Effect of lumbar interbody cage geometry on construct stability: a cadaveric study.
METHODS
Biomechanical study to investigate three-dimensional motion behavior of cadaveric spines in various surgical simulations.


OBJECTIVE
To determine the effect of cage geometry on the construct stability.


BACKGROUND
There is a wide variety of cage/spacer designs available for lumbar interbody fusion surgery. These range from circular, tapered, and rectangular with and without curvature. However, the effectiveness of cages with different designs and materials to stabilize a decompressed intervertebral space has not been fully studied.


METHODS
Six fresh ligamentous lumbar spine specimens (L1-S2) were subjected to pure moments in the six loading directions. The resulting spatial orientations of the vertebrae were recorded using Optotrak Motion Measurement System. Measurements were made sequentially for intact, bilateral spacer placements across L4-L5 using a posterior approach, supplemented with pedicle screw-rod system fixation, and after the cyclic loading in flexion-extension mode.


RESULTS
The stability tended to decrease after the bilateral cage placement as compared with the intact for all loading cases except flexion. In flexion, the angular displacement decreased to 80% of the intact. However, there was no significant statistical difference seen in stability between intact and after bilateral spacer placement. Following the addition of posterior fixation using pedicle screw-rod system, the stability significantly increased in all directions. Cyclic loading did not have any significant effect on the stability.


CONCLUSIONS
Stand-alone cages restore motion to near-intact levels at best, and supplement instrumentation is essential for significantly increasing the stability of the decompressed segment. The effects of cage geometry and Young's modulus of the cage material do not seem to influence the stability, as compared with the other cagedesigns, especially after supplemental fixation with a posterior system.
Vadapalli
Sasidhar
S
Spine Research Center, Department of Bioengineering, University of Toledo, OH 43606, USA.
Robon
Matt
M
Biyani
Ashok
A
Sairyo
Koichi
K
Khandha
Ashutosh
A
Goel
Vijay K
VK
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D004867:Equipment Design; D005260:Female; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability / Q000517:prevention & control; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation*