Abstract

Traditional L5-S1 axial fixation is lack of antirotation biomechanical stability. As a new axial fixation for lumbosacral spine, the antirotation biomechanical stability of L5-S1 locking axial fixation with inner poke has not been verified. Six normal human fresh cadaver lumbosacral spine specimens (L3-S5) were used to construct spondylolysis model by osteotome successively, and then, the six specimens were subjected to L5-S1 axial fixation (control group), L5-S1 locked axial fixation with inner poke (experimental group 1), L5-S1 locked axial fixation with inner poke combine with pedicle screw fixation (experimental group 2) and L5-S1 axial fixation combine with pedicle screw fixation (experimental group 3), respectively, and the range of motion of L5-S1 segment were measured under axial rotation state with maximum torque is 10 Nm. All rotation tests were performed by the spine 3-dimensional motion machine. The results showed that the specimens of control group resulted in more range of motion than other experimental groups in axial rotation. Compared to the traditional axial fixation , the total rotation range of motion of L5-S1 locked axial fixation with inner poke group was significantly decreased (t=-5.065, P=0.04). When L5-S1 locked axial fixation with inner poke combined with pedicle screw fixation, the total rotation range of motion was smaller significantly (t=4.39, P=0.007). The rotation range of motion of experimental group 2 is the smallest in all groups. In conclusion, L5-S1 locking axial fixation with inner poke allowed less rotational motion compared to the traditional axial fixation on the fixed segment and supplied with pedicle screws can improve its performance further in the term of antirotation. The results of this study showed that L5-S1 locking axial fixation with inner poke can improve antirotation function of the traditional axial fixing screw.