Multiaxial spine testing apparatus: system characterisation by evaluation of analogue and cadaveric lumbar spines

A custom 6 degrees-of-freedom test system was developed to collect unconstrained pure-moment biomechanical data from excised multi-segmental human spines. In this study, two characterisation methods were utilised. First, a polyethylene analogue model was created to establish test system baseline performance. Second, 22 lumbar spines (L1–L5) were tested to understand system operation under actual usage accounting for specimen stiffness and coupled motions. Each lumbar spine was tested in the anatomical planes (flexion-extension, lateral bending, and axial rotation) under two different conditions (intact and after implantation with an interbody cage at L3–L4). Specimen range of motion, neutral zone, and force/torque component errors generated by the test system were similar to previously reported data. Pure-moments were repeatable throughout the experiment in both cadaveric conditions, indicated by consistency in range of motion and neutral zone at the non-index levels. This characterisation will assist with interpretation of experimental data generated by the test system.