Original article
Insertional torque of the lumbar pedicle screw during surgery

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Abstract

The purposes of this study were to determine if the intraoperative insertional torque of pedicle screws correlates with the degree of osteoporosis and if insertional torque can be used as a predictor of screw loosening and clinical results in elderly patients. Pedicle screw fixation was performed in 25 patients. Their mean age at the time of surgery was 72.2 years (range 65-79 years). The mean follow-up period was 2.8 years (range 1.0-4.8 years). The insertional torque of the pedicle screws was measured using a Kannon-type torque wrench with a special connector. In the present study, 136 screws were evaluated. The mean insertional torque was 12.2 ± 5.0 kgf-cm. A negative relation was found between insertional torque and the grade of osteoporosis. Roentgenograms showed the radiolucency of 18 screws in eight patients. Radi- olucency appeared as early as 6 months postoperatively. However, there was no significant relation between insertional torque and the presence of screw loosening. Furthermore, there was no significant difference in the clinical results between patients with low insertional torque and those with high insertional torque. This study demonstrated that intraoperative insertional torque is not an objective predictor of screw loosening or clinical results.

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    As discussed above, the relationship between insertion torque and pull-out strength is not clearly established in biomechanical studies with donor material. In addition, no correlation between insertion torque and screw loosening could be demonstrated in a clinical study [35]. Consequently, there is a need for methods to predict screw anchorages, ideally already in the surgery planning phase.

  • Value of standard radiographs, computed tomography, and magnetic resonance imaging of the lumbar spine in detection of intraoperatively confirmed pedicle screw loosening—a prospective clinical trial

    2019, Spine Journal
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    Rates from 1% to 40% are reported [1–4] depending on age, bone quality, and number of fused levels [5]. However, in most reports, the judgment of screw fixation is based on plain radiograph assessment [6–11]. A radiolucent zone surrounding a pedicle screw can be a sign of screw loosening, but a loose screw is not always surrounded by a radiolucent zone [7].

  • Effect of osteoporosis on the clinical and radiological outcomes following one-level posterior lumbar interbody fusion

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    Cage subsidence was defined as a displacement of cages by > 2 mm into the upper or lower endplates in the reconstructive images of CT scans. Loosening of screws was assessed with a 1 mm thickness criterion of radiolucency in the lateral radiographs or CT images [15,16]. Other implant failures were evaluated by plain radiographs.

  • Pull out strength calculator for pedicle screws using a surrogate ensemble approach

    2016, Computer Methods and Programs in Biomedicine
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    Studies to date have found a conflicting relationship between insertion torque and pullout strength. Several experimental studies have reported a positive correlation between insertion torque and pull out strength in biomechanical tests [11–13] whereas some found no correlation [14–16]. Since insertion torque is measured during screw placement, this seldom alters screw selection in clinical practice [10].

  • Intraoperative mechanical measurement of bone quality with the densiprobe

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    In vitro, correlations were shown between insertional torque and pullout force, insertional torque and number of cycles to ultimate pedicles screw pullout, and between the maximum insertion torque and screw pullout force (15,16). Clinical trials could not show a correlation between insertion torque and prediction of mechanical failure in vivo (17,18). One major limitation of this method is that the measurement of screw insertion torque is based on the subjectively defined endpoint of maximum insertional torque (19).

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