Morphologic Evaluation of Cervical and Lumbar Facet Joints: Intra-Articular Facet Block Considerations

Study Design: Needle orientations for lumbar and cervical facet injection were measured in cadavers and compared with facet angles measured on magnetic resonance images (MRIs). Objectives: To establish facet orientation relative to clinical procedures of a facet joint block in the cervical and lumbar spine. Methods: Needle orientation angles were measured from 20 unembalmed human cadaveric specimens (13 cervical and 7 lumbar). Spinal needles were inserted into the midpoints of the facet joint spaces from C3 to C7 and L1 to L5. Needle trajectories were measured with an optical tracking system. For comparison, facet angles from 100 clinical MRIs of lumbar spines were also measured. Facet orientations on MRIs were measured at their intersection with the transverse plane, and angles were quantified using image analysis software. Results: Typical angles for insertion of the needle into the cervical facets were oriented closer to the coronal plane, whereas insertion angles for lumbar needles were oriented closer to the sagittal plane. Relative to the sagittal plane, the mean cervical angle was 72 degrees and the mean lumbar angle was 33 degrees. The insertion points of the cervical facets were a mean of 29 mm from the midsagittal plane compared with a mean of 22 mm for the lumbar facets. MRI-based facet joint angles correlated poorly with actual injection angles, which were overestimated 5 to 23 degrees, depending on the lumbar level. Conclusions: Knowledge of the quantitative anatomy of the facets may help improve clinical diagnosis and treatment. These data also may aid in constructing more realistic computer simulations.