Estimation of Lumbar Spine Load Sharing using a Detailed Finite Element Model driven by X-Ray Kinematics in Flexion Task

Spinal diseases are prevalent and costly. Excessive mechanical loads on the spine play a crucial role in the etiology of back disorders. To estimate spinal loads one needs to calculate unknown muscle forces through either an optimization or EMG-driven approach. Both approaches involve several assumptions and simplifications regarding anatomy of muscles, mechanical properties of the spinal tissues, and estimation of the muscle forces. An alternative approach is to estimate spinal loads through effect of muscle forces, i.e., kinematics generated by muscles rather than forces generated by muscles. The present study hence aims to estimate spinal loads using a detailed finite element (FE) model of the T12-S1 spine driven by kinematics obtained through upright x-ray imaging.  For this, kinematics (angular and translational displacements) of the T12 through S1 vertebrae were first measured in vivo in three healthy individuals when performing flexion from relaxed upright posture. The measured kinematics were subsequently prescribed to the FE model to estimate load sharing among the joint structures. In agreement with the measured data, the L1-L2, L2-L3, L3-L4 and L4-L5 average intradiscal pressure was estimated to be ~2.6, ~2.8, ~2.1 and ~2 MPa in flexion, respectively.