The rhomboids are two bilateral, superficial muscles located in the upper back. They consist of two functionally similar muscles called rhomboid minor and rhomboid major. Together with trapezius, levator scapulae and latissimus dorsi, they comprise the superficial layer of the extrinsic back muscles.
The rhomboid muscles extend between the nuchal ligament, spinous processes of thoracic vertebrae and scapula. Under innervation from the dorsal scapular nerve, the rhomboids primarily retract the scapula superomedially and rotate the glenoid cavity. Therefore, the rhomboids are important to stabilize the scapula into position and reinforce the shoulder.
This article will discuss the anatomy and function of the rhomboid muscles.
Rhomboid minor: Nuchal ligament, Spinous processes of vertebrae C7-T1
Rhomboid major: Spinous process of vertebrae T2-T5
Rhomboid minor: Root (medial end) of spine of scapula
Rhomboid major: Medial border of scapula (from inferior angle to root of spine of scapula)
|Action||Scapulothoracic joint: Draws scapula superomedially, Rotates glenoid cavity inferiorly; Supports position of scapula|
|Innervation||Dorsal scapular nerve (C4-C5)|
|Blood supply||Dorsal scapular artery, deep branch of transverse cervical artery, dorsal branch of upper five or six posterior intercostal arteries|
Origin and insertion
Rhomboid minor is a small, cylindrical muscle that consists of two layers; dorsal and ventral. They partially envelop the levator scapulae inferiorly. Rhomboid minor originates from the nuchal ligament and spinous processes of the seventh cervical (C7) and first thoracic (T1) vertebrae. The muscle extends obliquely in an inferolateral direction, to insert into the base of the medial end of the spine of scapula; the dorsal layer attaches dorsolateral and inferior to levator scapulae while the ventral layer inserts inferomedially to levator scapulae. At the insertion point of the ventral layer, the fasciae of rhomboid minor and serratus anterior muscles unite. In certain individuals, a thin muscle called rhomboid occipitalis can extend between rhomboid minor and the occipital bone.
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Rhomboid major is a broad quadrilateral muscle that originates from the spinous processes of the second to second to fifth thoracic vertebrae (T2-T5). The muscle extends obliquely in an inferolateral direction to insert into the medial border of scapula, between the inferior angle and root of the spine of scapula. The attachment takes place both on the dorsal and costal aspects of the medial border of scapula.
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The rhomboid muscles overlie the deep (intrinsic) muscles of the back and are covered by the trapezius muscle. The exception is a small triangular region over the inferior border of rhomboid major (triangle of auscultation). This area is bordered by the latissimus dorsi muscle inferiorly, trapezius muscle superomedially and rhomboid major superolaterally. It is an important clinical landmark that serves for lung auscultation from the back.
The rhomboids are generally completely separate muscles, but they can be fused in certain individuals. Rhomboid minor partially overlaps the superior portion of rhomboid major.
Both rhomboid muscles are innervated by the dorsal scapular nerve (C4-C5), a branch of the brachial plexus.
Rhomboid minor and major receive arterial blood from three sources:
The main action of the rhomboid muscles is scapular retraction around the scapulothoracic joint. Scapular retraction is a simultaneous sliding of the scapula superiorly and medially along the trunk. This superomedial movement of the scapula rotates the glenoid cavity inferiorly, dropping the shoulder girdle. By opposing excessive scapular protraction, the rhomboids help to maintain a correct posture when sitting, standing and walking.
In addition, the contraction of the rhomboids fixes and stabilizes the scapula into position. This provides an anchor point in space from which various muscles of the upper limb can act and a fulcrum around which the upper limb can move.
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The rhomboid muscles can have a great impact on upper body posture and shoulder mechanics. Poor upper body posture typically includes a number of features. One is that the shoulders, and specifically the scapulae, tend to become protracted. This will often lead to pain in the upper back, especially along the medial border of the scapulae. Therefore, strengthening muscles responsible for scapular retraction, such as the rhomboids, will help relieve the pain and improve upper body posture.
The constant postural strain experienced by the rhomboid muscles can make them dysfunctional. This can limit the superior rotation of the scapula and glenoid cavity, leading to poor shoulder mechanics. In turn, soft tissues in the shoulder region can become injured and painful, especially during activities that involve arm elevation above shoulder height. Such examples include sporting activities like tennis and volleyball.