Transversus Thoracis Muscle Anatomy

The transversus thoracis muscle is a thin, fan-shaped muscle lies on the inner surface of the anterior thoracic wall and plays important roles in respiratory mechanics. Understanding its detailed anatomy proves valuable for thoracic surgeons, pulmonologists, and pain management specialists dealing with thoracic pathologies.

Transversus Thoracis Muscle Anatomy

The transversus thoracis muscle forms part of the innermost layer of the thoracic wall musculature. It presents as a thin, flat muscular sheet positioned on the posterior aspect of the sternum and costal cartilages. The muscle fibers run horizontally, creating a transverse orientation that contributes to its name. The muscle thickness varies between individuals but typically measures between 1-3 mm, making it a delicate structure requiring careful dissection during surgical procedures.

Origin and Insertion

The transversus thoracis originates from the posterior surface of the lower sternum, including the xiphoid process, and from the adjacent costal cartilages of the lower true ribs. From this origin, its fibers extend laterally and slightly upward in a fan-like arrangement. The muscle inserts onto the inner surfaces of the costal cartilages of the 2nd through 6th ribs, and occasionally the 1st rib as well. This arrangement creates multiple digitations that appear as distinct muscular slips attaching to their respective costal cartilages. The muscle fibers often demonstrate variability in their extent and attachment points, with some individuals showing more extensive development than others.

Neurovascular Anatomy

The neurovascular supply of the transversus thoracis muscle derives primarily from the anterior branches of the intercostal neurovascular bundles. The muscle receives innervation from the intercostal nerves corresponding to the levels at which it exists, primarily intercostal nerves 2-6. These nerves provide motor innervation that allows the muscle to contribute to respiratory mechanics.

The arterial supply comes predominantly from branches of the internal thoracic (internal mammary) artery, which runs parallel to the sternum on the deep surface of the anterior thoracic wall. Venous drainage follows a similar pattern, with blood returning via tributaries of the internal thoracic veins that eventually drain into the brachiocephalic veins. The lymphatic drainage of this region courses to the parasternal and anterior mediastinal lymph nodes.

Functional Significance

The transversus thoracis muscle serves several functional roles in respiratory physiology. During expiration, particularly forced expiration, the muscle contracts to pull the anterior portions of the ribs downward and inward, thereby decreasing thoracic volume. This action assists in expelling air from the lungs and makes the muscle particularly active during activities requiring forceful expiration, such as coughing, sneezing, or speaking with projection. The muscle appears to work synergistically with other expiratory muscles, including the innermost intercostal muscles and the abdominal wall musculature, to modulate intrathoracic pressure.

During quiet breathing, the transversus thoracis exhibits minimal activity, becoming progressively more engaged as respiratory demands increase. Research employing electromyographic studies has demonstrated increased activity in this muscle during expiratory maneuvers against resistance, suggesting its role in managing increased respiratory workloads. Additionally, some evidence suggests that the transversus thoracis contributes to postural stability of the anterior thoracic wall during movements that engage the upper limbs and trunk.

Clinical Relevance

The transversus thoracis muscle holds several important clinical implications for medical professionals. Surgeons performing procedures involving the anterior thoracic wall, particularly sternotomy approaches, must navigate around this structure. During internal mammary artery harvesting for coronary artery bypass grafting, the transversus thoracis serves as an important landmark, as the internal thoracic vessels run anterior to this muscle.

Pain syndromes affecting the anterior chest wall may involve the transversus thoracis muscle. Trigger points within this muscle can refer pain across the anterior chest, potentially mimicking cardiac pathology and contributing to diagnostically challenging presentations. Pain specialists may target this muscle with trigger point injections or other interventions when addressing anterior chest wall pain syndromes unresponsive to conventional treatments.

Pathological processes affecting the mediastinum or pleura may involve or infiltrate the transversus thoracis muscle. Advanced imaging techniques, including CT and MRI, can visualize this muscle and help determine the extent of disease processes affecting the anterior thoracic wall. Clinicians interpreting cross-sectional imaging should familiarize themselves with the normal appearance of this muscle to accurately detect pathological changes.

The transversus thoracis muscle also becomes relevant in thoracic drainage procedures. When placing anterior chest tubes or performing ultrasound-guided pleural procedures, awareness of this muscle layer helps clinicians navigate the thoracic wall layers safely. Furthermore, in traumatic injuries to the anterior chest wall, disruption of this muscle may occur in conjunction with rib or sternum fractures, potentially contributing to respiratory compromise.

Congenital variations in the development and attachment of the transversus thoracis muscle exist and may occasionally be encountered during thoracic surgical procedures. Recognition of these variants prevents misidentification of structures during dissection. Anatomical studies have documented considerable variability in the extent and development of this muscle between individuals, with some specimens demonstrating more extensive muscular tissue than others.

Developmental Considerations

Embryologically, the transversus thoracis muscle develops from the thoracic hypaxial myotome, sharing its developmental origin with the intercostal muscles. This common origin explains the close functional and anatomical relationship between these muscle groups. During fetal development, the muscle differentiates relatively late compared to other thoracic wall musculature, achieving its definitive arrangement during the later stages of intrauterine development.

The transversus thoracis represents the thoracic continuation of the transversus abdominis muscle, with both muscles forming part of the deep transverse layer of the trunk musculature. This developmental relationship explains their similar fiber orientation and functional characteristics in respiratory mechanics.

Understanding the detailed anatomy of the transversus thoracis muscle enhances clinical practice across multiple specialties, including thoracic surgery, interventional pain management, and diagnostic imaging. Its relationships with critical neurovascular structures of the anterior thoracic wall make it an important anatomical landmark deserving greater attention in clinical education and practice.

Resources

1. Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 42nd Edition – https://www.elsevier.com/books/grays-anatomy/standring/978-0-7020-8047-5
2. Clinically Oriented Anatomy, 8th Edition – https://shop.lww.com/Clinically-Oriented-Anatomy/p/9781496347213
3. Tang A, Bordoni B. Anatomy, Thorax, Muscles. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538321/