Subscapular artery

The subscapular artery is the largest branch of the axillary artery and supplies blood to the muscles of the scapular and posterior thoracic regions. It plays a critical role in vascularizing the subscapularis muscle, parts of the serratus anterior, latissimus dorsi, and other muscles in the shoulder and back. The subscapular artery also gives rise to important branches such as the circumflex scapular artery and thoracodorsal artery.

Location

The subscapular artery arises from the third part of the axillary artery, near the lower border of the subscapularis muscle, just below the shoulder joint. It runs downward along the lateral border of the scapula, traveling posteriorly through the axilla. As it descends, the subscapular artery gives off branches, including the circumflex scapular artery, which curves around the scapula, and the thoracodorsal artery, which follows the lateral thoracic wall to supply the latissimus dorsi muscle. The artery terminates after giving rise to these branches, with its course being mainly in the posterior scapular region.

Structure and Anatomy

The subscapular artery is a significant branch of the axillary artery that provides vital blood supply to the scapular and posterior thoracic regions. It is the largest branch of the axillary artery and gives rise to several important arteries, including the circumflex scapular artery and the thoracodorsal artery. Below is a detailed description of its anatomy, including its origin, course, branches, and relationships with surrounding structures.

Origin

The subscapular artery originates from the third part of the axillary artery, which itself is a continuation of the subclavian artery. The subscapular artery typically arises near the lower border of the subscapularis muscle, which is located along the anterior surface of the scapula. This point of origin is situated within the axillary region, just below the shoulder joint. The artery is one of the most important branches of the axillary artery, especially in terms of supplying the posterior shoulder region.

Course

After originating from the axillary artery, the subscapular artery takes a downward and slightly posterior course as it travels along the lateral border of the scapula.

Lateral Border of the Scapula

Initially, the subscapular artery runs along the lateral border of the scapula. It descends through the axilla, traveling posteriorly along the underside of the subscapularis muscle. During its descent, it supplies several muscles and structures in the posterior scapular and thoracic regions. The artery is deeply positioned within the axillary region, making it relatively protected by surrounding muscles.

Termination and Branching

The subscapular artery quickly divides into its two main branches, the circumflex scapular artery and the thoracodorsal artery, which each supply distinct regions of the shoulder and thorax.

Branches

The subscapular artery gives rise to two major branches, both of which are critical for supplying the posterior shoulder and thoracic regions.

Circumflex Scapular Artery

The circumflex scapular artery is one of the most important branches of the subscapular artery. It originates from the subscapular artery shortly after its descent along the lateral border of the scapula.

• Course: The circumflex scapular artery passes posteriorly through the triangular space, which is bordered by the teres major, teres minor, and long head of the triceps brachii. It curves around the lateral border of the scapula and continues along the posterior surface of the scapula toward the infraspinous fossa.
• Function: The circumflex scapular artery provides blood to the teres major, teres minor, and infraspinatus muscles, and it also contributes to the blood supply of the scapula itself. It forms anastomoses with other arteries in the scapular region, including the suprascapular artery and dorsal scapular artery.

Thoracodorsal Artery

The thoracodorsal artery is the other major branch of the subscapular artery. It arises after the circumflex scapular artery has branched off and continues its course down the lateral thoracic wall.

• Course: The thoracodorsal artery runs along the lateral thoracic wall, following the path of the thoracodorsal nerve. It supplies blood to the latissimus dorsi muscle, which is responsible for many movements of the upper limb, including adduction, extension, and internal rotation of the shoulder.
• Termination: The thoracodorsal artery terminates near the inferior angle of the scapula, where it provides smaller branches to the latissimus dorsi and surrounding muscles.

Additional Small Branches

In addition to its two major branches, the subscapular artery may also give rise to small muscular branches that supply nearby muscles, including the subscapularis, serratus anterior, and portions of the intercostal muscles.

Anastomoses

The subscapular artery and its branches are part of an extensive anastomotic network that ensures continuous blood flow to the scapular and shoulder regions. These anastomoses are crucial in cases where one artery may be obstructed or injured, as they provide alternative pathways for blood flow.

