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A discoid meniscus is an abnormally formed meniscus (shock absorber) in the knee. It is more semi-circular rather than crescent shaped and has reduced stability compared to a normal meniscus.
The cause of a discoid meniscus is unknown. Proposed causes are due to a failure during embryological development, or that it is due to a lack of fixation to the tibia.
The symptoms of a discoid meniscus are highly variable. In some cases they may not have any symptoms at all, in the worst cases they can cause significant pain, swelling, discomfort and can cause the knee to ‘lock’ (get stuck and unable to move).
Commonly in young children, parents may notice a non-painful popping or clicking in the knee. In older children/adolescents they may feel as though the knee gives way, or if the meniscus has torn, they may have pain and swelling.
Initial X rays can often be reported as normal, as the signs on X ray are quite subtle (see image at right).
On MRI, the charactertic finding is a “bow tie” sign present on multiple slices (see MRI on right)