Assessment of acetabular morphology commonly made on supine AP pelvic radiographs may not accurately represent the functional acetabular orientation when standing (position of loading). When standing the pelvis has a different tilt to when supine and thus anterior and posterior acetabular coverage/prominence changes. This positional change may be affected by underlying acetabular morphology as part of mechanism to compensate for pathomechanics associated with acetabular under- or over- coverage. This study aims to 1) compare acetabular morphological characteristics between volunteers and symptomatic patients; 2) assess variations between supine and standing positions in both cohorts; and 3) test for differences according to distinct acetabular morphotypes. This is a prospective study from an academic referral center. Patients presenting at a young adult hip clinic with hip pain without arthrosis (n=288) (age: 36 ±9 years, 170 (58%) females) between 2020–24 were enrolled and formed the patient group. One hundred volunteers with well-functioning hips (Oxford hip score >45) (age 37 ±14 years; 45% females) were included. Supine and standing AP pelvic radiographs were analyzed to determine numerous acetabular parameters: lateral center-edge angle (LCEA), acetabular index (AI), anterior wall index (AWI), posterior wall index (PWI), cross-over-sign (COS), cross-over-ratio (COR), posterior wall sign (PWS), ischial spine sign (ISS). Acetabular morphology in cases of dysplasia was characterized as per the Ottawa Classification System. The patient cohort had lower LCEA (LCEA: 27±6 vs 31 ±6, p Volunteers and symptomatic patients exhibited similar variability in pelvic tilt change upon standing from the supine positions (average increase by 3.9°±3 Vs 4.6°±3, p=0.182), resulting in a decrease in AWI of 0.10 (patients) and 0.09 (volunteers) (p=0.473). On the contrary PWI increased by 0.09 (patients) and 0.09 (volunteers) (p=0.583). Patients with excessive retroversion demonstrated a significant pelvic tilt change of 5.6° when transitioning from supine to standing, resulting in AWI decrease by 0.14 and an increase in PWI by 0.15. In contrast, patients with excessive anteversion showed minimal pelvic tilt change of only 1.7° during the same transition, leading to an increase in AWI by 0.05 and a decrease in PWI by 0.018. Patients had slight morphological differences to controls, with lower LCEA and AWI. Both groups showed on average similar change in pelvic tilt when moving from supine to standing, leading to a reduction in AWI and an increase in PWI. However, morphotypes with excessive retroversion exhibited greater posterior tilt variation in both groups, resulting in a larger decrease in AWI and a greater increase in PWI, likely to compensate for anterior over-coverage. In contrast, excessive anteversion showed less tilt variation, producing smaller changes in AWI and PWI, likely to prevent anterior uncovering in the standing position.
Vorimore et al. (Wed,) studied this question.