Biomechanical Study Of A Kidney-Shaped N-HA/PA66 Cage For Transforaminal Lumbar Interbody Fusion

Objective:To evaluate the biomechanical stability of a new kidney-shaped N-HA/PA66 cage for transforaminal lumbar interbody fusion in vitro study. In this study, comparisons were made with the more common the bullet-shaped N-HA/PA66 cage, and then determine the feasibility for the new kidney-shaped N-HA/PA66 cage in clinical surgery.Method:Fifteen adult cadaveric lumbar spine specimens (L4/5) were used in this study. They were divided into three groups:intact group(group A), the new kidney-shaped N-HA/PA66 cage group(group B) and the bullet-shaped N-HA/PA66 cage group(groupC). A left-sided TLIF with one cage and with bilateral transpedicular fixation was performed at L4-L5 in B、C groups. The L4-L5 range of motion was obtained by applying pure moments of 10 Nm in right/left lateral bending, flexion/extension, and axial left/right rotation movements for each specimen. In the cyclic test, Overall,10,000 axial compression cycles, each ranging sinusoidal from 300 to 1000 N, were applied with a frequency of 3 Hz in B、C groups, and then the anterior/posterior disc height was evaluated in lateral plain radiograph, cage subsidence was evaluated.Results:1. The posterior transpedicular fixation significantly reduced the range of motion in flexion extension, lateral bending and axial torsion compared with the intact condition, respectively. There was no statistically significant difference in biomechanical stability among the new kidney-shaped N-HA/PA66 cage group and the bullet-shaped N-HA/PA66 cage group.2. In the cyclic test, the average height of intervertebral space was 13.26±1.07mm before cyclic test,12.29±0.98 mm under cyclic loading in the new kidney-shaped N-HA/PA66 cage group. The average height of intervertebral space was 13.33±1.11mm before cyclic test,11.80±1.07mm under cyclic loading in the bullet-shaped N-HA/PA66 cage. Cyclic loading caused subsidence in two cage groups, most distinct with bullet-shaped N-HA/PA66 cage (1.54±0.28mm) followed by the new kidney-shaped N-HA/PA66 cage (1.02±0.34mm). No statistically significant difference could be found among the two cage designs.Conclusions:1. The new cage design was Kidney shape and made of N-HA/PA66 material through the TLIF approach and peripheral placement, It is more matching with lumbar vertebral anatomy structure and the morphology of endplates, offering a larger contact area together with sufficient space for bone ingrowth, and avoiding dural sac retraction.2. The new kidney-shaped N-HA/PA66 cage exhibits similar biomechanical initial stability as the bullet-shaped N-HA/PA66 cage, The new kidney-shaped N-HA/PA66 cage seemed to have better resistance against subsidence than the bullet-shaped N-HA/PA66 cage under cyclic loading.