AP Ankle

The AP Ankle projection is the fundamental view for assessing the relationship between the distal tibia, distal fibula, and the talus. While it provides a clear view of the medial and superior joint spaces, the lateral aspect of the joint is naturally superimposed in this position. In the “Richie Standard,” a high-quality AP ankle must demonstrate the malleoli in profile and ensure the foot is properly dorsiflexed to prevent anatomy from being obscured.

The Goal

To demonstrate the distal third of the tibia and fibula, the medial and superior joint spaces, and the proximal portion of the talus in a frontal plane.

Patient Positioning

The Setup: Place the patient in a supine position with the affected leg fully extended.
Part Alignment: Adjust the leg so that the femoral condyles and the malleoli are parallel to the image receptor (IR).
Flexion: The foot must be dorsiflexed until the plantar surface is at a 90° angle to the lower leg.
- Richie’s Reasoning: If the foot is allowed to “point” (plantarflexion), the calcaneus can superimpose the ankle joint, and the joint space will not be clearly visualized.
Pro-Tip: If the patient cannot maintain dorsiflexion, use a long strip of gauze or a lead-free strap to have the patient gently pull the foot back toward them.

Technical Factors

Central Ray (CR): Perpendicular to the IR.
CR Entry Point: Directed to a point midway between the malleoli.
SID: 40″ standard.
Collimation: Must include the distal 1/3 of the tibia and fibula, the malleoli, and the proximal half of the metatarsals.

Image Evaluation Criteria (The “Richie” Checklist)

Joint Space: The superior and medial tibiotalar joint spaces should be open and clearly visible.
Superimposition: The lateral joint space (distal tibiofibular) will be superimposed by the distal fibula—this is normal for a true AP.
Alignment: The medial and lateral malleoli should be shown in profile.
Detail: Sharp visualization of the distal fibula and tibia is required to identify subtle avulsion fractures.
Physical Marker: A lead R/L marker must be present and not obscured by anatomy.

Why the AP Ankle Matters

The AP view is the first step in identifying a Pott’s fracture or significant ligamentous disruptions. It is the baseline for comparing the alignment of the talus within the “ankle mortise.” However, because of the natural anatomy, you cannot see the entire joint space here—which is why the Mortise view is its essential partner.

Richie’s Pro-Tips for the AP Ankle

Professional Presence: Ankle injuries are often accompanied by significant swelling (edema). Be gentle when positioning, and use the smallest amount of pressure necessary to achieve the correct alignment.

Watch for “Floppy Foot”: Patients naturally want to let their foot roll outward. If you allow this, you are actually taking an oblique view, not an AP. Keep that foot pointed straight up to ensure the malleoli are parallel to the IR.

Dorsiflexion is Non-Negotiable: A plantarflexed foot distorts the joint. If the patient is in too much pain to pull back, do your best to support them with sponges, but explain that the 90° angle is what makes the joint “visible.”

Physical Markers are Mandatory: Always use your lead markers to confirm the side of interest.