Musculoskeletal System
Rhomboids: scapular retraction and dorsal scapular nerve
The rhomboids are upper back muscles that retract the scapula (draw the shoulder blades together) and are supplied by the dorsal scapular nerve, a motor nerve from C5.
Remember
Weak scapular retraction with a normal shrug (lifting the scapula) points to the rhomboids and the dorsal scapular nerve, whereas a weak shrug points to trapezius or, among the muscles that nerve supplies, to levator scapulae (a muscle that lifts the scapula).
The two rhomboid muscles, major and minor, lie deep to trapezius. They run from the spinous processes (the bony points at the back of the vertebrae) to the medial border of the scapula, the edge of the shoulder blade nearest the spine. Rhomboid major starts at T2 to T5, and rhomboid minor lies just above it, starting at C7 and T1.
When they contract, they pull that border towards the vertebral column. This movement is retraction: the shoulder blades are drawn back and together. The rhomboids also rotate the scapula so that the glenoid cavity (the shallow socket of the shoulder blade that receives the head of the humerus) faces downwards. This is downward rotation, the reverse of the upward turn that serratus anterior (a muscle on the side of the chest wall) and trapezius give the scapula when the arm is raised overhead. Serratus anterior also protracts the scapula, which means it moves it forwards around the rib cage.
The dorsal scapular nerve arises from C5 in the neck and supplies both rhomboids and levator scapulae, a muscle that lifts the scapula. Because the nerve does not separate these three muscles, a neck injury can affect them together, and you decide between them by function. Weak retraction with a preserved shrug points to the rhomboids. Of the three, weak lifting of the scapula points to levator scapulae instead. Rhomboid major also helps levator scapulae to lift the medial border of the scapula, but retraction is its main action.
Trapezius is the near miss. It also retracts the scapula through its middle part, but it is a superficial muscle and a main shrugging muscle, so an injury to it would be expected to weaken the shrug as well.
Memory aid
squeezing a pencil between your shoulder blades
Picture squeezing a pencil between your shoulder blades: that squeeze is the rhomboids at work.
Key facts
- Rhomboid major
- arises from the spinous processes of T2 to T5 and attaches to the medial border of the scapula.
- Rhomboid minor
- arises from the spinous processes of C7 and T1 and attaches to the medial border of the scapula.
- Action
- both rhomboids retract the scapula and rotate it downwards.
- Nerve
- the dorsal scapular nerve, from C5, supplies rhomboid major, rhomboid minor and levator scapulae.
- Position
- the rhomboids lie deep to trapezius.
- Opposite pattern
- serratus anterior protracts the scapula and rotates it upwards.
- Bedside clue
- weak retraction with a normal shrug points to the rhomboids; a weak shrug points to trapezius and the accessory nerve that supplies it or, among the muscles the dorsal scapular nerve supplies, to levator scapulae.
Exam traps
- Trapezius does not explain weak retraction with a preserved shrug. It is a main shrugging muscle, so a trapezius injury would be expected to weaken elevation (lifting the scapula) too.
- Levator scapulae shares the dorsal scapular nerve but lifts the scapula, so it fits a weak shrug, not weak retraction.
- Retraction with upward rotation is half right. The rhomboids rotate the scapula downwards, and upward rotation belongs to serratus anterior and trapezius.
- Protraction with downward rotation borrows the rhomboid rotation but not the movement. Moving the scapula forwards is the work of serratus anterior, while the rhomboid major draws it back towards the spine.
- Long thoracic nerve injury affects serratus anterior and causes medial winging, where the medial border of the scapula lifts away from the chest wall, rather than mainly weak retraction.
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