Foot AP Axial is a radiography positioning projection of the Lower Extremity. Sole flat on IR, CR angled 10° cephalad toward heel. SID 40". The centering point is located base of the 3rd metatarsal, with the sole flat on IR. The central ray is angled 10 degrees cephalad toward the heel, perpendicular to the long axis of the metatarsals. Image-quality criteria include entire foot: all phalanges and metatarsals, navicular, cuneiforms and cuboid, tarsometatarsal joints opened by the cephalad CR angulation. A sample technique is 70 kVp with DR 1.25 or CR 2.5 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- All five metatarsals; the bases of the 2nd to 5th overlap slightly.
- Tarsometatarsal joints open and clear.
- Navicular; portions of the talus may be included (Merrill's).
- Cuboid and cuneiform bones.
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 supine or seated with the knee flexed.
- Place the affected foot flat on the IR.
- Rest the plantar surface of the foot flat on the IR.
Position & centering point
Base of the 3rd metatarsal, with the sole flat on IR.
Central ray
Angled 10 degrees cephalad toward the heel, perpendicular to the long axis of the metatarsals.
Exposure / technique
- kVp
- 70
- mAs
- DR 1.25 / CR 2.5
- SID
- 40" (102 cm)
- Notes
- CR 10 degrees toward the heel, perpendicular to the metatarsals (about 15 for a high arch, 5 for a low one); no angle for a foreign body. Sample technique: DR 1.25 / CR 2.5 mAs at 70 kVp, 40 in SID, for a 5 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Entire foot: all phalanges and metatarsals, navicular, cuneiforms and cuboid.
- Tarsometatarsal joints opened by the cephalad CR angulation.
- Intertarsal joint space between the 1st and 2nd cuneiforms shown.
- No rotation: near-equal spacing of the 2nd to 5th metatarsals; their bases overlap.
- Bone trabeculae sharp, no motion artifact.
- Collimation: 1 inch on all sides of foot, 1 inch beyond calcaneus shadows.
Common errors
- 1 CR not perpendicular to the metatarsals: about 15 degrees for a high arch, 5 for a low.
- 2 Plantar surface not resting flat and firmly on the IR.
- 3 CR not directed to the base of the 3rd metatarsal.
Clinical indications
- Fractures and fragment alignment, joint space abnormalities, soft tissue effusions.
- Suspected fracture of the midfoot or tarsals.
- Location of opaque foreign bodies, with no CR angle.