Range of Motion and Orientation of the Lumbar Facet Joints In Vivo

Study Design. Controlled laboratory study. Objective. To measure the range of motion of lumbar facet (zygapophyseal) joints in vivo during various functional weight-bearing positions of the upper body. Summary of Background Data. Determination of normal in vivo motion of the lumbar facet joints remains elusive despite numerous in vitro studies, animal models, and finite element simulations. Alterations in motion of the facet joints have been thought to be associated with various types of lumbar spine pathology including disc degeneration, facet degeneration, and neural impingement. Methods. Eleven healthy subjects underwent magnetic resonance imaging (MRI) to obtain three-dimensional models of the lumbar vertebrae from L2–L5. Each patient was then scanned using a dual-fluoroscopic imaging system while positioning the body in different postures: maximal forward-backward bend, side-to-side bending, and maximal left-right torsion. This fluoroscopic set-up was then recreated in solid modeling software where positions of the vertebrae were reproduced at each studied posture by matching the MRI-based models to the fluoroscopic images. The kinematics was measured using a Cartesian coordinate system placed in the center of each facet. The facet orientation in the sagittal and transverse plane was also determined. Results. During flexion-extension movements of the trunk, the facet joints rotated primarily along the mediolateral axis (average: 2°–6°) and were translated in the cephalad caudad direction (average: 2–4 mm). However, during lateral bending and twisting, the facet joints did not rotate or translate in 1 dominant direction. Instead, the resulting motion represented a coupling of rotation and translation in different directions (average: <5° and 3 mm). Further, the kinematic behavior of the facets of the upper lumbar spine (L2–L3 and L3–L4) were similar but different from that of the lower lumbar spine (L4–L5). Conclusion. These findings provide baseline information to enable the study of kinematic changes that occur in pathologic conditions of the spine and to determine how these might be affected following surgical intervention.