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Superior-segment Bilateral Facet Violation in Lumbar Transpedicular Fixation, Part I: A Biomechanical Study of
Yunfeng Xu1, Xiaofeng Le1, Qi Zhang1
1Department of Spine Surgery, Beijing Jishuitan Hospital, Xicheng District, Beijing, China.
Study Design:
This is an in vitro biomechanical study.
Objectives:
The aim of this study was to investigate the biomechanical variations of lumbar spine motor units and that under different moments after screw heads blocking superior-adjacent bilateral facets through the cadaver specimen biomechanical experiment.
Summary Of Background Data:
Facet joint violation by pedicle screws is not a rare adverse event in instrumented lumbar fusion surgery, and one of the most common types is the screw head blocking the superior-adjacent facet. However, its contribution to biomechanical instability at the supradjacent level is unknown.
Methods:
The range of motion (ROM) of 12 lumbar spines (L4-S1) were measured in flexion-extension, lateral bending, and axial rotation for L4/5. All specimens were randomly divided into two groups: the control group and the blocking group, each with 6 specimens. Spine were tested on intact and instrumented specimens, respectively. The relative ROM changes were compared between the blocking and control groups.
Results:
In the blocking group, the supradjacent-level flexion-extension ROM significantly decreased under all moments (7.5, 6.0, 4.5 Nm) relative to the intact spine and a significant decrease in the lateral bending relative ROM was found at 4.5 Nm. In the control group, no significant change of supradjacent-level ROM was found relative to the intact noninstrumented spine at each moment. When performing flexion-extension, the relative ROM change between the 2 groups was significantly different at 4.5 Nm. When performing lateral bending, the relative ROM change between the 2 groups was significantly different at moments of 6.0 and 4.5 Nm.
Conclusion:
When screw heads blocked superior-adjacent bilateral facets, the supradjacent-level flexion-extension ROM and lateral bending ROM decreased. In the long run, this may be a risk of persistent low-back pain due to frequent impingement.
Level Of Evidence:
N/A.
