Ankle AP is a radiography positioning projection of the Lower Extremity. Foot vertical on IR, CR perpendicular to ankle joint. SID 40". The centering point is located ankle joint space between medial and lateral malleoli.. The central ray is perpendicular to the ankle joint between the medial and lateral malleoli.. Image-quality criteria include ankle joint space open and clearly visible., medial and lateral malleoli symmetric and equidistant from the midline.. Standard exposure ranges from 60 to 70 kVp, 4 to 7 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Distal tibia and fibula clearly demonstrated.
- Medial and lateral malleoli symmetric.
- Ankle mortise (talocrural) joint space open.
- Anterior tibiofibular joint articulation.
- Entire talus within the mortise.
- Anterior and posterior margins of the talar dome.
Patient preparation
- Verify patient identity using two identifiers.
- Remove footwear, socks, and any radiopaque foot jewelry.
- Position the patient supine with the leg extended.
- Place the affected foot on the IR with long axis vertical.
- Align heel and toes so they are at the same distance from the tube.
Position & centering point
Ankle joint space between medial and lateral malleoli.
Central ray
Perpendicular to the ankle joint between the medial and lateral malleoli.
Exposure / technique
- kVp
- 60–70
- mAs
- 4–7
- SID
- 40" (102 cm)
- Notes
- Tabletop technique. Position foot vertical with heel and toes at same level.
Image-quality criteria
- Ankle joint space open and clearly visible.
- Medial and lateral malleoli symmetric and equidistant from the midline.
- Distal tibia and fibula, entire talus, and calcaneus visible.
- Anterior tibiofibular articulation open.
- Bone trabeculae sharp, no motion blur.
- Collimation: 1 inch on all sides of ankle, 8 inches lengthwise.
Common errors / ARRT traps
- 1 Foot rotated medially or laterally closes the ankle joint space.
- 2 Plantar flexion or dorsiflexion tilts the ankle mortise.
- 3 Off-centered CR clips the malleoli or distal tibia.
- 4 Unequal malleoli indicate foot rotation or table tilt.
Clinical indications
- Trauma evaluation for suspected ankle fracture or dislocation.
- Suspected malleolar fracture (medial or lateral).
- Assessment of ankle mortise alignment.
Aligned to the 2025 ARRT Content Specifications.