Which Acetabular Measurements Most Accurately Differentiate Between Patients and Controls? A Comparative Study

Background Acetabular morphology is an important determinant of hip biomechanics. To identify features of acetabular morphology that may be associated with the development of hip symptoms while accounting for spinopelvic characteristics, one needs to determine acetabular characteristics in a group of individuals older than 45 years without symptoms or signs of osteoarthritis. Previous studied have used patients with unknown physical status to define morphological thresholds to guide management.Questions/purposes: (1) To determine acetabular morphological characteristics in males and females between 45 and 60 years old with a high Oxford hip score (OHS) and no signs of osteoarthritis; (2) to compare these characteristics with those of symptomatic hip patients treated with hip arthroscopy or periacetabular osteotomy (PAO) for various kinds of hip pathology (dysplasia, retroversion, and cam femoroacetabular impingement); and (3) to assess which radiographic or CT parameters most accurately differentiate between patients who had symptomatic hips and those who did not, and thus, define thresholds that can guide management.Methods Between January 2018 and December 2018, 1358 patients underwent an abdominopelvic CT scan in our institution for nonorthopaedic conditions. Of those, we considered 5% (73) of patients as potentially eligible as controls based on the absence of major hip osteoarthritis, trauma, or deformity. Patients were excluded if their OHS was 43 or less (2% [28]), if they had a PROMIS less than 50 (1% [18]), or their T & ouml;nnis score was higher than 1 (0.4% [6]). Another eight patients were excluded because of insufficient datasets. After randomly selecting one side for each control, 40 hips were left for analysis (age 55 +/- 5 years; 48% [19 of 40] were in females). In this comparative study, this asymptomatic group was compared with a group of patients treated with hip arthroscopy or PAO. Between January 2013 and December 2020, 221 hips underwent hip preservation surgery. Of those, eight were excluded because of previous pelvic surgery, and 102 because of insufficient CT scans. One side was randomly selected in patients who underwent bilateral procedure, leaving 48% (107 of 221) of hips for analysis (age 31 +/- 8 years; 54% [58 of 107] were in females). Detailed radiographic and CT assessments (including segmentation) were performed to determine acetabular (depth, cartilage coverage, subtended angles, anteversion, and inclination) and spinopelvic (pelvic tilt and incidence) parameters. Receiver operating characteristics (ROC) analysis was used to assess diagnostic accuracy and determine which morphological parameters (and their threshold) differentiate most accurately between symptomatic patients and asymptomatic controls.Results Acetabular morphology in asymptomatic hips was characterized by a mean depth of 22 +/- 2 mm, with an articular cartilage surface of 2619 +/- 415 mm2, covering 70% +/- 6% of the articular surface, a mean acetabular inclination of 48 degrees +/- 6 degrees, and a minimal difference between anatomical (24 degrees +/- 7 degrees) and functional (22 degrees +/- 6 degrees) anteversion. Patients with symptomatic hips generally had less acetabular depth (20 +/- 4 mm versus 22 +/- 2 mm, mean difference 3 mm [95% CI 1 to 4]; p < 0.001). Hips with dysplasia (67% +/- 5% versus 70% +/- 6%, mean difference 6% [95% CI 0% to 12%]; p = 0.03) or retroversion (67% +/- 5% versus 70% +/- 6%, mean difference 6% [95% CI 1% to 12%]; p = 0. 04) had a slightly lower relative cartilage area compared with asymptomatic hips. There was no difference in acetabular inclination (48 degrees +/- 6 degrees versus 47 degrees +/- 7 degrees, mean difference 0.5 degrees [95% CI -2 degrees to 3 degrees]; p = 0.35), but asymptomatic hips had higher anatomic anteversion (24 degrees +/- 7 degrees versus 19 degrees +/- 8 degrees, mean difference 6 degrees [95% CI 3 degrees to 9 degrees]; p < 0.001) and functional anteversion (22 degrees +/- 6 degrees versus 13 degrees +/- 9 degrees, mean difference 9 degrees [95% CI 6 degrees to 12 degrees]; p < 0.001). Subtended angles were higher in asymptomatic at 105 degrees (124 degrees +/- 7 degrees versus 114 degrees +/- 12 degrees, mean difference 11 degrees [95% CI 3 degrees to 17 degrees]; p < 0.001), 135 degrees (122 degrees +/- 9 degrees versus 111 degrees +/- 12 degrees, mean difference 10 degrees [95% CI 2 degrees to 15 degrees]; p < 0.001), and 165 degrees (112 degrees +/- 9 degrees versus 102 degrees +/- 11 degrees, mean difference 10 degrees [95% CI 2 degrees to 14 degrees]; p < 0.001) around the acetabular clockface. Symptomatic hips had a lower pelvic tilt (8 degrees +/- 8 degrees versus 11 degrees +/- 5 degrees, mean difference 3 degrees [95% CI 1 degrees to 5 degrees]; p = 0.007). The posterior wall index had the highest discriminatory ability of all measured parameters, with a cutoff value of less than 0.9 (area under the curve [AUC] 0.84 [95% CI 0.76 to 0.91]) for a symptomatic acetabulum (sensitivity 72%, specificity 78%). Diagnostically useful parameters on CT scan to differentiate between symptomatic and asymptomatic hips were acetabular depth less than 22 mm (AUC 0.74 [95% CI 0.66 to 0.83]) and functional anteversion less than 19 degrees (AUC 0.79 [95% CI 0.72 to 0.87]). Subtended angles with the highest accuracy to differentiate between symptomatic and asymptomatic hips were those at 105 degrees (AUC 0.76 [95% CI 0.65 to 0.88]), 135 degrees (AUC 0.78 [95% CI 0.70 to 0.86]), and 165 degrees (AUC 0.77 [95% CI 0.69 to 0.85]) of the acetabular clockface.Conclusion An anatomical and functional acetabular anteversion of 24 degrees and 22 degrees, with a pelvic tilt of 10 degrees, increases the acetabular opening and allows for more impingement-free flexion while providing sufficient posterosuperior coverage for loading. Hips with lower anteversion or a larger difference between anatomic and functional anteversion were more likely to be symptomatic. The importance of sufficient posterior coverage was also illustrated by the posterior wall indices and subtended angles at 105 degrees, 135 degrees, and 165 degrees of the acetabular clockface having a high discriminatory ability to differentiate between symptomatic and asymptomatic hips. Future research should confirm whether integrating these parameters when selecting patients for hip preservation procedures can improve postoperative outcomes.Level of Evidence Level III, prognostic study.