Do Iliac Screws Placed Close to the Sciatic Notch Have Greater Pullout Strength?

Hani Chanbour; Steven G Roth; Jeffrey W Chen; Sasidhar Uppuganti; Jeffry S Nyman; Mir Amaan Ali; Christopher M Bonfield; Amir M Abtahi; Byron F Stephens; Scott L Zuckerman

doi:10.1227/ons.0000000000001159

Do Iliac Screws Placed Close to the Sciatic Notch Have Greater Pullout Strength?

Oper Neurosurg (Hagerstown). 2024 Apr 23. doi: 10.1227/ons.0000000000001159. Online ahead of print.

Authors

Hani Chanbour¹, Steven G Roth¹, Jeffrey W Chen², Sasidhar Uppuganti³, Jeffry S Nyman^{3

4}, Mir Amaan Ali¹, Christopher M Bonfield^{1

3}, Amir M Abtahi^{1

3}, Byron F Stephens^{1

3}, Scott L Zuckerman^{1

3}

Affiliations

¹ Department of Neurological Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
² Department of Neurological Surgery, Baylor College of Medicine, Houston, Texas, USA.
³ Department of Orthopedic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
⁴ Department of Biomedical Engineering, Vanderbilt University Medical Center, Nashville, Tennessee, USA.

PMID: 38651901
DOI: 10.1227/ons.0000000000001159

Abstract

Background and objectives: Optimal iliac screw position in relation to the sciatic notch remains unknown. In 12 cadavers undergoing S2 alar-iliac (S2AI) screw placement, we tested the pullout strength of screws placed in proximity to the sciatic notch (≤5 mm) vs farther away from the sciatic notch (>5 mm).

Methods: A biomechanical, cadaver-based study was performed on 12 cadavers undergoing bilateral S2AI screw insertion. The position of the S2AI screw regarding the sciatic notch was dichotomized as ≤5 mm from the sciatic notch on the right side and >5 mm on the left side, confirmed using c-arm fluoroscopy. The primary outcome was the pullout strength of the screw (N). Secondary outcomes were stiffness (N/mm), yield force (N), and work to failure (N mm). Ischial tuberosity was embedded into polymethyl methacrylate and secured to a custom 3-axis vise grip mounted to a 14.5-kN load cell. Pullout testing was performed at 5 mm/min. Force and displacement data were collected at 100 Hz and evaluated using MATLAB. The Mann-Whitney test was performed.

Results: Of 24 S2AI screws, 3 screws could not be tested because of cement-bone interface failure. A positive though nonsignificant trend of screw pullout strength was found for screws close to the notch compared with those farther from the notch (861.8 ± 340.7 vs 778.7 ± 350.8 N, P = .859). Similarly, screws close to the notch demonstrated a higher trend of stiffness (149.4 ± 145.4 vs 111.34 ± 128.2 N/mm, P = .320) and force to yield (806.9 ± 352.0 vs 618.6 ± 342.9 N, P = .455). Conversely, screws farther from the notch had a higher but similarly nonsignificant area under the force-displacement curve (10 867.0 ± 9565.0 vs 14 196.6 ± 9578.3 N mm, P = .455), which might be due to excess sheer/translation force that could not be reliably quantified.

Conclusion: Although placing S2AI screws ≤5 mm of the sciatic notch provided stronger fixation in 3 of 4 biomechanical testing categories, these results were not statistically significant. Therefore, placing S2AI screws ≤5 mm of the sciatic notch did not provide stronger fixation.