Optimal Sagittal position of a 20 mm interbody fusion cage

ABSTRACT

The current study was undertaken to investigate the biomechanical properties of a 20 mm long BAK cage [Spine Tech Inc., Minneapolis, MN] when implanted sequentially in one of three position anteriorly within the disc space flush with the ventral margin of vertebral bodies, posteriorly with the cage flush with the floor of the spinal canal, and midway between the above 2 positions. eight human cadaveric spines L2-S1 were load tested with 0, 1.5, 3.0, 4.5 and 6.0 Nm in flexion and extension, lateral bending and axial rotation. Testing was first performed in the intact state, after anterior L4-L5 discectomy, and following instrumentation with a 20 mm long BAK cage in either the anterior, mid-, or posterior positions selected at random. when compared to the discectomy state, 20 mm BAK fusion cages reduced spinal motion in all 6 directions of motion. This reduction achieved significance [p < 0.05] in extension with the cages in all 3 positions. Also in extension, the anterior cage position was significantly more rigid than the posterior cage construct. In left axial rotation a significant reduction in motion from the discectomy state was encountered with the cages in the anterior and midposition. the results suggest that when short 20 mm cages are inserted through a ventral approach, anterior location within the disc space may be biomechanically advantageous