Anatomy & Innervation
The rhomboid muscles are two diamond-shaped muscles of the shoulder girdle. Both extend from the vertebral column to the medial border of the scapula. They lie over the autochthonous back muscles but under the trapezius. In this area, they are both palpable and often visible. The rhomboid muscles are divided into two, as follows:
Rhomboid major muscle
It runs from the spinous processes of the 1st to 4th thoracic vertebrae to the medial border under the spine of the scapula.
Rhomboid minor muscle
It originates further up at the spinous processes of the 6th to 7th cervical vertebrae and inserts above the scapular spine.
Usually there is a small space between both rhomboid muscles. However in some cases one may find one single blended muscle instead. The innervation is supplied by the dorsal scapular nerve (C4-C5), a branch of the brachial plexus.
Both rhomboids perform the same motions as their muscle fibers run parallely towards the same direction. Their contraction causes a craniomedial movement of the scapula (adduction and elevation). At the same time, the inferior angle of the scapula is moved towards the vertebral column (rotation). That movement mainly supports lowering of the elevated arm. Another function of the rhomboid musculature is the stabilization of the scapula during both rest and arm movement.
Similar to all the muscles of the shoulder girdle, the rhomboid muscles are prone to pain and functional disturbances due to overstrain and poor posture. A common cause is the permanent pulling forward of the shoulder at work (e.g. at the computer).
- chronic pain at the medial border of the scapula
- weakness and coordination disorders in the shoulder up to the medial tilt of the shoulder blade (scapula alata)