Differentiation Between Transitional Segments and Other Common Alterations at the Lumbosacral Junction and/or at the Sacroiliac Joint in Ventrodorsal Radiographs of the Canine Pelvis
Ventrodorsal (VD) radiographs of the pelvis are the views most commonly used for the evaluation of the canine hip joints. Thereby, lumbosacral transitional segments are commonly recorded as incidental findings. Thus, it has also been reported that transitional segments may easily be overlooked in VD radiographs, especially if the osseous changes are only minimal and symmetric. An understanding of the variability of the radiographic appearance of transitional vertebrae is important for the interpretation of radiographs of the pelvis. Some changes may also be difficult to differentiate from degenerative alterations. Above all, any statistical analyses on the clinical significance of transitional vertebrae requires reliable diagnosis of all types of transitional vertebrae. Therefore, the aim of this study was to present radiographs and anatomical specimens of variations of lumbosacral transitional vertebrae, and to present some particular cases of degenerative diseases at the lumbosacral junction and sacroiliac joints which may simulate the presence of transitional vertebral anomalies. Additionally, the effect of different positioning of the pelvis on the radiographic appearance of transitional vertebrae will be addressed.
A sample of 145 radiographs of the pelvis, obtained from the Clinic of Radiology, University of Veterinary Medicine Vienna, was assessed for evidence of lumbosacral transitional vertebrae, calcification of the dorsal and/or ventral sacroiliac ligaments, ankylosis capsularis ossea at the sacroiliac joints, and osteophyte formation at the lumbosacral junction. The radiographs were attributed to those 3 breeds most frequently represented (i.e., Rottweiler, Golden Retriever, German Shepherd Dog). Complete lumbarization or sacralization and differentiation between lumbarization and sacralization were not provided because the total number of vertebrae remained unknown. To assist in radiographic examination and to test the reliability of radiographic interpretation, a sample of 800 mazerated canine spines was assessed to find specimens, which best possible correlated with the conditions seen in the radiographic study. Plain ventrodorsal radiographs (central and angled views) were taken from the mazerated pelvis and sacral bone specimens. In advance, bony alterations were selectively marked with a 1:1 mixture of latex (KiwoplastTM; Kurt Wolf & CO) and BaSO4 (MicropaqueTM; Guerbet).
Those alterations closely resembling the radiographic appearance of transitional vertebrae were identified to be (1) calcification of the dorsal and ventral sacroiliac ligaments (= pseudolumbarisation), which might be interpreted as costal process at S1 (or the corresponding vertebra in cases of numerical vertebral variations) and (2) osteophyte formation at the lumbosacral junction simulating excorporation of the cranial articular processes from the assembly of the sacral wing as seen in transitional vertebrae. Ankylosis capsularis ossea at the sacroiliac joint may not cause radiographic misinterpretation of transitional vertebrae, unless positioning of the sacrum is taken into account. New bone formation is visualized halfway between the cranial and caudal outlines of the wing of the ilium if either ankylosis capsularis ossea is depicted in a central view of the sacrum or costal processes are depicted in an angled view of the sacrum.
Lumbosacral transitional vertebrae radiographically may be detected by assessing the outline of the cranial margin of the wings of the sacrum, the shape of the transverse processes of the last lumbar vertebra, separation of the spinous process of the transitional vertebra from the assembly of the sacrum, presence of an intervertebral disc space between transitional vertebra and caudal adjoining vertebra, and excorporation of the cranial articular processes of the transitional vertebra from the assembly of the sacral wing. The radiographic appearance of the costal processes is especially difficult and depends on the positioning of the sacrum (angled or central sacral view). Therefore, other characteristics like separation of the spinous process of S1 and excorporation of the cranial articular processes of S1 from the assembly of the sacral wing should be assessed to assist in identification of a transitional segment. However, the later condition must clearly be differentiated from lumbosacral osteophyte formation.