Knee Pain Differential Diagnoses

Anatomic Location-Based Differential

The American College of Radiology suggests patellofemoral disorders, such as cartilage loss, subluxation/dislocation, and friction syndrome, are associated with anterior knee pain 1, 2
Patellar tendinopathy is a common cause of anterior knee pain 2
Fat pad impingement syndromes and Hoffa's disease, characterized by enhancing synovitis >2mm in Hoffa's fat, correlate with peripatellar pain 2
Deep infrapatellar bursitis is a potential cause of anterior knee pain 2
Medial plicae can cause anterior knee pain 2, 3
Osteochondritis dissecans (OCD) is a condition that can cause anterior knee pain 1
Medial compartment osteoarthritis is a common cause of medial knee pain 1
Iliotibial band syndrome is a common cause of lateral knee pain 2, 3
Lateral compartment osteoarthritis can cause lateral knee pain 1
Popliteal (Baker's) cysts can cause posterior knee pain and often communicate with the knee joint 4
Hamstring tendinopathy can cause posterior knee pain 2

Subchondral insufficiency fractures, previously termed spontaneous osteonecrosis, most commonly involve the medial femoral condyle in middle-aged to elderly females, and radiographs are often initially normal 1
Tibial stress fractures can occur in the knee 1, 2
Osteochondritis dissecans with potential loose bodies can cause knee pain 1, 3
Osteophytes can be a sign of osteoarthritis 2
Adhesive capsulitis can cause knee pain and stiffness 2, 3
Discoid meniscus is a rare condition that can cause knee pain 2
Pigmented villonodular synovitis is a rare condition that can cause knee pain and swelling 2, 3
Tumors and ganglion cysts can cause knee pain and swelling 2, 3
Synovitis/effusion can indicate the origin of pain in osteoarthritis 1

The American College of Radiology suggests that lumbar spine pathology must be considered when knee radiographs are unremarkable and clinical evidence suggests spinal origin 4, 5
Hip pathology can refer pain to the knee and should be evaluated if knee imaging is normal 4
A thorough clinical examination of the lumbar spine and hip should precede knee-focused imaging 4

Referred pain from the hip or lumbar spine should not be overlooked before attributing symptoms solely to knee pathology 4
Premature MRI should be avoided, as approximately 20% of patients with chronic knee pain undergo MRI without recent radiographs 4
Not all meniscal tears are symptomatic, particularly in patients over 45 years 4
In patients over 70 years, bilateral structural abnormalities can exist with primarily unilateral symptoms 4
Radiographs may be initially normal in subchondral insufficiency fractures, which later show articular surface fragmentation and subchondral collapse 1