With no recent injury or surgery, what explains this woman’s knee pain?

This 35-year-old woman presents with pain and locking when bending joint in her right knee. She has no recent injury and no history of surgery to this knee. She has patellofemoral maltracking, but what is the most important finding?

Sagittal T2 fat-suppression

Axial T2

Coronal T2 fat-suppression

Sagittal PD (SPIR)

Answer: The most important finding is the septated cystic structure involving the upper fibers of the anterior cruciate ligament. This is consistent with cystic mucoid degeneration with ganglion pseudocyst of the cruciate (arrows). Any combination of prior injury, microinstability and/or a small femoral notch (notch dysplasia or stenosis) can produce this finding. For more knee case review, visit MRI Online.

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