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Correlation between radiographic measures of acetabular morphology with 3D femoral head coverage in patients with acetabular retroversion.

Hansen BJ, Harris MD, Anderson LA, Peters CL, Weiss JA, Anderson AE - Acta Orthop (2012)

Bottom Line: The acetabular angle was similar between groups.Acetabular retroversion was associated with a slight but statistically significant increase in anterior acetabular coverage, especially in the anterolateral region.We found that a number of 2D radiographic measures of acetabular morphology were correlated with 3D model-based measures of total and regional femoral head coverage.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA.

ABSTRACT

Background and purpose: Acetabular retroversion may result in anterior acetabular over-coverage and posterior deficiency. It is unclear how standard radiographic measures of retroversion relate to measurements from 3D models, generated from volumetric CT data. We sought to: (1) compare 2D radiographic measurements between patients with acetabular retroversion and normal control subjects, (2) compare 3D measurements of total and regional femoral head coverage between patients and controls, and (3) quantify relationships between radiographic measurements of acetabular retroversion to total and regional coverage of the femoral head.

Patients and methods: For 16 patients and 18 controls we measured the extrusion index, crossover ratio, acetabular angle, acetabular index, lateral center edge angle, and a new measurement termed the "posterior wall distance". 3D femoral coverage was determined from volumetric CT data using objectively defined acetabular rim projections, head-neck junctions, and 4 anatomic regions. For radiographic measurements, intra-observer and inter-observer reliabilities were evaluated and associations between 2D radiographic and 3D model-based measures were determined.

Results: Compared to control subjects, patients with acetabular retroversion had a negative posterior wall distance, increased extrusion index, and smaller lateral center edge angle. Differences in the acetabular index between groups approached statistical significance. The acetabular angle was similar between groups. Acetabular retroversion was associated with a slight but statistically significant increase in anterior acetabular coverage, especially in the anterolateral region. Retroverted hips had substantially less posterior coverage, especially in the posterolateral region.

Interpretation: We found that a number of 2D radiographic measures of acetabular morphology were correlated with 3D model-based measures of total and regional femoral head coverage. These correlations may be used to assist in the diagnosis of retroversion and for preoperative planning.

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3D reconstruction of femur from CT image data from a control subject.Left: The femur head-neck junction was defined automatically (line at head-neck junction). The region of femoral head that was covered (blue) was determined by projecting the rim of the acetabulum to the femur (line representing boundary of covered region in blue).Right: Two planes were created at the center of the femoral head (white) to divide the head into four anatomical regions. A = anterior, P = posterior, M = medial, and L = lateral. Each region includes the portion of the head from the most superior aspect to the femoral head/neck junction inferiorly.
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Figure 2: 3D reconstruction of femur from CT image data from a control subject.Left: The femur head-neck junction was defined automatically (line at head-neck junction). The region of femoral head that was covered (blue) was determined by projecting the rim of the acetabulum to the femur (line representing boundary of covered region in blue).Right: Two planes were created at the center of the femoral head (white) to divide the head into four anatomical regions. A = anterior, P = posterior, M = medial, and L = lateral. Each region includes the portion of the head from the most superior aspect to the femoral head/neck junction inferiorly.

Mentions: Volumetric multidetector CT scan images of the entire pelvis were resampled to 1.0-mm-thick axial slices (transverse plane) for each subject. Surfaces of the femoral and pelvic cortical bone were reconstructed semi-automatically using Amira (v5.2.1; Visage Imaging, San Diego, CA) as described previously (Anderson et al. 2005). To measure femoral coverage, a cubic spline was fit to the rim of the acetabulum and projected to the nearest points on the surface of the femoral head to create a line of acetabular coverage (Figure 2). The femoral head-neck junction was defined automatically by first creating a contour map of principal curvatures across the entire femur, and then connecting nodal points of inflection (curvature = 0) circumferentially around the head to form a line (Figure 2). A plane was fit to the inflection points and the head was cut along this plane. Next, the femoral head was divided into anatomic regions by creating a plane based on 3 points: (1) the geometric center of the head when fitted to a sphere, (2) the center of the narrowest cross-section of the neck, and (3) the circumferential center of the femoral shaft. A second plane was then created perpendicular to the first. The bisecting planes defined 4 anatomical regions (Figure 2): anterolateral (AL), anteromedial (AM), posterolateral (PL), and posteromedial (PM). These regions included the entire femoral head from the most superior aspect of the head to the head/neck junction inferiorly in each respective region. The anterolateral and anteromedial regions were combined to define total anterior surface area and the posterolateral and posteromedial were combined to define the total posterior surface area. Using the line of acetabular coverage and the regionalized femoral head, the percent coverage of each region was determined. Coverage areas were calculated as a percent of the total region surface area: 100 × [covered area (mm2) / total area of region (mm2)].


