The medial plica

A medial plica is a remnant of an embryonic partition in the knee, and runs along the inner aspect of the kneecap.

It may also be called a 'medial shelf' - more a vertical shelf than a horizontal one, mind - and runs down from above the patella to the fat pad below the patella.

As the knee bends the 'shelf' of tissue may also give a sudden snap over the rounded ends of the femur bone.

When a medial plica becomes abnormally thickened, it can be felt with the finger as a string-like object to the inner aspect of the kneecap.