Question: what can cause pain under the kneecap?
Answer: Overuse. The quadriceps muscles of the thighs are the main shock absorbers for the knee joint. ... 
Patellar tendinitis. The patellar tendon connects the patella to the shin bone (tibia). ... 
Maltracking. ... 
Patellofemoral arthritis. ... 
Trauma. ... 
Exercise. ... 
No gain from pain. ... 
Pain relievers.