The Rhomboid minor or Rhomboideus minor is also called the musculus rhomboideus minor and is one of the deep extrinsic shoulder muscles (the deep posterior thoracoappendicular muscles) the others being levator scapulae and rhomboid major. The Rhomboid minor is a narrow ribbon like muscle that lies parallel to the rhomboid major and arises from the C7 and T1 vertebral spines to insert into the medial border of the scapula above the triangular area and below the attachment of levator scapulae. The two rhomboids (major and minor) lie deep to the trapezius muscle and form parallel bands that pass inferior and laterally from the vertebrae to the medial border of the scapula. There are variations of the rhomboids in some individuals in which the two rhomboid muscles fuse to form a single muscle.
Rhomboid Minor Action and Function
The two rhomboids act together the Rhomboid major and Rhomboid minor function as retractors and elevators of the scapula. The Rhomboids also assist the serratus anterior muscle in holding the scapula against the thoracic wall and fixing the scapula during movements of the upper limb.
Rhomboid Minor Origin and Insertion
Rhomboid minor originates from the lower end of ligamentum nuchae as well as the spines of C7 and T1 vertebrae. The point of insertion of the rhomboid minor is at the smooth triangular area of bone at the root of the spine of the scapular on the posterior surface.
Rhomboid Minor Nerve Supply
Rhomboid minor is innervated by the dorsal scapular nerve (the nerve to the rhomboid) through the C4 and C5 cervical segments of the spinal cord. The dorsal scapular nerve is a branch of the brachial plexus from the C5 root of the brachial plexus, it passes through scalenus medius muscle and then runs down deep but anterior to levator scapulae to supply it; this nerve lies on the serratus posterior superior muscle to the medial side of the descending branch of the transverse cervical artery. The dorsal scapular nerve supplies both rhomboid minor and major muscles on the deep surface.
Rhomboid Minor Blood Supply
The rhomboid minor gets blood supply from the dorsal scapular artery the same artery supplies rhomboid major.
Rhomboid minor Test
The Rhomboid minor is tested together with the major by placing the hand on the hip or behind the back, then, the elbow is pushed backwards against resistance while bracing the shoulder back. The rhomboid muscles are then palpated at the vertebral border of the scapula. If the rhomboids of one side are paralyzed, the scapula of the affected side remains further from the midline than that of the normal side giving rise to a winged scapula.
Clinical importance of Rhomboid minor muscle
Any injury to the dorsal scapular nerve affects the rhomboid minor and major muscles and this can lead to paralysis of the muscles which then causes scapula instability such as scapula winging during depression of the scapula or protraction.
Differences between Rhomboid major and minor
- The rhomboid major is wider than the rhomboid minor
- The rhomboid major is thinner than the minor (the rhomboid minor is thicker)
- The rhomboid minor lies superior to the rhomboid major