Biomechanical evaluation of two dorsal and two ventral stabilization techniques for atlantoaxial joint instability in toy-breed dogs

Abstract

To compare the biomechanical properties of atlantoaxial joints (AAJs) in canine vertebral column specimens stabilized with 4 techniques (dorsal wire, modified dorsal clamp, ventral transarticular pin, and augmented ventral transarticular pin fixation) after transection of the AAJ ligaments. 13 skull and cranial vertebral column segments from 13 cadaveric toy-breed dogs. Vertebral column segments from the middle aspect of the skull to C5 were harvested and prepared; AAJ ligament and joint capsule integrity was preserved. The atlantooccipital joint and C2 to C5 vertebral column segments were fixed with 2 transarticular Kirschner wires each. The occipital bone and caudalmost aspect of each specimen were embedded in polymethylmethacrylate. Range of motion of the AAJ under shear loading conditions up to 15 N was determined for each specimen during the third of 3 loading cycles with intact ligaments, after ligament transection, and after stabilization with each technique in random order. For each specimen, a load-to-failure test was performed with the fixation type tested last. All stabilization techniques except for dorsal clamp fixation were associated with significantly decreased AAJ range of motion, compared with results when ligaments were intact or transected. The AAJs with dorsal wire, ventral transarticular pin, and augmented ventral transarticular pin fixations had similar biomechanical properties. Dorsal wire, ventral transarticular pin, and augmented ventral transarticular pin fixation increased rigidity, compared with results for AAJs with intact ligaments and for AAJs with experimentally created instability. Additional studies are needed to assess long-term stability of AAJs stabilized with these techniques.