Effect of lumbar interbody cage geometry on construct stability: a cadaveric study.

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Spinal fusion research

Background:

• Lumbar interbody fusion surgery utilizes diverse cage designs (circular, tapered, rectangular).
• The impact of various cage geometries and materials on spinal stability post-decompression remains incompletely understood.

Purpose of the Study:

• To evaluate the influence of cage geometry on spinal construct stability.
• To compare the stability of different lumbar interbody fusion configurations.

Main Methods:

• Biomechanical analysis of six cadaveric lumbar spine specimens (L1-S2).
• Three-dimensional motion capture (Optotrak) under six pure moment loading directions.
• Sequential testing of intact, bilateral cage placement (L4-L5), and supplemental pedicle screw-rod fixation.

Main Results:

• Bilateral cage placement slightly decreased stability, except in flexion (80% of intact).
• No significant difference in stability between intact and caged states.
• Pedicle screw-rod fixation significantly increased stability across all loading directions.
• Cyclic loading did not substantially affect stability.

Conclusions:

• Stand-alone cages restore motion to near-intact levels, necessitating additional fixation.
• Supplemental posterior instrumentation is essential for robust spinal stability.
• Cage geometry and material properties appear to have minimal impact on stability compared to supplemental fixation.