Relationship between morphology of iliolumbar ligament and lower lumbar disc degeneration.

Previous imaging studies have shown little difference in the degree of disc degeneration between L4-L5 and L5-S1. We hypothesized that because the morphology of the iliolumbar ligament affects the stability of the lumbosacral junction, then it could determine the lower lumbar disc degeneration. Fifty-three male and 47 female patients were classified into three groups according to their disc degeneration grade-those in whom the L5-S1 disc was less degenerated (group A), more degenerated (group B), and equally degenerated (group C) compared to the L4-L5 disc on T2-weighted magnetic resonance images. The length and direction of the anterior and posterior iliolumbar ligaments were measured on T1-weighted axial images. The iliolumbar ligament was shorter in group A than in group B or C, and was oriented significantly more posteriorly in group A than in groups B or C. The morphology of the iliolumbar ligament, especially its length and direction, can be a factor influencing the development of disc degeneration at L4-L5 and L5-S1.