Lateral Patella is a radiography positioning projection of the Lower Extremity. Lateral recumbent, affected side down, knee flexed 5-10 degrees; horizontal beam with no flexion for severe trauma. SID 40". The centering point is located patellofemoral joint, knee flexed 5-10 degrees in true lateral. The central ray is perpendicular to the IR, to the patellofemoral joint in true lateral. Image-quality criteria include patella in true lateral profile, not rotated, anterior and posterior borders of the femoral condyles superimposed. A sample technique is 85 kVp with DR 2 or CR 2.8 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Patella in true lateral profile.
- Femoral condyles superimposed posteriorly.
- Patellofemoral joint space.
Patient preparation
- WARNING: with severe trauma, do not flex the knee: use a horizontal-beam lateral with no knee flexion (Bontrager).
- Verify patient identity using two identifiers.
- Remove shoes and any radiopaque items from the leg.
- Position patient lateral recumbent, affected side down; support the other knee behind it.
- Flex knee 5 to 10 degrees and place on IR in true lateral.
Position & centering point
Patellofemoral joint, knee flexed 5-10 degrees in true lateral.
Central ray
Perpendicular to the IR, to the patellofemoral joint in true lateral.
Exposure / technique
- kVp
- 85
- mAs
- DR 2 / CR 2.8
- SID
- 40" (102 cm)
- Notes
- Flex only 5-10 degrees: more may separate fracture fragments. A lateral patella line appears only in ARRT's 2027 outline (from March 1, 2027); the 2022 outline lists knee lateral. Bontrager prints digital 75 +/- 5 kV; the sample is Merrill's chart. Sample technique: DR 2 / CR 2.8 mAs at 85 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
- Patella in true lateral profile, not rotated.
- Anterior and posterior borders of the femoral condyles superimposed.
- Patellofemoral joint space open.
- Patella shown in profile anterior to the femoral condyles.
- Collimation: closely to the patella and knee joint (Bontrager); 4 x 4 inches (Merrill's).
Common errors
- 1 Knee flexion beyond 10 degrees draws the patella into the patellofemoral joint.
- 2 Over- or under-rotation leaves the femoral condyles not superimposed.
- 3 Flexing beyond 10 degrees risks separating a transverse patellar fracture.
- 4 CR not directed to the mid-patellofemoral joint.
Clinical indications
- Patellar fracture evaluation in lateral plane.
- Patellofemoral arthritis and cartilage loss.