Angle of insertion and confirmation of angles measured after in vitro implantation during laminar vertebral stabilization in vertebral columns obtained from canine cadavers

Abstract

Objective-To determine angles of insertion for laminar vertebral fixation of L1 and L2 by use of a locking plate in dogs and to confirm screw placement by use of computed tomography (CT). Sample-Vertebral specimens harvested from 8 canine cadavers. Procedures-The point of insertion and minimum and maximum insertion angles for laminar and facet screws for laminar vertebral stabilization were determined by use of CT. A precontoured locking plate was then placed by use of 1 locking screw in the lamina of each lumbar vertebra and 1 nonlocking screw in the facet joint. The position and angle of the screws were examined by use of CT, and penetration into the vertebral canal was recorded. Results-Mean ± SD insertion angles for L1 and L2 were 18 ± 4° and 21 ± 5° toward the vertebral canal and 11 ± 4.4° and 10 ± 3° in a dorsal direction, respectively. Insertion angles for the facet joint were between 24 ± 4° ventrally and 12 ± 2° dorsally. Insertion of the screw did not penetrate the vertebral canal for 23 of 24 (96%) screws. For 23 of 24 inserted screws, the previously determined angle was maintained and purchase of bone and cortices was satisfactory. Conclusions and Clinical Relevance-Placement of laminar and facet screws in canine vertebrae was possible and can be performed safely if angles of insertion determined preoperatively via CT are maintained. (Am J Vet Res 2011;72:1674-1680).