Deltoid Muscle of Arm

The deltoid muscle is a skeletal muscle that appears striated and has triangular shape. Like any other skeletal muscle, the deltoid is a voluntary muscle, which implies that it can be controlled consciously. This muscle gives the shoulder its round and bulky appearance. It lies above the shoulder joint, covering the joint anteriorly, posteriorly and laterally.

Anterior | Posterior

Deltoid Muscle Biceps Brachii Brachioradialis Muscle Palmaris Longus Muscle Extensor Carpi Radialis Longus Muscle Extensor Retinaculum Dorsal Interossei Muscle Extensor Carpi Ulnaris Muscle Extensor Digitorum Communis Muscle Extensor Carpi Radialis Brevis Muscle Triceps Brachii Muscle Biceps Brachii Muscle Posterior Brachialis Muscle

Deltoid Muscle of Arm

The deltoid is subdivided into anterior, medial and posterior portions, which are all innervated by the axillary nerve, particularly C5 and C6. The point of insertion for these three portions of the deltoid is the proximal end of the humerus known as the deltoid tuberosity. However, the subdivisions differ in terms of point of origin. The anterior portion originates at the lateral one third of the clavicle, particularly from the anterior border. The medial portion is attached to the acromion process on its superior surface. And, the posterior portion is attached to the spine of the scapula through its inferior margin.

FUNCTIONS

Overall, the main function of the deltoid muscle is it serves as prime mover for arm abduction. This means that it is the primary muscle responsible when you move your arm away from your trunk or sideward. With the help of the anterior portion of the deltoid, you can also flex your arm horizontally and rotate it medially at the shoulder. On the other hand, the posterior portion of the deltoid permits horizontal extension and lateral rotation of the arms at the shoulder.

CLINICAL IMPORTANCE

The deltoid muscle is truly significant as prime mover for arm abduction, but its significance is more than its value as a muscle that generates movement. It has been considered as an important muscle for intramuscular (IM) administration of medications, particularly vaccines.

For medical professionals, the deltoid is much easily accessible compared to other bigger muscles such as the gluteus (buttocks) muscles, which are the other options when injecting intramuscularly due to its size. Based on patient’s preference also, the deltoid is more comfortable to be exposed during administration of IM medications than the buttocks. However, the amount of medication that the deltoid muscle can take is limited to 0.5 cc and must not be more than 1.0 cc. In other words, it is not an ideal site for large volume of medications to be administered IM.

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