Topography of the scapular fascial compartments
Several isolated spaces formed by bones and fascia are distinguished in the scapular region:
- Supraspinous space (supraspinous compartment): corresponds to fossa supraspinata. Superiorly bounded by the superior border of the scapula, the fascial sheath of the subclavius muscle, and the coracoclavicular ligament (lig. coracoclaviculare). Inferiorly closed by the scapular spine (spina scapulae). Laterally the space is open. Internally, it contains the supraspinatus muscle (m. supraspinatus) along with suprascapular vessels and nerve. The compartment communicates with the infraspinous and subdeltoid cellular spaces.
- Infraspinous osteofibrous space: formed by the bone and infraspinous fascia (fascia infraspinata), which is firmly fused with the medial, lateral borders, and the scapular spine. Here are located the infraspinatus (m. infraspinatus) and teres minor (m. teres minor) muscles, as well as a layer of cellular tissue. Passing through the compartment are the suprascapular artery, vein, and nerve, the circumflex scapular artery (a. circumflexa scapulae), and fascia-piercing branches of the deep branch of the transverse cervical artery.
- Subscapular space: located on the anterior aspect of the scapula, formed by the fusion of the subscapular fascia with the bone margins. Contains the subscapularis muscle (m. subscapularis). Beneath its tendon, which runs into the subdeltoid space toward the humerus, lies a large synovial bursa (bursa synovialis subscapularis) closely adjacent to the anterior joint capsule and constantly communicating with its cavity.
Arterial blood supply and collateral circle
The most important functional feature of the region is the presence of the scapular arterial collateral circle. This is a network of anastomoses between the branches of three main arteries that ensures upper limb blood supply when main blood flow is impaired.
Vascular connection occurs in two main zones: within the infraspinous cellular tissue and deep within the infraspinatus muscle. A key role is played by the circumflex scapular artery (a. circumflexa scapulae), which originates from the axillary fossa and pierces the fascia near the lateral border of the scapula.
Clinical significance: the scapular circle can compensate for blood flow in the arm when the axillary artery (a. axillaris) is blocked. However, a prerequisite for this is that the obstruction must be located proximally (superiorly) to the origin of the subscapular artery (a. subscapularis).
Deep layer muscles
The deep muscular layer of the region is a complex structure. In addition to the supra- and infraspinatus muscles, the teres major muscle (m. teres major) is located here. It originates from the inferior angle of the scapula (angulus scapulae), the lower half of the lateral border, and the outer surface of the infraspinous fascia. The superior border of the teres major muscle is adjacent to the inferior border of the teres minor muscle, forming a topographical slit between them.
The levator scapulae, rhomboids, deltoid, latissimus dorsi, and the long head of the triceps brachii also participate in the topography of the region.
Cellular tissue connections and pathways of pus spread
Despite the isolation of the osteofascial compartments, the cellular tissue of the scapular region communicates with adjacent regions. This determines the typical pathways of purulent process spread:
- Into the lateral triangle of the neck — along the course of the suprascapular neurovascular bundle.
- Into the axillary fossa — infection spreads through the triangular space along the circumflex scapular vessels (a. et v. circumflexae scapulae).
- Into the subdeltoid space — along the tendons of the supra- and infraspinatus muscles.
The subscapularis muscle and its fascia also play a barrier role, forming the posterior wall of the axillary fossa and the posterior wall of the prescapular cellular space (the anterior wall of which is the serratus anterior muscle within the thoracic fascia).
Briefly: answers to topical questions
Branches of which three main arteries form the scapular arterial collateral circle?
The scapular arterial collateral circle is formed by branches of the subclavian and axillary arteries. The following vessels participate in forming anastomoses:
- Suprascapular artery (a. suprascapularis) — a branch of the thyrocervical trunk from the subclavian artery.
- Deep branch of the transverse cervical artery (r. profundus a. transversae colli) — branches off from the subclavian artery.
- Circumflex scapular artery (a. circumflexa scapulae) — a branch of the subscapular artery from the axillary artery.
What muscles and bones form the walls of the triangular space?
The walls of the triangular space are formed exclusively by muscular structures; bones do not participate in their formation. The boundaries of the space are:
- Superiorly — subscapularis muscle (m. subscapularis) and teres minor muscle (m. teres minor).
- Inferiorly — teres major muscle (m. teres major).
- Laterally — long head of the triceps brachii muscle (caput longum m. tricipitis brachii).
Which nerves provide motor innervation to the deep muscles of the scapular region?
Motor innervation to the deep muscles of the scapular region is provided by short branches of the brachial plexus. These include:
- Suprascapular nerve (n. suprascapularis) — innervates the supra- and infraspinatus muscles.
- Dorsal scapular nerve (n. dorsalis scapulae) — innervates the levator scapulae and rhomboid muscles.
- Thoracodorsal nerve (n. thoracodorsalis) — innervates the latissimus dorsi and teres major muscles.
- Subscapular nerve (n. subscapularis) — innervates the subscapularis muscle.
- Axillary nerve (n. axillaris) — runs toward the teres minor muscle.
What forms the walls of the quadrangular space, and what vessels and nerves pass through it?
The walls of the quadrangular space are formed by two muscles, the long head of the triceps muscle, and a bone. Its boundaries are:
- Superiorly — subscapularis muscle (m. subscapularis) and teres minor muscle (m. teres minor).
- Inferiorly — teres major muscle (m. teres major).
- Medially — long head of the triceps brachii muscle (caput longum m. tricipitis brachii).
- Laterally — surgical neck of the humerus (collum chirurgicum humeri).
The following structures pass through this space:
- Axillary nerve (n. axillaris).
- Posterior circumflex humeral artery (a. circumflexa humeri posterior).
Class and exam questions
Under what condition does the scapular collateral circulation circle function?
Blood flow blockage in the axillary artery must occur strictly superior (proximally) to the origin of the subscapular artery. Only in this case will blood bypass the obstruction.
What does the synovial bursa of the subscapularis muscle communicate with?
The subscapular synovial bursa (bursa synovialis subscapularis) is large and constantly communicates with the cavity of the shoulder joint capsule.
How can pus from the scapular region enter the axillary fossa?
Purulent extensions spread along the circumflex scapular artery and vein (a. et v. circumflexae scapulae), passing through the triangular space.
What else to study on this topic
- Anatomy and boundaries of the prescapular cellular space
- Formation of the triangular space and its contents
- Topography of the subdeltoid cellular space
- Ligamentous apparatus of the scapula: superior transverse ligament
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