The sternothyroid is a thin, flat muscle that runs from the back of the manubrium (the upper part of your breastbone) upward to the oblique line of the thyroid cartilage, the largest cartilage of the larynx. It belongs to a group called the infrahyoid or “strap” muscles, which sit in pairs on either side of the front of the neck, layered over the trachea and thyroid gland. Despite being one of the less famous muscles of the body, the sternothyroid plays a surprisingly active role in voice production, swallowing, and airway mechanics, and it shows up frequently in surgical decision-making during thyroid and head-and-neck operations.
Where It Sits and What It Connects
The sternothyroid lies deep to its neighbor, the sternohyoid muscle, which runs from the sternum up to the hyoid bone. Both muscles are sometimes called “strap muscles” because of their long, ribbon-like shape. The sternothyroid originates from the posterior surface of the manubrium of the sternum and sometimes from the first costal cartilage. It ascends and inserts onto the oblique line of the thyroid cartilage. Because it attaches to the larynx rather than the hyoid bone, the sternothyroid is the primary strap muscle that pulls the larynx downward. It is innervated by the ansa cervicalis, a loop of nerves formed by branches of the first three cervical spinal nerves, and it receives its blood supply largely from branches of the superior and inferior thyroid arteries.
Functionally, the sternothyroid acts as a depressor of the larynx. When it contracts, it draws the thyroid cartilage (and with it the entire laryngeal framework) inferiorly. This simple action turns out to have consequences for how you speak, how you swallow, and how your upper airway behaves during breathing.
The Sternothyroid’s Role in Voice and Pitch
Vocal pitch depends on the tension and length of the vocal folds inside the larynx. The cricothyroid muscle, an intrinsic laryngeal muscle, is the primary driver of pitch elevation because it tilts the thyroid cartilage forward to stretch the vocal folds. But the sternothyroid and the other strap muscles do not simply sit idle during phonation. Electromyographic recordings from untrained singers show that at the lowest frequencies a person can produce, the strap muscles (sternothyroid, sternohyoid, and thyrohyoid) are active while the cricothyroid is essentially silent. As the voice rises into the middle of the range, strap muscle activity drops and the cricothyroid takes over. Then, at the highest pitches, the strap muscles fire up again.1PubMed. Electromyographic activity of strap and cricothyroid muscles in pitch change
The pattern suggests the strap muscles are not directly controlling pitch in a fine-tuned way. Instead, they stabilize or reposition the larynx so that the cricothyroid can do its job at different extremes of the vocal range. Think of them as adjusting the platform so that the precision instrument can work properly. Research in rhesus macaques supports this idea from a different angle: electrically stimulating the sternothyroid muscle on its own raised the fundamental frequency of voice, and the maximum pitch elevation occurred when the sternothyroid was stimulated together with the cricothyroid or geniohyoid muscles.2PubMed. Effect of geniohyoid, cricothyroid and sternothyroid muscle stimulation on voice fundamental frequency of electrically elicited phonation in rhesus macaque In other words, the sternothyroid’s influence on pitch is real, but it acts in coordination with other muscles rather than as a solo operator.
When the Sternothyroid Causes Voice Problems
Because the sternothyroid directly pulls the larynx downward, abnormal activity in the muscle can interfere with speech. A recently reported case described a patient whose larynx visibly descended during phonation without any corresponding movement of the hyoid bone, a pattern that pointed specifically to dystonia of the sternothyroid muscle as the cause of the voice disorder.3Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics. Sternothyroid Muscle Dystonia as an Unusual Cause of Dysphonia: A Case Report and Review of Diagnostic and Therapeutic Strategies Dystonia is involuntary, sustained muscle contraction. When it strikes the sternothyroid, the larynx is pulled down inappropriately during speech, changing the resonance of the vocal tract and making the voice sound strained or effortful.
This diagnosis is rare and can be tricky to pin down. Most muscle tension dysphonia involves the intrinsic laryngeal muscles or the suprahyoid muscles, so clinicians are not always looking for a culprit below the larynx. The clue in this case was the disconnect between hyoid and laryngeal movement: normally when the larynx drops, the hyoid moves with it, because the thyrohyoid muscle links the two. Isolated laryngeal descent without hyoid movement narrows the suspects to the sternothyroid. Treatment strategies for sternothyroid dystonia can include targeted botulinum toxin injections, though the published experience is very limited.
Dividing the Muscle During Thyroid Surgery
The sternothyroid muscle drapes directly over the thyroid gland, which means surgeons performing thyroidectomy frequently need to decide whether to cut through it or carefully retract it to one side. Dividing the muscle makes it easier to expose the upper pole of the thyroid, especially in large goiters that extend below the sternum. But for years, surgeons worried that cutting the sternothyroid might degrade voice or swallowing afterward, given the muscle’s known involvement in laryngeal positioning.
