From the Guidelines
The best X-ray to visualize the knee is a weight-bearing three-view knee series, which includes anteroposterior (AP), lateral, and tangential axial views of the patellofemoral joint. This recommendation is based on the most recent and highest quality study available, which emphasizes the importance of weight-bearing views in evaluating arthritis and joint space narrowing 1. The AP view shows the femoral condyles, tibial plateau, and joint space; the lateral view demonstrates the patellofemoral relationship and joint effusion; and the tangential axial view specifically evaluates the patellofemoral joint and tracking.
Key Considerations
- Weight-bearing views are essential for evaluating arthritis and joint space narrowing, as they provide a more accurate representation of the joint's functional state 1.
- Standing AP views in full extension and a 45-degree flexion (Rosenberg view) are valuable for detecting early joint space narrowing 1.
- Additional specialized views may be necessary depending on the clinical scenario, such as intercondylar notch (tunnel) view for cruciate ligament avulsion fractures, oblique views for tibial plateau fractures, or stress views for ligamentous instability 1.
- While X-rays are excellent for bone visualization, they cannot directly show soft tissue structures like menisci or ligaments, and MRI would be the preferred imaging modality if soft tissue injury is suspected after initial X-ray evaluation 1.
Clinical Scenarios
- In cases of suspected periprosthetic infection, radiographs are an integral part of the workup, but they are neither sensitive nor specific for diagnosing infection 1.
- For evaluation of acute trauma to the knee, radiographs should be obtained if the patient meets Ottawa or Pittsburgh rule criteria, and a minimum of two radiographs (anteroposterior and lateral) of the affected knee should be obtained 1.
From the Research
X-Ray Views for Visualizing the Knee
- The anteroposterior (AP) and lateral views are commonly used to evaluate the knee, but they may not be sufficient to detect all cases of osteoarthritis or fractures 2, 3.
- Adding a skyline view or a tunnel view to the AP view can increase the sensitivity of X-ray imaging in detecting knee osteoarthritis or fractures 2, 4.
- The tunnel view is particularly useful in detecting joint space narrowing and osteophytes in the lateral and medial compartments of the knee 4.
- The skyline view is useful in evaluating the patellofemoral joint, but it may be technically challenging to obtain a satisfactory image 2.
Comparison of X-Ray Views
- A study comparing the AP and lateral views with a four-view examination (including a skyline view) found that the four-view examination was more sensitive in detecting acute knee fractures 3.
- Another study found that the combination of the AP and tunnel views was more sensitive than the AP view alone in detecting knee osteoarthritis 4.
Limitations of X-Ray Imaging
- X-ray imaging has limited sensitivity in detecting certain types of fractures, such as growth plate fractures, and may not be able to determine the exact characteristics of a fracture 5.
- X-ray imaging may not be sufficient to evaluate the extent of osteoarthritis or to detect early changes in the joint 6.
- Other imaging modalities, such as MRI or CT scans, may be necessary to provide a more accurate diagnosis or to evaluate the severity of knee osteoarthritis or fractures 5, 6.