[Hyperostosis triangularis ilii -- a sacro-iliac stress phenomenon Part. 2 (Incidence, prognosis, pathogenesis, aetiology, tracer studies, differential diagnosis) (author's transl)].

The anterior iliac margin adjacent to the sacro-iliac joint contains a physiological zone of hyperostosis. Its shape is that of a triangular pyramid. Because of its small size, it is radiological invisible, but is nevertheless an indication of the presence of normal stresses passing from the mass of the trunk to the lower extremities. If for any reason, such as is described in this paper, the stresses on the hyperostosis zone are increased, the latter becomes enlarged, while still keeping its shape. It then appears on the radiograph as hyperostosis triangularis ilii. In approximately 50% of cases there is a simultaneous but variable sacral hyperostosis. Observations on 40 patients, together with two autopsies and radionucleide investigations suggest that hyperostosis triangularis ilii represents a potentially reversible bone reaction of the physiological hyperostosis of the anterior iliac margin. The clinical differential diagnosis raised by the radiological finding of a "triangular ilium hyperostosis" is discussed.