Levatores costarum muscles
Levatores costarum consists of 12 small triangular muscles that connect the thoracic vertebrae with the adjacent ribs. Located along either side of the posterior aspect of the thoracic vertebra they descend adjacent to the spine, spanning the thoracic region from C7 to T12 levels.
Together with the intercostal muscles, serratus posterior superior and inferior and transversus thoracis, they form the intrinsic muscles of the chest wall. The intrinsic chest wall muscles are thought to play a role in forced respiration and in preventing the chest from moving inwards during inspiration (paradoxical breathing).
Along with being considered a chest wall muscle, the levatores costarum muscles can also be grouped with the deepest muscles of the back, together with the interspinales and intertransversarii muscles. These minor muscles form the fourth layer of the deep muscles of the back. Levatores costarum functions in elevating the ribs, and produces rotation and lateral flexion of the thoracic vertebrae.
|Origin||Transverse processes of the C7 – T11|
|Insertion||Superior border/external surface of rib one level below origin|
|Action||Elevation of the ribs
Rotation of thoracic spine
|Innervation||Posterior rami of spinal nerves T1 – T12|
|Blood supply||Posterior intercostal artery|
This article will discuss the anatomy and function of the levatores costarum muscles.
Origin and insertion
There are 12 separate muscle bundles that make up levatores costarum. Each originates from the transverse processes of one vertebra and passes obliquely to insert into the rib one level below. More specifically, the muscle bundle arises from the tip of the transverse processes of the associated vertebra (C7-T11). It then passes obliquely in an inferolateral direction to insert into the external aspect of the superior border of the rib, between the costal angle and tubercle of rib. The muscles are triangular in shape, with the apex pointing toward the origin and fanning out to form its base at the insertion.
The upper eight muscles (on each side) travel as single muscular bands from origin to insertion. In contrast, the lower four muscles split into two fasciculi called longi and breves (levatores costarum longi, levatores costarum breves). The short (breve) fascicle passes from the muscles’ origin to attach into the rib located immediately below, while the longer (longi) fascicle descends further to attach onto the rib located 2 levels below.
Levatores costarum is innervated by the lateral branches of the dorsal rami of thoracic spinal nerves (T1 – T12).
The dorsal branch of the posterior intercostal artery brings oxygenated blood to the levatores costarum muscles. The posterior intercostal artery is a direct branch of the thoracic aorta and travels along the lower border of each rib.
There are two major functions of levatores costarum. The first is to elevate the ribs and the second is to rotate and laterally flex the vertebra. Although it is able to elevate the ribs, there is some dispute about whether or not that levatores costarum plays an active role during inspiration.