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

ligamentum mucosus
The medial plica is a filmy band running along the medial side of the femur. It is not always present. 
mediopatellar plica
medial shelf


Part 7 of a course on Diagnostic Arthroscopy by Dr (Mr) Angus Strover