Deltoid fascia

The deltoid fascia is a dense, fibrous layer that envelops the deltoid muscle, playing a crucial role in its function and integration with the surrounding shoulder musculature.

• Superiorly, this fascia blends with the periosteum of the clavicle, acromion, and spine of the scapula, and extends to the upper part of the medial border of the scapula. Specifically around the acromion and lateral half of the scapular spine, it becomes continuous with the supraspinatus fascia, seamlessly contributing to the fascial envelope over the rotator cuff region.

• Inferiorly, the deltoid fascia blends with the brachial fascia and the lateral intermuscular septum, providing structural continuity with the upper arm.

• Anteriorly, it merges with the pectoral fascia.

• Posteriorly and inferiorly, it is intimately connected to the infraspinatus fascia, with the posterior deltoid fibers inserting directly into it and forming transverse fascial connections.

This extensive blending with neighboring supraspinatus and infraspinatus fascia integrates the deltoid into the broader myofascial network of the shoulder, supporting coordinated movement and efficient force transmission.

Beyond simply covering the muscle, the deltoid fascia is thickest in its central part. Here, it sends deep fibrous septa that penetrate between the fascicles (bundles of muscle fibers) of the deltoid. This contributes significantly to the deltoid's multipennate architecture, which, in turn, maximizes its strength and contractile force.