The histological features of the iliac cartilage growth plates in patients with Risser grade 0. a) A girl with L5 spondylolisthesis, (age: 12.3y, premenarche, Oxford stage 2). b) A girl with IS (age: 12.5y, premenarche, Oxford stage 2). The typical zonal structure of the growth plates was found in both subjects. In the hypertrophic zone, chondrocytes are organized in columns of cells that undergo differentiation, demonstrating remarkable growth activity in both subjects. A thicker hypertrophic zone, larger cell-nest area, and higher number of cells were observed in IS patients with Risser grade 0 (b) than in control patients with the same Risser grade (a). HE, 200×.