Subscapularis

Location and anatomy

The muscle is localized on the anterior aspect of the scapula and consists of superficial and deep layers. It lies within its own osteofascial compartment formed by the fusion of the subscapular fascia with the margins of the scapula.

• Origin (O): costal surface of the scapula — subscapular fossa (fossa subscapularis).
• Insertion (I): the muscle transitions into a broad, flat tendon that runs into the subdeltoid space and attaches to the lesser tubercle of the humerus (tuberculum minus humeri) and its crest (crista tuberculi minoris).

Topography and adjacent structures

The subscapularis muscle is an important landmark in topography and participates in the formation of several anatomical spaces:

• Posterior wall of the axillary fossa — formed by the subscapularis muscle (along with its fascia), latissimus dorsi, teres major, and the long head of the triceps.
• Prescapular fascial space — the muscle forms its posterior wall (the anterior wall is formed by the serratus anterior).
• Openings of the posterior wall of the axillary cavity — the inferior border of m. subscapularis (along with the teres minor) serves as the superior boundary for two important pathways for vessels and nerves:
• Quadrangular space (foramen quadrilaterum) — located more laterally, transmits the axillary nerve (n. axillaris) and the posterior circumflex humeral artery.
• Triangular space (foramen trilaterum) — located more medially, transmits the circumflex scapular artery (a. circumflexa scapulae).

Blood supply and innervation

• Blood supply: provided by a large branch, the subscapular artery (a. subscapularis). It originates at the lower border of the muscle and, before dividing into its terminal branches, gives off 2–3 subscapular branches (rr. subscapulares) directly to the muscle tissue.
• Innervation: sources indicate the subscapular nerve (n. subscapularis, segments C₅–C₇) and the thoracodorsal nerve (n. thoracodorsalis, segments C₅–C₈ from the posterior cord of the brachial plexus).

Function

As part of the motor system and the rotator cuff group, the subscapularis muscle performs the following tasks:

• Rotates the shoulder medially (internally).
• Adducts the arm toward the trunk.
• Participates in lowering the raised arm and moving the shoulder from front to back.
• Reinforces the articular capsule — prior to its insertion, the muscle tendon lies closely against the anterior aspect of the shoulder joint capsule.

Clinical significance: subscapular bursa

Between the tendon of the subscapularis muscle and the shoulder joint capsule lies a large subscapular bursa (bursa subtendinea m. subscapularis or bursa synovialis subscapularis).

It is of great clinical importance because it constantly communicates with the joint cavity. In cases of purulent periarthritis or arthritis, this bursa is frequently involved in the pathological process. If it ruptures, pus spreads into the osteofascial sheath of the subscapularis muscle.

Class and exam questions

What else to study on this topic

• Axillary cavity and its walls
• Triangular and quadrangular spaces
• Shoulder joint and its synovial bursae
• Subscapular artery (a. subscapularis)

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.