The incidence of temporary hypoparathyroidism after thyroid surgery is 14%-60%, and the incidence of permanent hypoparathyroidism is 4%-11%. The protection of parathyroids has always been the focus and difficulty of thyroid surgery. The anatomical position of the superior parathyroids is relatively fixed, and can be preserved in situ easily; while the anatomical position of inferior parathyroids varies greatly between patients. It is always difficult to look for, identify, and protect them. Concepts such as thyro-thymic ligament and "thymus-vascular-inferior parathyroid plane" were raised to help identify the inferior parathyroids. We found that this surgical strategy can protect inferior parathyroids in situ effectively in our retrospective studies. Thus, we are going to carry out a prospective study to compare the new method and the traditional method of thyroidectomy, to see if more inferior parathyroids can be protected in situ through the new surgical strategy.

Inclusion Criteria:

• initial thyroid surgery; thyroidectomy with/without central lymph node dissection

Exclusion Criteria:

• coexisting parathyroid disease; need lateral neck dissection; history of radio-iodine ablation treatment