Several prospective studies have addressed this question, and the consistent finding is that dividing the sternothyroid does not cause meaningful voice or swallowing problems. One study comparing patients who underwent partial cutting of the sternothyroid during total thyroidectomy with those whose muscle was left intact found a brief dip in maximum vocal frequency about two weeks after surgery in both groups, but by one month there was no difference between them.4PubMed Central. Partial Cutting of Sternothyroid Muscle during Total Thyroidectomy: Impact on Postoperative Vocal Outcomes A separate study measuring both acoustic parameters and patient-reported voice symptoms found no significant differences between the division and preservation groups at two weeks or three months.5PubMed. The functional impact on voice of sternothyroid muscle division during thyroidectomy
Swallowing outcomes tell a similar story. A prospective study of 114 patients undergoing thyroid surgery found no statistically significant change between preoperative and postoperative scores on a validated swallowing questionnaire, and the results held regardless of whether the sternothyroid was divided on one side or both.6PubMed. Impact of Sternothyroid Muscle Division on Patient-Reported Swallowing Outcomes Following Thyroid Surgery: A Prospective Study Taken together, these findings have largely reassured surgeons that cutting the sternothyroid to gain better access is a reasonable trade-off when the anatomy demands it. The muscle appears to recover or compensate well enough that patients do not notice a lasting functional deficit.
The Infrahyoid Flap in Head and Neck Reconstruction
Beyond thyroidectomy, the sternothyroid muscle has a second surgical life as a building block for reconstructive flaps. The infrahyoid musculocutaneous flap is a technique first described in the 1980s that uses the infrahyoid strap muscles, including the sternothyroid and sternohyoid, along with the overlying skin. The flap is nourished by the superior thyroid artery through perforating branches that travel through these muscles. Once the muscles are divided from their lower attachments, the entire paddle of muscle and skin can be rotated on its vascular pedicle to cover defects in the mouth, throat, midface, or parotid region after cancer surgery.7The American Journal of Surgery. The infrahyoid musculocutaneous flap in head and neck reconstruction
The infrahyoid flap is sometimes described as an underused option. It offers a thin, pliable tissue paddle that is harvested from a donor site in the same surgical field, avoiding the need to take tissue from a distant part of the body like the forearm or thigh. A comprehensive review of the technique reported success in a series of 40 cases with no total flap losses and only one instance of superficial skin necrosis.8PubMed. The infrahyoid flap: a comprehensive review of an often overlooked reconstructive method Its main limitation is size: the flap works well for small to medium defects but cannot cover the large tissue gaps that free flaps from distant sites handle. For oral cavity and oropharyngeal reconstruction where the defect is moderate, though, it remains a practical choice that spares the patient a second surgical site.
Anatomical Variations Worth Knowing About
The sternothyroid is not always the textbook muscle you would expect. A systematic review of infrahyoid muscle variations catalogued several anomalies: the sternothyroid was reported completely absent in one case, abnormally inserted in another, and bearing two extra slips in a third. An accessory “azygos” sternothyroid (a single midline muscle rather than the usual paired structure) has also been documented. Interestingly, every reported sternothyroid variation in that review occurred on the right side.9PubMed Central. Anatomical variations of the infrahyoid muscles and ansa cervicalis: a systematic review and an updated classification system for the omohyoid muscle
The list of described variants goes further: the sternothyroid can be doubled, can possess a membranous tendon in its belly, can form a cruciate (crossing) pattern with its partner from the opposite side, and can blend its fibers into neighboring muscles like the cricothyroid, inferior pharyngeal constrictor, or thyrohyoid.10International Journal of Anatomical Variations. Unilateral absence of the sternothyroid muscle: a case report It can also appear with separate medial and lateral bellies. These variations are individually uncommon, but collectively they turn up often enough that surgeons operating in the anterior neck should not be surprised if the anatomy deviates from the diagram.
For the patient, these anomalies are almost always functionally silent. People missing a sternothyroid on one side do not typically notice voice or swallowing trouble, because the remaining strap muscles and the opposite sternothyroid compensate. The primary significance is surgical: an unexpected variant can change the landmarks a surgeon uses to identify the recurrent laryngeal nerve, the thyroid vessels, or the parathyroid glands during neck operations.
