Acetabular angle
Updates to Article Attributes
The acetabular angle (also known as Sharp's angle)6 is a radiographic measurement used when evaluating potential developmental dysplasia of the hip (DDH). It is most useful in patients who have started to ossify the epiphysis since ossification diminishes the usefulness of ultrasound.
Measurement
The angle is formed by a horizontal line connecting both triradiate cartilages (Hilgenreiner line) and a second line that extends along the acetabular roofs. In the adult, where the triradiate cartilages are fused and therefore inapparent, the inferior margin of the pelvic teardrop is used instead. This, of course, shifts the horizontal line inferiorly and changes the value of the angle.
Interpretation
Normal values in children
The acetabular angle using the Hilgenreiner line should be <28º at birth. The angle should become progressively shallower with age and should measure <22º at and beyond 1 year of age.
Normal values in adults
The normal range is 33º to 38º. Angles >47º are seen in patients with acetabular dysplasia. A measurement between 39º and 46º is indeterminate.
Having the centre beam above or below the pubis can alter the measurement due to geometric distortion. Although a 5 cm error in beam alignment only changes the measurement by 4º, this does mean that these measurements should not be performed on an abdominal radiograph.
Related pathology
- increased acetabular angles
- neuromuscular disorders
- developmental dysplasia of the hip (DDH)
- decreased acetabular angles
See also
-<p>The <strong>acetabular angle</strong> (also known as Sharp's angle)<sup>6</sup> is a radiographic measurement used when evaluating potential <a href="/articles/developmental-dysplasia-of-the-hip">developmental dysplasia of the hip (DDH)</a>. It is most useful in patients who have started to ossify the epiphysis since ossification diminishes the usefulness of ultrasound.</p><h4>Measurement</h4><p>The angle is formed by a horizontal line connecting both <a href="/articles/triradiate-cartilage">triradiate cartilages</a> (<a href="/articles/hilgenreiner-line">Hilgenreiner line</a>) and a second line that extends along the acetabular roofs. In the adult, where the triradiate cartilages are fused and therefore inapparent, the inferior margin of the <a href="/articles/pelvic-teardrop-1">pelvic teardrop</a> is used instead. This, of course, shifts the horizontal line inferiorly and changes the value of the angle.</p><h4>Interpretation</h4><h5>Normal values in children</h5><p>The acetabular angle using the Hilgenreiner line should be <28º at birth. The angle should become progressively shallower with age and should measure <22º at and beyond 1 year of age. </p><h5>Normal values in adults</h5><p>The normal range is 33º to 38º. Angles >47º are seen in patients with <a href="/articles/acetabular-dysplasia">acetabular dysplasia</a>. A measurement between 39º and 46º is indeterminate.</p><p>Having the centre beam above or below the pubis can alter the measurement due to geometric distortion. Although a 5 cm error in beam alignment only changes the measurement by 4º, this does mean that these measurements should not be performed on an abdominal radiograph.</p><h4>Related pathology</h4><ul>- +<p>The <strong>acetabular angle</strong> (also known as <strong>Sharp's angle</strong>)<sup>6</sup> is a radiographic measurement used when evaluating potential <a href="/articles/developmental-dysplasia-of-the-hip">developmental dysplasia of the hip (DDH)</a>. It is most useful in patients who have started to ossify the epiphysis since ossification diminishes the usefulness of ultrasound.</p><h4>Measurement</h4><p>The angle is formed by a horizontal line connecting both <a href="/articles/triradiate-cartilage">triradiate cartilages</a> (<a href="/articles/hilgenreiner-line">Hilgenreiner line</a>) and a second line that extends along the acetabular roofs. In the adult, where the triradiate cartilages are fused and therefore inapparent, the inferior margin of the <a href="/articles/pelvic-teardrop-1">pelvic teardrop</a> is used instead. This, of course, shifts the horizontal line inferiorly and changes the value of the angle.</p><h4>Interpretation</h4><h5>Normal values in children</h5><p>The acetabular angle using the Hilgenreiner line should be <28º at birth. The angle should become progressively shallower with age and should measure <22º at and beyond 1 year of age. </p><h5>Normal values in adults</h5><p>The normal range is 33º to 38º. Angles >47º are seen in patients with <a href="/articles/acetabular-dysplasia">acetabular dysplasia</a>. A measurement between 39º and 46º is indeterminate.</p><p>Having the centre beam above or below the pubis can alter the measurement due to geometric distortion. Although a 5 cm error in beam alignment only changes the measurement by 4º, this does mean that these measurements should not be performed on an abdominal radiograph.</p><h4>Related pathology</h4><ul>
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