1. A NOVEL APPROACH FOR PREDICTING IN-VIVO LUMBAR SPINE LOADS AND KINEMATICS BASED ON MOTION ANALYSIS
M Eltoukhy, M Ziff, S Elmasry, F Travascio and S Asfour
Department of Industrial Engineering, University of Miami, Coral Gables, FL
INTRODUCTION
Low back pain, a widespread ailment in the United States, has been strongly associated with intervertebral disc degeneration [1]
Adverse mechanical loading conditions are considered to be a major cause for disc degeneration [2]
Determining loads on spine in a non-invasive form is a challenging task. Radiographic methods are currently available [3]. However, theses methods are only applicable for limited spine range of motion. Hence, they are not deployable for investigating spine biomechanics during complex functional activities
The model schematized spine as a kinematic chain of rigid bodies representing lumbar and thoracic vertebrae (T10 to S1) connected among each other by elastic segments, see Figure 2
Input data for the model were the locations of stereotactic markers placed at S1 and t10
Six subjects performed a flexion-extension exercise (40o to -10o) for model validation
Range of Motion , in degree
Thorax
Pelvis
Figure. 3: Relative range of motion ROM increased from L5-S1 to L1-L2 during Flexion/Extension exercise and ROM values are within literature results for all levels.
OBJECTIVES
To develop a method for experimentally evaluating spine kinematics
To apply the method for investigating loads on spine during functional activities
Maximum Force, in N
METHODS
A spine biomechanical model was developed in Vicon BodyBuilder® language to calculate kinematics and kinetics of relative spinal levels
The output of Motion capturing system (ViconNexus®) was analyzed and provided the input data to spine model, see Figure 1
Figure. 2: Spine levels T10 to S1 are represented by rigid bodies connected among each other via elastic elements.
Figure. 4: Constant normal force and decreasing shear force through S1 to L! levels during Flexion/Extension exercise.
RESULTS AND DISCUSSION
The relative sagittal rotation between adjacent vertebral levels increased progressively from level L5-S1 to L1-L2, see Figure 3
The relative range of motion results are in agreement with previous studies that used fluoroscopy [4,5]
Normal (compressive) forces were higher than shear (anterior-posterior) forces for all levels, see Figure 4
Normal forces were approximately constant across levels, while shear forces progressively decreased from S1 to L1
The spine biomechanical model, driven by motion capturing data, represent a valid method to determine the kinematics and kinetics of the lumbar spine during functional activities. This experimental approach does not entail motion constraints typical of radiographic methods.
REFERENCES
Deyo et al., 1987, Spine 3,
Stokes and Iatridis., 2004, Spine.
3 Ochia et al., 2006, Spine 18,
4 Wong et al., 2006, Spine 4,
5 Li et al. Eur Spine J. 18,
Figure. 1: A schematic of analytical frame work