Hercock CA, Pinchbeck G, Giejda A, Clegg PD, Innes JF. Musculoskeletal Research Group and Epidemiology Group, Faculty of Veterinary Science, University of Liverpool, Leahurst, Neston, Wirral. JSAP 2009 June 50 6 266-71 OBJECTIVE: To validate a disease-specific client-based clinical metrology instrument (questionnaire) for dogs with chronic osteoarthritis of the elbow joint. MATERIALS AND METHODS: This was a prospective cohort study involving 26 dogs with chronic osteoarthritis of the elbow with 24 associated clients. Validity (face and criterion), reliability and responsiveness of the metrology instrument (named "Liverpool Osteoarthritis in Dogs [elbow]") were tested in a sequence of studies. Face validity involved use of international peer review. Reliability was assessed using a test-retest scenario with a two week interval; peak vertical force as measured by a force platform was used as an external standard measure. Responsiveness was tested with a two week, single-blinded placebo-controlled intervention using a licensed non-steroidal anti-inflammatory drug. RESULTS: The reliability of Liverpool Osteoarthritis in Dogs (elbow) in the test-retest scenario was good; intraclass correlation coefficient is 0.89, 95 per cent confidence interval 0.75 to 0.95, compared with intraclass correlation coefficient 0.92, 95 per cent confidence interval 0.74 to 0.98, for peak vertical force. Responsiveness testing indicated that the "net" effect size (allowing for placebo effect) for Liverpool Osteoarthritis in Dogs (elbow) was 0.13 compared with (-)0.18 for the force platform. Criterion validity for Liverpool Osteoarthritis in Dogs (elbow) against peak vertical force was poor; Spearman's rank correlation is -0.24 (P=0.30). CLINICAL SIGNIFICANCE: Liverpool Osteoarthritis in Dogs (elbow) was considered reliable with satisfactory responsiveness. The poor criterion validity suggests a mismatch between force platform peak vertical force and client perceptions of lameness. This instrument requires further validation in larger studies with alternative client groups and alternative therapeutic interventions, but this initial validation suggests that Liverpool Osteoarthritis in Dogs (elbow) is worthy of continued investigation.