The size of the zygapophyseal joint facets.

The surface area A of the joint facets is estimated for the prezygapophyses (A pre) and for the postzygapophyses (A post) by assuming an elliptical shape. Of both zygapophyseal joints between adjacent vertebrae, the best preserved joint facet is used for the estimates. In case of slight deformations or other damages, the joint surface was reconstructed, and in case of severe damage, no data are given. The estimated error due to deformation and deviation from elliptical shape of the joint facets is about ten percent.