Pelvic deformity influences acetabular version and coverage in hip dysplasia

Abstract

Background: Although a wide variety of acetabular deformities in developmental dysplasia of the hip (DDH) have been reported, the morphologic features of the entire pelvis in DDH are not well characterized and their correlation with acetabular deformity is unknown.

Questions/purposes: We determined whether there was a rotational deformity of the entire innominate bone, and if so, whether it related to acetabular version and coverage.

Patients and methods: We examined the morphologic features of the pelvis using CT for 50 patients with DDH (82 hips). Forty normal hips were used as controls. The innominate rotation angle was determined at three levels in the axial plane. The acetabular sector angle served as an indicator of acetabular coverage of the femoral head. We evaluated the association between innominate rotation angles and acetabular version and coverage.

Results: We observed greater internal rotation of the innominate bone in patients with DDH than in the control subjects. Internal rotation of the innominate bone was associated with increased acetabular anteversion angle and acetabular inclination angle. In hips with acetabular retroversion (nine of 82 hips; 11.0 %), the entire innominate bone was externally rotated, compared with hips with acetabular anteversion. Internal rotation of the innominate bone also was associated with decreased anterior and superior acetabular coverage.

Conclusion: Our observations suggest structural abnormalities exist throughout the pelvis in DDH, and the morphologic abnormalities of the acetabulum are not caused solely by local dysplasia around the hip, but are influenced by the morphologic features of the entire pelvis.

Fig. 1A–C

Computer generated images show the innominate rotation angles. The reference point of the anterior superior iliac spine (ASIS) and the anterior inferior iliac spine (AIIS) were determined as the most anterior aspect of the iliac spines, respectively. The (A) superior iliac wing angle (SIA) is formed by the intersection of a line connecting the medial edge of the ASIS and the anterior margin of the sacroiliac joint, and a horizontal line on the axial plane. The (B) inferior iliac wing angle (IIA) is formed by a line connecting the anterior aspect of the AIIS and the posterior aspect of the ilium, and a horizontal line on the axial plane. The (C) ischiopubic angle (IPA) is a projection angle formed by the intersection of a line connecting the anterosuperior edge of the pubic symphysis and the ischial spine and a sagittal line on the axial plane for which we superimposed the sections that passed through the ischial spine and the pubic symphysis.

Fig. 2A–C

The (A) acetabular anteversion angle (AcAV) was determined in the axial plane passing through the femoral head center as the angle formed by the intersection of a line connecting the anterior and posterior edges of the acetabulum and a sagittal line. The (B) acetabular inclination angle (AI) was determined in the coronal plane passing through the femoral head center as the angle formed by a line connecting the superior and inferior edges of the acetabulum and a horizontal line. The (C) cranial anteversion angle (CA) is formed by the intersection of a line connecting the anterior and posterior edges of the acetabulum and a sagittal line in the axial plane 5 mm distal to the acetabular roof.

Fig. 3

The acetabular sector angle (ASA) is formed by the intersection of a line connecting the femoral head center and the acetabular edge with a horizontal line. The acetabular sector angle was measured in anterior, superior, and posterior directions.