In vitro kinematics study of human lumbar facet joints

Abstract

BACKGROUND: Facet joints are important in accommodating spinal motion and maintaining spinal integrity. It is believed that the anatomy and biomechanical behavior of the joints vary along the lumbar spine. The objective of current study is to develop an experimental method for tracking the in vitro facet joint motions with a motion analysis system. METHODS: Biomechanical tests were conducted on a human cadaveric lumbar spine specimen to study the facet joint kinematics. Pure moment of ±7.5Nm was applied by MTS spine loading fixture to simulate the principal spinal motions. By using a commercial motion analysis system, the three-dimensional rotations and displacements of the facet joints at L3-L4 and L4-L5 levels were measured and calculated. RESULTS: Under flexionextension, the L3-L4 and L4-L5 facet joint rotations and displacements had maximum values of 1.47º and 3.78º, and 0.88 mm and 1.27 mm, respectively. It was found that the two sides showed similar values in both parameters. Similar results in the motion pattern were obtained for lateral bending. However, under axial rotation, there was an asymmetric behavior in the facet joint motions between right and left sides at the two levels, showing larger rotations on the right facets. DISCUSSIONS: This pilot study demonstrates the in vitro kinematics study of the lumbar facet joints and further investigation will be conducted with larger sample size. To study the relationship between the joint bio mechanics and anatomical structures, facet joint orientation and geometry are to be correlated with the motion data at different spinal levels.