Lateral Knee is a radiography positioning projection of the Lower Extremity. Supine rotated lateral, knee flexed 20-30 degrees. SID 40". The centering point is located knee joint, knee flexed 20-30 degrees in true lateral.. The central ray is 5-7 degrees cephalad to the knee joint.. Image-quality criteria include medial and lateral femoral condyles superimposed in true lateral., knee joint space open showing anterior and posterior compartments.. Standard exposure ranges from 60 to 75 kVp, 5 to 10 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Distal femur with condyles superimposed.
- Tibial plateau in lateral relationship.
- Patella in lateral profile.
- Femorotibial joint space in lateral aspect.
- Anterior and posterior joint recesses.
- Proximal fibula visible posterior.
Patient preparation
- Verify patient identity using two identifiers.
- Remove shoes and any radiopaque items from the leg.
- Position patient supine, roll toward lateral side of affected knee.
- Flex knee 20 to 30 degrees and adjust on IR in true lateral.
- Place support roll under the flexed knee for comfort.
Position & centering point
Knee joint, knee flexed 20-30 degrees in true lateral.
Central ray
5-7 degrees cephalad to the knee joint.
Exposure / technique
- kVp
- 60–75
- mAs
- 5–10
- SID
- 40" (102 cm)
- Notes
- Knee flexed 20-30 degrees allows visualization of posterior joint.
Image-quality criteria
- Medial and lateral femoral condyles superimposed in true lateral.
- Knee joint space open showing anterior and posterior compartments.
- Patella in true lateral position, not rotated.
- Fibula visible posteriorly and not superimposed on tibia.
- Anterior and posterior joint recesses clearly visualized.
- Collimation 1.5 inches anterior and posterior, 1.5 inches above and below.
Common errors / ARRT traps
- 1 Insufficient knee flexion prevents visualization of posterior compartment.
- 2 Excessive flexion closes joint space and obscures anatomy.
- 3 Medial or lateral rotation distorts condylar superimposition.
- 4 Off-centered CR clips patella or posterior condyles.
Clinical indications
- Knee trauma evaluation, posterior condyle or plateau fracture.
- Assessment of knee effusion and fat pad sign.
- Anterior or posterior knee subluxation evaluation.
- Post-operative follow-up in lateral plane.
Aligned to the 2025 ARRT Content Specifications.