The meniscus is a piece of cartilage that provides a cushion between your thighbone (femur) and shinbone (tibia). There are two menisci in each knee joint, and they normally have a half-moon shape. A discoid meniscus has an abnormal disc shape, similar to a hockey puck but hollow in the middle.

A discoid meniscus occurs in the womb before birth when the cartilage does not properly develop. It is commonly detected in childhood or adolescence. It is most often present in one knee, but approximately 20% of people have it in both knees.

The abnormal shape and thickness of the discoid meniscus make it more prone to injury and tearing. Symptoms include:

• Pain and tenderness in the knee, most frequently on the outer side
• Sharp pain with running, jumping, or deep squatting
• Swelling in the knee
• Catching, locking or “popping” of the knee while walking or squatting
• Loss of knee motion or strength in the quadriceps (thigh) muscle
• Discomfort during daily activities, such as walking up and down stairs

A knee specialist at Lancaster Orthopedic Group will assess the knee and evaluate the motion, strength, flexibility, tenderness and swelling. He or she may also recommend diagnostic imaging, such as ultrasound, X-ray, or MRI to identify a discoid meniscus or a tear in the meniscus.

If the discoid meniscus is asymptomatic, it can be left in place. When there is pain or popping, arthroscopic surgery to contour the discoid lateral meniscus to resemble a normal meniscus may be recommended.