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Median Sacral Crest

crista sacralis mediana

The median sacral crest is the bumpy ridge running down the middle of the back of the sacrum. It is formed by the fused spinous processes of the upper sacral vertebrae and usually shows three or four small tubercles. Below it the crest ends at the sacral hiatus, where the arches of the lowest sacral vertebrae are missing.

Anatomical Data

Structure & Landmarks

Articulations	No joint; fused spinous processes of the sacral vertebrae
Landmarks	Three or four spinous tubercles (S1-S4) Ends inferiorly at the sacral hiatus Attachment of the supraspinous ligament and thoracolumbar fascia Origin of erector spinae and multifidus fibres nearby
Ossification	Each tubercle forms from the fused spinous processes of the sacral vertebrae, which ossify from the vertebral arch centres; the sacral segments fuse from adolescence to about 25 years.

Clinical Relevance

Clinical Notes

The median sacral crest can be felt in the midline of the lower back between the buttocks and is a landmark for finding the sacral hiatus for caudal epidural injections. An absent or split crest at S1 is a common, usually harmless sign of spina bifida occulta. Because the bone is close to the skin, the area over the crest is a frequent site of pressure ulcers in bedbound patients.

Pathology

Common Injuries & Conditions

Sacral Pressure Ulcer

Skin breakdown over the bony median sacral crest in people who lie or sit for long periods, which can extend down to bone.

Spina Bifida Occulta

Failure of the vertebral arches to fuse in the midline, often at L5 or S1, shown by a gap in the median sacral crest and usually causing no symptoms.

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