Design of axial screw for lumbosacral vertebrae and the biomechanical analysis

doi:10.3969/j.issn.2095-4344.0325

Abstract

Abstract:

BACKGROUND: Percutaneous lumbar sacral anterior column internal fixation system (AxiaLIF) through anterior sacral approach has been applied in clinical practice in the United States and Europe and has achieved good clinical efficacy. However, there are some problems such as internal fixator subsidence, and poor in controlling rotation ability.

OBJECTIVE: The axial screw of lumbosacral vertebra was designed according to the anatomic data of lumbar lateral radiographs and CT cross-sectional measurements from Chinese healthy populations, and then three-dimensional movement and axial compression tests were conducted on biospecimens in vitro, and the stability of the fixed segment and the axial compressive stiffness were evaluated by biomechanical analysis.

METHODS: Six fresh adult spine specimens (L₃-S₅ segments) were selected, then the biomechanical tests were performed sequentially in normal, isthmic fracture, conventional axial screw fixation, and self-designed axial screw fixation groups. The L₅/S₁ segment in each experimental group was measured under flexion, left flexion and left rotation, and axial compressive displacement was tested.

RESULTS AND CONCLUSION: (1) In the three-dimensional movement experiment, the range of motion in the isthmic fracture group was significantly larger than that in the normal group in flexion and extension and left rotation (P < 0.05). There was no significant difference between isthmic fracture and normal groups in left bend direction (P > 0.05). (2) The range of motion in the conventional and self-designed axial screw fixation groups was significantly smaller than that in the normal group in flexion and extension and left lateral direction (P < 0.05), but the range of motion in left rotation direction showed no significant difference (P > 0.05). There was no significant difference in the range of motion between conventional and self-designed axial screw fixation groups (P > 0.05). (3) In the axial load compression test of 1 000 N, the order of compression displacement was as follows: self-designed axial screw fixation group < conventional axial screw fixation group < normal group < isthmic fracture group (P < 0.05). (4) According to the mechanical formula EF=P/vL and compression displacement results, the axial compressive stiffness values were calculated, which the highest value was in the self-designed axial screw fixation group, followed by conventional axial screw fixation group, normal group, and the lowest in the isthmic fracture group (P < 0.05). (5) These results indicate that the self-designed axial screw in all directions of motion can significantly improve the stability of the lumbosacral motion under posterior column instability, which is comparable to that of the common axial screws. But it is obviously better than common axial screw in axial compressive stiffness, which provides an effective solution for the prevention of segment subsidence and loss of lordosis in the fixation of the vertebral column with axial screws.

Key words: Lumbar Vertebrae, Internal Fixators, Biomechanics, Tissue Engineering

CLC Number:

R318

Zeng De-hui, Wang Wen-jun, Zhang Wei, Song Xi-zheng, Yang Wen-ren, Xiang Liang, Hou Wei. Design of axial screw for lumbosacral vertebrae and the biomechanical analysis[J]. Chinese Journal of Tissue Engineering Research, 2018, 22(27): 4369-4374.

Figures/Tables 2

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