The "thickened" ligamentum flavum: is it buckling or enlargement?

BACKGROUND AND PURPOSE Thickening of the LF is ascribed to buckling due to DSN. Uncertainty exists as to whether this can occur without DSN. Our primary hypothesis was that facet degenerative changes alone, independent of DSN, can thicken the LF. Our secondary hypothesis was that inflammatory changes surrounding degenerative facet joints may incite thickening. MATERIALS AND METHODS Fifty-two patients were divided into 1 of 3 groups: group 1 (normal lumbar spine, n = 21), group 2 (LF thickening and FH with normal height of the L4-5 disk, n = 18), and group 3 (LF thickening and FH with decreased height of the L4-5 disk, n = 13). LF thickness measured on axial T1WI at the midpoint of the LF length was compared with that in group 1. Facet joints were evaluated for spurring, joint fluid, and cortical irregularity, indicating facet degeneration. Enhancement of the facet joints and LF thickening were also evaluated (n = 2). The Student t test was used to compare groups. RESULTS Normal LF thickness (group 1) was 3.1 mm, whereas LF thickness averaged 4.9 mm in group 2 and 5.3 mm in group 3 (both P < .001). Patients with asymmetric LF thickness showed greater LF thickness on the side with greater FH. There was more LF enhancement on the side with greater facet degenerative disease. CONCLUSIONS LF thickening can be secondary to facet degenerative changes, independent of DSN. Inflammatory changes may be an inciting factor for LF thickening.