Surface Anatomy; the relationship between trapezius & deltoid

There is an incredibly intimate relationship between the Deltoid & Trapezius. These two muscle groups share the bony attachments of the clavicle, acromion and spine of the scapula, therefore if either become tightened or reactive to postural dysfunction (rounded shoulders) one or both of them will react. This creates pain in localised areas, or referred pain up into the neck and head or down the arm.

In terms of our treatments due to their intimate relationship we would always work on both. The deltoid, particularly the anterior aspect, carries huge muscle tension and the therapist must take time to slowly work through the adhesions before moving on.

Let's explore this marriage between muscles in more detail...

Let's take a moment to recap Trapezius and Deltoid and the incredibly important relationship between them.

Trapezius

The trapezius is a large muscle spanning most of the upper back. The trapezius is responsible for stabilising the scapula and controlling the scapula during shoulder and upper limb movements. The trap is divided into three areas. The upper trap is key in scapular elevation and lateral neck flexion. The middle trap retracts the scapula. The lower trap depresses the scapula.

Deltoid

The deltoid is a thick triangular muscle that lies over the glenhumeral joint and gives the shoulder its rounded contour. The deltoid spans the clavicle, acromion and the spine of scapula. Again there are three parts to this muscle. The clavicular part is involved in flexion and internal rotation of the arm. The acromial part gives abduction of the arm beyond the initial 15 degrees. The Spinal part is responsible for extension and external rotation of the arm.