Anterior Strap Muscles of the Neck
The anterior strap muscles (also called infrahyoid muscles) are a group of four paired muscles located in the anterior neck, deep to the platysma and superficial cervical fascia, lying anterior to the thyroid gland and trachea 1.
The Four Strap Muscles
The anterior strap muscles consist of:
- Sternohyoid (SH)
- Sternothyroid
- Thyrohyoid
- Omohyoid (OMO)
These muscles are positioned deep to the cervical strap muscles and anterior to the trachea and esophagus in the lower anterior portion of the neck 1.
Innervation
All four strap muscles receive motor innervation from the ansa cervicalis (C1-C3 nerve roots) 2, 3.
- The sternohyoid is innervated inferiorly by a branch from the ansa cervicalis below the loop 3
- The hypoglossal nerve (CN XII) contributes to innervation of the infrahyoid strap muscles via the ansa cervicalis 2
- The ansa cervicalis provides the terminal inferior branch that is critical for maintaining muscle function 3
Blood Supply
The arterial supply follows a segmental pattern with distinct upper and lower territories 3:
Upper Strap Muscles
- Superior thyroid artery (STA) supplies the upper sternohyoid and upper belly of the omohyoid
- This arterial branch most commonly terminates at the cricothyroid membrane level 3
- The arterial lumen diameters are approximately threefold larger in branches entering the upper sternohyoid compared to lower portions 3
Lower Strap Muscles
- Inferior thyroid artery supplies the inferior sternohyoid 3
Venous Drainage
- Each arterial branch has an accompanying venous tributary that parallels the arterial supply 3
Important Vascular Anatomy
- Small intramuscular arteries without axial supply exist within the middle third of the upper sternohyoid, lower sternohyoid, and upper omohyoid 3
- The vascular supply runs laterally and deep to the muscle 3
Primary Actions
The strap muscles function as depressors of the hyoid bone and larynx, playing essential roles in:
- Swallowing
- Phonation
- Respiration
- Stabilization of the hyoid and laryngeal complex during head and neck movements
Clinical Significance
Surgical Considerations
During thyroid surgery, the strap muscles represent a critical anatomical layer that must be managed carefully 1, 4:
- The thyroid gland sits deep to the cervical strap muscles 1
- In emergency haematoma evacuation after thyroid surgery, both superficial and deep layers (strap muscles) must be opened to prevent ongoing haematoma formation 4
- The SCOOP protocol specifically requires opening the strap muscles to expose the trachea in airway emergencies 4
Flap Viability
An inferiorly based sternohyoid flap can maintain neurovascular integrity when properly designed 3:
- Release the superior and medial borders
- Dissect vascular supply laterally and deep to the muscle
- Preserve the inferior terminal ansa cervicalis branch 3
This approach is feasible because the arterial supply enters from lateral and deep positions, and the inferior nerve branch provides motor innervation 3.
Anatomical Relationships
The strap muscles are intimately related to: