A 58-year-old female, known case of multinodular goiter underwent sub-total thyroidectomy. After 8 days, patient again presented to the OPD with hoarseness of voice. The nerve which was damaged during the surgery supplies all the muscles marked except: –

**Core Concept**
The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve that supplies the intrinsic muscles of the larynx, except for the cricothyroid muscle, which is innervated by the external branch of the superior laryngeal nerve (EBSLN). The RLN is at risk during thyroid surgery due to its close proximity to the thyroid gland.

**Why the Correct Answer is Right**
The RLN supplies all the intrinsic muscles of the larynx except for the cricothyroid muscle, which is responsible for tensing the vocal cords. Damage to the RLN during thyroid surgery can lead to vocal cord paralysis, causing symptoms such as hoarseness of voice. The RLN runs a tortuous course, making it vulnerable to injury during surgical procedures.

**Why Each Wrong Option is Incorrect**
**Option A:** This muscle is innervated by the recurrent laryngeal nerve (RLN). Therefore, damage to the RLN during surgery would affect its function.
**Option B:** This muscle is also innervated by the RLN. Damage to the RLN would lead to paralysis of this muscle as well.
**Option C:** This muscle is innervated by the recurrent laryngeal nerve (RLN). Damage to the RLN would affect its function.

**Clinical Pearl / High-Yield Fact**
The cricothyroid muscle is the only intrinsic muscle of the larynx not supplied by the recurrent laryngeal nerve, but rather by the external branch of the superior laryngeal nerve. This makes it a key landmark during thyroid surgery to avoid damage to the RLN.

**Correct Answer:** D.

✓ Correct Answer: B. MUSCLE A