Use of computed tomography image processing for mapping of human cervical facet surface geometry.

Vertebral facets transmit a significant percent of spinal loading, provide translational, rotational, and axial stability for the spine, and are responsible for the coupling between lateral bending and rotational motions. The shape and the orientation of vertebral facets vary with level and are influenced by degenerative processes. These variations may play an important role in many cases of neck pain, back pain, and instability. To determine whether the shape and orientation of cervical facets can be accurately measured from computed tomography (CT) data, the surfaces of 39 human cervical facets were non-invasively digitized from reconstructed three-dimensional CT data and then invasively digitized using a hand-held three-dimensional probe before and after bleaching away the cartilage. Digitized data describing the facet surfaces were fit to both plane and spherical surfaces. For the adult cervical vertebrae that we measured, the presence of cartilage had no significant effect on the measured shape or orientation of the facets. The orientation of the facet surfaces measured from CT data was within 11 deg of that measured using the hand-held probe. Quantitative measurements of facet shape (flat or spherical) and surface irregularity were similar between CT and hand digitized surfaces. These results suggest that individual facet geometries can be accurately quantified using non-invasive CT examinations. Non-invasively determined variations in facet geometries may assist in the diagnosis of back pain, neck pain and instability.