Presenter discusses different patellofemoral imaging techniques
KOALA, Hawaii — As the most important factor in most patellofemoral problems, patella positioning can be measured several different ways, according to a presenter here.
“The Caton-Deschamps is when you measure the length of the cartilage to the tibia and that’s the most commonly used in patellofemoral surgery because it makes the most sense if you’re trying to lower it,” Elizabeth A. Arendt, MD, professor and vice chair in the department of orthopedic surgery at the University of Minnesota, said in her presentation at Orthopedics Today Hawaii. “Insall-Salvati tends to be the most popular in the United States.”
However, Arendt noted femoral-based images provide a better view of the trochlear groove, which provides stability to the patella.
“The one [measurement] that has become the most popular is to measure the cartilage surface of the patella to the overlap with the cartilage surface of the trochlea,” Arendt said.
One way to measure the Q angle is with the tibial tubercle-trochlear groove (TT-TG) distance, which has been traditionally done from the overlap between the center of the trochlea to the center of the tibial tubercle, according to Arendt. Although previously published literature has shown a measurement of greater than 20 mm on CT imaging led to the risk of instability, Arendt noted that this measurement is variable.
“It’s a different measurement on MRI because we’re using different points, obviously, and it’s a little bit lower than 20 mm, approximately 15 mm would be normal,” she said.
Arendt noted the TT-TG measurement is made up of medialization of the trochlear groove, rotation between the femur and the tibia, and lateralization of the tibial tubercle.
“My encouragement is it’s just a measurement, but make sure that it’s your lateral tibial offset that you’re looking at and not something else,” Arendt said.
When using measurements on the axial plane, Arendt said it is good to have a low degree of flexion, such as a 20° Laurin view or 30° Merchant view. To achieve a low flexion view, Arendt noted there should be a longer lateral trochlea facet.
“If it’s about one-third and two-thirds, that’s a good low flexion view,” she said. “If you have 50-50, you’re getting too high to be useful for a lot of ways that we use these sulcus angles. We do look at approximately 145° as being normal in a 20° to 30° view and after that, it’s considered trochlea dysplasia.”
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Arendt EA. The patellofemoral joint injuries and their treatment. Presented at: Orthopedics Today Hawaii; Jan. 8-12, 2023; Koala, Hawaii.
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