The Impact of Neck Dissection on the Functional Integrity of Spinal Accessory Nerve in Head and Neck Cancers

Background and objective Neck dissection remains a cornerstone in the management of head and neck cancers with cervical lymph node metastasis. Despite advances in nerve-sparing surgical techniques, shoulder dysfunction remains a recognized complication following neck dissection. This study aimed to evaluate whether anatomical preservation of the spinal accessory nerve (SAN) correlates with its functional integrity and postoperative shoulder function following neck dissection in head and neck cancer patients. Methods This prospective, longitudinal observational study enrolled 25 patients undergoing selective neck dissection (SND) or modified radical neck dissection (MRND) for biopsy-proven head and neck malignancies. Preoperative and postoperative assessments conducted at two and four weeks included clinical shoulder examination, goniometric range of motion (ROM), Shoulder Pain and Disability Index (SPADI), and electromyography (EMG) of the trapezius muscle. Radiological assessment of sternocleidomastoid (SCM) and trapezius muscle volume was performed preoperatively and at six months. Intraoperative nerve monitoring (IONM) was employed in all cases. Results All patients had normal preoperative shoulder function. At two weeks postoperatively, significant deterioration was observed in shoulder abduction, shrug strength, cervical rotation, and SPADI scores (p < 0.001). Partial recovery was noted at four weeks; however, deficits persisted in a subset of patients. Postoperative EMG demonstrated significant changes on the operated side (p = 0.031). At six months, a statistically significant reduction in the trapezius muscle volume was observed (p < 0.001), with a greater percentage reduction in volume in the MRND group compared to the SND group. IONM parameters did not significantly differ between dissection types and did not consistently correlate with postoperative functional outcomes. Conclusions Anatomical preservation of the SAN does not necessarily ensure functional integrity. Early postoperative shoulder dysfunction occurs even in nerve-sparing procedures, with more pronounced structural changes following a modified radical neck dissection. Multimodal postoperative assessment and early rehabilitation are essential. Larger studies with longer follow-up periods are warranted to further clarify the prognostic role of IONM.