EXPRESS: Pull-out strength of cannulated compression headless screws and cortical screws in the feline sacrum

The aim of this study was to compare the pull-out strength of cannulated compression headless screws (CCHSs) of two different lengths with that of cortical screws in the feline sacrum.

In this experimental study, 30 cadavers of adult Domestic Shorthair cats were randomly assigned to three groups: single 2.4 mm cortical screws engaging 60 % of the sacral width (CS 60, n = 10), 2.5 mm CCHSs engaging 60 % of the sacral width (CCHSs 60, n = 10), and 2.5 mm CCHSs engaging 40 % of the sacral width (CCHS 40, n = 10). Screws were inserted into feline sacra and tested for pull-out strength using a universal testing machine at a constant displacement rate of 0.2 mm / sec up to 20 mm. Peak pull-out force (PPF), displacement at PPF and stiffness were calculated from the load-displacement curves and compared among groups using Fisher's ANOVA and the Welch test. Post-hoc pairwise comparisons were performed using Student's t-tests and the Games-Howell test. Statistical significance was set at p ≤ 0.05.

Pairwise comparison of PPF showed significant differences between the CS 60 and CCHS 60 groups (p = 0.05) and between the CS 60 and CCHS 40 groups (p = 0.05). No significant difference was detected between the CCHS 60 and CCHS 40 groups (p = 0.98). For displacement at PPF and stiffness, no significant differences were identified in the pairwise comparison.

Fully threaded cortical screws provide greater holding strength than partially threaded CCHSs in cadaveric feline sacra. In addition, a single short CCHS offers holding strength comparable to that of a CCHS of the conventionally recommended length.