Subscapular vein

The subscapular vein is a large vein located in the posterior region of the shoulder. It runs along the lateral border of the scapula, accompanying the subscapular artery. The vein drains blood from the muscles around the scapula, including the subscapularis, teres major, and latissimus dorsi muscles. It originates from smaller tributaries such as the circumflex scapular vein and thoracodorsal vein, and ascends toward the axilla (armpit). The subscapular vein eventually drains into the axillary vein, which is responsible for venous return from the upper limb and shoulder to the heart.

Structure and Anatomy

Location

The subscapular vein is located in the posterior shoulder region, running along the lateral border of the scapula (shoulder blade). It accompanies the subscapular artery and is part of the venous drainage system of the upper back and shoulder, particularly in the region beneath the scapula. The vein extends from smaller tributaries that drain the muscles around the scapula and ascends toward the axilla (armpit), where it connects with the axillary vein.

Origin

The subscapular vein originates from the confluence of smaller tributaries, including:

• The circumflex scapular vein, which drains blood from the scapular region and passes through the triangular space formed by the teres major, teres minor, and the long head of the triceps brachii muscles.
• The thoracodorsal vein, which drains the latissimus dorsi muscle, a large muscle in the back that contributes to the movement of the shoulder and upper limb.

These tributaries come together near the lateral border of the scapula to form the subscapular vein.

Course

The subscapular vein runs along the lateral edge of the scapula, paralleling the course of the subscapular artery. As it ascends, it travels in close proximity to the muscles attached to the scapula, including the subscapularis, teres major, and latissimus dorsi. The vein passes beneath the lower border of the subscapularis muscle as it approaches the axillary region. It then continues upward and medially, where it drains into the axillary vein.

Relations

• Anterior relations: The subscapular vein is related anteriorly to the subscapularis muscle, a large triangular muscle that covers the anterior surface of the scapula and forms part of the rotator cuff.
• Posterior relations: Posteriorly, the subscapular vein is bordered by the teres major and latissimus dorsi muscles, both of which contribute to the movement of the upper limb and shoulder.
• Lateral relations: Laterally, the subscapular vein is positioned near the lateral border of the scapula, which forms part of the framework for the upper back and shoulder.
• Medial relations: Medially, the subscapular vein runs close to the axillary artery and other major vascular structures in the axilla. It is also closely related to the circumflex scapular artery and vein.

Tributaries

The subscapular vein receives blood from several important tributaries that drain the surrounding muscles and tissues:

• Circumflex scapular vein: This vein drains the muscles and tissues around the scapula and is one of the main tributaries of the subscapular vein. It passes through the triangular space and joins the subscapular vein near the lateral border of the scapula.
• Thoracodorsal vein: This tributary drains the latissimus dorsi muscle, which is located in the lower back and extends upward toward the shoulder. The thoracodorsal vein plays a key role in collecting venous blood from this large muscle.
• Muscular tributaries: The subscapular vein also receives smaller tributaries from the muscles around the scapula, including the teres major, subscapularis, and parts of the infraspinatus muscle.

Termination

The subscapular vein terminates by draining into the axillary vein, which is located in the axillary region (armpit). After collecting blood from the scapular region and its associated muscles, the subscapular vein empties into the axillary vein, which is responsible for transporting blood from the upper limb and shoulder to the central venous system.

Surrounding Structures

• Anteriorly: The subscapular vein lies deep to the subscapularis muscle, which covers the anterior surface of the scapula. The subscapular artery accompanies the vein, running parallel to it.
• Posteriorly: The vein is bordered posteriorly by the teres major and latissimus dorsi muscles, which are key structures in the movement of the shoulder and upper arm.
• Lateral relations: The lateral edge of the scapula runs alongside the subscapular vein as it courses toward the axilla.
• Medially: The subscapular vein is related medially to the axillary vein and axillary artery, which it joins near the axillary region.

Communication with Other Veins

The subscapular vein communicates with several other veins, allowing for efficient drainage of blood from the upper back and shoulder region:

• Axillary vein: The subscapular vein drains directly into the axillary vein, which is a major venous structure responsible for returning blood from the upper limb to the heart.
• Thoracodorsal vein: As one of its main tributaries, the thoracodorsal vein communicates with the subscapular vein, draining blood from the latissimus dorsi muscle and other structures in the lower back.
• Circumflex scapular vein: This vein drains into the subscapular vein and is involved in the venous drainage of the scapular region, providing a pathway for blood to flow from the back of the shoulder to the axilla.

Variations

The anatomy of the subscapular vein can exhibit anatomical variations in terms of size, course, and the number of tributaries it receives. In some individuals, the subscapular vein may be larger or smaller depending on the extent of venous drainage in the region. Additionally, the exact point at which the vein joins the axillary vein may vary, with some variations in the level of the junction. The size and prominence of the circumflex scapular and thoracodorsal veins, which drain into the subscapular vein, can also vary between individuals.

Function

Venous Drainage of the Scapular Region

The primary function of the subscapular vein is to provide venous drainage for the scapular region, which includes the muscles and tissues around the scapula (shoulder blade). It collects deoxygenated blood from several important muscles involved in shoulder movement, such as the subscapularis, teres major, and latissimus dorsi. These muscles play a key role in shoulder stabilization and movement, and the subscapular vein ensures that the metabolic waste and deoxygenated blood produced by these muscles are efficiently drained and returned to the central venous system.

