New Biomechanical Approach for Evaluation of Spinal Pedicle Screw Fixation Stability



Pull-out test is the conventional biomechanical tool for stability assessments of bone screws. Recently, modal analysis methods (MAM) have gained interest in the fixation stability measurement of dental implants which can be adopted as a new fixation measurement technique for spinal pedicle screws.


To test the applicability and accuracy of MAM in predicting the fixation stability of pedicle screws, two different modal analysis approaches were used. First, pedicle screws were incorporated into polyurethane (PU) foam. Then, the time response of an accelerometer attached to the head of the screw and excited by a shock hammer was recorded to perform classical modal analysis (CMA). Simultaneously, sound modal analysis (SMA) was carried out using a sound recording device to obtain the frequency response of the screw-block structure. Lastly, the destructive pull-out test was performed to extract its tangential stiffness (TS) and yield force (YF).


Linear regression analysis showed a good correlation between CMA and SMA (R2 = 0.99, P < 0.001). Moreover, the two methods did not deviate from the y = x hypothesis. Also, the 1st natural frequency of both methods was the highest in the 30 mm insertion depth and high-density PU (p < 0.05). The same was observed for the TS and YF in pull-out tests.


Standard deviation numbers in the SMA were significantly less than those in the CMA. The accuracy, excellent repeatability, and non-destructive nature of SMA can make it an ideal tool to estimate screw fixation strength in future in-vivo orthopedic applications.

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The authors would like to express their gratitude for the financial support of INSF Grant #97014214 to partially cover the PhD thesis expense of the first author.


The financial support of Iranian National Science Foundation (INSF) Grant #97014214 was covered partially PhD. Thesis expense of the first author.

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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Mohammadjavad Einafshar. The first draft of the manuscript was written by Mohammadjavad Einafshar and Ata Hashemi edited and revised the manuscript. Ata Hashemi supervised and conceptualized the study. All authors read and approved the final manuscript.

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Correspondence to Ata Hashemi.

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Einafshar, M., Hashemi, A. New Biomechanical Approach for Evaluation of Spinal Pedicle Screw Fixation Stability. J. Med. Biol. Eng. 41, 447–455 (2021).

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  • Primary stability
  • Modal analysis
  • Pull-out characterization
  • Acoustic analysis
  • Screw stability evaluation