The effect of lengthening the tibia, by callotasis on the articular cartilage in the knee, was investigated histologically in 18 rabbits. The distraction rate was 1 mm per day. On the right tibia, the distraction frequency was in 2 steps (0.5mm/12 hours), while on the left it was in 120 steps (0.0083 mm/12 minutes). The 18 animals were divided into 3 subgroups based on length gain. Cartilage and subchondral bone samples were examined by light and fluorescent microscopy. The incidence of cartilage degeneration on the 2-step side was 2/5, 5/6, and 6/7 at 10, 20, and 30 percent length increases. On the 120-step side it was 0/5, 1/6, and 1/7 at the same length increases. The intensity of tetracycline fluorescence of the subchondral plate on the 2-step side was higher than that on the 120-step side, showing 1.7, 2.0, and 2.3-fold increases at 10, 20, and 30 percent length increases. Our study suggests that increasing the frequency of distraction in callotasis can help to prevent damage to articular cartilage in adjacent joints.