Enlargement of the ligamentum flavum is a clinical entity producing low-back pain with sciatic radiation. Trauma of relatively slight degree was the etiological factor in the majority of our patients. Pathological changes in the involved ligaments were demonstrated microscopically.

The clinical syndrome is difficult to differentiate from lumbosacral or sacro-iliac disorders, and lipiodol studies are required in order to reach a final diagnosis. It is seldom possible to differentiate the defects in the column of lipiodol from those produced by rupture of an intervertebral disc. Compression of nerve roots by the enlarged ligament produces the symptoms and signs. After their exit from the dura, the nerve roots lie in the very narrow space between the ligamentum flavum and the intervertebral disc. Even a slight enlargement of the ligament, a posterior protrusion of the intervertebral disc, or a combination of the two, will produce compression of the nerve roots.

Seven patients with enlargement of the ligamentum flavum were operated on over a period of seven months. This would indicate that the condition is much more common than is supposed and that many such cases have undoubtedly been overlooked in the past. Operative removal of the enlarged ligament produced prompt relief of pain with gradual improvement in the impaired motor and sensory functions.