Lateral Distal Femur is a radiography positioning projection of the Lower Extremity. Lateral recumbent on affected side. Knee joint included. The centering point is located midpoint of the IR (Bontrager); midfemur and center of the IR (Merrill's). Knee joint must be on the IR. The central ray is perpendicular to mid femur, centered to include the knee joint. Image-quality criteria include distal two-thirds of femur including knee joint visible, anterior and posterior margins of the femoral condyles superimposed. A sample technique is 87.5 kVp with DR 3.6 or CR 7.1 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Distal two-thirds of the femoral shaft.
- Superimposed medial and lateral femoral condyles.
- Patella in lateral profile.
- Knee joint, which does not appear open.
- Trabecular pattern of the distal femur.
Patient preparation
- Verify patient identity using two identifiers.
- Remove radiopaque items from the leg.
- WARNING: do not attempt this position with severe trauma (Bontrager), or with a fracture or possible destructive disease (Merrill's). Use the horizontal-beam lateral, patient supine.
- Position patient in lateral recumbent on the affected side.
- Flex the affected knee about 45 degrees.
- Place the unaffected leg behind the affected leg to prevent over-rotation.
- Confirm pregnancy status when applicable.
- Collimate closely. Bontrager says to shield outside the region of interest; Merrill's shields the gonads when the patient or caregiver requests it. Follow your department's policy.
Position & centering point
Midpoint of the IR (Bontrager); midfemur and center of the IR (Merrill's). Knee joint must be on the IR.
Central ray
Perpendicular to mid femur, centered to include the knee joint.
Exposure / technique
- kVp
- 87.5
- mAs
- DR 3.6 / CR 7.1
- SID
- 40" (102 cm)
- Notes
- Grid required for adult femur. 14"x17" lengthwise IR. Trauma may use cross-table lateral. Bontrager prints digital 80 +/- 5 kV; the sample is Merrill's chart. Sample technique: DR 3.6 / CR 7.1 mAs at 87.5 kVp, 40 in SID, for a 15 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Distal two-thirds of femur including knee joint visible.
- Anterior and posterior margins of the femoral condyles superimposed.
- Knee joint included; it does not appear open because of beam divergence.
- Patella seen in lateral profile anterior to the femur.
- No rotation of the distal femur or knee.
Common errors
- 1 Improper rotation prevents condylar superimposition.
- 2 Unaffected leg not placed behind the affected leg.
- 3 Failure to include the knee joint on the receptor.
Clinical indications
- Not for severe trauma (Bontrager), or a fracture or possible destructive disease (Merrill's): use the horizontal-beam lateral, patient supine.
- Mid- and distal femur, including the knee joint, for bone lesions.