Fig. 2
From: Straighter low lumbar curvature in isthmic spondylolisthesis at L4
Diagram of progress of single level IS. There is a tendency of forward slippage of the vertebra with spondylolytic lesions in IS at L4 or L5 (a, d). With the anterior slippage of the vertebra, the segments above the spondylolisthesis hyperextend and the lordosis increases in the cranial zone of the lumbar spine to limit the excessive forward shifts of the center of gravity (b, e). Segmental lordosis of L4/5 in L5 IS increased while that of L5/S1 in L4 IS remained nearly unchanged. With the same degree of degeneration and lordosis of the lesion segment, LLL of the IS at L4 was smaller than that at L5 (c, f)