Dominic Stone
The infrahyoid muscles, also known as strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. They are called strap muscles because of their long and flat shape, similar to a belt or strap. The four infrahyoid muscles are the sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles. These muscles have both a superficial layer, composed of the sternohyoid and omohyoid, and a deep layer, consisting of the sternothyroid and thyrohyoid. The infrahyoid muscles are responsible for depressing the hyoid bone during swallowing and play an active role in the movement of the larynx.
| Characteristics | Values |
|---|---|
| Definition | A group of four pairs of muscles in the anterior (frontal) part of the neck |
| Location | Below the hyoid bone, within the muscular triangle |
| Innervation | Branches of the ansa cervicalis (C1, C2, and C3) |
| Arterial Supply | Branches of the superior thyroid artery |
| Venous Drainage | Superior, middle, and inferior thyroid veins |
| Function | Depress the hyoid bone during swallowing, position the hyoid bone, and facilitate larynx movement |
| Shape | Long and flat, resembling a strap or belt |
| Number of Muscles | Four pairs of muscles |
| Names of Individual Muscles | Sternohyoid, sternothyroid, thyrohyoid, and omohyoid |
| Superficial Layer Muscles | Sternohyoid and omohyoid |
| Deep Layer Muscles | Sternothyroid and thyrohyoid |
| Omohyoid Composition | Two bellies (superior and inferior) connected by an intermediate tendon |
| Sternohyoid Origin | Sternum, sternoclavicular joint, and medial end of the clavicle |
| Sternohyoid Insertion | Hyoid bone |
| Sternothyroid Origin | Manubrium of the sternum, costal cartilage of rib 1 |
| Sternothyroid Insertion | Thyroid cartilage |
| Thyrohyoid Function | Elevates the larynx when the hyoid bone is fixed |
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What You'll Learn
The four infrahyoid muscles
The infrahyoid muscles, also known as strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. They are called strap muscles because they are long and flat, resembling a strap. The four infrahyoid muscles are the sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles.
The sternohyoid muscle is the most superficial of all the infrahyoid muscles. It originates from the sternum and sternoclavicular joint and ascends to insert onto the hyoid bone. It functions to depress the hyoid bone. The sternothyroid muscle is located underneath the sternohyoid in the deep plane of the neck. It arises from the manubrium of the sternum and attaches to the thyroid cartilage. It functions to depress the thyroid cartilage.
The thyrohyoid muscle is a short band of muscle that is thought to be a continuation of the sternothyroid muscle. It arises from the thyroid cartilage of the larynx and ascends to attach to the hyoid bone. It functions to depress the hyoid bone, but it can also elevate the larynx if the hyoid bone is stabilized by the suprahyoid muscles. The omohyoid muscle is divided into two muscle bellies: the superior belly, which arises from the hyoid bone, and the inferior belly, which arises from the scapula. These two bellies are connected by an intermediate tendon anchored to the clavicle. The omohyoid functions to depress the hyoid bone.
The infrahyoid muscles, along with the suprahyoid muscles, are important for several functions related to speech, swallowing, and the movement of the larynx. They control the positioning of the hyoid bone, which can be elevated or depressed depending on the activation of the infrahyoid or suprahyoid muscles, respectively.
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The origin, insertion and innervation of the individual muscles
The infrahyoid muscles, or strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. The four infrahyoid muscles are the sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles. The origin, insertion, and innervation of the individual muscles are described below:
Sternohyoid
The sternohyoid muscle originates from the sternum and the posterior surface of the medial end of the clavicle. It inserts on the inferior border of the hyoid bone. It is innervated by the anterior rami of C1-C3, carried by a branch of the ansa cervicalis. It receives its arterial supply from the branches of the superior thyroid artery.
Sternothyroid
The sternothyroid muscle originates from the posterior surface of the manubrium of the sternum, as well as the costal cartilage of rib 1. It inserts on the thyroid cartilage. It is innervated by the ansa cervicalis (C1-C3), arising from the cervical plexus.
Thyrohyoid
The thyrohyoid muscle originates at the oblique line of thyroid cartilage and inserts on the inferior border of the body and greater cornu of the hyoid bone. Unlike the other infrahyoid muscles, the thyrohyoid is not innervated by the ansa cervicalis. Instead, it is innervated by nerve fibres from the anterior ramus of spinal nerve C1, which travels with the hypoglossal nerve (CN XII).
Omohyoid
The omohyoid muscle consists of two bellies, superior and inferior, united at an angle by an intermediate tendon. The inferior belly originates at the superior border of the scapula. It inserts into the lower border of the hyoid bone. It is innervated by the ansa cervicalis (C1-C3), arising from the cervical plexus.
