Superior spinal accessory nerve function after robotic versus open selective neck dissection in papillary thyroid carcinoma: a retrospective and prospective cohort study

Selective neck dissection (SND) involving levels II–IV for N1b papillary thyroid carcinoma (PTC) may compromise spinal accessory nerve (SAN) function. Robotic thyroidectomy via the bilateral axillo-breast approach (BABA RT) offers technical advantages for SAN preservation. We compared SAN functional outcomes following BABA RT versus open thyroid surgery (OTS) with SND for N1b PTC in a prospective cohort (50 patients per group; July 2024 to December 2024) and a 1:1 propensity score–matched (PSM) retrospective cohort (121 per group; December 2020 to June 2024). SAN function was assessed via electromyography (EMG), active shoulder abduction, trapezius muscle strength, and the Shoulder Pain and Disability Index (SPADI). Oncologic outcomes were evaluated. The prospective cohort showed BABA RT outperformed OTS at 3 months postoperatively: greater SPADI reduction (median difference MD, -5.5 95% CI, -8.0 to -3.0; p < 0.001), greater shoulder abduction (MD, 9.5° 95% CI, 6.8 to 12.1; p < 0.001), and better EMG scores and trapezius muscle strength (p < 0.001). 76.0% of BABA RT patients achieved shoulder abduction ≥ 151° within 3 months versus 14.0% with OTS (p < 0.001). This advantage persisted at 6 months, with a higher rate of SPADI ≤ 2 (56.0% vs. 28.0%; p = 0.005). A retrospective PSM-matched cohort confirmed the SPADI advantage at 6 months. Both cohorts showed BABA RT retrieved more level IIb nodes with comparable oncologic safety. BABA RT provides superior SAN functional outcomes and higher level IIb nodal yield than OTS, supporting its use in selected patients with N1b PTC.