The Ischial Spine Sign: Does Pelvic Tilt and Rotation Matter?

Abstract

Although the ischial spine sign (ISS) has been advocated to detect acetabular retroversion, it is unknown whether the sign is valid on anteroposterior (AP) pelvic radiographs with tilted or rotated pelves. We therefore evaluated reliability of the ISS as a tool for diagnosing acetabular retroversion in the presence of considerable pelvic tilt and/or malrotation. We obtained radiographs of 20 cadaver pelves in 19 different malorientations resulting in 380 pelvis images (760 hips) for evaluation. In addition, 129 clinical radiographs of patients' hips that had varying pelvis orientations were reviewed. We found an overall sensitivity of 81% (90%), specificity of 70% (71%), positive predictive value of 77% (80.7%), and negative predictive value of 75% (85%) in the cadaver (patient) hips. Our data suggest the ISS is a valid tool for diagnosing acetabular retroversion on plain radiographs taken using a standardized technique regardless of the degree of pelvic tilt and rotation.

Supine and Standing AP Pelvis Radiographs in the Evaluation of Pincer Femoroacetabular Impingement

“…We used standing films as the functional position and compared values from that position with values from the supine position. In another study [5], the ischial spine was found to be more prominent with forward tilt. Through these studies, it has been shown that increased forward tilt of the pelvis results in more-prominent crossover and ischial spine signs, both signs of acetabular retroversion and a cause for pincer impingement.…”

“…Although 46 hips were used for analysis, the inclusion of more hips can allow for more accurate analysis and detect trends and correlations. The reason for a small cohort was attributable to strict exclusion criteria, mainly malrotated films, which can have an effect on the presence or absence of a crossover sign [5]. The limitation of the quality of radiographs is important.…”

“…During this study period, all patients younger than 60 years who were evaluated for hip pain when the diagnosis of fracture was not being considered received supine and standing radiographs and formed the basis of this retrospective study. Patients were excluded if the sacrococcygeal joint or coccyx tip was not observed owing to a lead shield or bowel gas obstruction (n = 31), if they had arthritis of Tönnis grade 2 or greater (n = 26), malrotation greater than 5 mm [5,11] (n = 24), previous hip or proximal femoral surgery (n = 5), or previous lumbar fusion (n = 2). Malrotation was measured by drawing a vertical line through the center of the symphysis and the sacrum and measuring the distance between these two.…”

Periacetabular Osteotomy Provides Higher Survivorship Than Rim Trimming for Acetabular Retroversion

“…The number of surgical hip dislocations with rim trimming reached the maximum between 2004 and 2008. During this time, we learned that acetabular retroversion (defined as having all three signs) is a result of rotation of the hemipelvis [8,15,16,44,49]. In addition, the size of the lunate surface and the outer margin of the acetabular rim are normal in retroversion [44] and can theoretically be reduced in a critical way by rim trimming [3].…”

“…Acetabular retroversion was initially understood as a prominent overgrowth of the anterior acetabular wall [4], but there is increasing evidence that acetabular retroversion is a rotational abnormality of the entire hemipelvis [15,16,28,36,44,49] rather than focal overgrowth.…”