An ankle X-ray is a common diagnostic tool used to capture images of the bones and soft tissues surrounding the ankle joint. This procedure helps medical professionals identify fractures, dislocations, and alignment issues following an injury or trauma. Since the ankle is a complex structure involving the tibia, fibula, and talus, a single image is insufficient for a complete assessment. The joint’s overlapping bones require the X-ray beam to be angled from multiple, precise directions to ensure all surfaces are clearly visualized.
The Standard Three-View Ankle Series
The standard protocol for a comprehensive ankle examination requires a series of three distinct views, often called the “three-view series.” This series is composed of the Anteroposterior (AP) view, the Lateral view, and the specialized Mortise view. These three projections provide a complete, three-dimensional picture of the tibiotalar joint and surrounding anatomy. The combination allows medical professionals to assess the alignment of the tibia, fibula, and talus and to accurately measure the joint space width.
Interpreting Each Specific View
Each of the three images provides unique and necessary anatomical information for a full diagnosis.
The Lateral view captures the ankle from a side profile, making it the preferred image for assessing the posterior structures. This projection is effective for visualizing the posterior malleolus of the tibia, the calcaneus (heel bone), and the dome of the talus. It is also used to detect joint effusions, which are signs of fluid accumulation within the joint capsule. For completeness, the image must extend far enough to ensure the base of the fifth metatarsal is included, as this is a common site for avulsion fractures.
The Anteroposterior (AP) view is taken from the front, with the patient’s foot pointed straight ahead. This image primarily assesses the overall width of the ankle joint and the relationship between the talus and the distal tibia. While it shows the ankle mortise—the socket formed by the tibia and fibula—overlap of the distal fibula and tibia often obscures the lateral joint space. The AP view is useful for evaluating the lateral process of the talus and for identifying soft tissue swelling around the malleoli.
The Mortise view, technically an AP oblique projection, is the most informative view for assessing joint integrity. It is achieved by internally rotating the patient’s leg approximately 15 to 20 degrees, which positions the medial and lateral malleoli parallel to the X-ray film. This rotation eliminates the bone overlap seen in the standard AP view, providing an unobstructed look at the entire talocrural joint space. This view is the standard for evaluating the syndesmosis, the strong ligamentous complex connecting the distal tibia and fibula.
On a healthy Mortise view, the clear joint space between the talus and the malleoli should appear uniform across its surface. This space should measure no greater than about four millimeters in width. Widening of this measurement is a direct indication of ligamentous instability, demonstrating the importance of the Mortise view for classifying injury severity.
Situations Requiring Additional Projections
While the standard three-view series is sufficient for most acute injuries, certain clinical situations necessitate further imaging beyond the initial protocol.
One variation is the use of weight-bearing views, taken while the patient is standing and applying their body weight to the injured foot. These functional images can reveal dynamic changes, such as joint malalignment or subtle fracture displacement, that are not apparent when the patient is lying down. This is relevant for assessing the true stability of the ankle joint, which is often compromised only when loaded. Weight-bearing X-rays are frequently requested to assess joint stability in the presence of suspected chronic pain.
A second set of specialized images includes stress views, performed by gently applying manual or mechanical force to the ankle during the X-ray capture. This technique evaluates the integrity of ligaments, especially when a severe high ankle sprain, known as a syndesmotic injury, is suspected. The applied force can expose instability by demonstrating an abnormal widening of the joint space, confirming a ligament tear. For injuries extending beyond the main ankle joint, such as complex calcaneal fractures, specific projections like the Broden view or oblique views may be ordered to better characterize the fracture pattern.