Measurements of ligamentum flavum thickening at lumbar spine using MRI

As the ligamentum flavum (LF) covers most of the posterolateral part of the lumbar spinal canal, its thickening can be attributed to the development of lumbar canal encroachment. Nevertheless, there have been few reports describing the natural history of the LF.

To investigate the natural history and to subsequently clarify the pathogenesis of LF thickening, we conducted a transverse radiological study of the LF at the lumbar spine using magnetic resonance images.

One hundred and sixty-two patients complaining of low back pain and/or leg pain were evaluated (n = 162; mean age 52.1 years). The thickness of LF was measured at L2-3, L3-4, L4-5 and L5-S levels (n = 648). The relationships among thickness, age, and spinal level were examined.

One hundred and sixty-two patients complaining of low back pain and/or leg pain were evaluated (n = 162; mean age 52.1 years). The thickness of LF was measured at L2-3, L3-4, L4-5 and L5-S levels (n = 648). The relationships among thickness, age, and spinal level were examined.

The following results were obtained. (1) LF thickness increased with age; however, the increments at L4-5 and L3-4 were larger than one at L2-3 and L5-S1. (2) At L4-5, LF was over 3.0 mm thick in patients in the 20-29 age bracket, and in many of them it was more than 3.5 mm thick. (3) All patients with a thickened LF at L2-3 (>3.0 mm) had very thick LFs at all spinal levels. (4) In elderly patients, there was no correlation between the thickness of LF and the decrease of the disc height. In this study, we concluded that thickening of LF at L4-5 had already started in patients in the 30-39 age bracket and that thickening of the LF was not the buckling of the LF into the spinal canal with disc degeneration. The thickness of LF at L2-3 may serve as an indicator of lumbar spinal canal stenosis at multiple levels.