Boundaries and External Landmarks
The region is located lateral to the scapular zone and completely corresponds to the contours of the deltoid muscle (m. deltoideus). Externally, it is bounded by the following lines:
- Superior: runs along the lateral third of the clavicle, the acromion, and the lateral third of the scapular spine.
- Inferior: a conventional line on the lateral surface of the arm connecting the lower edges of the latissimus dorsi (m. latissimus dorsi) and pectoralis major (m. pectoralis major) muscles.
- Anterior and posterior: correspond to the borders of the deltoid muscle.
Normally, the clavicle, acromion, scapular spine, and the bulk of the muscle itself are easily palpable. An important diagnostic sign: in shoulder dislocations, this characteristic muscular convexity becomes smoothed out, and a depression is visualized in its place.
Projections of major structures
Strict landmarks are used for surgical approaches:
- Cephalic vein (v. cephalica) is projected along the course of the deltopectoral groove (sulcus deltopectoralis).
- Neurovascular bundle (including the axillary nerve, n. axillaris, and posterior humeral circumflex vessels) is projected on a vertical line dropped downwards from the posterior-lateral angle of the acromion. The distance to the bundle averages 6 cm (the surgical neck of the humerus is located at the same level). If the arm is abducted to a right angle, the distance decreases to 2.5–3.0 cm.
- Inferior recess of the articular capsule (recessus axillaris) lies under the posterior border of the muscle. Its projection is a point on the same vertical line, 4 cm below the posterior angle of the acromion (or 2 cm above the nerve projection). In arthritis of the shoulder joint, palpation of this point causes acute tenderness.
Layer-by-layer topography
The tissue structure of the deltoid region from superficial to deep:
- Skin: relatively thick and immobile.
- Subcutaneous adipose tissue: well-developed, has a cellular structure at the posterosuperior border. Approximately at the middle of the posterior border of the muscle, a branch of the axillary nerve—the superior lateral cutaneous nerve of the arm (n. cutaneus brachii lateralis superior)—emerges from beneath the fascia.
- Superficial fascia: very poorly developed.
- Deep fascia (fascia deltoidea): along the superior border, it firmly fuses with bony structures (clavicle, acromion, spine of the scapula). It consists of superficial and deep layers, forming an osteofascial sheath for the muscle. Numerous fascial septa penetrate the muscle, dividing it into clavicular, acromial, and spinal parts. Anteriorly, in the sulcus deltopectoralis, the fascia splits to allow the passage of v. cephalica into the subclavian region.
Subdeltoid fascial space
The space is located between the deep layer of the deep fascia (covering the deep surface of the muscle) and the proximal end of the humerus with the joint capsule.
The neurovascular bundle passes here, and the subdeltoid synovial bursa (bursa subdeltoidea) is located. It surrounds the greater tubercle of the humerus, to which the tendons of the supraspinatus, infraspinatus, and teres minor muscles attach. Often, this bursa communicates with the subacromial bursa (bursa subacromialis).
The cellular tissue of the space serves as a pathway for the spread of purulent streaks to adjacent zones:
- Into the axillary fossa (along the bundle through the quadrilateral space).
- Into the supraspinatus and infraspinatus spaces of the scapula (along the tendons of the respective muscles).
- Into the subtrapezial space (upwards under the acromion and posteriorly).
Nerves, vessels, and collateral circulation
The main nerve of the region is the axillary nerve (n. axillaris). Emerging from the axillary fossa through the foramen quadrilaterum, it lies adjacent to the inferior recess of the joint capsule and winds around the surgical neck of the bone. Damage to the nerve (compression by callus or bone fragments in a neck fracture, involvement in purulent omarthritis) causes loss of cutaneous sensation and paralysis of the deltoid muscle. The main symptom is the inability to abduct the arm to the horizontal level.
An arterial network forms on the deep surface of the muscle, providing collateral circulation during the occlusion of main vessels. Here, the anterior and posterior humeral circumflex arteries anastomose, as well as the deltoid branch of the thoracoacromial artery.
Of particular importance is the connection between the deltoid branch of the deep brachial artery and branches of the axillary artery. However, in slowly progressive stenosis, the small diameter of these anastomosing vessels may become a limiting factor, and the network may fail to compensate for the impaired blood flow.
Briefly: answers to topical questions
What forms the walls of the quadrilateral space?
The walls of the quadrilateral space (foramen quadrilaterum) are formed by muscles and bone.
- Superior wall — subscapularis muscle (m. subscapularis) and teres minor muscle (m. teres minor).
- Inferior wall — teres major muscle (m. teres major) and upper edge of the tendon of the latissimus dorsi muscle (m. latissimus dorsi).
- Medial wall — long head of the triceps brachii muscle (caput longum m. tricipitis brachii).
- Lateral wall — surgical neck of the humerus (collum chirurgicum humeri).
Which nerves innervate the skin of the deltoid region?
The skin of the deltoid region is innervated by a branch of the axillary nerve.
- Superior lateral cutaneous nerve of the arm (n. cutaneus brachii lateralis superior) — branches off from the axillary nerve (n. axillaris), emerges from beneath the deep fascia approximately at the middle of the posterior border of the deltoid muscle, and innervates the skin over it, as well as over the lateral surface of the shoulder joint.
What structures pass through the deltopectoral groove?
The superficial vein of the upper extremity passes through the deltopectoral groove (sulcus deltopectoralis), which serves as the boundary between the deltoid and pectoralis major muscles.
- Cephalic vein (v. cephalica) — is projected along the course of the groove, lies within the splitting of the deep fascia (fascia deltoidea), and heads towards the subclavian region.
To which anatomical structures does the deltoid muscle attach?
The deltoid muscle (m. deltoideus) is divided into three parts:
- Clavicular part (pars clavicularis).
- Acromial part (pars acromialis).
- Spinal part (pars spinalis).
The muscle attaches to the humerus in the area of the deltoid tuberosity (tuberositas deltoidea), located slightly above the middle of the humeral shaft on the anterolateral surface.
Class and exam questions
Where and how is the neurovascular bundle projected?
Projected 6 cm below the posterolateral angle of the acromion (on a vertical line). When the arm is abducted to a right angle, this distance decreases to 2.5–3.0 cm.
Where can pus spread from the subdeltoid space?
Purulent streaks can spread into the axillary fossa, the supraspinatus and infraspinatus spaces of the scapula, and the subtrapezial space.
Which symptom indicates damage to the axillary nerve?
The main motor deficit is the inability to abduct the arm to the horizontal level due to paresis or paralysis of the deltoid muscle.
What else to study on this topic
- Mechanisms of collateral formation during axillary artery occlusion at various levels
- Topography of the quadrilateral space (foramen quadrilaterum)
- Structural features and communications of the synovial bursae of the shoulder joint
- Topography of the deltopectoral groove (sulcus deltopectoralis) and the course of the v. cephalica
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