MECHANICAL-BEHAVIOR OF THE HUMAN LUMBAR AND LUMBOSACRAL SPINE AS SHOWN BY 3-DIMENSIONAL LOAD-DISPLACEMENT CURVES

The lumbar region is a frequent site of spinal disorders, including lo w-back pain, and of spinal trauma. Clinical studies have established t hat abnormal intervertebral motions occur in some patients who have lo w-back pain. A knowledge of normal spinal movements, with all of the i nherent complexities, is needed as a baseline. The present study docum ents the complete three-dimensional elastic physical properties of eac h lumbar intervertebral level from the level between the first and sec ond lumbar vertebrae through the level between the fifth lumbar and fi rst sacral vertebrae. Nine whole fresh-frozen human cadaveric lumbar-s pine specimens were used. Pure moments of flexion-extension, bilateral axial torque, and bilateral lateral bending were applied, and three-d imensional intervertebral motions were determined with use of stereoph otogrammetry. The motions were presented in the form of a set of six l oad-displacement curves, quantitating intervertebral rotations and tra nslations. The_curves were found to be non-linear, and the motions wer e coupled. The ranges of motion were found to compare favorably with r eported values from in vivo studies. CLINICAL RELEVANCE: Knowledge of the physical characteristics of the spine is clinically important when ever loads or displacements, or both, are applied to the spine. It is necessary to understand not only the amounts of spinal motion, but als o the motion characteristics of non-linearity and coupling, which are documented in the present study, in order to better understand the cli nically important problems, and treatment, of spinal instability in as sociation with low-back pain and after spinal trauma.