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The arterial supply to the infrahyoid muscles
The infrahyoid muscles, also known as the strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. The four infrahyoid muscles are the sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles. The arterial supply to the infrahyoid muscles is via the superior and inferior thyroid arteries, with venous drainage via the corresponding veins.
The superior thyroid artery is a branch of the external carotid artery, while the inferior thyroid artery is a branch of the thyrocervical trunk, which itself arises from the subclavian artery. The superior thyroid artery also gives rise to the cricothyroid artery, which enters the cricothyroid muscle's superficial surface and contributes to its blood supply. The muscular branches of the inferior thyroid artery supply the infrahyoid, anterior scalene, longus colli, and inferior pharyngeal constrictor muscles.
In addition to the superior and inferior thyroid arteries, the internal mammary artery, also called the internal thoracic artery, contributes to the arterial supply of the infrahyoid muscles. The skin overlying these muscles is supplied by tributaries arising from these three arteries. An unusual branch of the lingual artery also supplies the infrahyoid muscles.
The omohyoid muscle is divided into a superior and inferior belly, which originates from the hyoid bone and arises from the superior border of the scapula, respectively. The two bellies are connected by an intermediate tendon, which is anchored to the clavicle by the deep cervical fascia. The omohyoid muscle functions to depress and draw the hyoid bone posteriorly.
The sternohyoid muscle is located in the superficial plane of the neck and originates from the sternum and sternoclavicular joint. It ascends to insert onto the hyoid bone and functions to depress the hyoid bone.
The sternothyroid muscle is located in the deep plane of the neck and arises from the manubrium of the sternum, attaching to the thyroid cartilage. It functions to depress the thyroid cartilage.
The thyrohyoid muscle is a short band of muscle, thought to be a continuation of the sternothyroid muscle. It arises from the thyroid cartilage of the larynx and ascends to attach to the hyoid bone. It functions to depress the hyoid bone or elevate the larynx if the hyoid bone is fixed.
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The role of the strap muscles in thyroid surgery
The strap muscles, also known as the infrahyoid muscles, are composed of four paired muscles: the sternohyoid, the sternothyroid, the omohyoid, and the thyrohyoid. These muscles have both a superficial layer, composed of the sternohyoid and the omohyoid, and a deep layer, consisting of the sternothyroid and the thyrohyoid. The thyroid gland is a midline endocrine structure located in the anterior neck, in front of the trachea. The sternocleidomastoid muscle and the infrahyoid muscles cover its lateral and anterior borders.
The USMF technique involves cutting the strap muscles close to the clavicle and along the anterior margin of both sternocleidomastoid muscles, followed by total thyroidectomy. The strap muscles are then separated from the thyroid gland and elevated to the superior level of thyroid cartilage. After tumor resection, the muscle flap is sutured back to its original position. Studies have shown that the USMF approach provides superb surgical field exposure, with comparable voice and swallowing functions to those obtained by the midline approach. No significant differences were found in postoperative voice analysis, vocal cord function, or swallowing assessments between the USMF and midline approach groups.
In conclusion, the strap muscles play a crucial role in the USMF technique for difficult thyroid surgeries. By providing a wide surgical field exposure, the USMF technique overcomes the challenges associated with the conventional midline approach. The USMF approach has been found to be safe and effective, with no reported cases of postoperative complications such as hematoma, vocal cord paralysis, permanent hypocalcaemia, wound infection, or flap necrosis.
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The shape of the strap muscles
The strap muscles, also known as the infrahyoid muscles, are composed of four paired muscles in the anterior (frontal) part of the neck. These muscles are long and flat, resembling straps. They are located below the hyoid bone, within the muscular triangle.
The four infrahyoid muscles are:
- Sternohyoid
- Sternothyroid
- Thyrohyoid
- Omohyoid
The sternohyoid muscle is located in the superficial plane of the neck, along with the omohyoid muscle. The sternothyroid muscle is located underneath the sternohyoid in the deep plane of the neck. The thyrohyoid is a short band of muscle, thought to be a continuation of the sternothyroid muscle.
The omohyoid muscle is comprised of two muscle bellies, which are connected by a muscular tendon. The superior belly arises from the hyoid bone, while the inferior belly arises from the scapula. These two muscle bellies are connected by an intermediate tendon, which is anchored to the clavicle by the deep cervical fascia.
The stylopharyngeus muscle is considered by many to be one of the strap muscles, but it is not an infrahyoid muscle.
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Frequently asked questions
Strap muscles, also known as infrahyoid muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. They are called strap muscles because of their long and flat shape, similar to a belt or strap.
The four infrahyoid muscles are the sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles.
Strap muscles are responsible for depressing the hyoid during swallowing. They also play a role in the movement of the larynx.
