• Stephan Deckelmann, Ronald Schwyn, Bas Van der Pol, Markus Windolf, Paul F Heini, and Lorin M Benneker.
• From the *AO Development Institute, Davos, Switzerland; †Department of Traumatology and Reconstructive Surgery, BG-Trauma Center Bergmannstrost, Halle (Saale), Germany; ‡AO Research Institute, Davos, Switzerland; and §Department of Orthopaedic Surgery, Inselspital, University of Bern, Bern, Switzerland.
• Spine. 2010 Mar 15;35(6):607-12.

Study DesignCadaver study.ObjectiveTo determine bone strength in vertebrae by measuring peak breakaway torque or indentation force using custom-made pedicle probes.Summary Of Background DataScrew performance in dorsal spinal instrumentation is dependent on bone quality of the vertebral body. To date no intraoperative measuring device to validate bone strength is available. Destructive testing may predict bone strength in transpedicular instrumentations in osteoporotic vertebrae. Insertional torque measurements showed varying results.MethodsTen human cadaveric vertebrae were evaluated for bone mineral density (BMD) measurements by quantitative computed tomography. Peak torque and indentation force of custom-made probes as a measure for mechanical bone strength were assessed via a transpedicular approach. The results were correlated to regional BMD and to biomechanical load testing after pedicle screw implementation.ResultsBoth methods generated a positive correlation to failure load of the respective vertebrae. The correlation of peak breakaway torque to failure load was r = 0.959 (P = 0.003), therewith distinctly higher than the correlation of indentation force to failure load, which was r = 0.690 (P = 0.040). In predicting regional BMD, measurement of peak torque also performed better than that of indentation force (r = 0.897 [P = 0.002] vs. r = 0.777 [P = 0.017]).ConclusionTranspedicular measurement of peak breakaway torque is technically feasible and predicts reliable local bone strength and implant failure for dorsal spinal instrumentations in this experimental setting.

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