Accuracy of Conventional Radiography and Computed Tomography in Predicting Implant Position in Relation to the Vertebral Canal in Dogs

Abstract

Vertebral column stabilization is performed for dogs suffering from instability secondary to trauma, neoplasia, caudal cervical spondylomyelopathy, infection and other. A common stabilizing technique involves bicortical placement of positive profile end-threaded Steinman pins into the vertebral body and pedicles. Bicortical placement of these pins carries a high risk for iatrogenic trauma of important neurovascular structures. A clinical frustration has been the difficulty determining exact implant position based on postoperative conventional spinal survey radiographs. Implant position within the vertebral column may be better determined using a different imaging modality such as computed tomography as this would allow for evaluation of tissues in different anatomic planes. The goal of this study was to compare the accuracy of radiography and computed tomography in predicting implant position in relation to the vertebral canal in the cervical and thoracolumbar vertebral column in an in vitro imaging and anatomic study. Twelve medium-sized canine cadaver vertebral columns were utilized for this study. Steinman pins were placed into cervical and thoracolumbar vertebrae based on established landmarks but without predetermination of vertebral canal violation. Radiographs and CT exams were obtained and evaluated by 6 individuals. A random subset of pins was evaluated for ability to distinguish left from right pins on radiographs. The ability of the examiner to correctly identify vertebral canal penetration for all pins was assessed both on radiographs and CT. Spines were then anatomically prepared and visual examination of pin penetration into the canal served as the gold standard. Results revealed a left/right accuracy of 93.1%. Overall sensitivity of radiographs and CT to detect vertebral canal penetration by an implant were significantly different and estimated as 50.7% and 93.4%, respectively (P < 0.0001). Sensitivity was significantly higher for complete vs. partial penetration and for radiologists vs. non-radiologists for both imaging modalities. Overall specificity of radiographs and CT to detect vertebral canal penetration was 82.9% and 86.4%, respectively (P = 0.049). In conclusion, CT was superior to radiographic assessment and is the recommended imaging modality to assess penetration into the vertebral canal. The clinical relevance of this finding is that CT is significantly more accurate in identifying vertebral canal violation by Steinman pins and should be performed postoperatively to assess implant position