Articular facets of the human spine. Quantitative three-dimensional anatomy.

This study provides the quantitative three-dimensional surface anatomy of the articular facets for the entire human vertebral column based on a study of 276 vertebrae. Means and standard errors of the means for linear, angular, and area dimensions of the superior and inferior articular facets were measured for all vertebrae from C2 to L5. Facet orientations were described as angles with respect to the sagittal and transverse planes and also as card angles. The plane angles are similar to the angles seen on traditional radiographic views--radiographs and computed tomographic scans. The card angles, a new concept, are better at helping visualize the three-dimensional orientations of the facets. Excluding the superior C2 facet, the following minimum and maximum dimensions were found for the facets from C3 to L5: width = 9.6-16.3 mm; height = 10.2-18.4; surface area = 72.3-211.9 mm2; interfacet width = 20.8-40.6; interfacet height = 12.2-33.0 mm; transverse plane angle = 41.0-86.0; sagittal plane angle = 67.4-154.8; X-card angle = 41.0-86.0; and Y-card angle = 5.8-66.1. The quantitative anatomy of the facets may improve the understanding of the spinal anatomy, help improve the clinical diagnosis and treatment, and provide the necessary data for constructing more realistic mathematical models of the spine.