PATHOANATOMY OF ACETABULAR BICOMPARTMENTALIZATION IN CHILDREN WITH AVASCULAR NECROSIS OF THE FEMORAL HEAD

Abstract

Introduction: In severe Legg-Calve-Perthes (LCPD) disease with subluxated femoral head, the acetabulum sometimes takes a bicompartmental appearance. This study analyzed acetabular pathoanatomy using a 3-D CT program.

Materials and Methods: A 3-D CT software program that affords the section of 2-D image in any plane was used to analyze the acetabular pathoanatomy, with specific reference to the morphology of the inner surface of the acetabulum. Thirteen children with the bicompartmental acetabulae (12 LCPD and 1 AVN subsequent to septic hip arthritis) were evaluated.

Results: The anterior half of the acetabulum was concentric. The contour of the acetabular margin in the posterior half of the acetabulum consisted of two different arcs – an arc of the iliac acetabulum (superior) and the other arc of the acetabular fossa of the ischium (medial). The junction of these two arcs was located at the triradiate cartilage, which was increased in mediolateral thickness at this point. The osteochondral articular margin of the ischium posterior to the non-articular acetabular fossa was thickened forming a ridge. The mediolateral thickness of the non-articular acetabular fossa was thinner than that of the normal contralateral side. The combination of these focal morphologic changes of the acetabular fossa rendered the bicompartmental appearance on plain AP radiograph of the pelvis.

Discussion: The authors conclude that bicompartmentalization of the acetabulum apparently reflects the altered biomechanics of the hip joint due to the subluxated femoral head. The abnormal osteocartilaginous hypertrophy appears to be caused by synovial irritation and an eccentric molding effect of the subluxated femoral head.