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In vitro study of shear force on interbody implants.
Robin Hitchcock1, William Sears, R Mark Gillies
1UNSW Graduate School of Biomedical Engineering, Sydney, Australia. robinh@resmed.com.au
Journal of Spinal Disorders & Techniques
|February 8, 2006
Summary
Serrated interbody implants significantly reduce vertebral translation under shear forces compared to smooth implants. This suggests serrations may decrease nonunion rates in lumbar interbody fusions.
Area of Science:
- Spinal biomechanics
- Orthopedic implant technology
- Surgical fusion techniques
Background:
- Lumbar spine lordosis and body weight generate shear forces at the lumbosacral disc.
- These forces cause translational motion, potentially leading to nonunion in lumbar interbody fusions.
- Pedicle screw stabilization partially resists but does not eliminate this motion.
Purpose of the Study:
- To investigate the effect of surface serrations on interbody implants.
- To determine if serrations resist shear forces and sagittal translation in vitro.
- To assess the potential impact on nonunion rates in spinal fusion.
Main Methods:
- In vitro study using porcine cervical spine segments.
- Applied 25 N anteroposterior shear load with 300 N compressive preload.
- Compared anterior vertebral translation between smooth and serrated interbody spacers after discectomy.
Main Results:
- Serrated spacers showed significantly less anterior vertebral translation (0.046 +/- 0.013 mm) than smooth spacers (0.152 +/- 0.075 mm) (P < 0.01).
- Surface serrations markedly increased resistance to shear forces in the tested model.
Conclusions:
- Surface serrations on interbody implants enhance resistance to shear forces.
- Serrated implants are expected to reduce micromotion at fusion sites.
- This reduction in micromotion may lower the incidence of nonunion in clinical lumbar interbody fusions.