AP PELVIS PROJECTION (BILATERAL HIPS): PELVIS

Tuesday, November 6, 2012

Warning: Do not attemp to interally rotate legs if a hip fracture or dislocation is suspected. Take with affected  leg "as is".

Pathology Demonstrated:

  • Fractures, joint dislocation, degenerative disease, and bone lesions are demonstrated.


Technical Factors

  • IR size - 35 x 43 cm (14 x 17 inches), crosswise
  • Moving or stationary grid
  • 80 +- 5 kV range or 90 +- 5 kV range
  • mAs: 12
  • or for lower gonadal dose at 90 kV
  • mAs: 8


Shielding:

  • Shield gonads on all male patient. Ovarian shielding on females, however, generally is not possible without obscurring of essential pelvis anatomy (unless interest is in area of hips only.)


Patient Position:

  • With patient supine, place arms at sides or across superior chest; provide pillow for head and support for under knees.


Part Position:

  • Align midsagital plane of patient to center line of table and to CR.
  • Ensure that patient is not rotated; distance from tabletop to each ASIS should be equal.
  • Separate legs and feet, then internally rotate long axes of feet and lower limbs 15 to 20 degree. Technologist may have to place sandbags against feet to retain this position.


Central Ray:

  • CR is perpendicular to IR, directed midway between level of ASISs and the symphisis pubis. This is approximately 2 inches (5 cm) inferior to level of ASIS.
  • Center cassette to CR.
  • Minimum SID is 40 inches (100 cm)


Collimation:

  • Collimate to lateral skin margins and to upper and lower IR borders.


Respiration:

  • Suspend respiration during exposure.


Note: If performed as part of a hip routine, centering should be about 2 inches ( 5cm ) lower to level of midfemoral heads or neck to nclude more of proximal femora.

Radiographic Criteria:

Structure Shown:

  • Pelvic girdle, L5, sacrum and coccyx, femoral heads and neck, and greater trochanter are visible.


Position:

  • Lesser trachanters should not be visible at al; for many patients, only the tips are visible. Greater trochanters should appear equal in size and shape.
  • No rotation is evidenced by symmetric appearance of the iliac alae, or wings, the ischial spines, and the two obturator foramina. A foreshortened or closed obturator foramen indicates rotation in that direction. ( A closed or narrowed right obturator foramen compared with the left indicates rotation toward the rigth.)
  • The right and left ischial spine (if visible) should appear equal in size.


Collimation and CR:

  • Correct centering evidenced by demonstration of entire pelvis and superior femora without foreshortening on collimated field.
  • Midsagittal plane of patient should be aligned with central axis of IR.
  • Collimation borders are minimal on larger patients. Smaller patients should show equal lateral collimation borders just lateral to greater trochanters.


Exposure Criteria:

  • Optimal exposure visualizes L5 and sacrum area and margins of the femoral heads and acetabula, as seen through overlying pelvic structures, without overexposing the ischium and pubic bones.
  • Trabecular markings of proximal femora and pelvic structures appear sharp, indicating no motion.

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