: This paper describes the theoretical background of Dynamic

Anterior lumbar interbody fusion (ALIF), under laparoscope or retroperitoneoscope is a well accepted procedure for treatment of degenerative spinal abnormalities. Interbody fusion cages have been shown to promote good initial fixation in a variety of animal models, however few studies have examined the effects of the type of cage or direction of insertion on initial fixation strength. The present study biomechanically measured the initial fixation strength of ALIF using a threaded interbody fusion cage on fresh porcine spine. We performed two studies; Study 1 compared the effects of the number and the direction of insertion of cylindrical cages at the L4/ 5,5 / 6 level on stiffness, and Study 2 investigated the effects of the type of cage and number using two types of cages (cylindrical and conical cages) at the L6/S1 level. In Study 1, there was significantly more stiffness with flexion in the single anterior group, the double anterior group, and the single anterolateral group compared to the control group (no cage insertion). In addition, stiffness was significantly better in the single anterolateral group than in the single anterior group. There was no differentces between any of the groups in any loading mode. In Study 2, for extension, there was significantly better stiffness in the groups that received cylindrical or conical cages compared to no-insertion controls. In lateral bending, the two cylindrical cage groups had significantly better stiffness than controls. There were no differences in flexion and axial torsion between any of the groups. Again, there were no significant differences between any of the groups in any loading mode.