed and tested on 40 patients who were due to undergo radical neck dissection. Action potentials of the three portions of the muscle were recorded after this blockade as well as after radical neck dissection, and compared. It was found that the electromyograms were congruent in 92.5% of the cases. Four patterns of innervation were demonstrated, ranging from complete substitution of the resected or blocked nerves to a remaining muscle activity of less than 20% after blockade or radical neck dissection.