What is the next step in managing a patient with knee pain and a normal knee radiograph?

Next Step: Order Non-Contrast MRI of the Knee

When knee radiographs are normal or show only joint effusion and pain persists, non-contrast MRI is the appropriate next imaging study. 1

Clinical Assessment Before Ordering MRI

Before proceeding to MRI, you must actively exclude referred pain sources that can masquerade as primary knee pathology:

Hip Evaluation

• Examine hip range of motion and assess for groin pain or positive impingement signs 1, 2
• Order pelvis and proximal femur radiographs if you find restricted hip motion, groin discomfort, or any clinical evidence of hip disease 1
• Hip pathology commonly refers pain to the knee, and ordering knee MRI before hip films wastes resources and delays accurate diagnosis 1

Lumbar Spine Evaluation

• Ask about low-back pain and radicular symptoms extending from buttock through posterior thigh to knee 1
• Order lumbar spine radiographs if the patient reports back pain, radiculopathy, or neurogenic claudication patterns 1, 2

Why MRI Is the Correct Next Step

MRI without IV contrast detects the full spectrum of radiographically occult knee pathology:

• Meniscal tears (sensitivity 86-100%) – the most common cause of mechanical clicking and persistent pain 1
• Articular cartilage defects and early osteochondritis dissecans 1
• Bone marrow lesions and subchondral insufficiency fractures that are invisible on plain films 1, 2
• Ligament injuries (ACL, PCL, collaterals) that may be clinically subtle 1
• Synovial pathology including plicae, loose bodies, and synovitis 1

Delaying MRI increases the risk that a repairable meniscal tear will progress to an irreparable degenerative tear 1

What NOT to Order

• Ultrasound – insufficient for comprehensive meniscal or intra-articular evaluation; only confirms effusion 1
• CT or CT arthrography – lower soft-tissue resolution than MRI; reserve for MRI contraindications 1
• Bone scan with SPECT/CT – low specificity and poor anatomic detail 3, 1
• MRI with IV contrast – not indicated for isolated mechanical symptoms; reserve for suspected infection, tumor, or inflammatory arthropathy 1

Interim Management While Awaiting MRI (1–2 Weeks)

• Activity modification: avoid deep squatting, pivoting, or movements that provoke symptoms 1
• NSAIDs: provide symptomatic relief when not contraindicated 1
• Physical therapy: initiate quadriceps strengthening and range-of-motion exercises; definitive treatment will be guided by MRI findings 1

Common Pitfalls to Avoid

• Do not attribute clicking to "normal joint sounds" when effusion and chronic pain coexist – this combination indicates structural pathology requiring MRI 1
• Do not aspirate a small chronic effusion unless signs of infection or crystal arthritis are present 1
• Do not order knee MRI without recent radiographs – approximately 20% of patients inappropriately receive MRI without radiographs within the prior year 1, 2
• Recognize that effusion alone is nonspecific and may reflect meniscal, cartilage, synovial, or ligament injury – MRI is needed for differentiation 1

Post-MRI Decision Algorithm

• Repairable meniscal tear, loose body, or unstable osteochondritis dissecans → orthopedic referral for arthroscopy 1
• Degenerative meniscal changes or mild chondromalacia → continued conservative management 1

Critical Age-Related Caveat

In patients over 70 years, the majority have asymptomatic meniscal tears, making MRI findings potentially misleading 2. In the 45–55 age group, meniscal tears are equally common in painful and asymptomatic knees 2. The presence of a meniscal tear on MRI does not automatically establish it as the pain source 2.