The lumbar multifidus is the single most important stabilising muscle of the lumbar spine. Its deep fibres provide intersegmental stability at each level, while the superficial fibres extend across multiple levels for spinal extension force.
| Origin | Sacrum and posterior iliac spine; Lumbar mammillary processes (L1-L5) |
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| Insertion | Spinous processes of L1-L5 and S1 spanning 2-4 levels above the origin |
| Nerve Supply | Dorsal rami of lumbar spinal nerves (L1-S3) |
| Blood Supply | Medial branches of the posterior sacral arteries |
| Actions | Extension of the lumbar spine; Contralateral rotation; The primary segmental stabiliser of the lumbar spine |
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Multifidus atrophy is the hallmark of lumbar disc disease and chronic low back pain — it occurs rapidly after disc prolapse at the affected level and does not spontaneously recover without specific activation. The multifidus is the primary target of specific stabilisation exercises (drawing-in manoeuvre). Ultrasound-guided multifidus injections assess segmental function.
Assessed by ultrasound real-time imaging during activation or by MRI cross-sectional area and fat fraction measurement at each lumbar level.
Ipsilateral multifidus atrophy at the L4-L5 or L5-S1 level in acute disc prolapse, failing to spontaneously recover and requiring specific segmental motor control rehabilitation.
