Evaluation of the efficacy of modal analysis in predicting the pullout strength of fixation bone screws

BACKGROUND: Pilot hole preparation has been shown to have an impact on the short and long‐term stability of the screw fixation constructs. PURPOSE: Investigation and comparison of two nondestructive modal analysis methods with conventional insertion torque (IT) and pullout tests in optimum pilot hole diameter detection. METHODS: Twenty conical core titanium screws were embedded in high‐density polyethylene blocks with different pilot hole diameters. The maximum IT was recorded for each screw during implantation. Then, two modal analysis methods including accelerometer (classical modal analysis [CMA]) and acoustic modal analysis (AMA) were carried out to measure the natural frequency (NF) of the bone‐screw structure. Finally, stiffness (S), pullout force (F(ult)), displacement at F(ult) (d(ult)) and energy dissipation (ED) were obtained from the destructive pullout test. RESULTS: The IT increased, as the pilot hole diameter decreased. The maximum value of IT was observed in the smallest pilot hole diameter. The same trend was found for the F(ult) and the first NF derived from both modal methods except for 5.5 mm pilot hole diameter. The natural NFs derived from CMA and AMA showed high correlations in different groups (R(2) = 0.94) and did not deviate from y = x hypothesis in linear regression analysis. The F(ult), d(ult), and ED were measured 4800 ± 172 N, 3.10 ± 0.08 mm and 14.23 ± 1.10 N.mm, respectively. DISCUSSION: No significant change was observed in “S” between the groups. The highest F(ult) and first NF were obtained for the 5.5 mm pilot hole diameter. Both CMA and AMA were found to be reliable methods and can promote the undesirable contradiction between F(ult) and IT.