Knee (AP view)

The Knee AP view is a standard projection to assess the knee joint, distal femur, proximal tibia and fibula and the patella. 

  • patient is supine on the table with the knee and ankle joint in contact with the table
  • leg is extended
  • ensure the knee is not rotated
  • anteroposterior projection
  • centring point
    • centre of the knee 1.5 cm distal to the apex of the patella
  • collimation
    • superior to include the distal femur
    • inferior to include the proximal tibia/fibula
    • lateral to include the skin margin 
    • medial to include medial skin margin
  • orientation  
    • portrait
  • detector size
    • 24 cm x 30 cm
  • exposure
    • 60-70 kVp
    • 7-10 mAs
  • SID
    • 100 cm
  • grid
    • no

The femoral and tibial condyles should be symmetrical, the head of the fibula is slightly superimposed bit the lateral tibial condyle. The patella is resting on the superior portion of the image superimposing the distal femur.

The fibula head is a great indication of rotation, if the fibula head is entirely superimposed, the image is not AP; to correct this you must internally rotate until the knee is in even contact wit the image detector.

Very slim patients may require a slight caudal angle to better visualise the joint space in an AP fashion. The opposite applies for larger patients (larger thighs mean the leg may be naturally flexed at rest), requiring a slight cephalic angle. Both angles roughly 5-8 degrees.


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Article Information

rID: 42333
Section: Radiography
Synonyms or Alternate Spellings:

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Cases and Figures

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    Figure 1: radiographic anatomy of the knee - AP view
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    Figure 2: Annotated
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