Acetabular angle

Changed by Henry Knipe, 20 Jul 2022

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The acetabular angle ~~(also~~, also known as the Sharp's angle)⁶ is,is a radiographic measurement most commonly used when evaluating for 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~~In children, the angle is formed by a horizontal plane of the pelvis defined by a line connecting both triradiate cartilages (Hilgenreiner line) and a second line that extends ~~along~~through to the lateral aspect of the acetabular ~~roofs~~roof ^7,8.

In ~~the adult~~adults, where the triradiate cartilages are fused and therefore inapparent, the horizontal plane of the pelvis defined as the inferior margin of the pelvic teardrop is used instead⁷. This, of course, shifts the horizontal line inferiorly and changes the value of the angle^ref.

Interpretation

Normal values in children

The acetabular angle using the Hilgenreiner line should be <28º at birth^ref. The angle should become progressively shallower with age and should measure <22º at and beyond 1 year of age^ref.

Normal values in adults

The normal range is 33º to 38º^6,8. ~~Angles >47º are seen in patients with~~An increased acetabular angle defining acetabular dysplasia varies between authors and is reported at >42º ⁶or ≥45º ⁷. When the angle is between the upper end of the normal range and an increased acetabular angle the terms "borderline" or "indeterminate" can be used ^6,7. A ~~measurement between 39º and 46º~~decreased acetabular angle is ~~indeterminate~~<32º ⁶.

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^ref.

Related pathology

increased acetabular angles
- neuromuscular disorders
- acetabular dysplasia ~~of the hip (DDH)~~
decreased acetabular angles
- Down syndrome
- achondroplasia

-<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>
~~-<li>increased acetabular angles<ul>~~
+<p>The <strong>acetabular angle</strong>, also known as the <strong>Sharp angle </strong><sup>6</sup>,<strong> </strong>is a radiographic measurement most commonly used when evaluating for 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>In children, the angle is formed by a horizontal plane of the pelvis defined by a 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 through to the lateral aspect of the acetabular roof <sup>7,8</sup>.</p><p>In adults, where the triradiate cartilages are fused and therefore inapparent, the horizontal plane of the pelvis defined as the inferior margin of the <a href="/articles/pelvic-teardrop-1">pelvic teardrop</a> is used instead <sup>7</sup>. This, of course, shifts the horizontal line inferiorly and changes the value of the angle <sup>ref</sup>.</p><h4>Interpretation</h4><h5>Normal values in children</h5><p>The acetabular angle using the Hilgenreiner line should be <28º at birth <sup>ref</sup>. The angle should become progressively shallower with age and should measure <22º at and beyond 1 year of age <sup>ref</sup>. </p><h5>Normal values in adults</h5><p>The normal range is 33º to 38º <sup>6,8</sup>. An increased acetabular angle defining <a href="/articles/acetabular-dysplasia">acetabular dysplasia</a> varies between authors and is reported at >42º <sup>6 </sup>or ≥45º <sup>7</sup>. When the angle is between the upper end of the normal range and an increased acetabular angle the terms "borderline" or "indeterminate" can be used <sup>6,7</sup>. A decreased acetabular angle is <32º <sup>6</sup>.</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 <sup>ref</sup>.</p><h4>Related pathology</h4><ul><li>increased acetabular angles<ul>
~~-<li><a href="/articles/developmental-dysplasia-of-the-hip">developmental dysplasia of the hip (DDH)</a></li>~~
~~-</ul>~~
~~-</li>~~
~~-<li>decreased acetabular angles<ul>~~
+<li><a href="/articles/acetabular-dysplasia">acetabular dysplasia</a></li>
+</ul>decreased acetabular angles<ul>
~~-</li>~~
~~-</ul><h4>See also</h4><ul>~~
+</li></ul><h4>See also</h4><ul>

References changed:

