A study on the use of the Osstell apparatus to evaluate pedicle screw stability: An in-vitro study using micro-CT.

Daisuke Nakashima,Morio Matsumoto,Ken Ishii,Takeo Nagura,Masaya Nakamura,Alejandro A Espinoza Orías

doi:10.1371/journal.pone.0199362

Daisuke Nakashima, Morio Matsumoto + Show 4 more

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https://doi.org/10.1371/journal.pone.0199362

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Abstract

Pull-out force and insertion torque have not been generally used as intraoperative measures for the evaluation of pedicle screw stability because of their invasiveness. On the other hand, resonance frequency analysis is a non-invasive and repeatable technique that has been clinically used in dentistry to evaluate implant stability e.g. by the Osstell apparatus. In this study, the characteristics of the implant stability quotient (ISQ) value obtained by the Osstell apparatus in the field of spinal surgery were investigated. Biomechanical test materials simulating human bone were used to provide a comparative platform for evaluating each fixation strength measure, including pull-out force, insertion torque, and the ISQ value. To perform pull-out force measurement and to repeat pedicle screw insertion and removal, loosening was artificially created, and its effect was investigated. The grade of loosening was quantified on a micro-CT image after pedicle screw removal. In the comparison of the 3 fixation strength measures, the correlations of the ISQ value with the pull-out force (R2 = 0.339 p <0.0001) and the insertion torque (R2 = 0.337 p <0.0001) were lower than the correlation between pull-out force and insertion torque (R2 = 0.918 p <0.0001). On a micro-CT study, the material volume of the internal threads disappeared after destruction of its integrity due to repeated pedicle screw insertion and removal. Material integrity destruction of the internal threads decreased only the pull-out force and the insertion torque, but it did not affect the ISQ value. The ISQ value only decreased when the material volume of the internal threads disappeared, probably because the ISQ value reflects the resistance against a force in the perpendicular direction of the screw, unlike the conventional measures of fixation strength, such as pull-out force and insertion torque, which reflect axial load.

Highlights

Implant stability is important in the field of orthopedics, because it secures implant fixation to the bone and is needed to avoid implant fixation failure [1,2,3,4]
In the field of spinal surgery, the rates of postoperative pedicle screw loosening were reported to be as high as 12% [5,6,7]
To measure resonance frequency analysis (RFA) with the Osstell ISQ1 (Osstell; Integration Diagnostics, Goteborg, Sweden), 2 neodymium magnets (Magfine, Miyagi, Japan) with a diameter of 4 mm, height of 2 mm, surface inductive flux of 331.7 mT, and magnetic attraction of 0.345 kgf were attached to the head of the pedicle screw using a cyanoacrylate-type of chemically reactive adhesive (Konishi Co., Osaka, Japan)

Summary

Introduction

Implant stability is important in the field of orthopedics, because it secures implant fixation to the bone and is needed to avoid implant fixation failure [1,2,3,4]. Pull-out force [1, 8,9,10,11,12] and insertion torque [1, 13, 14] are the measures of fixation strength that are generally used to evaluate the stability of implants, especially screws. Referred to as pull-out force, is measured destructively through laboratory mechanical testing and is defined as the maximum axial force required to pull the screw out from the bone [15]. This fixation strength cannot be measured in clinical situations because of its invasiveness. Pull-out force and insertion torque are not generally used as intraoperative measurement methods

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