Biomechanical analysis of lumbosacral fixation

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Spinal Instrumentation

Background:

• The lumbosacral junction is a critical area for spinal stability.
• Evaluating the biomechanical performance of various lumbosacral instrumentation techniques is essential for surgical success.

Purpose of the Study:

• To compare the biomechanical stability of ten different lumbosacral instrumentation techniques under flexion.
• To identify fixation strategies that maximize load-bearing capacity and stiffness at the lumbosacral junction.

Main Methods:

• In vitro biomechanical testing of 66 bovine lumbosacral spinal segments.
• Flexion testing to failure, measuring maximum moment, stiffness, and angulation.
• Strain measurements using an extensometer on the anterior lumbosacral intervertebral disc.

Main Results:

• Instrumentation extending fixation into the ilium (ISOLA Galveston, ISOLA iliac screws) demonstrated significantly greater maximum moment at failure.
• These iliac fixation techniques also showed superior maximum stiffness at failure.
• S2 pedicle fixation (Cotrel-Dubousset butterfly plate, Chopin block) enhanced flexural lever arm and stability.

Conclusions:

• Extending fixation into the ilium anterior to the middle osteoligamentous column significantly improves lumbosacral instrumentation stability.
• Fixation purchase between iliac cortices into superior acetabular bone offers the most robust biomechanical support.
• Understanding the lumbosacral pivot point aids in optimizing instrumentation design and placement.