Fig. 1.

Illustration of measuring method at the L4–L5 and L5–S1 level. Anterior height of L4 vertebral body (a–b), posterior height of L4 vertebral body (f–g), anterior height of L4/5 intervertebral disc (b–c), posterior height of L4/5 intervertebral disc (g–h), anterior height of L5 vertebral body (c–d), posterior height of L5 vertebral body (h–i), anterior height of L5/S1 intervertebral disc (d–e), posterior height of L5/S1 intervertebral disc (i–j), height of L4 spinous process (k–l), height of L5 spinous process (m–n)