1. Lee Y, Chung C, Koo K, Lee K, Kwon D, Park M. Measuring Acetabular Dysplasia in Plain Radiographs. Arch Orthop Trauma Surg. 2011;131(9):1219-26. <a href="https://doi.org/10.1007/s00402-011-1279-4">doi:10.1007/s00402-011-1279-4</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/21360130">Pubmed</a>
2. Ackland M, Bourne W, Uhthoff H. Anteversion of the Acetabular Cup. Measurement of Angle After Total Hip Replacement. J Bone Joint Surg Br. 1986;68(3):409-13. <a href="https://doi.org/10.1302/0301-620X.68B3.3733807">doi:10.1302/0301-620X.68B3.3733807</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/3733807">Pubmed</a>
3. Yoo W, Moon H, Cho T, Choi I. Does Shelf Acetabuloplasty Influence Acetabular Growth and Remodeling? Clin Orthop Relat Res. 2012;470(9):2411-20. <a href="https://doi.org/10.1007/s11999-011-2163-9">doi:10.1007/s11999-011-2163-9</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/22048866">Pubmed</a>
4. Rampal V, Klein C, Arellano E et al. Outcomes of Modified Dega Acetabuloplasty in Acetabular Dysplasia Related to Developmental Dislocation of the Hip. Orthopaedics & Traumatology: Surgery & Research. 2014;100(2):207-11. <a href="https://doi.org/10.1016/j.otsr.2013.12.015">doi:10.1016/j.otsr.2013.12.015</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/24629458">Pubmed</a>
5. Wenger D. Surgical Treatment of Developmental Dysplasia of the Hip. Instr Course Lect. 2014;63:313-23. - <a href="https://www.ncbi.nlm.nih.gov/pubmed/24720317">Pubmed</a>
6. Mannava S, Geeslin A, Frangiamore S et al. Comprehensive Clinical Evaluation of Femoroacetabular Impingement: Part 2, Plain Radiography. Arthrosc Tech. 2017;6(5):e2003-9. <a href="https://doi.org/10.1016/j.eats.2017.06.011">doi:10.1016/j.eats.2017.06.011</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/29399468">Pubmed</a>
7. Welton K, Jesse M, Kraeutler M, Garabekyan T, Mei-Dan O. The Anteroposterior Pelvic Radiograph. J Bone Joint Surg. 2018;100(1):76-85. <a href="https://doi.org/10.2106/jbjs.17.00500">doi:10.2106/jbjs.17.00500</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/29298264">Pubmed</a>
8. Sharp I. Acetabular Dysplasia. The Journal of Bone and Joint Surgery British Volume. 1961;43-B(2):268-72. <a href="https://doi.org/10.1302/0301-620x.43b2.268">doi:10.1302/0301-620x.43b2.268</a>
1. Lee Y, Chung C, Koo K, Lee K, Kwon D, Park M. Measuring Acetabular Dysplasia in Plain Radiographs. Arch Orthop Trauma Surg. 2011;131(9):1219-26. <a href="https://doi.org/10.1007/s00402-011-1279-4">doi:10.1007/s00402-011-1279-4</a>
2. Ackland M, Bourne W, Uhthoff H. Anteversion of the Acetabular Cup. Measurement of Angle After Total Hip Replacement. J Bone Joint Surg Br. 1986;68(3):409-13. <a href="https://doi.org/10.1302/0301-620X.68B3.3733807">doi:10.1302/0301-620X.68B3.3733807</a>
3. Yoo W, Moon H, Cho T, Choi I. Does Shelf Acetabuloplasty Influence Acetabular Growth and Remodeling? Clinical Orthopaedics & Related Research. 2012;470(9):2411-20. <a href="https://doi.org/10.1007/s11999-011-2163-9">doi:10.1007/s11999-011-2163-9</a>
4. Rampal V, Klein C, Arellano E et al. Outcomes of Modified Dega Acetabuloplasty in Acetabular Dysplasia Related to Developmental Dislocation of the Hip. Orthopaedics & Traumatology: Surgery & Research. 2014;100(2):207-11. <a href="https://doi.org/10.1016/j.otsr.2013.12.015">doi:10.1016/j.otsr.2013.12.015</a>
5. Wenger D. Surgical Treatment of Developmental Dysplasia of the Hip. Instr Course Lect. 2014;63:313-23. <a href="https://www.ncbi.nlm.nih.gov/pubmed/24720317">PMID 24720317</a>
6. Mannava S, Geeslin A, Frangiamore S et al. Comprehensive Clinical Evaluation of Femoroacetabular Impingement: Part 2, Plain Radiography. Arthroscopy Techniques. 2017;6(5):e2003-9. <a href="https://doi.org/10.1016/j.eats.2017.06.011">doi:10.1016/j.eats.2017.06.011</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/29399468">Pubmed</a>