Trochlear facet asymmetry

Changed by Joachim Feger, 20 Nov 2021

Updates to Article Attributes

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Trochlear facet asymmetry (FA) refers to the condition of the medial facet being abnormally small if compared to the lateral facet in trochlear dysplasia 1.

Usage

Facet asymmetry (FA) is also used as a measurement in magnet resonance imaging for trochlear dysplasia to make it more objective 1-3, this concept was adapted from axial radiographs 3.

Measurement

One option to measure facet asymmetry is the ratio between medial versus lateral trochlear facet length calculated as (medial facet) / (lateral facet)  1. Another option is to calculate it the other way around, that is (lateral facet) / (medial facet) 2.

Facet asymmetry is traditionally measured 3 cm above the joint line 1,3.

Interpretation

A threshold of <0.4 or 40% was suggestive of trochlear dysplasia and showed a sensitivity and specificity of 100% and 96% in that study 2.

History and etymology

The principle has been adapted for magnetic resonance imaging by Pfirrmann 1.

See also

  • -<p><strong><strong>Trochlear facet asymmetry (FA)</strong></strong> refers to the condition of the medial facet being abnormally small if compared to the lateral facet in <a href="/articles/trochlear-dysplasia">trochlear dysplasia</a> <sup>1</sup>.</p><h4>Usage</h4><p>Facet asymmetry (FA) is also used as a measurement in magnet resonance imaging for trochlear dysplasia to make it more objective <sup>1-3</sup>, this concept was adapted from axial radiographs <sup>3</sup>.</p><h4>Measurement</h4><p>One option to measure facet asymmetry is the ratio between medial versus lateral trochlear facet length calculated as (medial facet) / (lateral facet) <sup> 1</sup>. Another option is to calculate it the other way around, that is (lateral facet) / (medial facet) <sup>2</sup>.</p><p>Facet asymmetry is traditionally measured 3 cm above the joint line <sup>1,3</sup>. <sup> </sup></p><h4>Interpretation</h4><p>A threshold of &lt;0.4 or 40% was suggestive of trochlear dysplasia and showed a sensitivity and specificity of 100% and 96% in that study <sup>2</sup>.</p><h4>History and etymology</h4><p>The principle has been adapted for magnetic resonance imaging by Pfirrmann <sup>1</sup>.</p><h4>See also</h4><ul>
  • +<p><strong><strong>Trochlear facet asymmetry (FA)</strong></strong> refers to the condition of the medial facet being abnormally small if compared to the lateral facet in <a href="/articles/trochlear-dysplasia">trochlear dysplasia</a> <sup>1</sup>.</p><h4>Usage</h4><p>Facet asymmetry is also used as a measurement in magnet resonance imaging for trochlear dysplasia to make it more objective <sup>1-3</sup>, this concept was adapted from axial radiographs <sup>3</sup>.</p><h4>Measurement</h4><p>One option to measure facet asymmetry is the ratio between medial versus lateral trochlear facet length calculated as (medial facet) / (lateral facet) <sup> 1</sup>. Another option is to calculate it the other way around, that is (lateral facet) / (medial facet) <sup>2</sup>.</p><p>Facet asymmetry is traditionally measured 3 cm above the joint line <sup>1,3</sup>. <sup> </sup></p><h4>Interpretation</h4><p>A threshold of &lt;0.4 or 40% was suggestive of trochlear dysplasia and showed a sensitivity and specificity of 100% and 96% in that study <sup>2</sup>.</p><h4>History and etymology</h4><p>The principle has been adapted for magnetic resonance imaging by Pfirrmann <sup>1</sup>.</p><h4>See also</h4><ul>

References changed:

  • 1. Pfirrmann C, Zanetti M, Romero J, Hodler J. Femoral Trochlear Dysplasia: MR Findings. Radiology. 2000;216(3):858-64. <a href="https://doi.org/10.1148/radiology.216.3.r00se38858">doi:10.1148/radiology.216.3.r00se38858</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/10966723">Pubmed</a>
  • 2. Charles M, Haloman S, Chen L, Ward S, Fithian D, Afra R. Magnetic Resonance Imaging–Based Topographical Differences Between Control and Recurrent Patellofemoral Instability Patients. Am J Sports Med. 2013;41(2):374-84. <a href="https://doi.org/10.1177/0363546512472441">doi:10.1177/0363546512472441</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/23371940">Pubmed</a>
  • 3. Ngai S, Smitaman E, Resnick D. Trochlear Dysplasia. Radsource – June 2018. <a href="https://radsource.us/trochlear-dysplasia/#fn-6565-16">MRI Web Clinic</a>
  • 3. Ngai S, Smitaman E, Resnick D. Trochlear Dysplasia. Radsource – June 2018. <a href="https://radsource.us/trochlear-dysplasia/#fn-6565-16">MRI Web Clinic</a>
  • 4. Paiva M, Blønd L, Hölmich P et al. Quality Assessment of Radiological Measurements of Trochlear Dysplasia; a Literature Review. Knee Surg Sports Traumatol Arthrosc. 2017;26(3):746-55. <a href="https://doi.org/10.1007/s00167-017-4520-z">doi:10.1007/s00167-017-4520-z</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28315921">Pubmed</a>
  • 1. Pfirrmann C, Zanetti M, Romero J, Hodler J. Femoral Trochlear Dysplasia: MR Findings. Radiology. 2000;216(3):858-64. <a href="https://doi.org/10.1148/radiology.216.3.r00se38858">doi:10.1148/radiology.216.3.r00se38858</a>
  • 2. Charles M, Haloman S, Chen L, Ward S, Fithian D, Afra R. Magnetic Resonance Imaging–Based Topographical Differences Between Control and Recurrent Patellofemoral Instability Patients. Am J Sports Med. 2013;41(2):374-84. <a href="https://doi.org/10.1177/0363546512472441">doi:10.1177/0363546512472441</a>
  • 3. Ngai S, Smitaman E, Resnick D. Trochlear Dysplasia – <a href="https://radsource.us/trochlear-dysplasia/#fn-6565-16"> Radsource MRI Web Clinic June 2018 </a>
  • 3. Ngai S, Smitaman E, Resnick D. Trochlear Dysplasia. Radsource - June 2018. <a href="https://radsource.us/trochlear-dysplasia/#fn-6565-16">MRI Web Clinic</a>
  • 4. Paiva M, Blønd L, Hölmich P et al. Quality Assessment of Radiological Measurements of Trochlear Dysplasia; a Literature Review. Knee Surg Sports Traumatol Arthrosc. 2017;26(3):746-55. <a href="https://doi.org/10.1007/s00167-017-4520-z">doi:10.1007/s00167-017-4520-z</a>

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