Trochlear facet asymmetry
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At the time the article was created Joachim Feger had no recorded disclosures.View Joachim Feger's current disclosures
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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.
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Facet asymmetry 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.
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.
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.
- 1. Pfirrmann C, Zanetti M, Romero J, Hodler J. Femoral Trochlear Dysplasia: MR Findings. Radiology. 2000;216(3):858-64. doi:10.1148/radiology.216.3.r00se38858 - Pubmed
- 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. doi:10.1177/0363546512472441 - Pubmed
- 3. Ngai S, Smitaman E, Resnick D. Trochlear Dysplasia. Radsource – June 2018. MRI Web Clinic
- 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. doi:10.1007/s00167-017-4520-z - Pubmed