Intervertebral reaction force prediction using an enhanced assembly of OpenSim models

Area of Science:

• Biomechanics
• Computational Modeling
• Spinal Research

Background:

• OpenSim is crucial for biomechanical analysis, but lacks models for lumbar spine joint reactions during flexion and lifting.
• Existing models have limitations in accurately simulating these complex movements.

Purpose of the Study:

• To develop an enhanced OpenSim model of the upper body and lumbar spine.
• To enable computation of intervertebral joint reactions during flexion and lifting tasks.
• To improve the accuracy and applicability of OpenSim for spinal biomechanics.

Main Methods:

• Combined and improved existing OpenSim models for the upper body and lumbar spine.
• Enabled six degrees of freedom for lumbar vertebrae motion.
• Implemented motion segment stiffness and assigned mass properties.
• Modified body coordinate frames for easier sagittal alignment analysis.

Main Results:

• The enhanced model showed good agreement (within 10%) with experimental data for forward flexion and moderate (8 kg) lifting at L1-L2, L3-L4, and L4-L5.
• Discrepancies were observed in extended postures or during heavier lifting (20 kg) compared to in vivo measures.
• The model provides realistic lumbar spine joint reaction forces for specific tasks.

Conclusions:

• The developed OpenSim model is valuable for computing realistic lumbar spine joint reaction forces during flexion and moderate lifting.
• Model accuracy is good, considering limitations in both the model and validation datasets.
• The model and documentation are publicly available in the OpenSim repository.