Application of sacral-2-alar screws in lumbosacral stability

Objective To explore the maximum pull-out force of alar screws fixation in sacral 2 and investigate the effectiveness of this internal fixation method. Methods Five adult cadaver specimens fixed and wetted with formaldehyde solution were selected, as well as six fresh frozen cadavers. Randomly place three types of sacral screws on both sides of the same cadaver specimen, including: sacral-2-alar screws reinforced with bone cement (S2 group), S1 pedicle screw (S1 group), sacral-2-alar-iliac screws (S2AI group). The instantaneous maximum pull-out force values of three groups of sacral screws by applying axial pull-out force to the screws were recorded. Results The maximum axial pullout force of screws in 11 cadaver specimens was (521.80 ± 98.98)N in S2 group, (843.16±107.64)N in S1 group, and (536.04±145.78)N in S2AI group, and the difference among three groups was significant (F=25.52, P＜0.01). The strength of S2 group and S2AI group was comparable, and there was no significant difference between the two groups (P＞0.05). Conclusion Sacral-2-alar screws reinforced with bone cement have good mechanical properties and are suitable for clinical application.