[Prevalence, morphology, and pathologic implications of ossification of lumbar ligamenta flava: a large prospective CT study].

Ossifications of the ligamenta flava are described in all parts of the spine, particularly in the dorsal segment where they can produce thoracic myelopathy. Rarely reported in the cervical spine, they are only occasionally mentioned in the lumbar spine where the main reported pathology of the ligamentum flavum is the arthrosynovial cyst. To study the morphological appearances, the prevalence and the pathological implications of the lumbar ossified ligamenta flava, 1021 lower lumbar CT studies are prospectively reviewed totalizing 6080 ligamenta flava. The prevalence of clearly defined ossifications is 5.44%; it appears relatively independent from the age, sex, vertebral level and presence of spondylolysis. It significant increases with the presence and the stage of articular osteoarthritis. In more than 96% of cases, the ossifications remain confined to the lateral articular portion of the ligament and more central ossifications are very rare; therefore, the essential differential diagnosis is osteophytosis. The ossifications never cause radiculopathy except rarely, in association with more classical processes such as disk protrusions and osteophytosis. Our findings favours an essentially idiopathic and--to a lessen extent--a mechanical cause to explain ossification of the ligamenta flava.