Posterior Acetabular Sector Angle Research Articles

Pelvic Positioning Creates Error in CT Acetabular Measurements

CT allows for accurate measurement of acetabular orientation and shape, but malpositioning of the pelvis may lead to measurement variance. 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. 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. 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 -0.4°, 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 -1.07°, 0.52°, and -0.51°, respectively. Rotation had no affect on the variables. 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.

Axial plane coverage and torsion measurements in primary osteoarthritis of the hip with good frontal plane coverage and spherical femoral head

Mechanical factors play a role in pathogenesis of primary osteoarthritis of the hip. Torsion measures were made to detect whether there is a causal relationship between increase or decrease of femoral anteversion, acetabular anteversion, and osteoarthritis. There are no studies in the literature indicating a relationship between axial plane coverage and osteoarthritis of the hip. Deficient axial plane coverage of femoral head may also play a role in pathogenesis of osteoarthritis. Thirty patients with primary osteoarthritis of the hip and 29 control cases were included in the study. We used the method of Anda et al. (Acta Radiol Diagn 27:443-447, 1986; Comput Assist Tomogr 15:115-120, 1991) to measure axial plane anterior, posterior coverages in patients with primary osteoarthritis of the hip. The computerized tomography sections and pelvic radiographs indicated good frontal plane coverage and spherical femoral head. In addition to anterior acetabular sector angle, posterior acetabular sector angle, horizontal acetabular sector angles for axial plane coverage detection, femoral anteversion, acetabular anteversion, and McKibbin instability index were also measured. Posterior coverage was lower at osteoarthritic hips than the control group's hips (96.0±16.7, 104.2±10.6) (p<0.05). The results may indicate that in addition to other mechanical factors, axial plane coverage, especially the posterior coverage deficiency, may play a role in the pathogenesis of hip osteoarthritis.

Is there a relation between hip torsion, coverage and osteoarthritis of the knee?

Biomechanic factors play a role in the pathogenesis of knee osteoarthritis. The aim of the study was to find out whether there is a relation between femoral, acetabular anteversions, anterior, posterior acetabular coverages and primary osteoarthritis of the knee. Thirty patients with primary osteoarthritis of the knee and 29 control subjects were enrolled into the study. Femoral anteversion, acetabular anteversion, McKibbin's instability index, anterior acetabular sector and posterior acetabular sector angles were measured using tomographic scanograms. There was no difference between groups for each parameter (P > 0.05). This study did not show any relationship between the axial plane changes in the hip joint and primary knee osteoarthritis.

Residual axial plane deformities after hip reconstruction for developmental dysplasia of the hip after walking age

Children with developmental dysplasia of the hip after walking age can be treated with one-stage combined operations. In these procedures, complex deformity corrections at both frontal and axial planes are performed in the guidance of intraoperative stability tests. The reports about the results of these procedures focus on frontal plane assessments but neglect to assess axial plane corrections. We aimed to find out whether hips with unilateral developmental dysplasia of the hip, treated by one-stage combined procedures after walking age and which had good frontal plane containment at the last follow-up, had any axial plane deformities. Twenty-one patients were included in this study according to our described criteria. Mean age at the operation time was 38.04 months (range: 20-86 months), mean follow-up time was 55.54 months (range: 24-117 months) and mean age at latest follow-up was 93.46 months (range: 52-150 months). Femoral anteversions, acetabular anteversions and acetabular sector angles were measured bilaterally in the computed tomography examination. Operated hip measurements were compared with the contralateral hips. One-way variance analysis was used for statistical analysis. Femoral anteversion, acetabular anteversion and posterior acetabular sector angle values of the operated hips were found to be statistically lower than those of the contralateral hips. Our findings suggest that using the intraoperative stability test alone for planning osteotomies may lead to unsuitable femoral head coverage in axial plane although successful frontal plane containment can be obtained. We believe that strict preoperative planning that can be accomplished by a preoperative computed tomography examination should be performed in order to decide innominate osteotomy type and correction amounts.

Radiographic measurements of dysplastic adult hips.

Hip dysplasia is a not uncommon feature in adults and can vary from subtle acetabular dysplasia to complex sequelae of developmental dysplasia of the hip. This review article describes the most useful radiographic measurements used to evaluate the adult hip. The frontal projection of the pelvis permits measurement of the center-edge angle (CE angle) and "horizontal toit externe" angle (HTE angle), both of which assess the superior coverage of the acetabulum. The femoral neck-shaft angle (NSA) is also measured on this view. The false profile radiograph of the pelvis is described. It allows measurement of the vertical-center-anterior angle (VCA angle), which determines the anterior acetabular coverage and detects early degenerative hip joint disease. When surgery is contemplated, computed tomography (CT) is useful to better determine the anterior acetabular coverage by use of the anterior acetabular sector angle (AASA), and the posterior acetabular coverage by use of the posterior acetabular sector angle (PASA). CT also permits measurement of femoral anteversion. These measurements are particularly useful in the evaluation of acetabular dysplasia and for the preoperative assessment of the dysplastic hip.

Computed tomography measurements of the acetabulum in adult dysplastic hips: which level is appropriate?

A study has been performed to evaluate whether one or several levels are needed with computed tomography (CT) study to provide sufficient information regarding anteversion and acetabular support to the femoral head. A total of 23 hips in 14 adults with uni- or bilateral congenital hip dysplasia (center-edge angle less than 20 degrees) were assessed by obtaining 5-mm contiguous CT slices and performing acetabular measurements at four levels. Both anterior and posterior acetabular supports as quantified by the anterior and posterior acetabular sector angles were significantly lower than normal at all levels. The sector angles increased in the proximal cuts, whereas the acetabular anteversion increased caudally. Because no important additional information was gained by measuring at different levels, we conclude that CT study at one level is sufficient for acetabular measurements and suggest that the slice through the center of the femoral head is the most appropriate one.

Acetabular Angles and Femoral Anteversion in Dysplastic Hips in Adults

Transpelvic CT was used to quantify the relationship between the acetabulum and proximal femur in 21 adult patients (33 hips) with congenital hip dysplasia (defined by a center edge angle of less than 20 degrees). The anterior and posterior acetabular sector angles (AASA and PASA) were measured, as well as the degree of acetabular and femoral anteversion. The results demonstrated deficient anterior acetabular support (i.e., decreased AASA) in approximately two-thirds of the dysplastic hips and reduced posterior support (i.e., decreased PASA) in one-third. The acetabular anteversion was normal. The femoral anteversion. however, was greater than normal in most hip. As important additional information is obtained by CT compared with conventional radiography, CT is recommended when operative procedures aimed at preventing or postponing osteoarthrosis are considered.