What is the mechanism of injury for patellar tendonitis

The patellar tendon is a structure that attaches the quadriceps muscle group to the tibia. Patellar tendonitis, also known as jumper's knee, is the condition that arises when the patellar tendon and the tissues that surround it, become inflamed and irritated. This is usually due to overuse, especially from jumping activities. It is a common affliction of volleyball, basketball, soccer players, and runners. Rapid acceleration, deceleration, jumping, and landing concentrate a large amount of stress on the extensor mechanism of the knee. 

Patellar tendonitis can be classified by the following techniques: 

Stage 0 - No Pain 
Stage 1 - Pain only after intense sports activity; no undue functional impairment 
Stage 2 - Pain at the beginning and after sports activity; still able to perform at a satisfactory level 
Stage 3 - Pain during sports activity; increasing difficulty in performing at a satisfactory level 
Stage 4 - Pain during sports activity; unable to participate in sport at a satisfactory level 
Stage 5 - Pain during daily activity; unable to participate in sport at any level (14) 

In mostly stages 1-4, this condition can be treated by a conservative approach. The therapy includes strengthening the muscles around the knee and continuation of non-contact aerobic exercise. The athlete is encouraged to continue exercising and working out despite the tendonitis. In addition to this, the knee should be frequently iced. 

In severe cases of tendonitis, approximately 10% of cases in athletes, surgery must be performed to alleviate the pain of tendonitis. Six weeks after the surgery in most cases, the athlete could begin their physical therapy to begin playing their respective sport again. Most cases for these surgeries are Stage 5, but many times, especially in professional athletes, surgery is requested because the patient doesn't want to deal with the non-operative therapies and the pain of tendonitis.