Morphological characterization of arthritic footpad. Shown are comparisons of the typical morphology of normal (n = 14) and arthritic (n = 34) footpads. (A) Photographs of typical normal and swollen arthritic footpads. The green rods serve as a reference for standardizing the magnification. The black lines on the green rods are 2-cm scale bars. (B) X-rays of a normal and a representative arthritic foot. In the latter, the image at right shows soft tissue swelling (arrow) and bone destruction at the ankle as well as loss of bone density and misalignment at the metatarsophalangeal joints (arrowhead). (C) Hematoxylin and eosin staining of normal and arthritic animal thin sections. In the latter, the image at right shows bone damage (arrows), cellular infiltrates and soft tissue swelling (arrowheads). Original magnification, ×40. (D) A necrotic focus (arrow) adjacent to a bony area within the arthritic joint. Original magnification, ×400.