Various radiographic rating scales (RRSs) for use in horses with distal tarsal joint osteoarthritis (DTJ OA) have been described in the literature but little information is available on their reliability in use. The aim of the first experiment of the study was to develop a RRS based on the consensus of experts in equine diagnostic imaging and orthopaedics, and to test the RRS for reliability. For this purpose 17 experts were invited to participate in an iterative consultation process (Delphi) designed to develop an agreement on the importance of radiographic features, reported to be consistent with DTJ OA. This process was conducted by electronic questionnaire. Rradiographic features for which an agreement was found, were incorporated in the RRS, which used a visual analogue scale. To test the RRS's reliability nine equine surgeons from two academic institutions applied the RRS on two occasions, and a verbal descriptive rating scale, to three sets of tarsal radiographs, each comprising 4 standard radiographic views. Reliability was assessed using Bland-Altman plots and by calculating the 95% agreement limits. ANOVA was used to identify significant interactions between the ratings of different assessors made from different views and on each occasion. Of 17 invited experts nine participated and completed the consultation process. Seven radiographic features were identified and used in the RRS. Rating of DTJ OA was different for the nine equine surgeons (assessors). The most precise assessor's second ratings were between 16 mm higher and 18 mm lower than the 1st. Significant variables were: "joint", "assessor" and "assessment" (univariable ANOVA); and "joint and assessor" and "assessor and assessment" (multivariable ANOVA). Reliability of the verbal descriptive rating scale was higher than for the RRS. The RRS developed for radiographic interpretation of DTJ OA as a result of the Delphi consultation process was less reliable than the use of a verbal descriptive rating scale. The repeatability of the RRS was not affected by the assessors' professional experience. In conclusion the RRS would not be useful clinically. Osteoarthritis of the DTJ, affecting the distal intertarsal (DIT) and tarsometatarsal (TMT) joint, is a common cause of hindlimb lameness in horses. Management options include i.a. treatment of the affected joints but only anecdotal information is available on the outcome. The aim of the second experiment of this study was to document short and long term treatment outcome in horses receiving i.a. methylprednisolone acetate (MPA; Depo-MedroneV) or triamcinolone acetonide (TR; Adcortyl) with or without hyaluronic acid (HA; Hyonate) as treatment of DTJ OA.Cases were selected by searching medical records. Inclusion criteria included ? 50% improvement in lameness following i.a. analgesia of the DIT and/or TMT joint and i.a. treatment with TR (+/- HA) or MPA. Change in lameness grade between examinations was tested using a Wilcoxon signed rank test for each horse, and between horses, grouped according to radiographic severity of DTJ OA and treatment, using a Mann Whitney test. Significance was set at P<0.05. Long term outcome was assessed using an owner telephone questionnaire. A positive treatment outcome was no lameness with the horse able to perform as intended without NSAID administration. Horses treated once with i.a. MPA or TR (+/- HA) showed improvement in hindlimb lameness after a median of 56 days (P<0.000). No difference was found between the use of MPA and TR (P=0.81). In horses treated twice, no further improvement was seen after the first treatment (P=0.141). Lameness in horses with diffuse increased radiopharmaceutical uptake (IRU) of the DTJ identified at scintigraphy tended to improve, in contrast to horses with focal IRU (Pfocal = 0.1; Pdiffuse = 0.032). Radiographic severity of OA did not affect outcome. 13/34 horses (38.2%) had a positive and 21/34 (61.8%) a negative long term outcome. It was concluded that intra-articular corticosteroids can be effective in the management of DTJ OA in horses
