What is the likely diagnosis for a patient with medial knee pain and a popping sensation, but a negative x-ray?

Diagnosis for Medial Knee Pain with Popping and Negative X-ray

For a patient with medial knee pain and popping sensation but negative x-ray, the most appropriate diagnosis is "internal derangement of the knee" or more specifically "suspected medial meniscal tear," and you should proceed directly to MRI for definitive diagnosis. 1

Clinical Reasoning

The majority (93.5%) of patients presenting with acute knee injuries have soft-tissue injuries rather than osseous injuries, making x-ray negative findings expected in most cases. 1 Your patient's presentation of medial-sided pain with popping is classic for meniscal pathology, which cannot be adequately evaluated by radiography alone.

Most Likely Differential Diagnoses to Document:

• Medial meniscal tear - The medial meniscus is more vulnerable to injury due to its intimate attachment to the medial collateral ligament, and popping sounds are commonly caused by meniscal tears 2, 3
• Medial collateral ligament injury - Often occurs in conjunction with meniscal pathology 3
• Internal derangement of the knee, unspecified - This is an acceptable umbrella diagnosis when imaging confirmation is pending 1

Immediate Next Steps

MRI without IV contrast is the indicated next examination when initial radiographs are negative but pain and mechanical symptoms persist. 1 The ACR Appropriateness Criteria explicitly state that MRI has many distinct advantages for evaluating the injured knee with negative radiographs, with 96% sensitivity and 97% specificity for detecting meniscal tears. 1

Why MRI is Critical Here:

• MRI shortened diagnostic workup, reduced additional procedures, and improved quality of life in the first 6 weeks, potentially reducing productivity loss 1
• Earlier surgical intervention becomes possible with more accurate diagnosis 1
• Clinical examination alone has low diagnostic benefit in acute knee trauma, with higher-than-suspected incidence of injuries found on MRI 1

Important Clinical Pitfalls

• Do not dismiss the diagnosis simply because x-rays are negative - X-rays only detect 83% of fractures and miss virtually all soft-tissue injuries 1
• Popping with pain warrants investigation - Popping sounds with associated pain, swelling, or instability indicate potential structural damage requiring treatment 2
• Avoid delaying MRI - In patients <40 years old with acute knee injury, knee effusion >10 mm on lateral radiograph should prompt immediate consideration for knee MRI, which can decrease delayed diagnosis, improve outcomes, and decrease disability 1

Alternative if MRI is Contraindicated:

• Ultrasound is the primary alternative with 88% sensitivity and 90% specificity for meniscal tears, though it has limited visualization of portions of the menisci 4
• CT can be secondary alternative but has lower sensitivity for soft-tissue injuries 4

Documentation Strategy

For your medical record, appropriate diagnostic codes include:

• "Internal derangement of left knee" (most comprehensive) 1
• "Suspected medial meniscal tear, left knee" 2, 3
• "Left knee pain with mechanical symptoms" 1

Order MRI knee without contrast as the definitive diagnostic test, as this will provide the accurate diagnosis needed for treatment planning and will likely reveal meniscal pathology, ligamentous injury, or other soft-tissue abnormalities causing her symptoms. 1