title: Forces in spinal cannulation and breaches ex vivo.
abstract: BACKGROUND
  Pedicle screw insertion, to stabilize or correct the spine, relies on creating a probe path with the correct trajectory to prevent unsafe breaching of the cortical wall. Safe pedicle cannulation is aided when the surgeon can feel the difference between a safe and unsafe path. Pedicle probe forces and torques are currently unknown. The purpose of this study was to investigate the forces and torques encountered while cannulating the pedicle tract in both correct and incorrect cannulations.
  
  
  METHODS
  Two experienced surgeons used a standard lumbar probe modified to incorporate a 6 degree-of-freedom load cell to cannulate and breach the T12 to S1 vertebrae of six fresh frozen cadavers (3 males, 3 females, ages 65 to 92). A total of 76 pedicles were tested.
  
  
  RESULTS
  Cannulation axial forces averaged 48 N (standard deviation = 13 N), medial breach 129 N (standard deviation = 25 N), and lateral breach 86 N (standard deviation = 27 N). Cannulation values were significantly lower than the breach values in all 6 degrees of freedom (p < 0.001). There were significant differences between specimens, including males and females, and between degrees of freedom, but no significant right and left differences or by vertebral level.
  
  
  CONCLUSIONS
  A large range of cannulation and breach forces and torques were measured due to variations in bone quality and geometry, as experienced clinically. This is the first time that the absolute and relative force and torque levels have been reported, to our knowledge.
authors.affiliation: Biomedical Engineering, University of Calgary, Calgary, AB, Canada McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada.
authors.forename: Aubrey
authors.initials: A
authors.lastname: Blair-Pattison
authors.affiliation: McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada Department of Surgery, University of Calgary, Calgary, AB, Canada.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Hu
authors.affiliation: McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada Department of Surgery, University of Calgary, Calgary, AB, Canada.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Swamy
authors.affiliation: Biomedical Engineering, University of Calgary, Calgary, AB, Canada McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada Department of Civil Engineering, University of Calgary, Calgary, AB, Canada carolyn.anglin@gmail.com.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Anglin
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D002102:Cadaver; D002404:Catheterization / Q000295:instrumentation* / Q000379:methods; D005260:Female; D017276:Friction; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D008297:Male; D019919:Prosthesis Implantation / Q000295:instrumentation* / Q000379:methods; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical
keywords: Spine; education; forces; pedicle; scoliosis; spine fusion; training