Spine-Equivalent Beam Modeling Method With In Vivo Validation for the Analysis of Sagittal Standing Flexion

Motivated by the need to incorporate human spine mechanics into the design loop of wearable spine assistive devices, this article presents a spine-equivalent beam (SEB) model for analyzing kinematics and mechanics of a human spine in sagittal standing flexion. The model is capable of handling loads resulted from the head, arms, external payload, torso weight, and back muscle effects, and it also handles pelvis rotation. The derivation of the physiologically equivalent parameters is discussed, including initial curvature, cross-sectional area, area moment of inertia, force/moment of the back muscles, and the equivalent Young's modulus. The SEB model and its equivalent parameters are validated with published in vivo measurement collected by telemeterized implant embedded on subjects who have undergone vertebra body replacement surgery. Results show that the model is capable of predicting flexion angles and compression force experienced by the intervertebral discs throughout the flexion process, which provides a practical yet effective approach to incorporate the spine mechanics into the design of wearable spine assistive devices.