The cricothyroid is the only intrinsic laryngeal muscle innervated by the external branch of the superior laryngeal nerve rather than the recurrent laryngeal nerve. By tilting the thyroid cartilage forward relative to the cricoid it stretches and tenses the vocal cords, raising vocal pitch. Cricothyroid dysfunction from superior laryngeal nerve injury produces inability to produce high-pitched notes — a subtle but diagnostically important voice change distinct from the hoarseness of RLN palsy.
| Origin | Anterolateral surface of the cricoid arch |
|---|---|
| Insertion | Inferior border and anterior horn of the thyroid cartilage (two heads: oblique and straight) |
| Nerve Supply | External branch of the superior laryngeal nerve (CN X) |
| Blood Supply | Superior laryngeal artery |
| Actions | Tilts the thyroid cartilage forward, elongating and tensing the vocal cords; Increases vocal pitch by lengthening the vibrating portion of the vocal cord |
|---|
Without cricothyroid action the voice is limited to its lower frequency range, as the muscle is essential for producing the head voice and falsetto registers that require maximum cord elongation.
The external branch of the superior laryngeal nerve is at risk during thyroid surgery as it passes close to the superior thyroid artery before reaching the cricothyroid. Its injury produces the subtle voice change of pitch limitation rather than the obvious hoarseness of RLN damage, and may go unrecognised unless specifically tested by asking the patient to sing the highest notes they can reach.
The cricothyroid muscle is palpable in the midline neck between the thyroid and cricoid cartilages, becoming firm during high-pitched vocalisation.
Cricothyroid denervation from thyroid surgery producing inability to produce high vocal pitches without hoarseness, a subtle complication that may be missed without specific voice testing.
