Comparison of lumbosacral fixation devices

Area of Science:

• Spine biomechanics
• Orthopedic surgery
• Spinal instrumentation

Background:

• Posterior spinal fusion to the sacrum is common for scoliosis and other spinal deformities.
• Nonunion rates can be high with conventional methods when extending fusions to the sacrum.
• Various instrumentation techniques exist for lumbosacral fusion, each with potential biomechanical advantages and disadvantages.

Purpose of the Study:

• To compare the biomechanical stability of three different spinal instrumentation methods for lumbar-to-sacral fusion.
• To evaluate the stiffness and resistance to various forces (torsion, flexion, extension, lateral bending) of Harrington distraction rods, Luque rods, and Harrington compression rods.

Main Methods:

• Three spinal instrumentation constructs (Harrington distraction, Luque, Harrington compression) were tested on a spine simulator.
• Each construct was subjected to sequential loading in torsion, flexion, extension, and lateral bending.
• Stiffness constants (Ks) were determined for each test mode, with reproducibility exceeding 94%.

Main Results:

• Harrington distraction rods demonstrated poor resistance to flexion and torsion but good resistance to lateral bending and extension.
• Harrington compression rods and Luque rods exhibited equivalent stiffness in resisting flexion and torsion.
• Harrington compression rods were effective in resisting extension, while Luque rods showed good resistance to lateral bending.

Conclusions:

• Harrington distraction rods have limited utility in lumbosacral junction fixation, primarily for correcting and resisting lateral bending.
• Harrington compression rods and Luque rods provide comparable and superior stability in flexion and torsion compared to Harrington distraction rods.
• The choice of instrumentation significantly impacts the biomechanical performance of lumbosacral fusions.