The hyoid bone is a small, horseshoe-shaped structure situated in the anterior midline of the neck. It is unique among the 206 bones of the human skeleton because it is the only bone that does not directly articulate with any other bone. This makes it a “floating bone,” suspended entirely by a complex arrangement of muscles, ligaments, and fascia. This bone acts as a central anchor point for several groups of muscles that facilitate essential functions like swallowing and speech production.
Anatomy and Position of the Hyoid Bone
The hyoid bone is composed of five distinct parts: a central main body, two larger projections known as the greater horns (cornua), and two smaller projections called the lesser horns. The central body forms the base of the U-shape. The two greater horns extend backward and laterally, providing a large surface area for muscle attachment. The smaller lesser horns project upward from the junction of the body and the greater horns.
This bone is positioned superior to the thyroid cartilage and inferior to the base of the lower jaw, or mandible. Its approximate position is at the level of the third or fourth cervical vertebra (C3-C4) in the neck. The hyoid’s unique suspension is maintained by a network of muscles that attach to the skull, mandible, tongue, larynx, and sternum.
The muscles anchoring the hyoid are categorized into two groups: the suprahyoid muscles, which are superior to the bone, and the infrahyoid muscles, located inferiorly. The suprahyoid group includes the digastric, stylohyoid, mylohyoid, and geniohyoid muscles, which primarily function to elevate the hyoid. Conversely, the infrahyoid group functions to depress the bone. This muscular arrangement allows the hyoid to be highly mobile, moving both vertically and horizontally within the neck space.
Essential Functions in Vocalization and Deglutition
The hyoid bone serves as a stable foundation for the tongue and the muscles in the floor of the mouth. Its position allows for precise control over the shape and movement of the tongue, which is necessary for the complex articulation required in human speech. The bone’s movements are coordinated to adjust the tension of the vocal cords and the position of the larynx, influencing the pitch and resonance of the voice.
The hyoid is involved in the three phases of swallowing, or deglutition. During the pharyngeal stage, the suprahyoid muscles contract, pulling the hyoid bone in a superior and anterior direction. This upward and forward movement is linked to the movement of the larynx. The elevation of the hyoid pulls the larynx upward, closing the laryngeal inlet and preventing food or liquid from entering the trachea and lungs.
Immediately following this upward motion, the infrahyoid muscles contract to return the hyoid and larynx to their resting positions, preparing the airway for respiration. The hyoid acts as a system enabling the coordinated muscular effort needed for both phonation and safe swallowing. The stability provided by the bone allows the extrinsic muscles of the tongue, such as the hyoglossus, to exert force efficiently. The continual adjustment of the hyoid’s position ensures that the respiratory and digestive tracts are correctly managed during these alternating physiological processes.
Significance in Trauma and Forensic Science
The hyoid bone holds relevance in forensic pathology due to its susceptibility to fracture under specific types of neck trauma. Because it is suspended only by soft tissue, it is a point of concentrated stress when force is applied to the neck. A fracture of the hyoid bone is regarded as an indicator of manual strangulation, or throttling, in a forensic context.
Fractures often occur in the greater horns of the hyoid bone, which are the most slender parts. The incidence of hyoid fracture in strangulation cases is influenced by the age of the victim. In older adults, the hyoid components often fuse together, or ossify, making the bone more brittle and susceptible to fracture from compressive force. Conversely, in children and younger individuals, the hyoid remains largely cartilaginous and flexible, meaning it is less likely to fracture.
While a hyoid fracture strongly suggests neck compression, its absence does not rule out strangulation as a cause of death. However, when a fracture is present, especially in the greater cornua, it offers compelling evidence to forensic investigators regarding the mechanism of injury.