From the Guidelines
For a right knee injury, the recommended initial imaging is a plain radiograph (X-ray) of the knee. This is based on the most recent and highest quality study, which suggests that radiographs should be the first imaging study in the setting of significant acute trauma to the knee 1. X-rays should be obtained first to evaluate for fractures, dislocations, joint effusions, and degenerative changes. Standard views typically include anteroposterior (AP), lateral, and sunrise (or merchant) views, with optional weight-bearing and tunnel views depending on the clinical scenario.
Key Considerations
- X-rays are quick, inexpensive, widely available, and expose patients to minimal radiation while providing valuable information about bony structures.
- If the X-ray is negative but clinical suspicion for injury remains high, magnetic resonance imaging (MRI) would be the next appropriate step, particularly for suspected soft tissue injuries such as meniscal tears, ligament injuries (ACL, PCL, MCL, LCL), or cartilage damage 1.
- MRI has many distinct advantages for the evaluation of the injured knee in the setting of negative radiographs, including the ability to diagnose patterns and severity of bone marrow contusions, predict associated soft-tissue injuries, and facilitate diagnosis of anterolateral ligament injuries and posterolateral corner injuries.
- The choice of imaging should always be guided by the mechanism of injury, physical examination findings, and the patient's clinical presentation.
Additional Imaging Options
- Ultrasound may be considered for evaluating superficial structures like tendons or for detecting joint effusions.
- CT scans are reserved for complex fractures or when MRI is contraindicated.
- The American College of Radiology (ACR) appropriateness criteria suggest that knee radiographs are usually appropriate as the initial imaging study for patients 5 years of age or older with a fall or acute twisting trauma to the knee when at least one of the following is present: focal tenderness, effusion, or inability to bear weight 1.
From the Research
Initial Imaging for Right Knee Injury
The recommended initial imaging for a right knee injury includes:
- Plain radiography, which is a quick and cost-effective way to identify a wide range of problems, including fracture, degenerative changes, osteochondral defects, and effusions 2
- Computed tomography (CT) scan, which is the test of choice to better delineate fractures in patients who have knee trauma 2, 3
Role of MRI in Knee Injury
Magnetic resonance imaging (MRI) is useful for evaluating cartilage, menisci, and cruciate and collateral ligaments, especially if arthroscopy is contemplated 2
- MRI can aid in the evaluation of sports-related injuries involving the ligaments, tendons, menisci, osseous structures, and articular surfaces 4
- Quantitative MR parameter mapping techniques, such as T₁ρ MRI, can quantify biochemical changes in articular cartilage and evaluate joint injury, cartilage degeneration, and soft tissue repair 5
Comparison of Imaging Modalities
- X-ray (XR) imaging has a low sensitivity in identifying knee fractures, and CT scanning should be performed in patients whose fracture type and fracture characteristics are not able to be determined exactly with XR imaging 3
- 3D MRI can provide high-resolution visualization of ligaments, tendons, and articular cartilage, and can be used to better advantage in visualizing small and curved structures 6