Cause	Comment
Articular cartilage injury	May describe history of trauma; mechanical symptoms may occur if loose body present; may have effusion; may have tenderness of involved structure (e.g., femoral condyles, patella)
Bone tumors	Pain may be insidious; may have tenderness of bony structures
Chondromalacia patellae	Retropatellar pain; may have history of trauma; may have effusion on examination
Hoffa's disease	Pain and tenderness localized to infrapatellar fat pad
Iliotibial band syndrome	Typically presents with lateral pain and tenderness over lateral femoral epicondyle
Loose bodies	Symptoms variable; may have intermittent sharp pain, locking, or effusion
Osgood-Schlatter disease	Tenderness and swelling at insertion of patellar tendon at tibial tubercle in an adolescent
Osteochondritis dissecans	Symptoms variable; may have intermittent pain, swelling, or locking
Patellar instability/subluxation	Intermittent pain with sensation of instability or movement of patella; may have swelling; locking can occur with loose body formation; may have tenderness over medial retinaculum
Patellar stress fracture	May have tenderness directly over patella
Patellar tendinopathy	Tenderness of tendon; tendon may be thickened if chronic
Patellofemoral osteoarthritis	May have crepitus or effusion; characteristic radiographic findings
Patellofemoral pain syndrome	Anterior knee pain “behind” or around patella; usually no effusion; may have findings of patellar maltracking
Pes anserine bursitis	Pain usually described as medial rather than anterior; tenderness over pes anserine bursa
Plica synovialis	May be medial or lateral to patella; if symptomatic, tenderness can be demonstrated on examination
Prepatellar bursitis	Characteristic swelling anterior to patella following trauma
Quadriceps tendinopathy	Tenderness over tendon
Referred pain from the lumbar spine or hip joint pathology	Symptoms depend on origin of pain; knee examination usually normal
Saphenous neuritis	Pain usually medial but poorly localized; may have history of surgery
Sinding-Larsen-Johansson syndrome	Tenderness at patellar tendon insertion at inferior pole of patella in an adolescent
Symptomatic bipartite patella	May have tenderness directly over patella with characteristic radiographic findings