Pediatric hip (frog leg lateral view)

The frog leg lateral view is a special radiographic of the pelvis to evaluate the hip. Some departments will perform this routinely instead of the AP pelvis view to reduce exposure and maintain high diagnostic accuracy ¹. Bilateral examination allows for better visualisation of the hip joints and femoral neck, and therefore is an important view in the assessment of: 

• slipped capital femoral epiphysis

• perthesPerthes disease

Patient position

• the patient is supine with no rotation of the pelvis
• the affected limb flexed at the knee approximately 30° to 40°, and the hip abducted 45° (this can be bilateral)
• if unilateral the heel of the affected limb should rest against the medial aspect of the contralateral knee
• if it is a bilateral examination, both knees are to be resting on sponges, giving the appearances of "frog legs"

Technical factors

• lateral projection
• centring point
  • : midway between the anterior superior iliac spine and the pubic symphysis
• collimation
  • superior to the iliac crest
  • inferior to the proximal third of the femur
  • lateral to the skin margins
• orientation
  • landscape
  : landscape
• detector size
  • : 24 x 30 cm or will vary depending on the patient's size
• exposure ²
  • 63-70 kVp
  • 2-5 mAs
• SID
  • : 100 cm
• grid
  • : highly variable due to the view being a specialised paediatric projection

Image technical evaluation

• the entirety of the bony pelvis is imaged from superior of the iliac crest to the proximal shaft of the femur
• the obturator foramina appear equal
• the iliac wings have an equal concavity
• greater trochanters of the proximal femur are in profile

Practical points

Preparing the room beforehand (set up the detector, exposure and prepare lead gowns) is extremely beneficial for pelvis imaging as young children will often begin to cry the moment they are placed supine.

Ideally, if parental holding is required, the parent holds the child from the feet-end in order to be in the child's direct line of sight. This is to avoid the child rotating their pelvis to look at their parent;

• this will require clear instructions for the parents to follow so that they do not allow rotation of the child's pelvis or motion artifact from kicking
• if the parent is accompanying the child by holding them in position, whilst the parent puts on a lead gown, it is the radiographer's responsibility to ensure the baby does not roll off the x-ray table

Radiation protection considerations

• If the paediatric patient can be kept still using other methods such as distraction techniques, or swaddling, this is ideal to avoid scattered radiation to parents and staff ³
• lead shielding may be used in some departments, for paediatric patients. Nevertheless; nevertheless, as x-ray dose reduction technology advances; the consequence of missing valuable information obscured by lead shielding and requiring a repeat should be considered, especially for first presentation ⁴
• in some institutions, paediatric patients with hip pain may be assessed with a single frog leg view to reduce radiation exposure. This is evidence to support this approach, but individual practice will vary by department ⁵