Biomechanical testing of adjacent double segment lumbar fractures treated with the spinal external fixator

doi:10.3969/j.issn.2095-4344.2013.09.010

Abstract

Abstract:

BACKGROUND: Overactive adjacent motion segment is an important factor for adjacent segment degeneration after thoracolumbar fracture fixation, which can cause stress concentration on this segment, and the cephalad adjacent segment is more prone to degeneration than caudal adjacent segment. The more the fixed segments are, the higher the stress concentration of the adjacent segment, and the larger the degeneration rate.
OBJECTIVE: To assess the biomechanical stability and range of motion degeneration of the upper adjacent vertebrae by the biomechanics testing of the pedicle screw external fixation for adjacent double segment lumbar burst fractures.
METHODS: There were 14 vertebra samples (T₁₄-S₁) from six fresh adult pig spinal specimens. Each of them underwent a biomechanical test in the following order to minimize the inter-group interference, including normal group, fracture group (L₃ and L₄vertebral specimens were made into the burst fracture models), external fixation group (L₂ and L₅ vertebral specimens were fixed with spine external fixtor) and internal fixation group (the L₂ and L₅vertebral specimens received the traditional open posterior fixation after the spine external fixtor removed). The range of motion of L₂-₅and the upper adjacent segment L₁ were measured under flexion, extension, lateral bending and axial rotation angles before and after internal fixation and external fixation.
RESULTS AND CONCLUSION: Range of motion in the fracture group, internal fixation group and external fixation group was significantly larger than that of the normal group (P < 0.05). Range of motion of L2-5 in the internal fixation group and external fixation group was significantly less than that of normal and fracture groups (P < 0.01). There was no significant difference in immediate stability index between the internal fixation group and external fixation group (P > 0.05). Compared with normal group, the range of motion of the upper vertebra L₁ after internal and external fixation was increased; there was no significant difference in range of motion of upper vertebrae L₁ under flexion and extension between external fixation group and normal group (P > 0.05), but there was significant difference under lateral bending and axial rotation (P < 0.01). There was significant difference in range of motion of the upper vertebra L₁ under flexion, extension, lateral bending and axial rotation between internal fixation group and the normal group (P < 0.01). Compared with traditional internal fixation, the immediate stability index of the spinal external fixation in treating adjacent double segment burst fractures was equal. Both two fixation methods could increase the range of motion of the adjacent upper vertebra under lateral bending and rotation. But the spinal external fixation could not increase the range of motion of adjacent upper vertebrae under flexion and extension.

Key words: bone and joint implants, spinal implants, burst fracture, adjacent vertebral body, adjacent segment degeneration disease, spine external fixator, percutaneous pedicle screw, biomechanics, minimally invasive surgery, angular displacement, immediate stability, range of motion degeneration, provincial grants-supported paper

CLC Number:

R318

Yi Guo-liang, Song Xi-zheng, Wang Wen-jun, Yao Nü-zhao. Biomechanical testing of adjacent double segment lumbar fractures treated with the spinal external fixator[J]. Chinese Journal of Tissue Engineering Research, 2013, 17(9): 1586-1591.

Figures/Tables 3

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