Pediatric knee (AP view)

The anteroposterior knee view for pediatrics is one of two views in order to examine the knee joint, patella, distal femur and proximal tibia and fibula. Depending on the child's age and the departmental protocol, additional views such as the skyline and intercondyler views may also be performed.

Indications

This projection demonstrates the knee in its natural anatomical position. It is useful in diagnosing fractures, soft tissue effusions and joint space abnormalities in pediatric patients.

Patient position

• the patient is supine with the affected leg extended

• the affected knee is in contact with the image receptor and knee is not rotated

Technical factors

• anteroposterior projection

• centering point

  • 1.5 cm distal to the apex of the patella

• collimation

  • lateral to the skin margins

  • superior to include the distal femur

  • inferior to include the proximal tibia and fibula

• orientation  

  • portrait

• detector size

  • 18 cm x 24 cm

• exposure ¹

  • 50-60 kVp

  • 1-2 mAs

• SID

  • 100 cm

• grid

  • no

Image technical evaluation

Tibial and femoral condyles are symmetrical demonstrating no rotation of the knee. The medial aspect of the fibular head is seen to partly superimpose the tibia ². A physical metal marker is ideal for pediatric imaging. 

Practical points

Preparing the room beforehand (setting up the detector, exposure and preparing lead gowns) is important as pediatric patients may not remain still when their affected knee is moved onto the detector. 

Immobilization techniques

It is important for the radiograph to be free from motion artifact and rotation to avoid repeated x-rays.

• it may be necessary for the parent or radiographer to hold the patient in position

• ideally the parent should be in the child's direct line of sight

• techniques will vary based on the department

• distraction techniques can be utilized to avoid scattered radiation to parents and staff ³