Pelvis (hip surveillance)

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Hip surveillance radiographs are part of a concerted effort to monitor and enable early detection of hip displacement in patients with cerebral palsy or neuromuscular disorders. The radiographs consist of a modified AP pelvis in which the patient's legs are in a neutral position, with the patellae facing anteriorly. The screening process is a multi-faceted effort, involving the medical imaging team, physiotherapists and orthopedics.

Patient position

  • patient is supine
  • legs are in a neutral position, often with the knee caps facing anteriorly 

Technical factors

  • AP projection
  • centering point
    • the midpoint of the anterior superior iliac spine and the pubic symphysis 
  • collimation
    • some departments only image the hip region rather than the entire pelvis after the first presentation, in this case, collimation should only be superior to the ASIS
      • laterally to the skin margins
      • superior to above the iliac crests
      • inferior to the proximal third of the femur
  • orientation  
    • landscape 
  • detector size
    • will vary with patient size and age
  • exposure
    • 63-70 kVp
    • 2-5 mAs
  • SID
    • 100 cm
  • grid
    • if patient thickness is above 10 cm use of a grid is advisable

Image technical evaluation

  • the pelvis should be horizontal
  • there should be neutral abduction/adduction of the limbs (there is a tolerance of 6 degrees)
  • clear visualization of the triradiate cartilages
  • no rotation evident via the obturator foramina appearing equal and iliac wings having an equal concavity

Practical points

  • it is of uttermost importance these radiographs are performed to the criteria mentioned above, the radiographer must ensure the patella of the patient is facing upwards with a neutral abduction/adduction of the legs for accurate assessment of migration percentage via Hilgenriener’s line
  • positioning these patients can be challenging and require radiographers with experience in immobilization techniques to ensure reproducibility of examinations
  • patients with significant lordosis will have a tilted pelvis in the natural supine position, this can overcome by placing a sponge beneath the legs.
  • overall, ensure the radiographer documents how the examination was performed for future reference