Pelvic Obliquity Impacts Acetabular Coverage Measurements, and the Elevated Hip Is More Frequently Symptomatic in Hip Preservation Patients

Purpose To quantify the impact of femoral head height discrepancies on pelvic‐based versus ground‐based measurements for lateral center‐edge angle (LCEA) and Tönnis angle and to determine whether these discrepancies affected the clinical presentation of patients who presented to a hip preservation clinic. Methods Consecutive patients who underwent a primary hip arthroscopy between May 2021 and August 2021 and consecutive patients who underwent a primary periacetabular osteotomy between January 2020 and December 2023 with available preoperative standing anteroposterior radiographs were included. Patients were excluded if they (1) had undergone a previous surgery in either hip prior to the primary operation or (2) were less than 18 years of age at the time of surgery. The LCEA to the sourcil edge, LCEA to the bone edge, and Tönnis angle were calculated, referencing off (1) the pelvis and (2) the horizontal to the ground. Differences between measurements were calculated in degrees, and differences in femoral head heights to approximate pelvic obliquity were calculated in millimeters. Comparisons were made via regression analysis. Results Fifty hip arthroscopy patients and 75 periacetabular osteotomy patients were included. Regression analysis showed that LCEA to the sourcil edge was impacted by the difference in femoral head height when comparing the pelvic‐based measurement with the ground‐based measurement ( B = 0.298; R 2 = 0.775; 95% confidence interval = 0.274‐0.322; P < .001). Furthermore, in patients with a femoral head height difference of 10 mm or more, 100% (8/8) of patients who underwent a periacetabular osteotomy and 75% (6/8) of patients who underwent a hip arthroscopy reported more symptoms on the more elevated hip. Conclusions Differences in femoral head height on standing anteroposterior radiographs impact ground‐ versus pelvic‐based radiographic measurements of acetabular coverage by approximately 0.3° per millimeter of femoral head height difference and may result in functional undercoverage of the elevated hip. Level of Evidence Level IV, retrospective case series.