A knee X-ray is a common diagnostic imaging procedure that creates images of the bones within the knee joint. This non-invasive test helps healthcare providers visualize the kneecap (patella), the thigh bone (femur), and the shin bone (tibia). X-rays are used to assess conditions such as fractures, dislocations, and various forms of arthritis. The procedure is quick, painless, and exposes the patient to minimal radiation.
Why Multiple Views Are Essential
A single X-ray image of the knee provides a limited, two-dimensional perspective. This means certain abnormalities might be obscured or not fully visible from one angle. Multiple views provide a more comprehensive assessment of its structures. Different angles help visualize various parts of the joint, detect subtle fractures, evaluate joint space, and understand bone alignment. This multi-view approach is crucial for accurate diagnosis and for guiding appropriate treatment decisions.
Anterior-Posterior (AP) View
The Anterior-Posterior (AP) view is a standard projection where the X-ray beam passes from front to back. Patients typically lie on their back or stand with the knee extended against the detector. The AP view primarily reveals the joint space width between the femur and tibia, which is important for assessing cartilage health and osteoarthritis. It also helps evaluate the general alignment of the femur and tibia, and identify fractures or other bony abnormalities within these main structures of the knee.
Lateral View
The Lateral view captures the knee from the side, with the X-ray beam directed from medial to lateral or vice versa. Patients usually lie on their side with the knee slightly bent, or stand. This view is useful for examining the relationship between the patella and femur, and for assessing the depth of the joint space. It can also reveal fluid buildup (effusions) or fractures not visible on the AP view.
Patellar View
The Patellar view, also known as the “Sunrise” or “Skyline” view, is specifically designed to visualize the kneecap and its femoral groove. The knee is typically bent at a significant angle, and the X-ray beam is angled to capture a tangential view of the patella. This view is crucial for examining the patella’s undersurface and the trochlear groove of the femur, involved in kneecap movement. It helps identify patellar tracking problems, dislocations, or arthritis behind the kneecap.
Weight-Bearing Views
Weight-bearing views are obtained while the patient stands, applying natural body weight to the knee joint. These include weight-bearing AP or lateral views, and specialized projections like the Rosenberg view. The Rosenberg view is a posteroanterior view taken with the knee flexed while standing, particularly sensitive for detecting joint space narrowing indicative of osteoarthritis. These views highlight cartilage loss and joint space narrowing not apparent on non-weight-bearing images, which can underestimate joint degeneration severity. By simulating the knee’s functional state, weight-bearing X-rays provide information for diagnosing and managing conditions that worsen under load, such as advanced arthritis.