Knee AP
Position the Patient
- Seated or supine
- Leg extended
- Femoral condyles parallel to IR
Words That Work
“Straighten your leg and let it relax. Keep your kneecap pointing straight up, like a headlight aimed at the ceiling, and don’t let your leg roll inward or outward. Hold still.”
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AP knee positioning
Set Up the Shot
- Center here
- Central ray
- 1/2" below patellar apex; 5° cephalic; Thin knee: 3° cephalic; Thick knee: 7° cephalic
- Include this in the field
- Collimation
- Distal femur → proximal tib/fib
- Set the distance
- SID
- 40"
- Check the technique
- Technique
- 60-70 kVp
- Follow facility protocols
Common Pitfalls
- •Joint space not open (incorrect CR angle for body habitus)
- •Rotation (patella not centered)
- •Patella or joint not centered on IR
Evaluate the Image
What should be visible?
- Distal femur
- Proximal tibia/fibula
- Open knee joint space
Does the image pass?
- ✓Joint space open
- ✓Patella centered
- ✓No rotation