Evaluation of traditional and novel radiographic vertebral ratios in Great Danes with versus without cervical spondylomyelopathy

Abstract

Great Danes are predisposed to osseous-associated cervical spondylomyelopathy (Wobbler syndrome). The first aim of this prospective study was to compare values measured using previously published intravertebral and intervertebral ratio methods and a novel ventrodorsal ratio method in radiographs of clinically normal and affected Great Danes. The second aim was to determine whether these ratios could be used as predictors of sites of spinal cord compression based on magnetic resonance imaging (MRI). Thirty dogs (15 normal, 15 affected) were prospectively enrolled. Lateral and ventrodorsal radiographs were obtained and six measurements were recorded from C3-T1. For each vertebral location, intravertebral ratios and intervertebral ratios were calculated from lateral views, and the ratio of the distance between the articular process joints vs. vertebral body width (novel ventrodorsal ratio) was calculated from ventrodorsal views. Values for these three ratios were compared, by vertebral location and dog group. Intravertebral and intervertebral ratios did not differ between dog groups. The ventrodorsal ratio was significantly smaller in affected Great Danes at C5-6 (P = 0.005) and C6-7 (P < 0.001). The ventrodorsal ratio was significantly associated with MRI presence of spinal cord compression. For each 0.1 unit increase in this ratio value, there was a 65% decrease in the odds of spinal cord compression being present at that site, independent of vertebral location (P = 0.002). Findings from this study supported use of the novel ventrodorsal ratio as an initial radiographic screening method for Great Danes with suspected cervical spondylomyelopathy.

Keywords: cervical spine; dog; radiography; vertebra; wobbler syndrome.

FIG. 1

Locations of traditional radiographic measurements obtained in lateral views. (A) Vertebral body height, (B) minimum intravertebral sagittal diameter, (C and D) locations for the intervertebral measurements for determination of the minimum intervertebral sagittal diameter. (Reprinted with permission from da Costa and Johnson []).

FIG. 2

Locations of radiographic measurements obtained in the ventrodorsal views and used for calculation of the novel ventrodorsal ratio. (A) Distance between articular process joints, (B) vertebral body width, and (C) vertebral body length.

FIG. 3

Dot plot demonstrating the estimated probability of spinal cord compression based on a novel ventrodorsal ratio. Probability estimated from a random-effects logistic regression model.