title: DensiProbe Spine: a novel instrument for intraoperative measurement of bone density in transpedicular screw fixation.
abstract: METHODS
  Cadaver study.
  
  
  OBJECTIVE
  To determine bone strength in vertebrae by measuring peak breakaway torque or indentation force using custom-made pedicle probes.
  
  
  BACKGROUND
  Screw 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.
  
  
  METHODS
  Ten 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.
  
  
  RESULTS
  Both 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]).
  
  
  CONCLUSIONS
  Transpedicular 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.
authors.affiliation: 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.
authors.forename: Stephan
authors.initials: S
authors.lastname: Deckelmann
authors.forename: Ronald
authors.initials: R
authors.lastname: Schwyn
authors.forename: Bas
authors.initials: B
authors.lastname: Van der Pol
authors.forename: Markus
authors.initials: M
authors.lastname: Windolf
authors.forename: Paul F
authors.initials: PF
authors.lastname: Heini
authors.forename: Lorin M
authors.initials: LM
authors.lastname: Benneker
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D002102:Cadaver; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery; D008297:Male; D016343:Monitoring, Intraoperative / Q000295:instrumentation* / Q000379:methods; D019637:Orthopedic Procedures / Q000295:instrumentation* / Q000379:methods; D065289:Pedicle Screws; D019415:Torque; D016474:Weight-Bearing