Fig. 2. Mmp9^-/- mice exhibit an accumulation of cartilage during non-stable fracture healing. (A) SO-FG staining of wild-type (top, +/+) and Mmp9^-/- callus tissues (bottom, -/-) at 10, 14 and 21 days indicates that cartilage persists in the Mmp9^-/- callus up to 21 days. (B) Histomorphometric measurements of total callus and cartilage volumes in wild-type (n=12) and Mmp9^-/- (n=17) mice at 10 and 14 days. There is a statistically significant increase in the volume of cartilage in Mmp9^-/- calluses compared with wild-type calluses at 14 days (asterisks, Student's t-test, P=0.02). Bars represent mean±s.e.m. Scale bar: 1 mm.