2015 ACVIM Forum Research Abstract Program

Dogs affected by AA subluxation do not have a higher incidence of Chiari-like malformation, syringohydromyelia, or hydrocephalus than control dogs, and their neurologic grade is not associated with MRI findings. However, lack of a dens and/or odontoid ligaments are associated with larger subluxations. The main objectives of this study were 1-to propose an objective method for the determination of ideal implant placement in the atlantoaxial joint, 2-to develop a mathematical model allowing calculation of implants 3D position and 3-to assess the validity of the mathematical model. Current literature on atlantoaxial anatomy and ventral atlantoaxial stabilization techniques was reviewed to identify safe bone corridors. Each bone corridor was geometrically simplified and ideal implant placements defined as axes centered within the simplified corridor. CT images of the craniocervical junction were obtained in 27 dogs and each previously defined ideal implant was positioned using OsiriX. For each implant an insertion point, an exit point and 4 safety margin points were localized. Mathematical equations calculating 2 projected angles (ProjA) and 4 safety angles (SafA) from those point coordinates were determined. A sample of 12 simulated implants was randomly selected and each angle was mathematically calculated and compared to direct measurements obtained with OsiriX measurement tools (2 observers x 2 repeats). 9 bone corridors and 13 ideal implant placements could be objectively defined. OsiriX could be used successfully to simulate the ideal implant positions in all cases. There was excellent agreement between the calculated and measured values for both ProjA (q c =0.9992) and SafA (q c =0.9997). Absolute differences between calculated and measured values were respectively [Pro-jA=0.44 AE 0.53°; SafA=0.27 AE 0.25°] and [ProjA=0.26 AE 0.21°; SafA=0.18 AE 0.18°], for each observer.