What imaging studies are recommended for a patient with a history of knee injuries or previous surgeries who reports intermittent knee buckling, to rule out conditions such as ligamentous instability or osteoarthritis?

Imaging for Knee Buckling

Start with plain radiographs of the knee (anteroposterior, lateral, and tangential patellar views), then proceed to MRI without contrast if radiographs are normal or show only effusion and symptoms persist, as this is the most effective pathway for detecting the ligamentous instability, meniscal tears, and cartilage damage that cause buckling. 1

Initial Imaging Approach

• Plain radiographs are mandatory first and should include anteroposterior (or Rosenberg/tunnel view), lateral, and tangential patellar projections 1
• Radiographs identify fractures, osteoarthritis, loose bodies, osteochondritis dissecans, and signs of prior injury (Segond fractures, tibial spine avulsions) that may cause instability 1
• Weight-bearing films are particularly important as they reveal joint space narrowing and alignment abnormalities (varus/valgus deformity) associated with osteoarthritis, which is present in nearly half of patients with buckling 2, 3

When to Proceed to MRI

MRI without IV contrast is indicated when:

• Radiographs are normal or show only joint effusion but buckling persists 1
• Clinical suspicion remains high for ligamentous injury (ACL, PCL, collateral ligaments) or meniscal tears 1
• There is a history of prior knee injury or surgery suggesting internal derangement 1, 2

Why MRI Without Contrast is Sufficient

• MRI without contrast detects all relevant pathology causing buckling: ligament tears (96% sensitivity for meniscal tears, high accuracy for ACL/PCL injuries), bone marrow contusions, cartilage defects, and loose bodies 1, 4, 5
• Contrast is unnecessary for ligamentous instability, meniscal pathology, or bone marrow edema—the primary causes of buckling 5
• MRI shortened diagnostic workup and improved quality of life in the first 6 weeks in randomized studies of knee injuries 1

Clinical Context for Buckling

• Buckling occurs in 12% of community-dwelling adults and is strongly associated with quadriceps weakness and knee pain, even when radiographs show no osteoarthritis 3
• Over half of patients with buckling have normal radiographs, making MRI essential for diagnosis 3
• Buckling significantly impairs physical function independent of pain severity (46.9% report work limitations vs 21.7% without buckling) 3
• The sensation of instability without actual buckling is even more common (27%) and carries similar functional consequences 6

Alternative Imaging (Limited Role)

• CT without contrast may be used if MRI is contraindicated, with 87.5-100% sensitivity for ACL tears and 86-100% sensitivity for loose bodies, though it has low sensitivity for meniscal and other soft-tissue injuries 1, 4
• Ultrasound can evaluate effusions, popliteal cysts, and guide aspiration but does not assess internal derangement 7

Critical Pitfall to Avoid

Do not order MRI without obtaining radiographs first—approximately 20% of patients inappropriately receive MRI without recent (within one year) plain films, which wastes resources and may miss fractures or alignment issues that alter management 1, 7

Consider Referred Pain

• If knee radiographs are completely normal and buckling persists, obtain hip radiographs (anteroposterior pelvis and lateral hip) to exclude hip pathology causing referred knee pain 1, 7
• Consider lumbar spine radiographs if there is clinical suspicion for radicular symptoms 1, 7