3D Printable Analogue Spine Models: Towards Cost and Time Effective Spinal Biomechanical Research

Biomechanical studies of the spine have traditionally employed either cadavers or finite element modelling techniques, but both of these approaches have inherent cost and time limitations. Cadaveric studies introduce significant variability in measurements across patients, while finite element modelling can be computationally demanding depending on the required level of detail. 3D printable analogue spine models have been proposed in this research as a low-cost and high-fidelity approach to support these conventional methods. An L1–S1 analogue spine model was developed, incorporating vertebral bodies, intervertebral discs, and intertransverse and interspinous ligaments. Stereolithography 3D printing was used exclusively to manufacture the model. A custom bending jig was employed to apply load-controlled pure bending moments of up to 7.5 Nm in flexion–extension, lateral bending, and axial rotation to the model. The results were then compared to historical ex vivo L1–S1 data to evaluate model accuracy. The use of viscoelastic materials in the construction of the analogue model contributed to a hysteretic response during loading and unloading, simulating the mechanical behaviour of a human spine. Specifically, the model’s range of motion (ROM) during flexion was estimated to be \(12.92\pm 0.11^\circ \) when subjected to a load of \(+\)7.5 Nm, as compared to an ex vivo ROM of 16.58\({ }^\circ \). The model exhibited bilateral symmetry during lateral bending (LB) and axial rotation (AR). Notably, the ROM in LB was measured at \(13.55\pm 0.11^\circ \) under \(+\)7.5 Nm (ex vivo: \(13.32^\circ \)), and \(-13.79\pm 0.19^\circ \) under \(-\)7.5 Nm (ex vivo: \(-17.1^\circ \)), whereas the ROM in AR was recorded as \(19.82\pm 0.19^\circ \) under \(+\)7.5 Nm (ex vivo: \(14.44^\circ \)) and \(-15.57\pm 0.12^\circ \) under \(-\)7.5 Nm (ex vivo: \(-13.81^\circ \)). The 3D printed analogue model of the lumbar spine presented in this study demonstrated rotational stiffness within 20% of the ex vivo responses, with a high degree of repeatability. Further testing incorporating a wider range of materials is necessary to improve model stiffness control and statistical significance.