Trochlear facet asymmetry

Changed by Joachim Feger, 3 Jun 2020

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~~Facet~~Trochlear facet asymmetry (FA)

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~~Facet~~Trochlear facet asymmetry (FA) in ~~trochlear dysplasia~~ 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 traditionally measured 3cm 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 Pfirrmann¹.

-<p><strong><strong>Facet asymmetry (FA)</strong></strong> in trochlear dysplasia refers to the condition of the medial facet being abnormally small if compared to the lateral facet <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 traditionally measured 3cm above the joint line<sup>1,3</sup>. <sup> </sup></p><h4>Interpretation</h4><p>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 <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>
~~-<li><a title="Trochlear dysplasia" href="/articles/trochlear-dysplasia">trochlear dysplasia</a></li>~~
~~-<li><a title="Patellofemoral instability" href="/articles/patellofemoral-instability">patellofemoral instability</a></li>~~
+<p><strong><strong>Trochlear facet asymmetry (FA)</strong></strong> in refers to the condition of the medial facet being abnormally small if compared to the lateral facet in trochlear dysplasia <sup>1</sup>.</p><h4>Usage</h4><p>Facet asymmetry (FA) is also used as a measurement in magnet resonance imaging for <a href="/articles/trochlear-dysplasia">trochlear dysplasia</a> 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 traditionally measured 3cm above the joint line <sup>1,3</sup>. <sup> </sup></p><h4>Interpretation</h4><p>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 <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>
+<li><a href="/articles/trochlear-dysplasia">trochlear dysplasia</a></li>
+<li><a href="/articles/patellofemoral-instability">patellofemoral instability</a></li>

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>
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>

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