Cartilage damage was introduced by interleukin-1 (IL-1) injection, and 2 days later transforming growth factor-β (TGF-β) was injected intra-articularly combined with Ad-luciferase or Ad-Smad7. Two weeks after adenoviral transfection, knee joints were isolated for assessment of fibrosis. (a) Synovial thickness had increased significantly (p < 0.005) after exposure to TGF-β. The TGF-β-induced increase was reduced by simultaneous overexpression of Smad7 (p < 0.05). (b) The number of procollagen type I-expressing cells had increased after TGF-β exposures accordingly (p < 0.0005). This was also partially blocked by Smad7 (p < 0.005). Error bars display standard error.