Development of a Finite Element Model for Evaluating Stress Distribution in the Lumbar Spine of Nigerian Manual Material Handlers

Low back pain from occupational manual material handling is a major musculoskeletal disorder burden in Nigerian workplaces, and finite element modelling of lumbar spine stress distribution provides biomechanical insights into injury mechanisms that are not obtainable from clinical observation alone. This study develops and validates a finite element model of the lumbar spine for evaluating stress distribution under manual material handling conditions representative of occupational tasks in Nigerian manufacturing and construction sectors, with model development based on morphometric data from a Nigerian male population sample. Lumbar spine geometry was derived from CT scan data of twenty Nigerian adult males at the University of Ibadan Teaching Hospital, with material properties assigned from published literature for cortical and trabecular bone, intervertebral disc fibrous ring and nucleus, and spinal ligaments. The multi-body finite element model was constructed in ABAQUS and validated against published in vitro cadaveric spine load-deflection data. Manual material handling loading conditions modelled include symmetric forward flexion lifting at standardized knee and trunk angles, asymmetric lifting with trunk rotation, and push-pull task simulations. Von Mises stress distributions in the lumbar vertebral bodies and intervertebral discs were computed for each loading scenario. Results demonstrate that disc annulus stress concentrations at the L4-L5 and L5-S1 levels were significantly higher in asymmetric lifting than symmetric lifting conditions at equivalent load magnitudes, and that Nigerian male spine morphometry produced higher posterior element stress concentrations than published model predictions based on European morphometric datasets. The study provides a basis for Nigerian-specific manual handling ergonomic guideline development. Keywords: finite element model, lumbar spine, manual material handling, biomechanics, Nigeria.