Biomechanical comparison of pedicle screw fixation strength between traditional trajectory and the single and double endplates penetrating screw trajectories in cadaver spine.

PURPOSE: We have developed and reported on the usefulness of single and double endplates penetrating screw trajectories (SEPST/DEPST), which penetrate the endplates of the vertebrae to increase the fixation strength in patients with diffuse idiopathic skeletal hyperostosis (DISH). The purpose of this study is to compare the peak insertion torque (PIT) and pullout force (POF) of traditional trajectory (TT) and SEPST/DEPST using cadaveric spine.

METHODS

The eighth thoracic vertebra to the fifth lumbar vertebra from six formalin-fixed adult human cadavers (two males, four females; age at death 85.7 ± 8.8 years) were used and PIT and POF were evaluated in the following three studies. Firstly, a comparison among TT/SEPST/DEPST. Secondly, a comparison of reinsertion of screws with DEPST (re-DEPST) in vertebrae inserted with TT and removed, assuming reoperation. Lastly, a comparison between the endplate thread screw (ETS) which has a smaller pitch and the conventional cancellous thread screw (CTS) was made.

RESULTS

SEPST/DEPST had a 32-70% higher PIT and a 45-82% higher POF than TT, and DEPST was about 1.4 times higher than SEPST. Assuming reoperation, the results show that fixation with re-DEPST provided almost the same fixation strength as initial TT insertion. ETS, which was considered useful for DEPS, showed a relatively higher fixation strength than CTS, however, the difference was not significant.

CONCLUSION

The present study using cadaver demonstrated the strong fixation of SEPST/DEPST and its usefulness for revision surgery, however, there were no significant differences in the mechanical properties between ETS and CTS.