The knee pain can be associated with any condition so a proper examination and diagnosis is required if it bothers you. It can be knee
injury due to knee
sprain , prior knee
injury ,dislocated knee , dislocated patella, femoral condyle fracture, torn ligament , knee overuse , knee infection due to any bacterial infection , knee inflammation due to synovitis or bursitis or Knee arthritis due to arthritis , osteoarthritis , rheumatoid arthritis or gout and any tumor.