Acetabular Morphology and Spinopelvic Characteristics: What Predominantly Determines Functional Acetabular Version?

Abstract

Background: In addition to the relative size of the acetabular rim and how the pelvis is positioned in space, the plane in which the acetabular version is calculated also affects its measurement. Purpose: To determine the relative contribution of pelvic and acetabular characteristics on morphological version (measured relative to the anterior pelvic plane angle [APPA]) and functional version (measured relative to the horizontal table). Study Design: Cross-sectional study; Level of evidence, 3. Methods: Included were 50 acetabular dysplasia patients and 109 asymptomatic controls. Using image analysis software, morphological parameters of the pelvis and acetabulum were determined from 2-dimensional computed topography: pelvic incidence, pelvic tilt angle, sacral slope, APPA, morphological and functional acetabular versions, and subtended angles (measure of acetabular rim prominence relative to the femoral head center) around the acetabular clockface in 30° increments. Correlation and multivariable regression analyses were performed with morphological and functional version as dependent variables and spinopelvic and acetabular parameters as independent variables. Results: Morphological version was moderately associated with differences between anterior and posterior subtended angles ( R = 0.68 [ P < .001] and R = 0.57 [ P < .001] for differences at 165° and 15° and 135° and 45°, respectively). Functional version was moderately associated with pelvic tilt angle ( R = 0.56; P <.001) and the difference in subtended angles between anterior and posterior rims ( R = 0.61 [ P < .001] and R = 0.50 [ P < .001] for differences at 165° and 15° and 135° and 45°, respectively). Multivariate analysis revealed a good model for predicting morphological version ( R 2 = 0.44; P < .01) and functional version ( R 2 = 0.58; P < .01). Subtended angle difference between 165° and 15° ( B = 0.36 [95% CI, 0.24-0.49]; P < .001) was most strongly related to morphological version, and pelvic tilt angle ( B = 0.57 [95% CI, 0.46-0.68]; P < .001) was most strongly related to functional version. Conclusion: Functional acetabular version was influenced most strongly by pelvic tilt angle rather than the relative prominence of the acetabular rims. Before determining surgical management for version abnormalities, it would be prudent to assess pelvic mobility and characteristics in different functional positions. In patients with minimal pelvic tilt change dynamically, corrective osteotomy would be the treatment of choice to improve functional version.

Pelvic tilt from supine to standing in patients with symptomatic acetabular retroversion of the hip

“…Very little subsequent work has been done on this relationship, with Tannast et al 10 in 2012 suggesting that acetabular retroversion was caused by the external rotation of the hemipelvis and, more recently, that functional or ‘physiological’ acetabular retroversion was associated primarily with PT angle. 13 This is in keeping with our findings that the radiological signs of acetabular retroversion decreased when the posterior PT increased from the supine to standing positions. Functional acetabular retroversion can be due to a low PT angle.…”

“…However, the ischial spine sign suggests that these appearances are partially a feature of external rotation of the hemipelvis, 9,10 and more recent work suggests that in addition to this external rotation deformity, there is some degree of prominence of the iliac wing anteriorly, 11 as well as lower pelvic tilt (PT) angle and external rotation of the iliac wing. 12 Functional acetabular retroversion has been associated with PT, 13 and the effect of PT on the interpretation of radiological parameters, in particular the assessment of acetabular retroversion, has been clearly illustrated. 14,15…”

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

“…Of those, we considered 5% (73 [146 hips]) as potentially eligible as controls based on the absence of major hip osteoarthritis, trauma, or deformity. The asymptomatic group had, partially, been used in a previous study [12], and further selection based on symptoms and daily life functioning was done for the current study. These patients were contacted by telephone or email and answered standardized and validated questionnaires regarding hip and overall function, including the OHS (range 0 to 48) [11,36] and the Patient-Reported Outcome Measurement Information System (PROMIS) general and mental health score (range 0 to 100) [15].…”

“…CT with threedimensional (3D) reconstruction allows for better characterization, and it can account for pelvic tilt, rotation, and obliquity [50]. Furthermore, additional characteristics such as the ratio between acetabular cartilage and fossa areas [46] and spinopelvic characteristics, which influence pelvic tilt and acetabular orientation [12,29], are considered important predictors of symptomatic hip disease [22,26,39].…”

CORR Insights®: Which Acetabular Measurements Most Accurately Differentiate Between Patients and Controls? A Comparative Study

“…They found that morphological anatomical anteversion is mainly dependent on acetabular morphology and the prominence of anterior and posterior acetabular rims and is only weakly related to pelvic measurements. They also suggested that functional anteversion is more important in determining treatment, as it has been found to be strongly associated with pelvic tilt; assessment of pelvic mobility is very important before deciding the treatment of hip version abnormalities [1]. In this issue of Clinical Orthopaedics and Related Research ® , Verhaegen et al [10] included the patient's activity status, spinopelvic parameters, functional anteversion, and CT measurements; they compared the asymptomatic hips with a symptomatic cohort to try to identify parameters more likely to be associated with painful hips.…”