Rhomboid muscles

The rhomboid muscles (Latin: musculi rhomboidei) consist of two separate pairs of extrinsic muscles - rhomboid minor and rhomboid major. Together with the trapezius, levator scapulae and latissimus dorsi, both rhomboid muscles belong to the superficial muscle group of the back that connects the upper limb to the trunk. The rhomboid muscles are located in the upper back and participate in upper limb movements, stabilize the position of the scapula and contribute to the stabilization of the shoulder girdle. There are some variations in the anatomy of rhomboid musculature, and sometimes both rhomboid muscles are fused into a single muscle.

Rhomboid major

The rhomboid major (Latin: musculus rhomboideus major) is a quadrangular-shaped muscle located inferior to the rhomboid minor muscle. As one of the superficial muscles of the back, it connects the scapula with the vertebrae of the spine. It lies deep to the trapezius muscle.

Origin

The rhomboid major muscle originates from the spinous processes of the second to fifth thoracic vertebrae (Th2 - Th5).

Insertion

The rhomboid major inserts on the medial margin of the scapula between the inferior angle and the root of the scapular spine.

Action

The rhomboid major muscle acts at the scapulothoracic joint. This muscle retracts the scapula by pulling it posteromedially. Also, it rotates the glenoid cavity inferiorly. Besides all the mentioned functions, the rhomboid major muscle supports the scapula by protracting its medial border and keeping it in position at the posterior thoracic wall.

Innervation

The rhomboid major is innervated by the dorsal scapular nerve (C4 - C5).

Blood supply

The rhomboid major muscle receives arterial blood supply from the dorsal scapular artery that typically arises from the subclavian artery. Sometimes instead of the subclavian artery, it can originate from the transverse cervical artery.

Rhomboid minor

The rhomboid minor (Latin: musculus rhomboideus minor) is a small extrinsic muscle of the upper back that connects the scapula with the spine. It lies deep to the trapezius, inferior to the levator scapulae and superior to the rhomboid major muscle.

Origin

The rhomboid minor muscle arises from the nuchal ligament and spinous processes of the seventh cervical to the first thoracic vertebrae (C7 - Th1).

Insertion

Fibers of the rhomboid minor insert on the root (medial end) of the scapular spine.

Action

The actions provided by the rhomboid minor muscle are the same as those of the rhomboid major muscle, and this muscle also acts at the scapulothoracic joint. Like the rhomboid major, the rhomboid minor muscle retracts the scapula, rotates the glenoid cavity inferiorly and supports the position of the scapula.

Innervation

The rhomboid minor is innervated by the dorsal scapular nerve (C4 - C5).

Blood supply

Like the rhomboid major, the rhomboid minor muscle also receives oxygenated blood from the dorsal scapular artery.