Foot Medial Oblique is a radiography positioning projection of the Lower Extremity. Foot rotated medially 30-40 degrees (Bontrager) or 30 (Merrill's), CR perpendicular. SID 40". The centering point is located base of the 3rd metatarsal, with the foot rotated medially 30 to 40 degrees. The central ray is perpendicular to the IR with the foot rotated medially 30 to 40 degrees. Image-quality criteria include entire foot visible, from toes to heel, third to fifth metatarsals free of superimposition; first and second free except at the bases. 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 3rd to 5th free of overlap.
- Lateral tarsometatarsal and intertarsal joints (Merrill's).
- Talar head separated from the navicular bone.
- Cuboid and the sinus tarsi.
- Bases of the third, fourth and fifth metatarsals.
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.
- Rotate the foot and leg medially (inward) 30 to 40 degrees.
Position & centering point
Base of the 3rd metatarsal, with the foot rotated medially 30 to 40 degrees.
Central ray
Perpendicular to the IR with the foot rotated medially 30 to 40 degrees.
Exposure / technique
- kVp
- 70
- mAs
- DR 1.25 / CR 2.5
- SID
- 40" (102 cm)
- Notes
- Rotate the foot medially 30 to 40 degrees, dorsum parallel to the IR (Bontrager); Merrill's uses 30 degrees. 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 visible, from toes to heel.
- Third to fifth metatarsals free of superimposition; first and second free except at the bases.
- Tuberosity at the base of the 5th metatarsal in profile.
- Lateral tarsals open: cuboid, sinus tarsi and the bases of the 3rd to 5th metatarsals.
- Bone trabeculae sharp, no motion artifact.
- Collimation: outer skin margins (Bontrager); 1 inch on all sides, beyond calcaneus and toes (Merrill's).
Common errors
- 1 Insufficient medial rotation fails to open the tarsal joints.
- 2 Past 30 degrees, Merrill's says the lateral cuneiform is thrown over the other cuneiforms.
- 3 CR not directed to the base of the 3rd metatarsal.
- 4 Third to fifth metatarsals superimposed, showing incorrect obliquity.
Clinical indications
- Evaluation of the cuboid, sinus tarsi and lateral tarsal alignment.
- Suspected midfoot fracture or dislocation.
- Location of opaque foreign bodies.