A biomechanical model for estimating loads on thoracic and lumbar vertebrae

Abstract

Background Biomechanical models are commonly used to estimate loads on the spine. Current models have focused on understanding the etiology of low back pain and have not included thoracic vertebral levels. Using experimental data on the stiffness of the thoracic spine, ribcage, and sternum, we developed a new quasi-static stiffness-based biomechanical model to calculate loads on the thoracic and lumbar spine during bending or lifting tasks. Methods To assess the sensitivity of the model to our key assumptions, we determined the effect of varying ribcage and sternal stiffness, maximum muscle stress, and objective function on predicted spinal loads. We compared estimates of spinal loading obtained with our model to previously reported in vivo intradiscal pressures and muscle activation patterns. Findings Inclusion of the ribs and sternum caused an average decrease in vertebral compressive force of 33% for forward flexion and 18% in a lateral moment task. The impact of maximum muscle stress on vertebral force was limited to a narrow range of values. Compressive forces predicted by our model were strongly correlated to in vivo intradiscal pressure measurements in the thoracic (r=0.95) and lumbar (r=1) spine. Predicted trunk muscle activity was also strongly correlated (r=0.95) with previously published EMG data from the lumbar spine. Interpretation The consistency and accuracy of the model predictions appear to be sufficient to justify the use of this model for investigating the relationships between applied loads and injury to the thoracic spine during quasi-static loading activities.

Biomechanical Trade-Offs in Manual Material Handling: Some Tasks Reduce Lumbar Loading But Increase Thoracic Loading

“…In particular, we found that flexion tasks (including stoop lifts) are associated with large increases in lumbar compressive force but only small increases (or even decreases) in thoracic compression, indicating that these postures, while potentially injurious to the lumbar spine, are of lower risk to the thoracic spine. These results are comparable to a previous biomechanical model of the thoracic and lumbar spine that predicted an increase of 185% in the compressive for in the lumbar spine, but only a 25% increase in the thoracic spine after flexing 30° from an upright posture (Iyer et al, 2010).…”

Vertebral Strength and Estimated Fracture Risk Across the BMI Spectrum in Women

“…According to previously published methods, (16,36,37) in the biomechanical model, the body was divided into sections, and each section’s length, weight, and center of mass position were estimated, and the muscle forces required to maintain static equilibrium during each activity were calculated. For each activity, the applied load to the L4 vertebral body was determined by totaling all forces (from body weight and muscle loading) in the axial direction of L4.…”

Too Fit To Fracture: outcomes of a Delphi consensus process on physical activity and exercise recommendations for adults with osteoporosis with or without vertebral fractures

“…The torque generated is not dependent only on the mass, but on the moment arm, or the distance from the pivot point to the point where the force is applied. For example, carrying a load out in front with elbows bent 90°, or in one hand at the side of the body imposes a greater compressive load on the spine than dividing the weight between two hands and carrying it at one's sides, close to the body (Box 4) [24,25]. In the thoracic spine, holding 11 lbs (5 kg) in each hand with elbows flexed to 90° has been reported to increase the compressive loads at T8 and T12, ~ 3.0 and 3.5 times that of standing, respectively [22].…”