A Biomechanical Model of the Lumbosacral Joint for Lifting Activities.

Abstract

Damage to ligaments, muscles and the disc at the lumbosacral joint have all been implicated as potential sources of low-back pain. Given the difficulty of examining these deep-lying structures in-vivo, little progress has been made towards underst and ing the response and limitations of these tissues to different common physical activities which are clinically reported to produce low-back pain. In order to study the responses of these complex tissues, a computerized biomechanical model was developed. The resulting model allows one to estimate the stress and strain in each of the above-mentioned tissues for sagittal-plane two-h and ed lifting tasks. The model contains three components, all of which were constructed as a part of the thesis effort. The three components are; (1) a vertebral re-orientation kinematic model, (2) a flexible-endplate intervertebral disc model, and (3) a ligament/muscle kinetic model. These specific models were combined into a general biomechanical model of the low-back, which was then evaluated by both sensitivity analyses and comparison with data of other investigators. The evaluation of the model on simulated lifting activities suggested that typical lifting tasks can lead to excessive disc compressive forces, muscle moment generation requirements, and possibly lumbodorsal fascia strains. On the other h and , annulus rupture due directly to strain on the tissue appears unlikely unless disc degeneration has taken place possibly from earlier endplate fracture, of which there is a relatively high risk. Also, strains on ligaments other than the lumbodorsal fascia are very low relative to levels thought to cause micro-damage for each respective ligament. In a review of jobs requiring repeated load lifting, high values of lumbodorsal strain, disc compression and muscle force required for trunk extension were all found to be associated with higher incidence rates of low back pain.