Pelvis (hip surveillance)

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
• centring 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 ¹
  • 63-70 kVp
  • 2-5 mAs
• SID
  • 100 cm
• grid
  • if patient thickness is above 10 cm use of a grid is advisable ¹

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 visualisation 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 immobilisation 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