A new multi-direction tester for evaluation of the spinal biomechanics

Biomechanical testing of the spine has been performed to help understand the normal function of the spine as well as to evaluate the effects of injury and surgical procedures on spinal behavior. The purpose of this study was to develop a tester which could produce continuous loading for the entire range of motion of the spine. The spinal tester frame was built out of modular aluminum extrusions and servo motors combined with a planetary reduction gearbox used to drive the apparatus. A self-written software package running in Borland C ⁺⁺ Builder provided an interface allowing the user to define desired motions and collect the load and displacement data. A polyurethane tube used for testing the accuracy of the spinal tester was rotated at a constant speed of l°/sec until a maximum loading of 2 Nm was achieved in right-left lateral bending, flexion-extension and right-left axial rotation in sequence. A spinal unit function from a sheep spine was also tested in the same procedures for evaluating the changes in range of motion and neutral zone after discectomy and implantation. The results showed that the errors between recorded value and calculated value of the polyurethane tube were 2.16%, 2.66% and 1.72% in flexion-extension, lateral bending and axial rotation, respectively. In the sheep spine, the range of motion and neutral zone were increased after discectomy and recovered after implantation in flexion-extension and lateral bending. In conclusion, an apparatus producing cyclic continuous pure moment movement was built. This multi-directional spinal tester was an effective and practical machine in the biomechanical study of spine.