Distribution of osteoclasts and osteoblasts within local bone erosions. Paraffin-embedded sections of hindpaws of mice transgenic for human tumor necrosis factor were simultaneously stained for (a, c) osteoclasts and (b, d) osteoblasts. The distribution and density of osteoclasts and osteoblasts were assessed in three different compartments within bone erosions: the surface adjacent to the articular cartilage (subchondral surface), the inner frontier of erosion (inner surface), and the surface adjacent to cortical bone (cortical surface). The size of local bone erosions was correlated to the numbers of (e) osteoclasts and (f) osteoblasts within these lesions. Spearman's correlation coefficients are given. The numbers of osteoclasts correlated positively (r = 0.82, P < 0.0001) with the area of bone erosion, whereas the numbers of osteoblasts correlated negatively (r = -0.38, P < 0.05).