Abstract
BackgroundLateral pedicle wall perforations occur frequently during pedicle screw insertion. Although it is known that such an occurrence decreases the screw pull-out strength, the effect has not been quantified biomechanically.Materials and methodsTwenty fresh cadaveric lumbar vertebrae were harvested, and the bone mineral density (BMD) of each was evaluated with dual-energy radiography absorptiometry (DEXA). Twenty matched, 6.5-mm pedicle screws were inserted in two different manners in two groups, the control group and the experimental group. In the control group, the pedicle screw was inserted in a standard fashion taking adequate precaution to ensure there was no perforation of the wall. In the experimental group, the pedicle screw was inserted such that its trajectory perforated the lateral wall. Group assignments were done randomly, and the maximal fixation strength was recorded for each screw pull-out test with a material-testing system (MTS 858 II).ResultsThe average BMD for both groups was 0.850 g/cm2 (0.788–0.912 g/cm2). The average (and standard deviation) maximal pull-out forces were 1,015.8 ± 249.40 N for the experimental group and 1,326.0 ± 320.50 N for the control group. According to a paired t-test, the difference between the two groups was statistically significant (P < 0.001).ConclusionThe results of this study confirm that the maximal pull-out strength of pedicle screws decreases by approximately 23.4% when the lateral wall is perforated.
Highlights
The use of pedicle screws in the lumbar region is a wellestablished technique that has been shown to provide immediate stability and rigid fixation that facilitates correction of a deformity in both sagittal and coronal planes [1,2,3,4,5]
The results of this study confirm that the maximal pull-out strength of pedicle screws decreases by approximately 23.4% when the lateral wall is perforated
Differences in bone mineral density (BMD) between individual vertebrae were not statistically significant, which showed the specimens were normal and not affected by osteoporosis. In both the experimental and control groups formed from 20 vertebral bodies, the fixation strength was measured (Tables 1 and 2)
Summary
The use of pedicle screws in the lumbar region is a wellestablished technique that has been shown to provide immediate stability and rigid fixation that facilitates correction of a deformity in both sagittal and coronal planes [1,2,3,4,5]. To ensure optimal placement for achieving the requisite stability, the screw must be meticulously placed and insertion obtained in good quality bone. Various techniques have been developed to ensure optimal placement of pedicle screws in the pedicles. In the straight-ahead technique as described by Roy-Camille [6], screw insertion begins at the intersection of a horizontal line bisecting the transverse process and a longitudinal line bisecting the facet joint. The screw is inserted straight ahead, parallel to the vertebral endplates. It is known that such an occurrence decreases the screw pull-out strength, the effect has not been quantified biomechanically
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