Computed tomography evaluation of proposed implant corridors in canine thoracic vertebrae.

OBJECTIVE: Identify acceptable implant corridors in the normal canine thoracic vertebrae (T) from T1 to T9. STUDY DESIGN: Retrospective study. SAMPLE POPULATION: Computed tomographic (CT) studies of normal canine thoracic spines (n = 39). METHODS: CT imaging studies of normal T1-T9 canine spines were evaluated by five independent observers. Each identified a proposed corridor, measured the width, length, and angle off mid-sagittal that the corridor occupied. RESULTS: CT studies were from 39 dogs weighing 3.19-60 kg (mean 10.72, SD 9.9 kg). Vertebral corridors ranged in average width from 3.8 to 5.2 mm, the widest being located at T1. They ranged in average length from 13.3 to 17.5 mm, shortest being T1 and longest being T6. The angle of corridors varied the most between individual vertebrae at T1-T3. The average corridor angles were: T1 = 38°, T2 = 32°, T3 = 27°, T4 = 26°. T5-T9 angle ranged from 23° to 24°. CONCLUSION: The average dimensions of corridors measured in dogs weighing 3.1-60 kg were consistent with those of commercially available cortical screws and pins. CLINICAL SIGNIFICANCE: Corridor trajectories identified in this population can be achieved from a dorsal approach between T5 and T9. A dorsal approach for implant placement would be challenging for T1-T4 due to the variability found in these vertebrae as well as regional anatomical constraints.

Radiation exposure associated with percutaneous fluoroscopically guided lag screw fixation for sacroiliac luxation in dogs.

OBJECTIVE: To determine radiation exposure to surgical personnel and to evaluate the accuracy of a modified percutaneous lag screw fixation technique for sacroiliac luxation (SIL) under fluoroscopic guidance in dogs. STUDY DESIGN: Cadaveric experimental study. SAMPLE POPULATION: Seventeen beagle cadavers with iatrogenic SIL. METHODS: Seventeen beagles with iatrogenic SIL underwent reduction and stabilization with 3.5-mm screws. Hypodermic needles (14 gauge) and fluoroscopy were used to orient two Kirschner wires for temporary stabilization and to guide drilling of glide and pilot holes using cannulated drill bits. Duration of surgery and radiation exposure were recorded. Postoperative computed tomographic evaluation of screw position and angulation was performed. RESULTS: Average time for fixation was 15.85 minutes (range, 6.37-33.5). Cumulative radiation doses of 0.4 mrem for the dominant arm of the assistant and 0 mrem for the primary surgeon were recorded. The mean dorsoventral and craniocaudal screw angles were 0.68° ± 3.4° (range - 5.4° to 9.5°) and 1.9° ± 3.2° (range - 4.3° to 9.1°), respectively. Sixteen of the 17 dogs had 100% sacral screw purchase, with the remaining case achieving 93.4% purchase. CONCLUSION: Fluoroscopy-assisted percutaneous placement of 3.5-mm cortical screws in lag fashion performed with 14-gauge needles in conjunction with Kirschner wires and cannulated drill bits yielded repeatable accurate screw placement with low levels of ionizing radiation exposure to the surgical team. CLINICAL SIGNIFICANCE: The described technique may be a viable method for minimally invasive osteosynthesis fixation of SIL with low levels of radiation exposure to the surgical team. These results provide evidence to support further evaluation of radiation exposure in clinical cases and can aid in study design and sample size determination.