Bilateral standing anterior posterior x-ray of a 13-year-old girl with a 4-month history of anterior lateral left knee pain
A lateral x-ray of the patient’s knee
A 13-year-old girl presents with a 4-month history of anterior lateral left knee pain. She reports episodic “popping” and pain in the knee while running. She denies any swelling or feeling of instability in the knee. Examination reveals pain over the lateral joint line, which is made worse with knee extension and valgus stress. Bilateral standing anterior posterior and lateral x-rays are taken.
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A discoid meniscus should be suspected in adolescent patients who present with insidious onset of lateral joint line pain and “popping” with knee extension. A discoid meniscus is an anatomic variant in which the meniscus is wider and thicker than normal and therefore more prone to getting stuck in the knee.1
Discoid menisci are relatively uncommon. They occur in 3% to 5% of the US population, with the lateral meniscus much more commonly involved than the medial meniscus. Discoid menisci are usually asymptomatic and are often found incidentally during knee arthroscopy. They most often become symptomatic during adolescence, and the most common symptoms are “locking” or “popping” as the knee is extended.
X-rays are often normal and magnetic resonance imaging is the study of choice for diagnosing discoid menisci. The current standard of treatment is arthroscopic knee surgery to trim the meniscal tissue to a normal crescent shape.2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).