Radical neck dissection(RND) has been a standard treatment for the head and neck cancer with metastasis to the cervical lymphatics. The sacrifice of the spinal accessory nerve innervating trapezius muscles creates a definite deficit of the shoulder function. Therefore, the modified radical neck dissection(MRND) preserving one or more structures of the spinal accessory nerve, internal jugular vein or sternocleidomastoid muscle was introduced to minimize the postoperative morbidities.

We studied the shoulder function by clinical examinations and electrodiagnosis for the various types of neck dissection in 39 cases of 24 patients and compared the results of each test according to the types of neck dissection.

Correlation between the clinical parameter and electrodiagnostic results showed a statistical significancy.

The functional results of trapezius muscle in the group of modified radical neck dissection were better than those of the radical neck dissection. The fact that 80% of the cases in the RND group presented incomplete denervation of the trapezius muscle, suggests the innervation of other nerves to this muscle.

Forty five percents of the cases in the MRND group which presented partial denervation of the trapezius muscle, might be due to the damages during operations.

To preserve the spinal accessory nerve, a careful manipulation of the nerve is required. Further studies including an anatomic dissection and intraoperative electrophysiologic evaluation of the trapezius muscle should be performed for the better rehabilitation outcomes.