Two patients with high-grade spondylolisthesis. The first patient (A) has relatively rectangular L5 and S1 vertebrae. The lumbosacral kyphosis is not significant and the sacral slope is high. In the second patient (B), the L5 vertebra is trapezoidal and there is significant doming of sacrum. Lumbosacral kyphosis is important and the sacrum is more vertical.