Accuracy of Radiographic Detection of the Cranial Margin of the Dorsal Lamina of the Canine Sacrum

Abstract

An elongated sacral lamina has been described as one of the contributing factors for dogs with cauda equina syndrome due to degenerative lumbosacral stenosis (DLSS); however, published evidence is lacking on the accuracy of radiographic screening for the presence of this lesion. Objectives of this prospective, cross-sectional cadaver study were to describe the accuracy and repeatability of detection of the cranial sacral lamina margin on plain lateral radiographs of the lumbosacral junction in dogs. Twenty-five medium and large breed canine cadavers were radiographed before and after placement of a radiopaque hook in the cranial margin of the sacral lamina. Three independent evaluators placed digital markers at the perceived margin on preinterventional radiographs. The distance from perceived location to the true location on postinterventional radiographs was recorded for each dog and observer. A discordance threshold (distance between perceived and actual margin) of 1.5 mm was subjectively defined as clinically relevant. The three evaluators demonstrated good repeatability, although the accuracy for margin detection was only fair (mean discordance 1.7 mm). Evaluators demonstrated greater accuracy in identifying the landmark in juveniles (1.4 mm) vs. adults (1.8 mm; P < 0.01). Results of this study indicated that observer repeatability is good and accuracy is fair for correctly identifying the radiographic cranial margin of the sacral lamina in dogs. This should be taken into consideration when interpreting elongation of the sacral lamina in radiographs of dogs with suspected DLSS, especially adults.

Evaluation of the rostral projection of the sacral lamina as a component of degenerative lumbosacral stenosis in German shepherd dogs

“…Despite reaching statistical significance, the difference in X between the affected and unaffected groups was only in the order of 3 mm. Because the mean discordance found by Blume et al was 1.7 mm, there was a significant overlap in the X dimension between the affected and unaffected groups. However, it must be noted that observer accuracy improved with consensus and experience, so radiologists trained in using postinterventional radiographs in comparison with their prior perception of laminal position would be a precluding factor for this use of radiographs.…”

“…In this retrospective study, the position of the rostral edge of the sacral lamina projected toward the cranial sacral end plate reference line to a lesser extent in GSD thought to be affected by DLSS in comparison to their unaffected counterparts, a finding that was opposite to what we had hypothesized. The descriptions by Wright suggested that rostral projection of the sacral lamina could be a contributing factor to CES due to telescoping of the sacral lamina into the LS vertebral canal and foramina, decreasing the interarcuate space during flexion and extension, resulting in a greater degree of nerve root compression . Telescoping describes a loss of disc spacing and a rotation of the sacral lamina during extension such that the sacral lamina and articular process narrow the IVF.…”

“…This allowed us to validate the positioning technique used in this study. A potential source of observer error in this study was introduced through having a relatively inexperienced clinician (HS) perform all of the measurements because localization of the sacral lamina improves with experience and consensus . To minimize this error, a supervised training program with several random cross‐checks with a more experienced observer (AW) was performed.…”

“…The descriptions by Wright 10 suggested that rostral projection of the sacral lamina could be a contributing factor to CES due to telescoping of the sacral lamina into the LS vertebral canal and foramina, decreasing the interarcuate space during flexion and extension, resulting in a greater degree of nerve root compression. 11,19,20 Telescoping describes a loss of disc spacing and a rotation of the sacral lamina during extension such that the sacral lamina and articular process narrow the IVF. An anatomical variant, a more rostrally projecting sacral lamina in GSD, would exacerbate sacral telescoping and could predispose a dog to CES in combination with L7/S1 intervertebral disc degeneration, LS step formations, TVA, or SO.…”

“…3,4,17,18 However, the lack of widespread accessibility of advanced imaging and higher associated costs may preclude their use as a screening modality for a breeding program. Blume et al 19 investigated the accuracy of radiographic determination of the extent of rostral projection of the sacral lamina. Observed sacral lamina position was compared with actual position by using cadavers.…”