During embryologic development mesenchymal tissue form a shelf-like membrane called synovial plica and these folds resorb over time. However, remnants of the plica may remain as incomplete folds within the knee joint
There are discernible synovial folds:
- Inferior (ligamentum mucosum)
Plica may be asymptomatic in 50 % of cases
Direct trauma to the knee may cause the plica to become inflamed and symptomatic. The resolving trauma and/or inflammation to the plica may cause a residual hard bowstring plica. It is usually the medial plica that becomes symptomatic. The medial plica runs from the medial aspect of the knee joint to the infrapatellar fat pad.