Correlation between radiographic measures of acetabular morphology with 3D femoral head coverage in patients with acetabular retroversion.

Hansen BJ, Harris MD, Anderson LA, Peters CL, Weiss JA, Anderson AE - Acta Orthop (2012)

3D reconstruction of femur from CT image data from a control subject.Left: The femur head-neck junction was defined automatically (line at head-neck junction). The region of femoral head that was covered (blue) was determined by projecting the rim of the acetabulum to the femur (line representing boundary of covered region in blue).Right: Two planes were created at the center of the femoral head (white) to divide the head into four anatomical regions. A = anterior, P = posterior, M = medial, and L = lateral. Each region includes the portion of the head from the most superior aspect to the femoral head/neck junction inferiorly.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3369147&req=5

Figure 2: 3D reconstruction of femur from CT image data from a control subject.Left: The femur head-neck junction was defined automatically (line at head-neck junction). The region of femoral head that was covered (blue) was determined by projecting the rim of the acetabulum to the femur (line representing boundary of covered region in blue).Right: Two planes were created at the center of the femoral head (white) to divide the head into four anatomical regions. A = anterior, P = posterior, M = medial, and L = lateral. Each region includes the portion of the head from the most superior aspect to the femoral head/neck junction inferiorly.
Mentions: Volumetric multidetector CT scan images of the entire pelvis were resampled to 1.0-mm-thick axial slices (transverse plane) for each subject. Surfaces of the femoral and pelvic cortical bone were reconstructed semi-automatically using Amira (v5.2.1; Visage Imaging, San Diego, CA) as described previously (Anderson et al. 2005). To measure femoral coverage, a cubic spline was fit to the rim of the acetabulum and projected to the nearest points on the surface of the femoral head to create a line of acetabular coverage (Figure 2). The femoral head-neck junction was defined automatically by first creating a contour map of principal curvatures across the entire femur, and then connecting nodal points of inflection (curvature = 0) circumferentially around the head to form a line (Figure 2). A plane was fit to the inflection points and the head was cut along this plane. Next, the femoral head was divided into anatomic regions by creating a plane based on 3 points: (1) the geometric center of the head when fitted to a sphere, (2) the center of the narrowest cross-section of the neck, and (3) the circumferential center of the femoral shaft. A second plane was then created perpendicular to the first. The bisecting planes defined 4 anatomical regions (Figure 2): anterolateral (AL), anteromedial (AM), posterolateral (PL), and posteromedial (PM). These regions included the entire femoral head from the most superior aspect of the head to the head/neck junction inferiorly in each respective region. The anterolateral and anteromedial regions were combined to define total anterior surface area and the posterolateral and posteromedial were combined to define the total posterior surface area. Using the line of acetabular coverage and the regionalized femoral head, the percent coverage of each region was determined. Coverage areas were calculated as a percent of the total region surface area: 100 × [covered area (mm2) / total area of region (mm2)].

Bottom Line: The acetabular angle was similar between groups.Acetabular retroversion was associated with a slight but statistically significant increase in anterior acetabular coverage, especially in the anterolateral region.We found that a number of 2D radiographic measures of acetabular morphology were correlated with 3D model-based measures of total and regional femoral head coverage.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA.

ABSTRACT

Background and purpose: Acetabular retroversion may result in anterior acetabular over-coverage and posterior deficiency. It is unclear how standard radiographic measures of retroversion relate to measurements from 3D models, generated from volumetric CT data. We sought to: (1) compare 2D radiographic measurements between patients with acetabular retroversion and normal control subjects, (2) compare 3D measurements of total and regional femoral head coverage between patients and controls, and (3) quantify relationships between radiographic measurements of acetabular retroversion to total and regional coverage of the femoral head.

Patients and methods: For 16 patients and 18 controls we measured the extrusion index, crossover ratio, acetabular angle, acetabular index, lateral center edge angle, and a new measurement termed the "posterior wall distance". 3D femoral coverage was determined from volumetric CT data using objectively defined acetabular rim projections, head-neck junctions, and 4 anatomic regions. For radiographic measurements, intra-observer and inter-observer reliabilities were evaluated and associations between 2D radiographic and 3D model-based measures were determined.

Results: Compared to control subjects, patients with acetabular retroversion had a negative posterior wall distance, increased extrusion index, and smaller lateral center edge angle. Differences in the acetabular index between groups approached statistical significance. The acetabular angle was similar between groups. Acetabular retroversion was associated with a slight but statistically significant increase in anterior acetabular coverage, especially in the anterolateral region. Retroverted hips had substantially less posterior coverage, especially in the posterolateral region.

Interpretation: We found that a number of 2D radiographic measures of acetabular morphology were correlated with 3D model-based measures of total and regional femoral head coverage. These correlations may be used to assist in the diagnosis of retroversion and for preoperative planning.

Show MeSH