The Prevalence of Acetabular Retroversion Among Various Disorders of the Hip

Background CT allows for accurate measurement of acetabular orientation and shape, but malpositioning of the pelvis may lead to measurement variance. Purpose We therefore sought to determine: (1) whether acetabular anteversion measurements using the femoral head centers differed from those using the posterior ischia, and (2) the extent to which changing obliquity, rotation, and tilt of a pelvis in a CT scanner affected the measurement of acetabular variables. Methods A radiopaque human pelvis model with articulated hips was suspended from a plastic sheet as part of an adjustable frame. Changes in the transverse and sagittal planes created rotation and tilt, while rotating the frame in the coronal plane created obliquity. CT scans were obtained, varying the combinations of obliquity, rotation, and tilt by intervals of 5°, up to 20°. Acetabular anteversion (AA), anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), and horizontal acetabular sector angle (HASA) were measured. Results The two methods for measuring AA yielded values differing by 1°to 4°but correlated (r = 0.981) across the spectrum of pelvis positioning. Pelvic obliquity and tilt were linearly associated with changes in the measurements. For each 1°-increase in pelvic obliquity, AA changed À0.4°, and AASA, PASA, and HASA changed 1.93°, 0.99°, and 2.80°, respectively. For each 1°-increase in pelvic tilt, AA changed 0.8°, and AASA, PASA, and HASA changed À1.07°, 0.52°, and À0.51°, respectively. Rotation had no affect on the variables. Conclusions Small changes in pelvic obliquity and tilt were associated with variances in acetabular measurements. The measured changes were directly proportional to the changes in obliquity and tilt, and were additive. Pelvic rotation created no changes in measurement. Clinical Relevance Incorrect interpretation of acetabular anteversion and coverage may lead to unsatisfactory acetabular fragment positioning during reorientational surgery. Although intraoperative positioning of an acetabular fragment may not be as precise as the tools for preoperative planning, it is important for a surgeon to have the most precise data available for planning a procedure, and know where error can occur in collecting the data.Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.

Section: Discussionmentioning

confidence: 99%

“…Plain radiographs are important for assessing the acetabular shape and morphologic features [15,25,30,31,43,46]. Accurate assessment of acetabular version and anterior and posterior femoral head coverage can be difficult, and changes in patient positioning can lead to errors in measurement [4,24,45,48].…”

Section: Introductionmentioning

confidence: 99%

Pelvic Positioning Creates Error in CT Acetabular Measurements

Bosse¹,

Lee

Henderson

et al. 2011

“…Most of these studies suggest a primary abnormality of the femur with subsequent alterations of the acetabulum (eg, in Legg-Calvé-Perthes disease) [4,6,9,10,12,18,19,32], proximal femoral focal deficiency [5], or slipped capital femoral epiphysis [14]. We are aware of only two reports [8,26] suggesting variations of acetabular morphology influencing femoral growth.…”

Section: Discussionmentioning

confidence: 99%

“…For example, hips with Legg-Calvé-Perthes disease or proximal femoral focal deficiency have a higher incidence of dysplasia, acetabular retroversion, and incongruity [4][5][6]. This might be due to a premature or eccentric fusion of the triradiate cartilage with subsequent alterations of the articular cartilage and changes of the acetabular dimension [12].…”

Section: Introductionmentioning

confidence: 99%

Femoral Morphology Differs Between Deficient and Excessive Acetabular Coverage

Steppacher

Tannast

Werlen

et al. 2008

146

111

Structural deformities of the femoral head occurring during skeletal development (eg, Legg-Calvé-Perthes disease) are associated with individual shapes of the acetabulum but it is unclear whether differences in acetabular shape are associated with differences in proximal femoral shape. We questioned whether the amount of acetabular coverage influences femoral morphology. We retrospectively compared the proximal femoral anatomy of 50 selected patients (50 hips) with developmental dysplasia of the hip (lateral center-edge angle [LCE] B 25°; acetabular index C 14°) with 45 selected patients (50 hips) with a deep acetabulum (LCE C 39°). Using MRI arthrography we measured head sphericity, epiphyseal shape, epiphyseal extension, and femoral head-neck offset. A deep acetabulum was associated with a more spherical head shape, increased epiphyseal height with a pronounced extension of the epiphysis towards the femoral neck, and an increased offset. In contrast, dysplastic hips showed an elliptical femoral head, decreased epiphyseal height with a less pronounced extension of the epiphysis, and decreased head-neck offset. Hips with different acetabular coverage are associated with different proximal femoral anatomy. A nonspherical head in dysplastic hips could lead to joint incongruity after an acetabular reorientation procedure.

“…A retroverted acetabulum with excessive anterior coverage increases the risk for impingement of the anterolateral femoral neck against the acetabular rim. The prevalence of radiographic acetabular retroversion was 20% among patients with idiopathic hip osteoarthritis, compared with 5% among the general population, and the appearance of the retroversion was created by deficiency of the posterior wall of the acetabulum [3,6]. To identify the presence of acetabular retroversion, some authors have proposed radiographic signs, such as the Each author certifies that he or she, or a member of his or her immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.…”

Section: Introductionmentioning

confidence: 95%

New Radiographic Index for Evaluating Acetabular Version

Koyama

Hoshino

Suzuki

et al. 2013

Background Several qualitative radiographic signs have been described to assess acetabular retroversion. However, quantitative assessment of acetabular version would be useful for more rigorous research purposes and perhaps to diagnose and treat hip disorders. Questions/purposes We developed a new quantitative index for acetabular version (p/a ratio). We determined the average p/a, compared it with previous radiographic signs for acetabular retroversion, and evaluated its relationship with anatomic acetabular version. Methods We calculated the p/a ratio by measuring p (distance from acetabular articular surface to posterior wall) and a (distance from acetabular articular surface to anterior wall) on plain hip AP radiographs and dividing p by a. P and a were assessed on the perpendicular bisector of the line between the teardrop and the lateral edge of the acetabulum. Using 185 hip radiographs from patients with suspected idiopathic osteonecrosis, we measured p/a and compared it with previous qualitative signs for acetabular retroversion. Using 62 hip CT images from patients with no osteoarthritis, we measured the anatomic anteversion at the height of the central femoral head and investigated its relationship with p/a. Results The average p/a was 2.05 in 185 hips, and most patients with a p/a greater than 2.05 had a negative qualitative retroversion sign. A correlation was observed between central anteversion and p/a (r = 0.84). Conclusions We believe this ratio can be considered a simple quantitative parameter to assess acetabular version using plain AP radiographs.