Patellar tendinopathy is a disorder of the patellar tendon

The condition used to be called patellar 'tendinitis' or 'tendonitis'. The term '-itis' in medicine means 'inflammation' - a process of irritation, increased blood supply, and infiltration of the area with special inflammatory cells - but these features are not actually seen in patellar tendinitis. So there is a lot of medical literature suggesting that the condition no longer be called 'patellar tendinitis' but 'patellar tendinopathy' or 'patellar tendinosis' instead, implying a degenerative condition rather than an inflammatory one. For your research, you need to search using all of these keywords.

In this disorder the tendon develops a mushy ('mucoid') degeneration, which weakens it, causes local discomfort, and may predispose the tendon to rupture.

Synonyms: 
Jumper's knee
Patellar tendinitis
Patellar tendinosis
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A discussion about the role of shockwave therapy for refractory patellar tendinopathy.

Overuse syndromes affecting the patella

Repetitive activities can stress anatomical structures and lead to 'overuse' symptoms.

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CLINICAL PUBLICATIONS

Current concepts in the treatment of patellar tendinopathy. Reinking MF. Int J Sports Phys Ther. 2016 Dec; 11(6): 854–866.