Fig. 3. Histological examination of the Mmp13^–/– trabecular bone defect. (A,B) Picrosirius Red stained tibia from 1-week-old mice show no apparent increase in trabecular bone (TB) in Mmp13^–/– mice compared with wild type, but the bone spicules in Mmp13^–/– mice are irregular in shape (indicated by arrow). At 3 weeks of age, Mmp13^–/– mice show increased trabecular bone (C,D). Unlike the increase of hypertrophic cartilage (HC), which resolves at 5 weeks of age, the increase in trabecular bone in Mmp13^–/– mice persists for months (E,F). Similar increases in trabecular bone can also be observed in femurs (G,H). Histological observations were confirmed by Micro-CT analyses on tibia of 16-week-old wild-type and Mmp13^–/– mice (I,J). SO, secondary site of ossification. Scale bars: 200 µm in A,B; 300 µm in C,D; 400 µm in E-H; 1 mm in I,J.