Serola Biomechanics, Inc.

Facets curl around edge of the sacrum

When horizontal lines are drawn from both sides of the upper articular surfaces of the SIJ, they would converge posterior to the sacrum, and when horizontal lines are drawn from both sides of the lower articular surfaces, they would converge anterior to the sacrum. As such, the upper part faces backwards and the lower part faces forwards. In effect, the articulation curls around the sacrum's edge.