Inter- and intra-observer agreement for grading radiographs of thoracolumbar spinous processes in healthy horses during a pre-purchase examination

Background: There is wide variability in radiographic grading systems in thoracolumbar spinous processes in horses. The aim of this study was to determine the agreement of grading different parameters, and combinations of those, in radiographs of the spinous processes of the equine thoracolumbar spine in the scope of a pre-purchase examination. We hypothesized that agreement is variable and interpretation of these radiographs is difficult. Methods: Radiographs of the thoracolumbar spine of healthy horses (N= 100) were assessed by three observers. Spinous processes were separately graded for interspinous space width, modelling, radiopacities, radiolucencies and isolated opacities dorsally. Inter- and intra-observer agreement was assessed for individual and combinations of parameters. Results: Agreement (inter- and intra-observer) was good for the following parameters: interspinous space width, isolated opacities dorsally, beak-shaped formations craniodorsally and modelling cranioventrally. The agreement increased slightly for a sum of specific parameters such as radiopacities, modelling, dorsal abnormalities and related abnormalities involving increased opacity, modelling and osseous cyst-like lesions. Agreement for the total radiographic abnormalities per back was moderate. Conclusions: Grading of thoracolumbar radiographs in horses without back pain showed good inter- and intra-observer agreement for specific parameters and these should be used in future grading of spinous processes. Limitations should be considered in pre-purchase examinations.