In unilateral recurrent laryngeal nerve (RLN) injury, the vocal cord assumes which position?

Explanation

## Unilateral RLN Injury — Cord Position and Mechanism **Key Point:** Unilateral RLN injury results in the affected vocal cord assuming a **paramedian position** (slightly lateral to the midline but not fully abducted). ### Anatomical Basis The RLN innervates all intrinsic laryngeal muscles EXCEPT the cricothyroid: 1. **Posterior cricoarytenoid** — ONLY abductor of the vocal cords 2. **Lateral cricoarytenoid** — adductor 3. **Interarytenoid muscles** — adductors 4. **Thyroarytenoid** — adductor and tensor 5. **Vocalis** — tensor ### What Happens After RLN Injury? | Muscle | Innervation | Status After RLN Injury | Effect | |--------|-------------|------------------------|--------| | Posterior cricoarytenoid | RLN | Paralyzed | **No abduction** | | Lateral cricoarytenoid | RLN | Paralyzed | Unopposed adduction | | Interarytenoid | RLN | Paralyzed | Unopposed adduction | | Cricothyroid | SLN | Intact | Weak adduction | **Result:** Loss of the sole abductor (posterior cricoarytenoid) + intact but weak adductors → the cord drifts to a **paramedian position** (the equilibrium between loss of abduction and weak residual adduction). ### Clinical Presentation **High-Yield:** - **Unilateral RLN injury** → hoarseness, weak voice, breathy quality (cord cannot fully adduct) - **Bilateral RLN injury** → airway obstruction, stridor, potential need for tracheostomy (cords block airway in paramedian position) **Clinical Pearl:** The paramedian position is NOT the same as the resting position of a normal cord. A normal cord abducts during inspiration (posterior cricoarytenoid active) and adducts during phonation (lateral cricoarytenoid, interarytenoid active). Loss of the abductor leaves the cord in a fixed, slightly adducted position. **Mnemonic: "PICA" for RLN-innervated muscles:** - **P**osterior cricoarytenoid (abductor) - **I**nterarytenoid (adductor) - **C**ricothyroid (NO — this is SLN) - **A**dductors (lateral cricoarytenoid, thyroarytenoid, vocalis)