Rotational Stability in a Feline Sacroiliac Luxation Model: Biomechanical Comparison of Cannulated Compression Headless Screws and Cortical Screws Applied in Positional or Lag Fashion

The purpose of this study was to compare the rotational stability of cannulated compression headless screws (CCHSs) with cortical positional and lag screws in a simulated cadaveric feline sacroiliac luxation (SIL) model. Thirty-six cadavers of domestic short-haired cats were assigned to three groups. A unilateral SIL model was stabilized using either a single 2.5 mm CCHS, a 2.4 mm cortical positional screw (PS) or lag screw (LS), each engaging 60% of the sacral width. The pelves were mounted in a mechanical testing machine and loaded through the acetabulum to simulate ground reaction forces. Constant displacement was applied at 0.5 mm/s until maximal failure occurred. Yield load, ultimate load, stiffness, and failure modes were compared among the three groups. At the yield load, a statistical trend was observed among the groups, and pairwise comparison showed a significant difference between CCHS and PS. However, no significant differences were identified among the groups for yield load, ultimate load, or stiffness. All specimens failed due to screw loosening, and failure modes differed between CCHSs and cortical screws. Overall, CCHSs and cortical screws placed in a positional or lag fashion showed comparable rotational stability under the single load-to-failure conditions used in this feline SIL model. These findings question the biomechanical advantage of compression screws regarding rotational strength in unilateral feline SIL.