The Sternothyroid in Other Mammals
Humans are not the only species with a sternothyroid, and comparative anatomy reveals how differently this muscle can be built depending on what the animal needs from its larynx. In male impala, the strap muscles form an elaborate sternum-to-larynx connection that allows dramatic repositioning of the voice box during their loud rutting calls. The sternothyroid and sternohyoid muscles in these antelopes are fused at their lower portions from the sternal origin up to a tendinous intersection near the fourth or fifth cervical vertebra, then diverge so the sternothyroid portion reaches the thyroid cartilage while the sternohyoid continues to the hyoid apparatus.11PubMed Central. Savannah roars: The vocal anatomy and the impressive rutting calls of male impala (Aepyceros melampus) – highlighting the acoustic correlates of a mobile larynx This architecture lets the animal pull its larynx far down the neck during vocalizations, dramatically lengthening the vocal tract and producing a much deeper-sounding call than you would predict from the animal’s body size.
Polygynous deer species show another set of adaptations. In all species and both sexes studied, the sternothyroid connects the sternum to the thyroid cartilage in the standard way, but the degree of fusion with the sternohyoid differs dramatically between species. In fallow deer, the two muscles separate fairly cleanly. In red deer, they are mostly fused, with only a slender ventral bundle of the sternohyoid peeling away near the top. In sika deer, the sternothyroid and sternohyoid are completely inseparable, with no structural boundary between them at all.12Journal of Anatomy. Roars, groans and moans: Anatomical correlates of vocal diversity in polygynous deer These differences track with the species’ vocalization styles: species that produce deep, dramatic rutting roars tend to have more extensive strap muscle fusion and longer sternothyroid muscles, giving them greater capacity to pull the larynx down and extend the resonating tube of the throat.
The comparative picture helps explain why the sternothyroid matters for voice even though it is not an intrinsic laryngeal muscle. In humans, laryngeal descent is modest compared to a bellowing red deer stag, but the principle is the same. The sternothyroid repositions the entire laryngeal framework in the neck, changing the length and shape of the vocal tract above the vocal folds. That repositioning shifts the resonance characteristics of the voice, affecting timbre and quality even when the vocal folds themselves are doing the same thing.
Studying the Muscle Without Cutting It Open
Because the sternothyroid sits relatively close to the skin surface in the anterior neck, it is accessible to surface electromyography, which is how researchers study its activity during speech and swallowing without invasive procedures. Electrode placement targets the area medial to the sternocleidomastoid muscle and below the thyroid cartilage.13Scientific Reports. Electromyographic activation patterns during swallowing in older adults The challenge is that multiple strap muscles overlap in that region, so surface electrodes inevitably pick up signal from the sternohyoid and omohyoid as well. Researchers deal with this limitation by using fine-wire intramuscular electrodes when they need to isolate a specific muscle’s contribution, though that approach is more invasive and typically reserved for research settings rather than clinical practice.
Ultrasound has also emerged as a useful tool for visualizing the strap muscles in real time. It can show the sternothyroid’s thickness, its movement during swallowing, and any asymmetries that might suggest unilateral weakness or the anatomical variants described earlier. For clinicians evaluating a patient with unexplained voice or swallowing symptoms after neck surgery, ultrasound of the strap muscles is a quick, noninvasive way to check whether the anatomy has been disrupted. Advances in high-resolution ultrasound have made it possible to distinguish the sternothyroid from the overlying sternohyoid in most patients, though body habitus and neck anatomy can make this difficult in some individuals.
Why Singers and Voice Professionals Care
Voice teachers and singing coaches have long talked about “laryngeal position” as a key element of vocal technique. Classical singing traditions generally favor a relatively low, stable larynx, which produces a warmer, rounder tone because of the longer resonating column above the vocal folds. Pop and belt singing styles often tolerate or encourage a higher larynx position for a brighter, edgier quality. The sternothyroid is one of the primary muscles that pulls the larynx down, so it is central to these technical discussions even if voice teachers rarely call it by name.
Excess tension in the strap muscles, including the sternothyroid, is a common finding in singers and speakers with muscle tension dysphonia. The irony is that while a certain amount of strap muscle engagement is normal and necessary for vocal control, over-engagement creates a stiff, pressed quality and can lead to vocal fatigue or pain. Voice therapy for these patterns often focuses on releasing extrinsic laryngeal muscle tension through manual techniques, resonant voice exercises, and postural adjustments. Understanding that the sternothyroid specifically pulls the larynx inferiorly helps therapists target their interventions: if a patient’s larynx is being held too low by excessive sternothyroid activity, the therapeutic approach differs from one where the suprahyoid muscles are pulling the larynx too high.
The evidence that surgically dividing the sternothyroid causes no lasting voice changes in ordinary speakers does not necessarily mean the same would hold for professional voice users operating at the extremes of their range. The studies on thyroidectomy and voice outcomes measured average conversational parameters and patient-reported symptoms. A professional soprano pushing her upper register or a bass singer relying on a maximally descended larynx might notice subtleties that standard clinical assessments would miss. This is why many laryngologists still prefer to preserve the strap muscles when operating on professional singers, even though the general evidence suggests division is safe for most people.