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

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.