The rhomboid muscles are in fact two muscles (rhomboid minor and major) that are typically grouped together due to their functional similarity. Their location in the upper back and their attachment to the scapula, make them a point of interest clinically, especially in populations in which upper body posture is poor.
To understand the rhomboids influence on upper body posture and their impact clinically, this article will first review the anatomy of the rhomboid muscles, including their bony attachments (origin and insertion), their actions and innervation. Finally, the rhomboids anatomy will be discussed in terms of their influence on upper body posture and their implication in proper shoulder mechanics.
The rhomboids are considered to be part of a group of muscles that make up the superficial musculature of the upper back (along with trapezius, latissimus dorsi, and levator scapulae). As a group, these muscles function to connect the upper limbs to the trunk, as opposed to the rotator cuff muscles that attach the upper limbs to the scapula. In each case, either the origin or insertion of this group of superficial back muscles will attach to the spine.
All muscles are named based on either their bony attachments, position/location, function, fiber orientation, or in this case, the shape of the muscle. A rhomboid is a geometric shape which has four sides, but the adjacent sides are of unequal length (see the shape to the left). Based on this figure you can imagine the spine running along the left side of the shape (or medially) and the scapula lying along the right side, or laterally, with the rhomboids being the shape itself.
|Origin, Rhomb. Minor||Nuchal ligament and spinous processes of C7 and T1 vertebrae|
|Origin, Rhomb. Major||Spinous processes of T2-T5|
|Insertion, Rhomb. Minor||Smooth triangular area at the medial end of the spine of the scapula|
|Insertion, Rhomb. Major||Medial border (closest to the spine) of the scapula, from the spine of the scapula to the inferior angle|
The rhomboid minor and major muscles are both innervated by the dorsal scapular nerve (C4,5), one of the minor branches of the brachial plexus that arises from the cervical portion of the spinal cord. This nerve branches from the brachial plexus very early, before the roots of the plexus have even formed their superior, middle, and inferior trunks. The nerve will move posteriorly, often piercing the middle scalene muscle, to then travel along the medial border of the scapula to supply both rhomboid muscles.
From the medial border of the scapula, the rhomboids run medially towards the spine, but also somewhat superiorly. If you imagine the rhomboid muscles pulling the scapula in these directions, you may be able to visualize that the rhomboids will retract the scapula (pull the scapula towards the spine), but also slightly elevate the scapula. In addition, the rhomboids will rotate the scapula inferiorly, or downwards, such that the glenoid cavity will point more towards the ground (from anatomical position) when the rhomboids contract. It is these actions, retraction and downward rotation of the scapula that make the rhomboids clinically important.
As with any muscle that attaches to the scapula, the rhomboid muscles can have a great impact on upper body posture and shoulder mechanics. As mentioned previously, there are two actions in which the rhomboid muscles are most often implicated clinically.
Poor upper body posture typically includes a number of features. One is that the shoulders, and specifically the scapulae, tend to become protracted. This can be due to a combination of muscles pulling the scapulae into protraction (i.e. the pectoralis minor and major, and the serratus anterior muscles), and a weakness in the muscles that oppose protraction, or retract the scapulae (i.e. the middle portion of the trapezius muscle, latissimus dorsi, and the rhomboid muscles). This will often lead to pain in the upper back, especially along the medial border of the scapulae. Activities that strengthen muscles, like the rhomboids, that retract the scapula, will help relieve the pain and improve upper body posture.
Downward rotation of the scapula/glenoid cavity
There are a number of muscles that rotate the scapula and the glenoid cavity downward, more so than muscles that rotate the scapula and glenoid cavity upwards. This is interesting, because in order to fully raise the arm to 180 degrees, 120 degrees of that movement comes from the glenohumeral joint (the joint between the glenoid cavity of the scapula and the head of the humerus of the upper arm). The other 60 degrees of motion actually comes from the rotation of the scapula on the posterior thoracic wall. In order for this 60 degrees of upward rotation to occur, the muscles that attach to the scapula and rotate it downward need to allow the upward rotation to take place. Muscles like the rhomboids, that are under constant postural strain, (see above) can eventually become dysfunctional and limit the upward rotation of the scapula and glenoid cavity. This can lead to poor shoulder mechanics that in turn can cause soft tissues in the shoulder region to become injured and painful, especially in activities that require the arm to be raised above the height of the shoulder, as in many sporting activities (i.e. tennis and volleyball, etc).