A patient met with recurrent laryngeal nerve palsy while undergoing thyroid surgery. Which of the following muscles of larynx is/are affected?
## **Core Concept**
The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve that supplies several intrinsic muscles of the larynx. These muscles are crucial for vocal cord movement and laryngeal function. The RLN innervates muscles involved in the opening and closing of the glottis.
## **Why the Correct Answer is Right**
The recurrent laryngeal nerve primarily innervates the **posterior cricoarytenoid**, **lateral cricoarytenoid**, **transverse arytenoid**, and **oblique arytenoid** muscles, as well as the **thyroarytenoid** (including the vocalis muscle). Among these, the **posterior cricoarytenoid** is the only muscle responsible for the abduction (opening) of the vocal cords. The other muscles are involved in adduction (closing) and fine tuning of the vocal cords. Therefore, damage to the RLN results in the paralysis of these muscles, leading to vocal cord immobility.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the muscles innervated by the recurrent laryngeal nerve.
- **Option B:** This option is incorrect as it inaccurately suggests muscles not primarily associated with RLN innervation in this context.
- **Option C:** This option might seem plausible but does not correctly identify all the muscles affected by RLN palsy.
## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the recurrent laryngeal nerve palsy typically results in a **paralyzed vocal cord that lies in a paramedian position**. This is because the only muscle not innervated by the RLN is the **cricothyroid**, which is responsible for tensing the vocal cord and is innervated by the external branch of the superior laryngeal nerve. This results in the affected vocal cord being positioned medially due to the unopposed action of the cricothyroid muscle.
## **Correct Answer:** D. All of the above except cricothyroid.