Instant and fatigue stability analysis of anterior lumbar interbody fusion with stand-alone cage

Abstract

To investigate the spinal segment instant and fatigue stability of anterior lumbar interbody fusion with stand-alone cage. The vertebrae L4 and S1 of 6 human lumbar specimens (L3 - S1) were embedded with dental base acrylic resin powder and fixed on mechanical machine, and the L4/L5 and L5/S1 disk spaces were left active. The 6 specimens underwent mechanical test as control group first, and then used as experimental group with a cage implanted in L5/S1. Instant instability was tested in three directions: flexion, extension, and lateral bend. The relative movement of L4/L5 and L5/S1 was recorded. Fatigue instability was tested after 50 000 times of flexion-extension movement, and the relative displacement between the cage and S1 was recorded. In the three directions of flexion, extension, and lateral bend, the relative movements of L5/S1 in the experimental group were 0. 83 +/- 0.26 degrees, 1.60 +/- 0.19 degrees, and 0.72 +/- 0.20 degrees respectively, all significantly decreased than those of the control group (3.60 +/- 0.30 degrees, 4.82 +/- 0.34 degrees, and 3.80 +/- 0.28 degrees respectively, all P < 0.01). The relative movement of L4/L5 of the experimental group were 5.82 +/- 0.36 degrees, 5.38 +/- 0.30 degrees, and 4.96 +/- 0.29 degrees in the three directions respectively, all significantly higher than those of the control group (4.16 +/- 0.33 degrees, 4.02 +/- 0.30 degrees, and 3.48 +/- 0.34 degrees respectively, all P <0.01). After 50 000 times of flexion-extension fatigue movement, the relative displacement between the cage and S1 was zero. Anterior lumbar interbody fusion with a stand-alone cage has excellent instant and fatigue stability, which can provide enough stability for clinical bone fusion without other internal fixation.