AP Medial Oblique Ankle is a radiography positioning projection of the Lower Extremity. Supine, ankle internally rotated 45 degrees. SID 40". The centering point is located ankle joint midway between the malleoli, with leg and foot internally rotated 45 degrees. The central ray is perpendicular to the ankle joint. Image-quality criteria include medial malleolus and talus partly superimposed, as expected at 45 degrees, ankle joint in the center of the collimated field. The SID is 40 inches (102 cm).
Anatomy demonstrated
- Medial malleolus of tibia, partly over the talus.
- Lateral malleolus of fibula in profile.
- Talus.
- Proximal half of the metatarsals, including the base of the 5th.
- Distal tibia and fibula.
Patient preparation
- WARNING: with possible spinal injury or severe trauma, do not attempt to move the patient; do not rotate a severely injured part or remove splints (Bontrager). Merrill's: do not attempt true AP or lateral positioning of a severely injured limb; take two projections 90 degrees apart, moving it as little as possible, and move the IR and tube if the patient cannot reach the position.
- Verify patient identity using two identifiers.
- Remove shoes and any radiopaque items from the foot and ankle.
- Position patient supine with leg extended, ankle over the IR.
- Internally rotate the leg and foot 45 degrees to free the lateral malleolus and open the distal tibiofibular joint.
- Dorsiflex the foot if needed so the sole is within 10-15 degrees of vertical.
Position & centering point
Ankle joint midway between the malleoli, with leg and foot internally rotated 45 degrees.
Central ray
Perpendicular to the ankle joint.
Exposure / technique
- kVp
- N/A
- mAs
- N/A
- SID
- 40" (102 cm)
- Notes
- Tabletop technique. No grid required for ankle projections. Bontrager gives digital 70 +/- 5 kV. Merrill's chart has no oblique row, so no mAs is printed.
Image-quality criteria
- Medial malleolus and talus partly superimposed, as expected at 45 degrees.
- Ankle joint in the center of the collimated field.
- Distal third of the leg, malleoli, talus and proximal half of the metatarsals included.
- Distal tibiofibular joint open with the lateral malleolus clear of the talus.
- Bone trabeculae sharp, no motion blur.
- Collimation: distal tibia and fibula to the midmetatarsal area, with the 5th metatarsal base (Bontrager).
Common errors
- 1 Lateral malleolus and talus more than slightly superimposed; the book expects no or slight overlap.
- 2 Leg and foot not rotated the full 45 degrees medially.
- 3 CR not directed midway between the malleoli.
- 4 Plantar flexion past 10-15 degrees from vertical puts the calcaneus over the lateral malleolus.
Clinical indications
- Ankle fracture or sprain evaluation.
- Assessment of the distal tibiofibular joint and lateral malleolus.
- Fractures of the distal fibula, lateral malleolus and base of the 5th metatarsal.