Effect of X ‐Ray Beam Angle and Superimposition on Radiographic Evaluation of Kissing Spines Syndrome

Introduction K issing S pines S yndrome ( KSS ) represents a major challenge in equine practice. Radiographic examination of dorsal spinous processes ( DSP ) is therefore often included in sale and insurance cases and in diagnosis of back problems. Measurement of interspinous spaces ( ISS ) on radiographs is often used when evaluating DSPs . Radiographic examination of the equine back usually consists of two to four images causing beam angle differences between the image center and image borders. In addition, radiographs are 2D representations of 3D structures causing superimposition of anatomical structures. The aim of this study was to investigate if x‐ray beam angle and superimposition affect radiographic evaluation of ISSs . Methods Beam angle effect was investigated using latero‐lateral radiographs of the thoracic DSPs . Importance of superimposition of anatomical structures was investigated by comparing radiographic measurements with measurements in comparable CT and MR images. Cadaver backs from six horses were included. Four had a diagnosis of KSS , while two were considered normal. Backs were placed in an upright position on a flat surface for all images. Data were analysed using a linear mixed model with a single random factor, ISS . Significance was set at P<0.05. Results X ‐ray beam angle significantly influenced measurement of ISS (P<0.02) with differences of up to 2 mm, when measured three positions apart. ISS widths measured in radiographs were significantly lower than in comparable CT (P<0.0001) and MR (P<0.0001) images with differences of up to 3 mm. Conclusions These findings suggest that radiographic assessment may result in incorrect evaluation of ISSs. Ethical Animal Research Cadaver material was included in the study with signed consent from the horse owners. Sources of funding: Access to imaging facilities was kindly donated by the participating equine clinics and G entofte H ospital ( CT ). There was no additional funding. Competing interests: none.