22-year-old female with instability of the right knee with starting and stopping. MENISCI: The medial and lateral menisci are intact.ARTICULAR CARTILAGE AND BONE: No articular cartilage defects are evident, and the bone marrow signal is normal.LIGAMENTS: The anterior and posterior cruciate ligaments are intact, as are the medial collateral ligament and lateral collateral ligament complex. EXTENSOR MECHANISM: The extensor mechanism is intact. There is mild edema in the superolateral aspect of the Hoffa's fat pad, which can be seen in patients with patellofemoral instability; however, we see no frank femoral trochlear dysplasia. The tibial tuberosity to trochlear groove distance is 1.4 cm, which is within normal limits. The Insall-Salvati ratio is 1.37, suggesting a mild patella alta deformity.ADDITIONAL
1.Mildly increased signal intensity in the superolateral aspect of Hoffa's fat pad indicating edema, which can be seen in patients with patellofemoral instability. There is a slight patella alta deformity, but we see no frank femoral trochlear dysplasia and the tibial tuberosity to trochlear groove distance is within normal limits.2.The ligaments and menisci are within normal limits.3.Nodular mass within the subcutaneous fat of the medial knee, which is nonspecific on this nonenhanced imaging study. The differential diagnosis includes an angiomatous lesion, particularly given its proximity to the saphenous vein. A peculiar lymph node is another possibility. Although I suspect that this is a benign entity, I cannot exclude the less likely possibility of a small but malignant lesion on the basis of this single imaging study. Further evaluation with contrast-enhanced MRI is recommended and referral to orthopedic oncology should be considered.