The plica is a fold of joint lining tissue that is left over from early development. During embryologic development, bands of tissue divide your knee into joints and these bands often remain in your joints as you develop and grow. Trauma to the knee, either directly or from overuse can cause these bands to become thick and inflamed. This results in pain in the front of the knee, often towards the inside of the joint.
The pain associated with Plica Syndrome usually occurs when the knee is bent and can be accompanied by abnormal catching, locking and clicking. Athletes who participate in sports that require rapid and forceful motions such as kicking and jumping (volleyball, basketball, soccer) are especially prone to this syndrome, as are athletes who risk direct violent contact such as football players.
Typically, non-operative treatment is all that is needed to treat the syndrome. This includes the use of medications and icing to reduce pain and inflammation along with stretching and strengthening exercises. Operation is usually not necessary and is only explored as an option if non-operative treatments fail to work.
Reference: Washington Orthopaedics & Sports Medicine; “Plica syndrome”; http://www.wosm.com/index.php/health-library/orthopaedic-conditions-and-treatments/131-plica-syndrome