• Circumflex Scapular Artery Anastomoses: The circumflex scapular artery forms important anastomoses with the suprascapular artery (a branch of the thyrocervical trunk) and the dorsal scapular artery (a branch of the subclavian artery or transverse cervical artery). These connections provide a collateral blood supply to the scapular muscles and bones.
• Thoracodorsal Artery Anastomoses: The thoracodorsal artery forms smaller anastomoses with the posterior intercostal arteries, which supply the thoracic wall and intercostal muscles. These anastomoses contribute to the vascular network of the thoracic wall.

Relationship to Surrounding Structures

The subscapular artery has important anatomical relationships with surrounding muscles, bones, and neurovascular structures in the axillary and scapular regions.

Subscapularis Muscle

The subscapular artery is closely associated with the subscapularis muscle, which is one of the muscles of the rotator cuff. As the artery descends, it travels along the inferior border of the subscapularis, supplying it with oxygenated blood through small muscular branches.

Latissimus Dorsi Muscle

The thoracodorsal artery, a branch of the subscapular artery, runs in close proximity to the latissimus dorsi muscle, which it supplies. The artery follows the path of the thoracodorsal nerve, and both structures are essential for the vascular and nervous supply to the latissimus dorsi.

Teres Major and Minor Muscles

As the subscapular artery gives rise to the circumflex scapular artery, it runs in close proximity to the teres major and teres minor muscles. These muscles help form the borders of the triangular space through which the circumflex scapular artery passes.

Axillary Nerve and Brachial Plexus

Although the subscapular artery is not directly associated with the axillary nerve, it travels through the axillary region, where the axillary nerve and branches of the brachial plexus are located. The artery supplies some of the muscles that are innervated by these nerves, such as the subscapularis (innervated by the upper and lower subscapular nerves) and latissimus dorsi (innervated by the thoracodorsal nerve).

Variations

The anatomy of the subscapular artery can show some variations. These include:

• Variable Origin: The point of origin of the subscapular artery may vary. In some cases, the artery may arise higher or lower along the axillary artery, or it may share a common trunk with other branches of the axillary artery.
• Variable Branching: In rare cases, the subscapular artery may give rise to additional branches or exhibit variations in the size or course of the circumflex scapular or thoracodorsal arteries.

Function

The subscapular artery serves as a crucial vessel in the vascular supply of the scapular and posterior thoracic regions. It plays a vital role in delivering oxygenated blood to key muscles and structures that are involved in upper limb movement, shoulder stabilization, and respiratory functions. Below is a detailed breakdown of the functions of the subscapular artery.

Blood Supply to the Subscapularis Muscle

The subscapular artery is primarily responsible for supplying blood to the subscapularis muscle, which is a critical part of the rotator cuff.

Nourishment of the Subscapularis Muscle: The subscapularis muscle is responsible for the internal rotation of the humerus at the shoulder joint and helps stabilize the shoulder. The subscapular artery delivers oxygenated blood to this muscle, ensuring that it remains functional and capable of performing these movements. The artery provides small muscular branches to nourish the subscapularis, maintaining its strength and endurance during repetitive shoulder movements.

Blood Supply to the Latissimus Dorsi Muscle

The subscapular artery gives rise to the thoracodorsal artery, which is the primary vessel supplying the latissimus dorsi muscle.

• Nourishment of the Latissimus Dorsi Muscle: The latissimus dorsi is one of the largest muscles in the back and is involved in shoulder and upper limb movements such as extension, adduction, and internal rotation of the arm. The thoracodorsal artery provides the necessary blood supply for this muscle, enabling it to perform these powerful movements. This artery ensures that the latissimus dorsi can generate the required force for actions like pulling, lifting, and climbing.
• Support for Upper Limb Movement: The blood supply to the latissimus dorsi also contributes to its role in stabilizing the trunk during various activities, supporting both the upper limb and core muscles during complex movements.

Blood Supply to the Scapular Muscles (Teres Major, Teres Minor, and Infraspinatus)

The subscapular artery gives off the circumflex scapular artery, which is responsible for supplying blood to several important muscles of the scapula, including the teres major, teres minor, and infraspinatus.

