Nondestructive acoustic modal analysis for assessing bone screw stability: An ex vivo animal study

Conventional insertion torque and pull-out tests are destructive and unsuitable for clinical bone screw fixation. This study evaluates screw stability using acoustic modal analysis (AMA) and Periotest compared to traditional methods in an ex vivo animal model. Titanium self-tapping screws (STS) and nonself-tapping screws (N-STS) were implanted in the proximal tibia of 12 rabbits. Four testing methods were used to assess screw stability: peak insertion torque (PIT) during implantation, AMA for natural frequency (NF), Periotest for Periotest value (PTV), and pull-out test for peak pullout force (PPF). Euthanization was performed at 0 (primary stability), 4, and 8 weeks (secondary stability). No significant difference in primary stability was found between STS and N-STS except for AMA (STS: NF 2434 ± 67 Hz, N-STS: NF 2572 ± 43 Hz; p = 0.62). Secondary stability increased significantly over time for both screw types (4-week: NF 3687 ± 36 vs. 3408 ± 45 Hz, PTV 1.4 ± 1.6 vs. -1.5 ± 1.8, PPF 236 ± 29 vs. 220 ± 34 N; 8-week: NF 3890 ± 39 vs. 3613 ± 31 Hz, PTV -3.2 ± 2.5 vs. -2 ± 4.3, PPF 248 ± 25 vs. 289 ± 28 N). Higher NF values for given PTV/PPF indicate potential clinical advantages. Significant differences between primary and secondary stabilities suggest osteointegration was mainly achieved in the 4-week group.