Canine joints were fixed in formalin, loaded in various positions and (while still loaded) embedded in castolite. The blocks containing the embedded joints were then sawed into three-millimeter slabs, the lengths of the congruent and total joint surfaces were measured on the slabs, and congruence ratios were calculated by dividing the average length of the congruent surface by the average length of the total articular surface. The ankle with the thinnest articular cartilage had the highest ratio, while the knee with the thickest cartilage had a ratio that was lowest with the menisci assumed not to be load-bearing and highest with the menisci considered to be load-bearing. Positional changes had little effect on the ratio, which correlated with cartilage thickness in an inverse, straight-line fashion.