Intertransversarii lumborum muscles
Intertransversarii are small muscles of the back found between contiguous transverse processes of the cervical, lumbar, and some thoracic, vertebrae. They comprise the deepest layer of the deep (autochtone) back muscles, along with interspinales and levatores costarum.
Lumbar intertransversarii consist of four pairs of muscles, located on either side of the vertebral column. Each pair has a medial and lateral component, respectively named intertransversarii laterales lumborum and intertransversarii mediales lumborum. This is in contrast to the cervical region, where the intertransversarii muscle pairs are divided into anterior and posterior parts. The intertransversarii muscles attach between the transverse processes of adjacent lumbar vertebrae. Slips of muscle fibers also extend into the thoracic region, reaching as far as T10 vertebral level. These thoracic intertransversarii are considered by some to be a continuation of the lumbar intertransversarii rather than a separate muscle group.
Lumbar intertransversarii functions are ipsilateral lateral flexion of the spine when contacting unilaterally, and stabilization of the lumbar spine when contracting bilaterally.
|Origin||Lateral lumbar intertransversarii: Transverse and accessory processes of vertebrae L1-L4
Medial lumbar intertransversarii: Accessory processes of vertebrae L1-L4
|Insertion||Lateral lumbar intertransversarii: Transverse process of succeeding vertebra
Medial lumbar intertransversarii: Mammillary processes of succeeding vertebra
|Action||Assists lateral flexion of the spine; Stabilises spine|
|Innervation||Anterior rami of spinal nerves|
|Blood supply||Dorsal branches of lumbar arteries|
This article will discuss the anatomy and function of intertransversarii laterales lumborum muscles.
Intertransversarii laterales lumborum
Lumbar intertransversarii are divided into four pairs of medial and lateral muscles. The lateral muscles, intertransversarii laterales lumborum, are small in size yet they also consist of two parts; anterior (ventral) and posterior (dorsal). In literature these are referred as intertransversarii laterales ventrales and intertransversarii laterales dorsales, respectively.
The anterior parts attach between the transverse processes of contiguous lumbar vertebrae. The posterior parts originate from the accessory process of one lumbar vertebra and insert onto the transverse process of the consecutive lumbar vertebra.
Lateral lumbar intertransverse muscles are found posterior to iliopsoas and deep to both multifidus lumborum and rotatores longi muscles. Lateral to them are the intertransverse ligaments and the quadratus lumborum muscle.
Intertransversarii laterales lumborum are supplied by the anterior rami of spinal nerves, in contrast to intertransversarii mediales lumborum which are innervated by the posterior rami of adjacent spinal nerves. Blood supply to these muscles comes from the dorsal branches of lumbar arteries.
Intertransversarii mediales lumborum
Medial lumbar intertransversarii are the thin muscular slips that attach between the accessory and mammillary processes of contiguous lumbar vertebrae L1-L4.
They are located between the intertransversarii laterales lumborum and lumbar vertebral bodies. Just like their lateral counterparts, they are innervated by the anterior rami of spinal nerves and vascularized by the dorsal branches of lumbar arteries.
The function of intertransversarii muscles is still not completely clear. It’s known that these muscles aren’t strong enough to cause prime movements of the spine when acting alone. However it’s suggested that when contracting unilaterally, they assist erector spinae, semispinalis and multifidus to laterally flex the trunk at the intervertebral joints to the same side (ipsilaterally). Besides this, these muscles have a proprioceptive role as they contain many muscle spindles; and therefore stabilize and balance the spine during body and trunk movements.
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