###### Abstract  
To prevent pedicle screw implant failure, a diagnostic technique that allows surgeons to evaluate implant stability easily, quickly, and quantitatively in clinical orthopedic situations is required. This study aimed to predict the insertion torque equivalent to laboratory-level evaluation accuracy. This serves as an index of the implant stability of pedicle screws placed in cadaveric bone, which relies on laser resonance frequency analyses (L-RFA) when irradiating with two types of lasers. The machine learning analysis was optimized using a dataset with artificial bone as teaching data. In this analysis, many explanatory variables extracted from the laser-induced vibration spectra obtained during an analysis/RFA evaluation were predicted by selecting important variables using the least absolute shrinkage and selection operator and performing a non-linear approximation using support vector regression. It was found that combining both artificial and cadaveric bone data with the bone densities as teaching data dramatically improved the determination coefficient from \(R^{2}=-0.144\) to \(R^{2}=0.858\) as the prediction accuracy and reduced the influence of differences between artificial and cadaveric bones. This technology will contribute to the development of preventive diagnostic technologies that can be used during surgery, which is necessary in order to further advance treatment technologies. laser; resonance frequency; vibration; orthopedic implant; pedicle screw; computed tomography; machine learning +
Footnote †: journal: Medical  
problematic, with reported incident and revision rates of 12% [3] and 40% [4], respectively. To overcome this problem, the initial implant stability is evaluated as an index [5,6]. The pullout force [7] and insertion torque tests [5,8] were used to evaluate the initial implant stability as an index. Pullout force tests are destructive laboratory tests that cannot be used in clinical situations. Although the insertion torque can be measured during surgery, it is a one-time, non-repeatable measurement, and is influenced by factors attributable to each surgeon, such as the implantation speed and applied force. To address this problem, laser resonance frequency analysis (L-RFA) was used to measure the implant stability of pedicle screws [9,10] and acetabular cups [11]. The L-RFA with laser technology was developed to replace hammering tests used for structural infrastructure [12]. Vibrations induced by active excitation are used as a basic principle of hammering inspection, and the induced vibration is detected by the ear, where the condition is determined by the sound information. For tunnel inspections, a hammering test is used to survey nonvisible internal defects in concrete walls and detect loose bolts. The principle of L-RFA is to replace active excitation with laser irradiation to induce vibrations via laser ablation or laser-induced photoacoustic-elastic waves (LIPTEW) [13]. By measuring and analyzing the LIPTEW with a laser Doppler vibrometer, the L-RFA realizes high-speed, remote, and quantitative evaluations. Implant stability diagnosis using RFA is widely used in the dental field with magnetic excitation [14]. This method is widely used because the oral cavity can be opened widely and still allows for fine magnet installation [15]. However, orthopedic implants are not used because of the low strength of magnetic excitation and the difficulty of intraoperative placement of fine magnets [16]. Because of the difficulty of excitation by magnets, the use of mechanical vibrators has been considered, but no clear correlation has been obtained [17, 18, 19]. However, the L-RFA reported in 2019 shows the potential for use in the orthopedic field [11]. The natural vibrations in the audible frequency range of the experimental sample were measured using L-RFA.