Repeatability and Intra‐ and Inter‐observer Agreement of Cervical Vertebral Sagittal Diameter Ratios in Horses with Neurological Disease

BACKGROUND Sagittal ratio values (SRVs) of cervical vertebrae are used for ante-mortem diagnosis of cervical vertebral stenotic myelopathy, but intraobserver and interobserver variability in measurement may influence radiographic interpretation of vertebral stenosis in horses with neurological disease. OBJECTIVES To determine intraobserver repeatability in SRVs, intra- and interobserver agreement in SRVs and whether or not agreement was influenced by animal age. ANIMALS Forty-two horses (>1 year old) with neurological disease from which laterolateral computed radiographic images of C2-C7 were obtained. METHODS Four observers made measurements from C2 to C7 for each horse and interobserver agreement for intra- and intervertebral SRVs was determined using Bland-Altman analysis (acceptable agreement: limits of agreement [LOA] ≤ 0.05) on all horses and those ≤3 (n = 25) and >3 (n = 17) years old. Each observer also made repeated measurements for 10 horses and intraobserver repeatability and agreement were determined. RESULTS Adequate intraobserver repeatability was achieved for 6 sites. Within observers, paired measurements had a median difference ≤5.7%, but a large range in differences often occurred, most frequently at intervertebral sites. For C5, C6, C7, and C3-4, LOA ≤ 0.05 were achieved by at least 1 observer. With the exception of C5 for 1 pair, LOA were >0.05 for interobserver agreement, regardless of animal age. LOA were largest at intervertebral sites. CONCLUSIONS AND CLINICAL IMPORTANCE Within and between observers, measurement error may limit the diagnostic accuracy of SRVs and result in discrepancies of diagnosis and treatment and warrants consideration when used clinically in horses with neurological disease.