Laser resonance frequency analysis of pedicle screw stability: a cadaveric model bone study

There is no evaluation method currently available to assess intraoperative pedicle screw fixation (PSF) strength. In this study, we established a laser-based resonance frequency analysis (RFA) system with high-speed, noncontact, quantitative measurements of PSF. Clinical investigations in the future can assess surgical failure risk of implants. We investigated the characteristics of the laser RFA and compared them with the conventional methods. We inserted a pedicle screw in the vertebral pedicle of human cadaver or model bone, followed by screw pull-out, peak torque, implant stability quotient (ISQ) value obtained by the magnetic dental RFA system, and fixation force of laser RFA. We compared the outcomes using best-fit linear or logarithmic approximations. For the model bone study, the resonance frequency (RF) versus peak torque/pull-out force (POF) demonstrated strong correlations using logarithmic approximation (vs. peak torque: R = 0.931, p < .001, vs. POF: R = 0.931, p < .001). RF strongly correlated with the ISQ value using linear approximation (R = 0.981, p < .001). For the cadaveric vertebrae study, the correlation coefficients between RF and the peak torque/POF were significant regardless of approximation method (peak torque: logarithmic: R = 0.716 vs. linear: R = 0.811; p < .001) (POF: logarithmic: R = 0.644 vs. linear: R = 0.548; p < .05). Thus, the results of this study revealed a constant correlation between RFA and conventional methods as a measurement validation, predicting favorable support for intraoperative PSF. RFA has the potential to be a new index for evaluating the implant fixation force.