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

Till Dominic Lerch; Adam Boschung; Florian Schmaranzer; Inga A S Todorski; Jan Vanlommel; Klaus A Siebenrock; Simon D Steppacher; Moritz Tannast

doi:10.1302/2633-1462.210.BJO-2021-0069.R1

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

Bone Jt Open. 2021 Oct;2(10):813-824. doi: 10.1302/2633-1462.210.BJO-2021-0069.R1.

Authors

Till Dominic Lerch^{1

2}, Adam Boschung¹, Florian Schmaranzer^{1

2}, Inga A S Todorski^{1

2}, Jan Vanlommel³, Klaus A Siebenrock¹, Simon D Steppacher¹, Moritz Tannast^{1

4}

Affiliations

¹ Department of Orthopedic Surgery and Traumatology, Inselspital Bern, University Hospital of Bern, University of Bern, Bern, Switzerland.
² Department of Diagnostic, Interventional and Paediatric Radiology, Inselspital Bern, University Hospital of Bern, University of Bern, Bern, Switzerland.
³ Department of Orthopaedic Surgery and Traumatology, Orthoclinic, Bruges, Belgium.
⁴ Department of Orthopaedic Surgery and Traumatology, Fribourg Cantonal Hospital, University of Fribourg, Fribourg, Switzerland.

PMID: 34619033
PMCID: PMC8558448
DOI: 10.1302/2633-1462.210.BJO-2021-0069.R1

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.

Keywords: Acetabular retroversion; CT scans; FAI; Femoroacetabular impingement; Hip; Hip dysplasia; Pelvic incidence; Pelvic tilt; acetabular rim; cam-type FAI; dysplastic hips; femoroacetabular impingement; hip pain; hips; pelvic incidence; pelvic tilting.