Ankle Lateral (Mediolateral) is a radiography positioning projection of the Lower Extremity. Patient lateral recumbent on affected side, CR perpendicular to ankle. SID 40". The centering point is located medial malleolus, with lateral border of foot on IR. The central ray is perpendicular to the IR, entering the medial malleolus in true lateral position. Image-quality criteria include tibiotalar joint open with an even joint space, distal third of the leg, talus, calcaneus and the 5th metatarsal tuberosity included. A sample technique is 70 kVp with DR 1.25 or CR 2.2 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Distal tibia and fibula in true lateral.
- Lateral malleolus seen through the distal tibia and talus.
- Tibiotalar joint.
- Talus in lateral profile.
- Medial and lateral talar domes superimposed (Merrill's).
- Calcaneus shown beneath the talus.
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 footwear, socks, and any radiopaque foot jewelry.
- Position the patient lateral recumbent on the affected side.
- Place the lateral border of the foot on the IR.
- Flex the knee about 45 degrees; place the other leg behind to prevent over-rotation.
- Dorsiflex the foot to 90 degrees as far as tolerated; do not force it.
Position & centering point
Medial malleolus, with lateral border of foot on IR.
Central ray
Perpendicular to the IR, entering the medial malleolus in true lateral position.
Exposure / technique
- kVp
- 70
- mAs
- DR 1.25 / CR 2.2
- SID
- 40" (102 cm)
- Notes
- Position patient on affected side. Flex knee for stability and patient comfort. Sample technique: DR 1.25 / CR 2.2 mAs at 70 kVp, 40 in SID, for a 7 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Tibiotalar joint open with an even joint space.
- Distal third of the leg, talus, calcaneus and the 5th metatarsal tuberosity included.
- No rotation: distal fibula over the posterior half of the tibia.
- Medial and lateral talar domes superimposed (Merrill's).
- Bone trabeculae sharp, no motion blur.
- Collimation: distal tibia and fibula to midmetatarsal (Bontrager); 1 inch on the sides, 8 inches lengthwise (Merrill's).
Common errors
- 1 Leg and foot not in a true lateral; support under the knee as needed.
- 2 Leaving the foot plantar flexed makes a true lateral harder to hold.
- 3 CR not directed to the medial malleolus.
- 4 Over- or under-rotation moves the fibula off the posterior half of the tibia.
Clinical indications
- Trauma evaluation for suspected ankle fracture or dislocation.
- Joint effusion, so the soft tissue must be shown.