The aim of this study was to compare diagnostic techniques for the assessment of cartilage damage in the carpal and fetlock joints in horses with arthritis. The techniques compared were synovial fluid analysis, as well as radiographic, thermographic, ultrasonographic, and arthroscopic examinations. Sixteen horses of both sexes with arthritis, weighing 438 ± 51 kg and at different ages were used as material Before a detailed examination, an evaluation of the conformation and symmetry of the musculoskeletal system was performed. Nerve blocks definitively localized lameness to a specific site. Thermographic, radiographic, ultrasonographic, and arthroscopic examinations were performed after routine clinical examination. Synovial fluid and sera were collected for further analysis. In conclusion, although all examination techniques may yield useful information, their severe limitations were revealed, particularly in the detection of early articular cartilage damage. Arthroscopy is more reliable than other methods in cases of joint capsule lesions and intra-capsular lesions, as well as cartilage and synovial hyperplasia. Arthroscopy is considered to be advantageous and necessary.