Does Pelvic Tilt Change After Periacetabular Osteotomy for Hip Dysplasia?

Background: The purpose of this study was to (1) evaluate preoperative pelvic tilt utilizing the sacro-femoral-pubic (SFP) angle on standing pelvic x-rays, and (2) determine if the SFP angle changes after a unilateral or bilateral PAO.

Methods: A retrospective review was conducted of PAOs performed by a single hip preservation surgeon from November 2018 to November 2023. Standing x-rays were reviewed at 4 time points: preoperative, subacute postoperative, 6-month follow-up, and 12-month follow-up. Data collected included demographics, lateral center-edge angle (LCEA), Tönnis angle, and sacro-femoral-pubic (SFP) angle (a surrogate metric for pelvic tilt). Linear mixed models and Wilcoxon signed-rank tests were used to evaluate preoperative to postoperative differences in pelvic tilt for the unilateral and bilateral PAO groups, respectively.

Results: Seventy-four patients met inclusion criteria, consisting of 53 unilateral and 21 bilateral PAO patients (18.5±4.1 vs. 21.3±5.1 y, 90.6% vs. 95.2% female, LCEA 17.5 deg±6.5 deg vs. 18.0 deg±5.5 deg and 18.0 deg±6.3 deg, respectively). The Average preoperative pelvic tilt, calculated from the SFP angle, for the unilateral and bilateral PAO patients were 9.1 degrees±5.5 degrees and 8.1 degrees±5.6 degrees, respectively. These values increased postoperatively at average 7-week (-0.3 deg±3.4 deg and 1.3 deg±3.7 deg), 6-month (1.1 deg±3.8 deg and 2.7 deg±3.4 deg), and 12-month (1.0 deg±4.1 deg and 2.7 deg±3.0 deg) follow-up. Significant differences in pelvic tilt were observed from preoperative x-rays to 6 months (P=0.002) and 12 months (P=0.001) for the bilateral PAO patients, whereas the unilateral group demonstrated similar pelvic tilt at all time points (P=0.09).

Conclusion: Patients undergoing bilateral PAO demonstrated an average increase in pelvic tilt of 2.7 degrees as measured by SFP angle at 6 months and 12 months postoperatively, suggesting a compensatory adaptation after surgery that may have implications in rehabilitation regimens and planned surgical corrections.

Level of evidence: Level III-therapeutic study.