The lumbar spinous processes are broad, horizontally projecting posterior bony projections of L1-L5, providing attachment for the supraspinous and interspinous ligaments, erector spinae aponeurosis, and multifidus. They are the largest spinous processes in the spine and are easily palpable in the lumbar midline, serving as the primary landmarks for spinal level identification.
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| Ossification | Each spinous process has a secondary ossification centre (apophysis) appearing at puberty and fusing by age 25. Failure of fusion produces a spina bifida occulta at the affected level. |
The L4 spinous process is at the level of the iliac crest intercristal line, the primary landmark for lumbar puncture, epidural injection, and spinal level identification. Kissing spine (Baastrup disease) is impaction of adjacent lumbar spinous processes in hyperlordosis, causing midline pain. Spinous process fractures from avulsion (clay-shoveller equivalent) or direct trauma are typically managed conservatively. Percutaneous interspinous process devices (X-Stop) are placed between adjacent processes for lumbar spinal stenosis.
Contact between adjacent spinous processes with lordosis causes midline pain and interspinous bursitis.
Direct blows or flexion injuries can fracture a lumbar spinous process; isolated fractures are stable.
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