Subject‐specific loads on the lumbar spine in detailed finite element models scaled geometrically and kinematics‐driven by radiography images

Abstract

Traditional load‐control musculoskeletal and finite element (FE) models of the spine fail to accurately predict in vivo intervertebral joint loads due mainly to the simplifications and assumptions when estimating redundant trunk muscle forces. An alternative powerful protocol that bypasses the calculation of muscle forces is to drive the detailed FE models by image‐based in vivo displacements. Development of subject‐specific models, however, both involves the risk of extensive radiation exposures while imaging in supine and upright postures and is time consuming in terms of the reconstruction of the vertebrae, discs, ligaments and facets geometries. This study therefore aimed to introduce a remedy for the development of subject‐specific FE models by scaling the geometry of an existing detailed FE model of the T12‐S1 lumbar spine. Five subject‐specific scaled models were driven by their own radiography image‐based displacements in order to predict joint loads, ligament forces, facet joint forces, and disc fiber strains during relaxed upright as well as moderate flexion and extension tasks. The predicted intradiscal pressures were found in adequate agreement with in vivo data for upright, flexion, and extension tasks. There were however large inter‐subject variations in the estimated joint loads and facet forces.

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