Lower pelvic tilt, lower pelvic incidence, and increased external rotation of the iliac wing in patients with femoroacetabular impingement due to acetabular retroversion compared to hip dysplasia

Abstract

Aims The effect of pelvic tilt (PT) and sagittal balance in hips with pincer-type femoroacetabular impingement (FAI) with acetabular retroversion (AR) is controversial. It is unclear if patients with AR have a rotational abnormality of the iliac wing. Therefore, we asked: are parameters for sagittal balance, and is rotation of the iliac wing, different in patients with AR compared to a control group?; and is there a correlation between iliac rotation and acetabular version? Methods A retrospective, review board-approved, controlled study was performed including 120 hips in 86 consecutive patients with symptomatic FAI or hip dysplasia. Pelvic CT scans were reviewed to calculate parameters for sagittal balance (pelvic incidence (PI), PT, and sacral slope), anterior pelvic plane angle, pelvic inclination, and external rotation of the iliac wing and were compared to a control group (48 hips). The 120 hips were allocated to the following groups: AR (41 hips), hip dysplasia (47 hips) and cam FAI with normal acetabular morphology (32 hips). Subgroups of total AR (15 hips) and high acetabular anteversion (20 hips) were analyzed. Statistical analysis was performed using analysis of variance with Bonferroni correction. Results PI and PT were significantly decreased comparing AR (PI 42° (SD 10°), PT 4° (SD 5°)) with dysplastic hips (PI 55° (SD 12°), PT 10° (SD 6°)) and with the control group (PI 51° (SD 9°) and PT 13° (SD 7°)) (p < 0.001). External rotation of the iliac wing was significantly increased comparing AR (29° (SD 4°)) with dysplastic hips (20°(SD 5°)) and with the control group (25° (SD 5°)) (p < 0.001). Correlation between external rotation of the iliac wing and acetabular version was significant and strong (r = 0.81; p < 0.001). Correlation between PT and acetabular version was significant and moderate (r = 0.58; p < 0.001). Conclusion These findings could contribute to a better understanding of hip pain in a sitting position and extra-articular subspine FAI of patients with AR. These patients have increased iliac external rotation, a rotational abnormality of the iliac wing. This has implications for surgical therapy with hip arthroscopy and acetabular rim trimming or anteverting periacetabular osteotomy (PAO). Cite this article: Bone Jt Open 2021;2(10):813–824.

Pelvic tilt from supine to standing in patients with symptomatic acetabular retroversion of the hip

“…However, the ischial spine sign suggests that these appearances are partially a feature of external rotation of the hemipelvis, 9,10 and more recent work suggests that in addition to this external rotation deformity, there is some degree of prominence of the iliac wing anteriorly, 11 as well as lower pelvic tilt (PT) angle and external rotation of the iliac wing. 12 Functional acetabular retroversion has been associated with PT, 13 and the effect of PT on the interpretation of radiological parameters, in particular the assessment of acetabular retroversion, has been clearly illustrated. 14,15 Positional changes in PT have previously been reported in patients with developmental dysplasia of the hip (DDH), [16][17][18][19][20] undiagnosed hip pain, 21,22 and awaiting total hip arthroplasty (THA), 23 but have not yet been studied in patients with acetabular retroversion.…”

Combined abnormalities of femoral version and acetabular version and McKibbin Index in FAI patients evaluated for hip preservation surgery

“…In addition, we did not standardize the values for AV to the anterior pelvic plane and had no three-dimensional information [ 52 ]. Given a mean pelvic tilt of 4° in a supine position, we could generally have underestimated AV [ 53 ]. However, by using the same method of previous studies [ 45 ], this allows for a direct comparison to the reported values from previous studies.…”

Diagnosis of acetabular retroversion: Three signs positive and increased retroversion index have higher specificity and higher diagnostic accuracy compared to isolated positive cross over sign

“…But we excluded patients with degenerative changes for the control group, therefore we believe that there should be no relevant bias. Another limitation is, that we did not evaluate the influence of pelvic tilt [51] on AV measurement. Previous studies using 3D models evaluated standardized measurements of AV while normalizing pelvic tilt [34] .…”

“…Measurement of the cross over sign (intersection of blue and red line) and of the retroversion index (X divided by Y) on schematic view is shown (B). Figures reprinted with permission from [51] …”

“…Due to the limitations of radiographs, the differentiation in cranial (focal) and central (global) AR was proposed based on CT scans [8] . Global AR was associated with a deformity of the iliac wing [51] and the hemipelvis [15] . Pelvic CT scans allow the exact measurement of acetabular version (AV) and diagnosis of AR.…”