Venous Return from the Subscapularis Muscle

One of the key functions of the subscapular vein is to drain venous blood from the subscapularis muscle, a large muscle that covers the anterior surface of the scapula and forms part of the rotator cuff. The subscapularis is responsible for internal rotation of the shoulder and plays a major role in shoulder stability. During muscle contraction, the subscapular vein collects the deoxygenated blood from this muscle and returns it to the central circulation, preventing the accumulation of metabolic byproducts and ensuring proper muscle function.

Drainage from the Latissimus Dorsi Muscle

The subscapular vein also drains blood from the latissimus dorsi muscle through its tributary, the thoracodorsal vein. The latissimus dorsi is one of the largest muscles in the back and plays a crucial role in extending, adducting, and medially rotating the arm. The subscapular vein ensures that venous blood from this large muscle is efficiently drained, especially during activities that involve heavy use of the back and shoulder, such as lifting, pulling, or climbing.

Venous Return from the Teres Major and Minor Muscles

The subscapular vein also contributes to the venous return from the teres major and minor muscles, which are important muscles in shoulder movement and stabilization. The teres major muscle assists with shoulder extension, adduction, and medial rotation, while the teres minor is part of the rotator cuff, assisting in external rotation of the shoulder. The subscapular vein helps remove deoxygenated blood from these muscles, maintaining circulation and preventing venous congestion.

Role in Communication with the Circumflex Scapular Vein

The subscapular vein plays a key role in communicating with the circumflex scapular vein, which drains the posterior aspect of the scapula. The circumflex scapular vein collects blood from muscles such as the teres minor, infraspinatus, and the skin and soft tissues overlying the scapula. The subscapular vein provides an efficient drainage route for this blood, ensuring that venous return from the entire scapular region is directed toward the axillary vein, and eventually the central venous system.

Venous Return During Shoulder and Upper Limb Movement

The subscapular vein supports venous return during movement of the shoulder and upper limb. When muscles like the subscapularis, latissimus dorsi, and teres major contract, they compress nearby veins, helping to push venous blood back toward the heart. This mechanism, known as the muscle pump, plays a significant role in ensuring that venous blood from the scapular region and shoulder is efficiently returned to the central circulation. The subscapular vein, due to its location and connections with key muscles, benefits from this muscle pump action, especially during physical activities involving arm movement.

Venous Drainage from the Thoracodorsal Region

Through its tributary, the thoracodorsal vein, the subscapular vein helps drain venous blood from the thoracodorsal region, which includes the lower and lateral back. The thoracodorsal vein collects blood from the latissimus dorsi muscle, one of the largest muscles in the back, and transfers it to the subscapular vein. This drainage ensures that blood from the back and shoulder is efficiently transported to the larger venous system, preventing venous stasis and maintaining circulation.

Contribution to the Axillary Venous System

The subscapular vein has an essential role in contributing to the axillary venous system, which is the major venous drainage system for the upper limb and shoulder. By draining into the axillary vein, the subscapular vein helps ensure that venous blood from the scapular region is directed into the central venous system. The axillary vein, which eventually drains into the subclavian vein, transports this blood back to the heart, completing the circulatory loop. Without the subscapular vein’s contribution, blood from the scapular region would face difficulty in being efficiently returned to the heart.

Regulation of Venous Pressure in the Scapular Region

The subscapular vein helps in regulating venous pressure within the scapular region. Through its connections with the circumflex scapular and thoracodorsal veins, the subscapular vein provides alternate routes for venous blood drainage. If pressure builds up in one part of the venous system, blood can be redistributed through the subscapular vein, preventing venous congestion or pooling. This regulation of pressure is important for maintaining smooth blood flow, especially during activities that involve sustained shoulder movements or heavy physical exertion.

Removal of Metabolic Waste from Muscles

Another important function of the subscapular vein is to remove metabolic waste produced by the muscles of the scapular region, particularly during physical activity. As muscles like the subscapularis, latissimus dorsi, and teres major contract, they produce waste products such as carbon dioxide and lactic acid. The subscapular vein helps remove these waste products by transporting the deoxygenated blood containing these byproducts away from the muscles and toward the heart, where it can be processed and oxygenated. This ensures that the muscles function efficiently and prevents the accumulation of harmful waste products.

Support in Thermoregulation

Though not a primary function, the subscapular vein plays a role in thermoregulation. During physical exertion or in warm environments, blood flow increases through the subscapular vein, helping to dissipate heat from the muscles and surrounding tissues. By transporting blood to larger venous channels like the axillary vein, the subscapular vein contributes to the body’s ability to regulate temperature and maintain homeostasis.

Clinical Significance

The subscapular vein is of clinical importance due to its involvement in various surgical procedures related to the shoulder and axilla. It is frequently encountered during surgeries such as axillary lymph node dissections, breast cancer surgery, and scapular flap procedures. Surgeons must be cautious of the subscapular vein during these operations to avoid damaging it, as injury could lead to significant bleeding or compromise venous drainage from the shoulder and scapular region.

The vein’s connection to the thoracodorsal vein and the circumflex scapular vein also makes it critical during reconstructive surgeries, where maintaining proper venous flow is essential for the success of procedures like muscle flaps used in post-mastectomy reconstruction.