The sagittal angle measurement by Cobb's angle method on plain X-ray. The adjacent segmental angle (ASA) was measured as total sum of intervertebral angles between flexion and extension lateral radiographs (A). To measure it, line along the end plate of adjacent vertebra body and line along the end plate of the most superior or inferior fused vertebra body were drawn. The total lumbar lordotic angle (TLA) was defined as the angle subtended by the superior end plate line of L1 and the superior end plate line of S1 (B).