A synovial plica is an infold of the joint lining or synovium - it is a normal anatomical structure but can sometimes become problematic.

The filmy band is actually a fold in the capsule of the knee, but that is not appreciated in this illustration.

This illustration gives a better example of how the plica folds in from the capsule surrounding the knee joint.
What causes a plica to become symptomatic?
If a plica is traumatised, it may become inflamed and eventually thickened, when it may be nipped between the bones of the knee causing sharp pain because the synovium itself is filled with pain-sensitive nerves.
What is the treatment for a symptomatic plica?
A symptomatic plica may settle down on its own with rest and anti-inflammatory medication, especially if symptoms have been brought on by some unusual activity. But once the condition becomes chronic then surgical excision of the plica is likely to give the best outcome.
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