Development and evaluation of a multi-axis loading simulator for the spine, pelvis, and lumbosacral region

The treatment of injuries and disorders of the pelvis, lumbar spine and lumbosacral junction remains challenging due to rising case numbers, complex anatomy and high biomechanical demands. Despite advances in surgical techniques and implant design, problems regarding stability and long-term functionality persist, requiring individualized solutions and a thorough biomechanical assessment. Biomechanical studies are essential for assessing implant performance under physiological conditions. This study therefore aims to develop and validate a versatile biomechanical loading simulator capable of reproducing common test protocols, improving the comparability of results and enabling a systematic evaluation of innovative implant and treatment concepts. A loading simulator with three active degrees of freedom (driven by controlled servo motors) and two passive degrees of freedom (low-friction linear slide bearings) was developed. Five pelvic specimens with an intact lumbar spine up to L2 were first subjected to a range-of-motion (ROM) analysis and subsequently to cyclic dynamic loading to test the functionality of the simulator. The ROM analysis resulted in mean absolute deviations (MAD) of less than 7.50 N for all translational degrees of freedom (DOF) and less than 0.87 Nm for the two unloaded rotational DOF. The maximum moment in the loading direction deviated by a MAD of less than 0.18 Nm. The cyclic loading protocol was achieved in the vertical force direction (60% body weight (BW)) with a MAD of less than 0.76% BW. The maximum and minimum moments to be applied in extension-flexion (± 5 Nm) were realized with a MAD of less than 0.23 Nm. In summary, the simulator developed demonstrates a high degree of accuracy, reproducibility and flexibility. It therefore provides a suitable platform for the biomechanical investigation of implants and stabilization concepts in the pelvic and spinal regions and offers a promising basis for future experimental studies.