Patellar dislocation | Figure 1

CincyKidsRad

Cincinnati Children's Radiology

Patellar dislocation

AP (image 1) and sunrise (image 2) radiographs of the knee shows patellar dislocation with lateral displacement of the patella (arrow). After reduction, the patella rests within the shallow femoral trochlea. There is soft tissue swelling medially (arrowhead) due to the disruption of the medial retinaculum. Patellar dislocations are more common in patients with trochlear dysplasia, which can appear on a radiograph as a shallow femoral trochlea on a sunrise view.

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19 y/o male, pain in right knee. He have had a non-treatment bilateral congenital patellar dislocation. Radiography show a bilateral patellar dislocation. MRI & Arthroscopy show tear of discoid medial meniscus, normal lateral meniscus and hypoplasia of femoral medial condyle in the right. Have you ever seen a same case? Or do you know any case has both discoid medial meniscus and congenital patellar dislocation?](https://app.figure1.com/case-detail/2cee0e95-ec40-4561-86f6-ff2b2f67a3cd)


Radiograph of the patella demonstrates a curvilnear bony fragment (white arrow) along the medial facet with lateral tilting and subluxation of the patella. Sag FS T2 MRI shows a large osteochondral defect (denoted by white arrows) interrupting the low signal intensity cartilage of the lateral femoral condyle. These findings are consistent with transient patellar dislocation. #MSKMonday](https://app.figure1.com/case-detail/64f94cc6-7c4f-4211-b088-819fd3fc4e47)


Sunrise (image 1) and PA (image 2) views of the knee show lateral dislocation of the patella. The dislocation is associated with a displaced osteochondral fracture (arrow) of the posterior aspect of the patella. Patellar dislocations typically occur due to a shallow femoral trochlea. In this case, the dislocation occurred due to direct trauma. Osteochondral fractures occur in 25% of traumatic patellar dislocations. #MSKMonday #MusculoskeletalMonday](https://app.figure1.com/case-detail/6682e890-dcab-4f86-9cb2-0d86f91e6661)


MRI of the knee shows multiple findings of patellar dislocation. There is a classic bone bruise pattern with bright signal in the lateral femoral condyle and the medial patellar facet (arrows). There is a large lipohemarthrosis (arrowhead) with a parfait effect and layering of three different signal intensities. Finally, there is disruption of the medial patellofemoral ligament (dashed arrow). Other findings are also present including cartilage disruption, soft tissue edema, and a flattened femoral trochlea. Patellar dislocation can occur from direct trauma or may be associated with congenital/anatomic differences such as femoral trochlea dysplasia, excessive lateral patellar tilt, and patella alta. #MSKMonday