Differential Diagnosis for Inferior Knee Pain After Fall with Normal X-Ray

Primary Differential Considerations

The American College of Radiology recommends considering ligamentous injuries, including ACL, PCL, or collateral ligament tears, with a mechanism of fall and instability 1, 2
Patellar tendinopathy or quadriceps tendon injury should be suspected, especially if pain is localized to the inferior pole of the patella or tibial tubercle 5
Bone marrow contusions or occult fractures that are radiographically invisible but detectable on MRI should be considered 1, 2, 6

The American College of Radiology recommends ordering MRI knee without IV contrast as the next imaging study after normal radiographs when pain persists, to evaluate for occult fractures, meniscal tears, ligament injuries, and bone marrow lesions 1, 2, 3, 4, 7

The American College of Radiology advises against assuming normal X-rays exclude significant injury, as meniscal tears, ligament injuries, and bone marrow contusions are invisible on radiographs but cause substantial morbidity 1, 2, 6
The American College of Radiology explicitly recommends not skipping MRI if symptoms persist, as it is the next appropriate study after negative radiographs in patients with ongoing pain 1, 2, 3, 4

The American College of Radiology suggests initiating physical therapy emphasizing quadriceps and hip strengthening, neuromuscular education, and movement retraining if MRI confirms soft tissue injury 5
The use of NSAIDs or acetaminophen (≤4g/day) for pain control is recommended, though NSAIDs are more effective than acetaminophen for knee pain 5
Glucosamine, chondroitin, and acupuncture should be avoided as they lack evidence of effectiveness 5