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 pre-operatively via CT are maintained.
Objective—To compare biomechanical characteristics of vertebral segments after vertebral body plating or laminar stabilization following complete incision of the annulus fibrosus.
Sample—Vertebral segments from T13 through L3 obtained from 18 canine cadavers.
Procedures—A 4-point bending moment was applied in flexion and extension to the intact vertebral segments to determine a baseline range of motion (ROM) and neutral zone (NZ). Vertebral columns were then destabilized by creating a defect in the intervertebral disk via complete incision of the ventral aspect of the annulus fibrosus. The bending moment was applied again after stabilization was accomplished via vertebral body plating or with laminar stabilization (n = 9 vertebral segments/stabilization technique). The ROM and NZ were compared with their baseline values and among treatment groups. Finally, load-to-failure testing was performed in flexion.
Results—Mean relative ROM and NZ for segments treated with laminar stabilization were significantly lower than those for segments treated with vertebral plates.
Conclusions and Clinical Relevance—Analysis of in vitro results suggested that laminar stabilization of vertebral segments provided greater stiffness than did vertebral body plating.