Radiographs Remain First Step in Chronic Knee Pain

Radiographs remain the preferred first imaging test for adults with chronic knee pain, helping identify osteoarthritis and signs that may justify further evaluation. Chronic knee pain affects more than 25% of people over 45 in the United States and may arise from joint wear, bone stress injury, kneecap tracking problems or long-standing soft tissue abnormalities. A 2026 update to the American College of Radiology Appropriateness Criteria, published in the Journal of the American College of Radiology, sets out when MRI or CT may be useful after radiographs.

Radiographs Guide Early Assessment
Radiography is usually appropriate as the first imaging test for adults with chronic knee pain. It can show features of osteoarthritis, including narrowing of the joint space, bony outgrowths, cyst-like changes and hardening of the bone beneath the joint surface. These findings can help confirm whether osteoarthritis is likely to explain pain. Radiographs also create a baseline for comparison over time and may support treatment planning, including decisions around surgery.

Standing radiographs are preferred because they can better show narrowing in the inner or outer part of the knee joint. Front and side views support assessment of the main knee compartments, while an additional kneecap view can help assess the patellofemoral compartment. Radiographs may also show findings beyond osteoarthritis, such as fluid in the joint, tendon thickening or soft tissue swelling. These findings may justify further imaging when symptoms persist or when the visible changes do not fully explain the clinical picture.

Several tests are usually not appropriate as first-line imaging in chronic knee pain. Ultrasound, MRI, CT, joint-injection imaging and bone scanning do not have supporting roles as initial tests in this setting. Their value depends on what radiographs show and what abnormality remains suspected.

Further Imaging Depends on Context
When radiographs show osteoarthritis, additional imaging is not automatic. MRI without intravenous contrast may be appropriate when symptoms do not match the severity or location of the radiographic changes. It may also help with treatment planning. MRI is less likely to alter non-operative management when radiographs show advanced osteoarthritis. In patients with minimal radiographic osteoarthritis, MRI may reveal additional causes of pain, including meniscal tears or stress-related bone injury.

CT without intravenous contrast has a narrower role when osteoarthritis appears on radiographs. Its main use is preoperative planning for knee arthroplasty, particularly when three-dimensional modelling is needed. The update notes improved postoperative function, pain and low complications in relation to CT-based planning compared with manual total knee arthroplasty.

Ultrasound has limited value when radiographs already show osteoarthritis. It does not assess the menisci, bone beneath the joint surface or cartilage well. It may have some use in showing changes in the joint lining after treatment. MRI with intravenous contrast, CT with contrast, CT arthrography, MR arthrography and bone scanning have no relevant support for routine use in this scenario. Noncontrast MRI remains the more useful cross-sectional test when the pain pattern and radiographs do not align.

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MRI Supports More Targeted Questions
After radiographs, MRI without intravenous contrast is usually appropriate when a tendon, meniscus or ligament abnormality is suspected. Radiographs may show indirect signs, such as swelling, bony attachment changes, meniscal displacement or joint fluid, but MRI provides a more complete view of soft tissues. It can assess meniscal tears, tendon problems and ligament abnormalities without using intravenous contrast.

MRI also has a central role when an osteochondral lesion or subchondral insufficiency fracture is suspected. If radiographs are normal but suspicion remains, MRI can show hidden fracture or bone marrow change. When radiographs already show a stress-related bone injury beneath the joint surface, MRI can reveal associated findings such as meniscal tearing or cartilage loss. For joint surface injury, MRI can show the size and stability of the cartilage abnormality and related bone changes. After repair, MRI can assess the treated bone and cartilage.

For suspected patellofemoral maltracking, radiographs often come first because they may show kneecap malalignment or patellofemoral arthritis. MRI can then add information on kneecap position, trochlear shape, cartilage changes, fat pad signal and signs of previous injury around the stabilising ligament. CT without intravenous contrast may help when surgical planning requires detailed measurements of kneecap alignment, trochlear depth and the relationship between the tibial tubercle or patellar tendon and the trochlear groove.

Imaging for chronic knee pain starts with radiographs because they can identify osteoarthritis, provide a baseline and reveal findings that justify further evaluation. MRI without intravenous contrast becomes important when radiographs do not match symptoms or when soft tissue, cartilage, bone stress or kneecap tracking abnormalities remain suspected. CT without intravenous contrast has a more selective role, mainly in surgical planning. Other imaging options have limited or no routine role across most chronic knee pain scenarios.

Source: Journal of the American College of Radiology

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