Interobserver agreement of lateral and oblique radiography and standing cone beam CT of the caudal cervical articular process joints of horses.

Caudal cervical articular process joint osteoarthritis (CAPJ OA) leads to career-altering clinical signs in the horse. Oblique radiographs and standing cone beam computed tomography (CBCT) facilitate the assessment of this area, however, the variability of interpretation of these images is currently unknown. This retrospective, secondary analysis, methods comparison study investigated interobserver agreement between clinicians and modality in grades of CAPJ OA on lateral and oblique radiographs and CBCT. We hypothesized that agreement between clinicians' grades of CAPJ OA would be lowest for oblique radiographs and highest for CBCT, and agreement between grades of CAPJ OA would be low for all pairs of modalities. Horses underwent lateral and oblique radiography and CBCT of the CAPJs of C5-C6 and C6-C7. Radiographs and CBCT images were graded retrospectively by four blinded clinicians using 3-point scales. Cohen's kappa analysis was used to evaluate interobserver agreement between grades of CAPJ OA, and agreement between grades of CAPJ OA between different modalities was explored using kappa-weighted analysis. Agreement between clinicians' grades of CAPJ OA was moderate for lateral radiographs (0.49), and fair for oblique radiographs (0.23) and CBCT (0.36). For all modalities, agreement was slight to fair between clinicians for CAPJs with grade 1 (normal, 0.21-0.32) or 2 (mild, 0.13-0.36) CAPJ OA, and moderate to substantial for grade 3 (moderate to severe, 0.45-0.77) CAPJ OA. Agreement between grades of CAPJ OA was fair for all pairs of modalities. This study provides important information regarding the inconsistency of interpretation of mild CAPJ OA on radiographs and CBCT amongst clinicians.