Femur (AP view)

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The anteroposterior femur view is part of a standard series examining the femur in its entirety, including the hip and knee joint. Due to the limitations of the image detector, these projections are often performed in two images per view to ensure inclusion of both knee and hip joints.

Indications

This view demonstrates the femur in its natural anatomical position allowing for assessment of suspected dislocations, fractures, localizing foreign bodies and osteomyelitis within the long bone. Depending on departments, this view can be crucial for orthopedic surgeons to determine the length of the femur for prosthetic purposes.

Patient position

  • patient is supine
  • lower limbs are internally rotated 15-25° from the hip (do not attempt this if a fracture is suspected)
  • if acquiring the entire femur in one image, place the detector in a diagonal position parallel with the femur

Technical factors

  • anteroposterior projection
  • centering point
    • for one image: mid femur region
    • for two images: 
      • proximal femur: place detector to include anatomy from ASIS to mid-femoral shaft
      • distal femur: place detector to include anatomy from mid-femoral shaft to knee joint
      • to ensure overlap of anatomy, a physical side marker can be positioned at mid-femur region
  • collimation
    • laterally to the skin margins
    • superior to ASIS
    • inferior to proximal third of tibia/fibula
  • orientation  
    • portrait
  • detector size
    • 30 cm x 43 cm
  • exposure
    • 65-70 kVp
    • 8-12mAs
  • SID
    • 100 cm
  • grid
    • yes

Image technical evaluation

  • entirety of the femur should be seen on the image with the long axis of the femur running parallel to the long axis of the image
  • greater trochanter should be seen in profile signifying adequate internal rotation of the limb 

Practical points

  • internal rotation can be assisted with the use of sandbags over the lateral edges of the patient's feet
  • for orthopedic requests of full femur length in one image, understanding the anatomy of the pelvic girdle and hip joint well can help in positioning the detector diagonally to include as much of the hip joint and its inferior components