Lateral Leg (Tibia & Fibula) is a radiography positioning projection of the Lower Extremity. Turned onto the affected side, knee slightly flexed, foot in true lateral. SID 40". The centering point is located mid-point between knee and ankle joints on the IR. The central ray is perpendicular to mid-leg in lateral position. Image-quality criteria include tibial tuberosity in profile; part of the fibular head superimposed by the tibia, distal fibula seen through the posterior half of the tibia. A sample technique is 70 kVp with DR 2.5 or CR 3.6 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Posterior borders of the femoral condyles superimposed at the knee.
- Entire tibia and fibula, the fibula partly behind the tibia.
- Femoral condyles; divergence may reduce their superimposition (Merrill's).
- Distal tibia and fibula in lateral relationship.
- Ankle joint in lateral position.
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. If the patient cannot be turned, take it cross-table with the IR on edge.
- Verify patient identity using two identifiers.
- Remove shoes and any radiopaque items from the leg.
- Position patient supine, turn onto the affected side; support the other leg behind it.
- Flex knee partially and place on IR in true lateral position.
- Adjust rotation so the plane of the patella is perpendicular to the IR.
- Keep both joints 1-2 inches from the IR ends. A diagonal leg needs at least 44 inches SID.
Position & centering point
Mid-point between knee and ankle joints on the IR.
Central ray
Perpendicular to mid-leg in lateral position.
Exposure / technique
- kVp
- 70
- mAs
- DR 2.5 / CR 3.6
- SID
- 40" (102 cm)
- Notes
- Turn the patient onto the affected side until the leg and foot are in a true lateral. Minimum SID is 40 inches; 44 to 48 inches reduces beam divergence and includes more of the part. Sample technique: DR 2.5 / CR 3.6 mAs at 70 kVp, 40 in SID, for a 12 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Tibial tuberosity in profile; part of the fibular head superimposed by the tibia.
- Distal fibula seen through the posterior half of the tibia.
- Posterior borders of the femoral condyles superimposed.
- Both knee and ankle clearly included on IR.
- Collimation: sides to skin margins (Bontrager); 1 inch sides, 1.5 inches beyond the joints (Merrill's).
Common errors
- 1 Plane of the patella not perpendicular to the IR leaves the leg rotated.
- 2 Joints placed too near the IR ends are projected off by beam divergence.
- 3 CR not directed to the midpoint of the lower leg.
Clinical indications
- Tibia or fibula fracture evaluation in lateral plane.
- Localization of lesions and foreign bodies.