Femoroacetabular impingement and the inclination of the pelvis in the sagittal plane (pelvic incidence): a radiographic comparison with an asymptomatic population

The purpose of this study was to investigate whether the inclination of the pelvis in the sagittal plane (pelvic incidence) in patients with symptomatic femoroacetabular impingement was different from that in a normal population.
A retrospective analysis was made of 30 consecutive male and female patients with a CT scan, who underwent hip arthroscopy for femoroacetabular impingement syndrome. The inclination of the pelvis in the sagittal plane was measured on lateral radiographs. The centre-edge angle, the orientation of the acetabulum (acetabular version) and the alpha angle were also measured. Each patient was subcategorised as having an abnormal cam-type morphology (alpha angle > 55°), a deep acetabulum (centre-edge angle > 39°) or acetabular retroversion (anterior acetabular version < 15°). The groups and subgroups were compared with a historical reference group from a previously published study of 300 volunteers. Each group was compared using the Student t test.
The mean inclination of the pelvis in the sagittal plane was 49.31° ± 12.34°, lower than in the asymptomatic historical group, which had a mean angle of 55.0° ± 10.6°. The subgroups with cam-type morphology, a deep acetabulum and acetabular retroversion had angles of 48.89° ± 11.81°, 38.30° ± 7.56° and 44.93° ± 11.32° respectively. All had a significantly lower such angle than the historical group.
The authors concluded that patients with femoroacetabular impingement may have a lower angle of inclination of the pelvis in the sagittal plane than the general population. The clinical significance of the difference of 5.7° in this angle remains unclear.
Source: “Arthroscopy”, December 2016