Do you see the unusual finding in this adolescent’s patella?

This 17-year-old male has patellar pain in his right knee. The cause of his pain is somewhat unusual. What is the most common locale of patellofemoral osteochondritis dissecans? What is the best treatment in a juvenile? What is the underlying cause?

Sagittal T2

Coronal STIR

Sagittal T1

Sagittal T2

Axial T2

 

The unusual finding is stage 2 osteochondritis dissecans (OCD). Take note of the approximately 12 x 5 x 9mm area of the patella just deep to the articular surface surrounded by thin linear hypointensity (arrow, image 5) suggesting fibrous attachment. A “puffy” appearance to the lesion (image 5) suggests a blister has formed in the overlying cartilage. There is no evidence of dislodgement at this time.

The most common location of patellofemoral OCD is the anterolateral femoral trochlear ridge. The best treatment in a juvenile is rest, especially if the growth plates are open. Most will heal. Sometimes lateral retinacular release is effective. The underlying cause of OCD is most likely repetitive friction microtrauma from an underlying femoral or patellofemoral dysplasia that devitalizes the superficial capsular blood supply to the bone.

For more knee case review, head to MRI Online.

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