IDENTIFICATION OF SAFE ANATOMICAL CORRIDORS ON THE LATERAL FACE OF THE VERTEBRAL BODIES OF THE THORACIC AND LUMBAR SPINE IN DOGS. PRELIMINARY ASSESSMENT OF SURGICAL STABILIZATION OF THE SPINE AS A RESULT OF TRAUMA.

Objective: 1) Identifying repere (safety corridors) for implants (screws/pins) application; 2) evaluation of the ideal tilt angle, of reliability of choosen repere by ex vivo drilling test; 3) evaluation of differences between vertebrae over thoraco‐lumbar spine. Study Design: Computed tomography and ex‐vivo prospective studies. Materials and Methods: Phase I: CT images of spine of 20 dogs of different breeds were used to define lateral safe corridors in cross section plane. The angle allowing the highest amount of bone purchase with safe margins for bicortical implants was defined as the optimal corridor. Width and height of the vertebral body, optimum (α), maximum (β) and minimum (γ) safe angles were measured at the ideal insertion point. Phase II: 10 canine bodies belonging to different breeds were included. Standard surgical access and drilling, without introducing implants, were performed. The last 8 thoracic vertebrae and the whole lumbar spine were tested. Tests were performed by the same surgeon, over a 3 months period. All specimens were subject to CT to compare obtained tilt angles with ideal ones. To compare measurements performed on vertebrae of different shape and size, the absolute values were transformed in ratios. Continuous data were compared by a van der Waerden Analysis of Variance; post hoc differences were explored with Tukey’s HSD. Results: Insertion points were the vertebro‐costal joint and the base of transverse process for thoracic and lumbar vertebrae, respectively. Optimum angle (α) was 90°. All three angles resulted significantly wider for almost all vertebrae compared to L7. The ratio between the safety margin and the vertebral height showed a significantly reduction in the last three lumbar vertebrae. Discussion: In vitro biomechanical studies on canine vertebrae demonstrated that an implant as near 90° to the longitudinal axis as possible increases the holding strength; such angle reduce risks of damaging of important anatomical structures1. Results of this study pointed out a progressive reduction, over a cranio‐caudal direction, of the security margin; particularly, last two lumbar vertebrae showed a remarkable reduction of such margin, a characteristic that influence β and γ angles amplitude. Conclusions: Lateral corridors used offer a good security margin and a good anchoring of synthesis means over the canine spine explored. Lateral approach allow easy screw orientation and a good visualization for bi‐cortical anchoring.