Poster Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Introduction. In scenarios where soft tissues are either not preserved (as in fossils) or are difficult to access (for example rare animal species), the osteological range of motion (oROM) is commonly used to infer the limits of spinal flexibility, the range of possible movements, and the functional implications of various vertebral configurations, but it suffers from several limitations. In this work, a novel automated tool for the estimation of the spinal range of motion (ROM) that also takes into account possible sliding contacts between the articulating surfaces as well as the influence of soft tissues is presented.

Methods. The tool takes the three-dimensional models of two adjacent vertebrae as inputs. The coordinates of the 6 points, 3 for each vertebra, were exploited to automatically build a simple finite element model of the motion segment consisting of 7 beam elements representing bone and soft tissues. The ROM calculation was defined as a series of optimization problems, with the general objective of performing the desired motion while minimizing the internal actions in the intervertebral beam and avoiding penetration between the two 3D models.

Results. The tool captured the most relevant features of the mobility of two test cases (the cervical and lumbar human spines), namely the high flexibility in flexion-extension, the posterior shift of the axis of rotation when the facet joints come into contact in extension, the high stiffness in axial rotation in the lumbar spine, as well as the coupling between lateral bending and axial rotation in the cervical spine (Figure). Besides, the tool predicted plausible flexion-extension ROM values also for a lumbar motion segment of the Xenarthran nine-banded armadillo, Dasypus novemcinctus, which exhibits peculiar anatomy and biomechanics.

Conclusions. While additional testing and refinement are mandatory before the tool can be used for real-life scenarios such as in paleontology or to investigate peculiar vertebral anatomies, its current capabilities already exceed those of the conventional methods used for the estimation of the oROM.

Figure caption. The left lateral bending simulation for the C5-C6 test case. Upper panel: location and orientation of the axes of rotation. Lower panel: rotations around the three axes (left), internal forces (center) and moments (right) in the beam representing the intervertebral joint throughout the lateral bending motion. The results of the simulation highlight the coupling between lateral bending and axial rotation, and the shift of the rotation axis when the facet joints come into contact.