Multifidus: Origin, Insertion, Nerve, Action & Low Back Stability

The Multifidus (plural: Multifidi) is a series of small, fleshy, triangular muscle fascicles located deep in the groove between the spinous processes and the transverse processes of the vertebrae. While it spans the entire spine, it is thickest and most critical in the lumbar region, serving as the primary local stabilizer of the lower back.

[Image of Multifidus muscle anatomy]

Quick Anatomy Snapshot

Group	Transversospinalis (Deep Back Muscles).
Origin (Proximal)	Posterior Sacrum, PSIS, Mammillary Processes (Lumbar), Transverse Processes (Thoracic), Articular Processes (Cervical).
Insertion (Distal)	Spinous Processes of vertebrae located 2 to 4 levels above the origin.
Nerve Supply	Medial branches of the Posterior Rami of the respective spinal nerves.
Primary Actions	Stabilization: "Stiffness" control of vertebral segments. Bilateral: Extension of the spine. Unilateral: Contralateral Rotation (turns spine to opposite side) and Lateral Flexion.

Deep Dive: The "Christmas Tree" Muscle

The Multifidus belongs to the Transversospinalis group (along with Rotatores and Semispinalis). Its name means "many split into two" or "multifaceted."

1. The Segmental Spans

Each bundle of the Multifidus spans 2 to 4 vertebral segments. This arrangement creates a "Christmas Tree" pattern of forces along the spine, allowing for fine-tuned control of individual vertebrae rather than just gross movement.

2. The Lumbar Powerhouse

While present in the neck (Cervical) and mid-back (Thoracic), the Multifidus is exceptionally developed in the Lumbar region. Here, it fills the deep "gutter" next to the spine. It is so strong in the low back that it provides two-thirds of the stiffness required to stabilize the lumbar spine.

Physio Corner: Clinical Relevance

💪 Functional Fact: The Multifidus is extremely rich in Muscle Spindles. This means its primary role is arguably proprioception—telling the brain exactly where the spine is in space—rather than just generating torque.

Palpation

Palpation is easiest in the lumbar spine. Locate the spinous processes. Slide your fingers just off the bone into the "gutter" lateral to the spine (but medial to the large Erector Spinae tubes). Ask the patient to lift the opposite leg slightly. You should feel the Multifidus swell deep under your fingers.

⚠️ Clinical Pathology: Fatty Infiltration
In patients with chronic Low Back Pain (LBP), the Multifidus rapidly atrophies and is replaced by fat tissue (fatty infiltration), visible on MRI. Unlike other muscles, the Multifidus does not spontaneously recover after the pain goes away; it requires specific stabilization exercises (e.g., "Bird Dog") to reactivate.

Functional Assessment

We cannot isolate the Multifidus from the Erector Spinae for standard strength testing, but we assess its firing pattern.

Testing Tip: Look for the "Multifidus Swell." A healthy muscle should firm up immediately upon contralateral limb loading. In chronic back pain, there is often a delay or "hollow" feel.

Step-by-Step Assessment

Test	Patient Action & Observation
Prone Leg Lift	Position: Prone (face down). Action: Patient lifts one leg slightly off the table. Palpation: Place fingers lateral to L4/L5 spinous processes. Result: You should feel immediate tension in the Multifidus on the side opposite the lifted leg.
Sorenson Test	Position: Prone, upper body off table (supported at hips). Action: Hold body horizontal. Observation: This tests global extensor endurance (Multifidus + Erector Spinae).

Frequently Asked Questions

Does Multifidus rotate the spine?

Yes. Because its fibers run obliquely Up and In (toward the spinous process), unilateral contraction pulls the spinous process toward the muscle, rotating the front of the body to the Opposite (Contralateral) side.

How is it different from Rotatores?

Rotatores: Span 1-2 segments, deepest layer, mostly proprioceptive.
Multifidus: Spans 2-4 segments, superficial to Rotatores, provides significant stabilization force.

What are the "Core" muscles?

The "Deep Core" cylinder consists of the Diaphragm (roof), Pelvic Floor (floor), Transversus Abdominis (corset), and Multifidus (posterior support).

Test Your Knowledge: Multifidus Quiz

1. To which muscle group does the Multifidus belong?

2. In which region of the spine is the Multifidus thickest?

3. What is the unilateral action of the Multifidus?

4. Where does the Multifidus insert?

5. Which nerve supplies the Multifidus?

6. What histological change happens to Multifidus in chronic back pain?

7. How many vertebrae does a single Multifidus bundle typically cross?

8. Where does the Multifidus originate in the Lumbar spine?

9. The Multifidus lies _______ to the Erector Spinae.

10. What is the primary sensory function of the Multifidus?

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Richardson, C. A., et al. (1999). Therapeutic Exercise for Spinal Segmental Stabilization. Churchill Livingstone.