multifidus

The multifidus is a deep intrinsic back muscle that forms part of the transversospinalis muscle group. It consists of small, short muscle bundles that lie close to the vertebral column and run obliquely from the transverse processes of one vertebra to the spinous process of a vertebra several levels above. The muscle spans the entire length of the spine, from the sacrum and iliac region superiorly to the cervical region, but it is particularly thick in the lumbar area. Each fasciculus typically attaches to the spinous process two to four segments above its origin.

Attachments and anatomy: The multifidus originates from structures including the posterior aspect of the sacrum, posterior superior iliac spine, and adjacent deep fascia, as well as from the transverse processes of vertebrae. It inserts onto the spinous processes of higher vertebrae, with the most substantial portions located in the lumbar spine. The muscle is organized into regional bundles that collectively stabilize the spine.

Function: The primary role of the multifidus is segmental spinal stabilization. It contributes to keeping the vertebral joints aligned during movement and supports posture. Its activity assists in extension, lateral flexion, and rotation of the spine, depending on the level and direction of contraction, and it provides proprioceptive feedback for spinal control.

Innervation and vascular supply: The multifidus is innervated by the dorsal rami of spinal nerves. Blood supply is segmental, derived from regional arteries that accompany the dorsal rami.

Clinical relevance: Atrophy or fatty degeneration of the multifidus has been associated with chronic low back pain. Imaging can reveal thinning of the muscle, and rehabilitation often emphasizes targeted activation and strengthening of the multifidus to improve spinal stability.