AP Medial Oblique Mortise Ankle is a radiography positioning projection of the Lower Extremity. Supine, leg internally rotated 15-20°. Mortise open. SID 40". The centering point is located midway between the malleoli. Leg internally rotated 15-20 degrees so intermalleolar line is parallel to IR. The central ray is perpendicular to the ankle joint. Image-quality criteria include medial and lateral mortise joints open, malleoli in profile, whole mortise open, with an even 3-4 mm space over the talus. The SID is 40 inches (102 cm).
Anatomy demonstrated
- Medial malleolus in direct profile.
- Lateral malleolus in direct profile.
- Talus, with the entire mortise open.
- Distal tibiofibular joint, with only minimal superimposition.
- Distal tibia and fibula.
- Tibiotalar articulation.
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 on the IR.
- Internally rotate the entire leg 15-20 degrees so intermalleolar line is parallel to IR.
- Bontrager: do not dorsiflex, so the 5th metatarsal base shows. Merrill's: sole at a right angle to the leg.
Position & centering point
Midway between the malleoli. Leg internally rotated 15-20 degrees so intermalleolar line is parallel to IR.
Central ray
Perpendicular to the ankle joint.
Exposure / technique
- kVp
- N/A
- mAs
- N/A
- SID
- 40" (102 cm)
- Notes
- Mortise view opens the lateral and medial mortise joints. Bontrager gives digital 70 +/- 5 kV. Merrill's chart has no mortise row, so no mAs is printed.
Image-quality criteria
- Medial and lateral mortise joints open, malleoli in profile.
- Whole mortise open, with an even 3-4 mm space over the talus.
- Distal tibia, fibula, and talus all clearly visible.
- Only minimal superimposition at the distal tibiofibular joint.
- Collimation: lateral skin margins, proximal metatarsals and distal tibia-fibula (Bontrager).
Common errors
- 1 Leg and foot not rotated the 15-20 degrees that sets the intermalleolar line parallel to the IR.
- 2 Lateral or medial mortise joint not open, showing incorrect obliquity.
- 3 CR not directed midway between the malleoli.
- 4 Under Bontrager, dorsiflexing can hide the base of the 5th metatarsal.
Clinical indications
- Pathology involving the entire ankle mortise.
- Assessment of the ankle mortise integrity.
- Fracture at the base of the 5th metatarsal, a common site.
- A common projection during open reduction surgery of the ankle.