AN EXPERIMENTAL-TECHNIQUE TO INDUCE AND QUANTIFY COMPLEX CYCLIC FORCES TO THE LUMBAR SPINE

THE HUMAN SPINE is a complex, heterogeneous nonlinear and viscoelastic structure. In addition, in vivo loading is not uniaxial. Although man y studies on the mechanical behavior of the spine under ''pure'' force s and single cycle load applications exist, little research is conduct ed with complex cyclic loads. In this study, we developed a technique to induce and quantify controlled complex physiological loads to the l umbar spinal column under cyclic (chronic) conditions. The methods des cribed include specimen preparation and mounting to induce controlled complex loading (cyclic compression-flexion vector was chosen as an ex ample), instrumentation, and biomechanical data to achieve the objecti ves. The results indicated that the specimen sustained the external lo ad in a combined compression-flexion mechanism without considerable of f-axis forces (lateral shears) and moments (lateral bending and torsio n). By mounting the anchoring bolt in appropriate places (such as an a nterolateral placement to induce compression-flexion-lateral bending), this technique can be used to apply and continuously quantify complex physiological acute or cyclic loads to describe the biomechanics of t he spine. This procedure of inducing complex loads eliminates the diff iculty in applying the principles of superposition, using the response from individual ''pure'' forces to account for the nonlinearity and v iscoelasticity of the human lumbar spinal column.