Intertransversarii 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. Unlike their lateral counterparts, they are innervated by the posterior rami of adjacent spinal nerves and vascularized by the dorsal branches of lumbar arteries.

Function

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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