Trunk biomechanical models based on equilibrium at a single-level violate equilibrium at other levels

Area of Science:

• Biomechanics
• Occupational Health
• Spinal Load Analysis

Background:

• Accurate estimation of muscle forces and spinal loads is crucial for evaluating injury risk and managing back disorders in occupational settings.
• Current multi-segmental spine biomechanical models often simplify analysis by considering net moment balance at a single spinal level, neglecting inter-level equilibrium.

Purpose of the Study:

• To quantify the extent of equilibrium violation in single-level spine models.
• To assess alterations in muscle force and spinal load estimations when models are applied at different spinal levels.
• To compare single-level model results with a kinematics-driven model and electromyography (EMG) data.

Main Methods:

• Utilized single-level free body diagram models for muscle force and spinal load estimation.
• Employed optimization and EMG-assisted methods.
• Compared results against a kinematics-driven model ensuring full-level equilibrium and against empirical EMG data.

Main Results:

• Single-level models demonstrated significant level dependency, altering estimations based on the considered spinal level.
• Gross violations of net moment equilibrium were observed at other spinal levels, with errors escalating in more demanding occupational tasks.
• Despite limitations, these models showed potential for estimating spinal compression forces.

Conclusions:

• Single-level biomechanical models of the spine are inadequate for accurately estimating muscle forces and loads due to inherent equilibrium violations and level dependency.
• The accuracy of these simplified models is compromised, particularly under high-demand tasks.
• While not ideal for comprehensive spinal load analysis, single-level models may retain utility for estimating spinal compression forces.