A Finite Element Study On The Biomechanical Effects On The Lumbar Spine And Paraspinal Muscles With Different Load-carrying Styles

Backgrounds:The main functions of the lumbar spine are transporting load of the upper body to the pelvis and keep the range of motion(ROM)of human torso,which plays a significant role in the human biomechanical structure.Therefore,the lumbar spine is continuously subjected to relative movement,high force and moment.As a result,incorrect load-carrying ways and overweight load may lead to the injury of paraspinal muscles and accelerate lumbar disc degeneration.Objectives:To research the changes of paraspinal muscle force,intervertebral compression force and stress distribution on lumbar spine,and to evaluate the biomechanical effectives on lumbar spine of different load-carrying styles and weight of load.Methods:The musculoskeletal models and finite element(FE)models of Ll-L5 lumbar spine with a backpack,shoulder bag or handbag were developed.Then the load of 5%,10%,15%or 20%body weight(BW)was added to the musculoskeletal models to run the inverse kinematical simulation,which calculated the paraspinal muscle force and intervertebral compression force.Then the results of the musculoskeletal models were input to the FE model as boundary conditions to analyze the stress distribution on lumbar vertebral bodies,intervertebral discs and ligaments.Results:Compared with the unload models,the increase of paraspinal muscle force was the least in the 3 load-carrying styles and balanced between the left and right sides.The paraspinal muscle force in the load side was higher than that in the contralateral side in the shoulder bag model,and the paraspinal muscle force in the contralateral side was higher.The paraspinal muscle force and intervertebral compression force increased with the degree of flexion increasing.The muscle force was higher,when the load position was more lateral.But the muscle contraction made the intervertebral compression force balanced in the two sides when using shoulder bags and handbags.The stress was concentrated in the posterior part of nucleus pulposus,the anterior part of annulus fibers,the anterior edge of vertebrae and vertebral arch isthmus.With the increase of load weight,the stress on nucleus pulposus and annulus fibers increased linearly in the backpack model and shoulder bag model,and the stress increased exponentially in the handbag model.Conclusions:The paraspinal muscle force and peak stress on the vertebrae and intervertebral discs was the least in the backpack model.With the increase of load weight,the increase of the paraspinal muscle force and the peak stress on the nucleus pulposus and annulus fibers was the least in the backpack model.The handbags caused the most burden on the paraspinal muscles,intervertebral discs and vertebrae.When using a handbag with more than 15%BW,the stress on annulus fibers and nucleus pulposus increased a lot.Therefore,people should avoid using handbags to carrying load that exceeded 15%BW to protect the lumbar spine.