The Influence of Passively Modeled Paraspinal Soft Tissues on Spinal Geometric Compensation: A Finite Element...

Area of Science:

• Biomechanics
• Spinal Anatomy
• Computational Modeling

Background:

• Paraspinal soft tissues, including muscles and the thoracolumbar fascia (TLF), play a crucial role in spinal stability and movement.
• Understanding their specific contributions to lumbar segmental mobility and overall spinal geometry is essential for diagnosing and treating spinal conditions.

Purpose of the Study:

• To investigate the influence of passively modeled paraspinal soft tissues (muscles and TLF) on lumbar segmental mobility and geometric compensation.
• To analyze the effects of altered TLF stiffness and paraspinal muscle contributions using a validated finite element model of the thoracolumbar spine.

Main Methods:

• Utilized a validated finite element model of the thoracolumbar spine, incorporating vertebrae, rib cage, discs, pelvis, ligaments, muscles, and the TLF.
• Simulated 30° and 60° flexion rotations with a fixed pelvic support and an applied follower load.
• Analyzed changes in lumbar intervertebral rotation (IVR), lumbar and thoracic range of motion (RoM), and curvature following simulated stiffening or removal of the TLF and paraspinal muscles.

Main Results:

• Increased TLF stiffness significantly reduced lumbar RoM by 5.1° at 60° flexion and led to compensatory increases in thoracic RoM (3.6°).
• Elevated TLF stiffness resulted in proportional increases in lumbar lordosis (3.6°) and thoracic kyphosis (3.3°).
• TLF removal produced inverse effects, while alterations in paraspinal muscle contributions showed no significant impact on spinal mobility or geometry.

Conclusions:

• The stiffness of the thoracolumbar fascia is a key determinant of lumbar segmental mobility.
• Changes in TLF stiffness can drive compensatory adjustments in the overall spinal geometric profile, influencing both lumbar and thoracic regions.
• Paraspinal muscles appear to have a less direct role in modulating spinal geometry and mobility compared to the TLF in this model.