Deltoid muscle

The deltoid muscle is a thick triangular-shaped muscle of the shoulder girdle. It arises from two bones – the scapula and the clavicle, and extends to the humerus of the upper arm. According to the origin of its fibers, the deltoid muscle can be divided into three parts - lateral - acromial part, posterior - spinal part, and anterior - clavicular part.

Origin: the acromial part originates laterally from acromion of the scapula, the spinal part - posteriorly from the spine of the scapula, and the clavicular part - anteriorly from the acromial end of the clavicle.

Insertion: muscle fibers merge together and insert into the deltoid tuberosity of the humerus, which is located in the middle of the lateral aspect of the humeral shaft.

Action: the deltoid enables movements of the upper limb, which are provided according to the activated part the muscle:

• Clavicular part – internal rotation of the upper arm;
• Spinal part – external rotation of the upper arm;
• Acromial part – abduction of the upper arm;
• Clavicular part and spinal part – adduction of the upper arm;
• Clavicular part and acromial part – flexion of the upper arm;
• Acromial part and spinal part – extension of the upper arm.

Innervation: axillary nerve, which originates from the anterior radices of spinal nerves C5 and C6.

Blood supply: deltoid branch of the thoracoacromial artery and acromial branch of the thoracoacromial artery, subscapular artery, anterior circumflex humeral artery and posterior circumflex humeral artery (all these vessels arise from the axillary artery), and deltoid branch of the deep brachial artery (arises from the brachial artery).