• Teres Major Muscle: The teres major muscle assists in the adduction and internal rotation of the arm. The circumflex scapular artery supplies blood to this muscle, ensuring that it functions properly during movements that involve pulling the arm inward or downward.
• Teres Minor Muscle: As part of the rotator cuff, the teres minor muscle is responsible for external rotation of the shoulder. The circumflex scapular artery provides the necessary blood supply to keep this muscle strong and functional, which is critical for stabilizing the shoulder joint during movement.
• Infraspinatus Muscle: Another rotator cuff muscle, the infraspinatus plays a key role in external rotation of the arm. The circumflex scapular artery ensures that the infraspinatus has an adequate blood supply to perform its role in stabilizing and rotating the shoulder joint.

Contribution to Collateral Circulation Around the Scapula

The subscapular artery, through its branches, is a key component of the collateral circulation in the scapular region. This collateral network helps maintain continuous blood flow even if one of the main arteries is obstructed or damaged.

• Anastomosis with Suprascapular and Dorsal Scapular Arteries: The circumflex scapular artery, a branch of the subscapular artery, forms anastomoses with the suprascapular artery and dorsal scapular artery. These connections ensure that the posterior scapular region, including the muscles and bones of the scapula, remains well-supplied with blood, even if one of the vessels is compromised.
• Support During Shoulder Movements: This network of arteries provides an important source of collateral blood flow during shoulder movements that may compress certain arteries. By maintaining adequate circulation, the subscapular artery helps prevent ischemia (lack of blood supply) in the shoulder and scapular regions during activity.

Blood Supply to the Thoracic Wall

The subscapular artery contributes to the blood supply of the lateral thoracic wall, primarily through the thoracodorsal artery.

• Nourishment of the Thoracic Wall Muscles: The thoracodorsal artery supplies portions of the serratus anterior muscle, which plays an important role in scapular stabilization and protraction (moving the scapula forward). The artery also provides blood to parts of the intercostal muscles, which are involved in respiration by supporting the movement of the rib cage.
• Support for Respiratory Function: By supplying the intercostal muscles and other thoracic structures, the subscapular artery indirectly supports respiratory movements. The intercostal muscles, which assist in expanding and contracting the rib cage, rely on the blood flow provided by the subscapular artery’s branches for oxygen and nutrients.

Blood Supply to the Scapula (Bone)

In addition to supplying the muscles, the subscapular artery, particularly through its circumflex scapular artery branch, provides blood to the scapula itself.

• Bone Nourishment: The scapula, like any bone, requires a continuous supply of blood to maintain its structure and function. The circumflex scapular artery delivers oxygenated blood to the periosteum (outer layer of the bone) of the scapula, ensuring that it remains healthy and capable of supporting the surrounding muscles.
• Bone Repair and Growth: In cases of injury, such as a scapular fracture, the blood supply from the subscapular artery plays a crucial role in bone repair and healing. The artery helps deliver the necessary nutrients for osteogenesis (bone formation) and regeneration.

Oxygen and Nutrient Delivery

Like all arteries, the primary function of the subscapular artery is to deliver oxygen and nutrients to the tissues it supplies.

• Tissue Repair and Maintenance: The subscapular artery ensures that the muscles, bones, and soft tissues in the scapular and thoracic regions receive a steady supply of oxygen and nutrients, which is essential for their maintenance, repair, and regeneration after injury or strain.
• Muscle Function and Endurance: The oxygen and nutrient delivery to muscles such as the latissimus dorsi, subscapularis, and teres major is vital for maintaining their function and endurance. Without proper blood supply, these muscles would fatigue quickly, leading to weakness or impaired movement.

Clinical Significance

The subscapular artery is of great clinical importance due to its role in supplying blood to key muscles and structures in the scapular and posterior thoracic regions.

• Surgical Procedures: The subscapular artery is often involved in shoulder and axillary surgeries. For example, during axillary lymph node dissections or reconstructive surgeries, care must be taken to avoid damaging this artery and its branches to prevent significant bleeding or compromise blood flow to the muscles it supplies, including the subscapularis and latissimus dorsi.
• Reconstructive Surgery: The thoracodorsal artery, a branch of the subscapular artery, is commonly used in latissimus dorsi flap procedures for breast reconstruction and other types of reconstructive surgery. The viability of the muscle flap depends on the intact blood supply from the subscapular artery.
• Scapular and Shoulder Injuries: Injuries, such as fractures of the scapula or trauma to the shoulder, may disrupt the blood flow provided by the subscapular artery and its branches. This can affect the healing of muscles, bones, and soft tissues in the region, potentially leading to complications such as ischemia.