Load sharing among spinal elements of a motion segment in extension and lateral bending

Area of Science:

• Biomechanics
• Spinal Mechanics
• Computational Modeling

Background:

• Understanding the forces within spinal elements is crucial for diagnosing and treating spinal conditions.
• Previous models often simplified the complex interactions between the intervertebral disk, facet joints, and ligaments.

Purpose of the Study:

• To develop and validate a linear optimization model for estimating forces in lumbar spine structures.
• To quantify the load distribution in a lumbar motion segment under extension and lateral bending moments, with and without compressive preload.

Main Methods:

• A semi-experimental protocol combined with a linear optimization model was used.
• Three-dimensional coordinates of spinal components were acquired using a morphometer.
• Vertebral motion was tracked with a Selspot II system under various loading conditions.

Main Results:

• In extension, facets carried 52 N and the disk 104 N (tensile) without preload.
• With 120 N preload during extension, facet load increased to 77.2 N, and disk load decreased to 37 N (tensile).
• Lateral bending showed load distribution across the facet, disk, and contralateral ligaments, with preload altering these forces significantly.

Conclusions:

• The linear optimization model effectively estimates spinal element forces under physiological loading.
• Compressive preload substantially modifies load distribution in the lumbar motion segment, highlighting its importance in spinal stability.
• Findings provide valuable data for biomechanical analyses and clinical interventions related to spinal disorders.