A total of 119 patients were included in a randomized, double-blind, placebo-controlled trial in order to assess the S/DMOAD properties in OA of chondroitin sulfate (CS 4&6, 3 x 400 mg/day, Condrosulf IBSA, Lugano, CH). Posteranterior roentgenographies of the interphalangeal (IP) joints were carried out at the start of the study and at yearly intervals. This enabled the investigators to document the radiological progression of the anatomical lesions in the pathological finger joints over a 3-year period. It was shown that the progression of OA in the IP finger joints in an individual can be determined by the evolution of his finger joints through previously described anatomical phases: 'N' (not affected), 'S' (classical OA), 'J' (loss of joint space), 'E' (erosive OA) and 'R' (remodeled joint). Structure/disease-modifying anti-OA drug (S/DMOAD) properties were searched for by assaying the number of patients developing OA in previously normal IP joints ('N' > 'S'), or progressing through the described anatomical phases of the disease ('S' > 'J', 'S' > 'E', 'J' > 'E', 'S' > 'R', 'J' > 'R', 'E' > 'R'). In the CS 4&6 group we observed a significant decrease in the number of patients with new 'erosive' OA finger joints. This result is particularly important since OA of the finger joints becomes a clinical problem (pain, functional loss) when 'S' joints progress to 'J' and especially 'E' phases. During and after these 'E' phases, joints will remodel and show the nodular deformities characteristic of Heberden's and Bouchard's nodes. Treated patients were protected against erosive evolution.