In vivo-like long-term compressive loading affects intervertebral disc swelling and flexibility – An ex vivo study

Brain and Spine, vol. 6, pp. 106336

Abstract

Results: In the main group, the use of locking screws led to significantly higher anti-rotation torque compared to the respective insertion torque (p < 0.05) with a median torque increase by 2.7-fold from 1.8 Nm to 4.6 Nm (Fig. 2 left).Significant (p < 0.05) high linear correlations were found between insertion and anti-rotation torque (r = 0.658) and between insertion torque and bone mineral density (r = 0.598).Significant medium linear correlation (p < 0.05, r = 0.385) was identified between anti-rotation torque and bone mineral density.In the control group, the use of locking screws significantly increased the anti-rotation torque compared to testing without locking screws (3.1 Nm vs. 1.2 Nm, p < 0.05, Fig. 2 right).Pedicle width and height did not significantly correlate with insertion and anti-rotation torques, respectively (p ≥ 0.05).Following screw removal, 19 longitudinal pedicle fractures were detected, which did not significantly affect the anti-rotation torque (p ≥ 0.05).Conclusion: In this in vitro study, novel locking screws were found to increase the resistance of pedicle screws against torque by about three times compared to the insertion torque, justifying their clinical use from a biomechanical point of view.As the variations in individual anatomy and screw entry points might be critical for correct positioning of pedicle and locking screws, preoperative planning and robotic assistance in screw implantation can be seen as mandatory to increase the anti-rotation torque and to reduce the risk of pedicle fractures.

Authors 12

1. A.K. Greiner-Perth

   Universität Ulm

   Affiliation as printed

   Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany

2. C. Liebsch

   Universität Ulm

   Affiliation as printed

   Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany

3. H. Unseld

   Universität Ulm

   Affiliation as printed

   Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany

4. D.L. Belavy
   Affiliation as printed

   Department of Nursing, Midwifery and Therapeutic Sciences, Division of Physiotherapy, University of Health Sciences, Bochum, Germany

5. G. Armbrecht

   Charité - Universitätsmedizin Berlin

   Affiliation as printed

   Center for Muscle and Bone Research, Charité – University Medicine Berlin, Berlin, Germany

6. K. Albracht Aachen Department of Medical Engineering and Technomathematics

   FH Aachen · German Sport University Cologne

   Affiliation as printed

   Department of Medical Engineering and Technomathematics, Aachen University of Applied Sciences, Aachen, Germany

   Institute of Movement and Neuroscience, Center for Health and Integrative Physiology in Space, German Sport University, Cologne, Germany

7. H. Brisby

   Sahlgrenska University Hospital

   Affiliation as printed

   Department of Orthopaedics, Sahlgrenska University Hospital, Gothenburg, Sweden

8. D. Falla

   University of Birmingham

   Affiliation as printed

   Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), University of Birmingham, Birmingham, United Kingdom

9. R. Scheuring

   Johnson Space Center

   Affiliation as printed

   Johnson Space Center, Houston, United States of America

10. R. Sovelius

    Finnish Defence Forces

    Affiliation as printed

    Finnish Defence Force, Aeromedical Centre, Helsinki, Finland

11. K. Rennerfelt

    Sahlgrenska University Hospital

    Affiliation as printed

    Department of Orthopaedics, Sahlgrenska University Hospital, Gothenburg, Sweden

12. H.-J. Wilke

    Universität Ulm

    Affiliation as printed

    Institute of Orthopaedic Research and Biomechanics, Ulm University Medical Centre, Ulm, Germany