Levatores costarum

The levatores costarum (Latin: musculi levatores costarum) is a group of twelve pairs of small triangular-shaped muscles located in the posterior thorax. They are located on either side of the thoracic spine, stretching between the transverse processes of the thoracic vertebrae and ribs. The levatores costarum lie superficially to the external intercostal muscles.

The levatores costarum are considered intrinsic muscles of the thoracic wall, as well as the deep muscles of the back. Together with the other thoracic muscles, the levatores costarum possibly are involved in forced respiration and prevent the thorax from moving inwards during inspiration. Together with the interspinales and intertransversarii muscles, the levatores costarum form the deepest layer of the deep back muscles and provide movements of the spine.

Origin

The levatores costarum muscles arise from the transverse processes of the seventh cervical to eleventh thoracic vertebrae (C7 - T11). Each muscle originates from one transverse process and passes obliquely downward in an inferolateral direction.

Insertion

Each muscle inserts on the superior border of a rib one level below the origin of the muscle. The insertion site can be found on the rib between the costal angle and rib tubercle. Each levatores costarum muscle is triangular-shaped, with the base projecting at its insertion site and the apex pointing towards the origin.

The upper eight muscle pairs appear as single muscular bands, while the lower four split into two fasciculi - long and short. These two bundles are called levatores costarum longi and levatores costarum breves. The short fascicles insert on the ribs one level below their origin, while the long fascicles descend further and attach to the rib located two levels below the origin.

Action

The levatores costarum muscles elevate the ribs and rotate the thoracic spine. Although these muscles elevate ribs, they are thought to play a relatively unimportant role during inspiration.

Innervation

The levatores costarum are innervated by the lateral branches of the dorsal rami of the spinal nerves.

Blood supply

The levatores costarum muscles are supplied by the dorsal branches of the posterior intercostal arteries that arise from the superior intercostal arteries and thoracic aorta.