Impacted "roof disc" as a cause of failure of lumbar disc surgery.

A clinical entity called roof disc is described. It is a centrally located disc extruction found posterior to the posterior borders of the vertebrae that is enclosed by the intact posterior longitudinal ligament; the roof disc exerts pressure against the dorsally lying thecal sac and its enclosed cauda equina roots, causing symptoms and signs incident to this pressure. The contention is made that, unless this roof disc is removed, the patient will continue to have symptoms. Three varieties are described and examples are presented. Its concealed location makes the conventional surgical approaches ineffective, including foraminotomy and laminotomy or laminectomy with standard discectomy.