AP PROJECTION: LEG

Friday, September 21, 2012

Pathology Demonstrated:

  • Pathologies involving fractures, foreign bodies, or lesions of the bone are demonstrated.


Technical Factors:

  • IR size - 35 x 43 cm (14 x 17 inches) divided in half, lengthwise (or diagonal, which requires 44 inches [110 cm] minimum SID)
  • Detail screen
  • 70 +- kV range
  • To make best use of anode heel effect, place knee at cathode end of xray beam.
  • mAs 6


Shielding:

  • Place lead shielding over gonadal area.


Patient Position:

  • Take radiograph with patient in the supine position; give pilow for head; leg should be fully extended.


Part Position:

AP Leg including tibia and fibula
  • Adjust pelvis, knee and leg into a true AP with no rotation.
  • Place sandbag againts foot if needed for stabilization, and dorsiflex foot to 90 degree to leg if posible.
  • Ensure that both ankle and knee joints are 1 to 2 inches (3 to 5 cm) from ends of IR (so that divergent rays will not project either joint off the IR).
  • For most adults, the leg must be placed diagonally (corner to corner) on one 35 x 43 cm (14 x 17 inches) IR to ensure that both joints are included. (Also, if needed, a second smaller IR may be taken of the joint nearest the injury site.)


Central Ray:

  • CR perpendicular to IR, directed to midpoint of leg
  • Minimum SID of 40 inches (100 cm); may increase to 44 or 48 inches (110 to 120 cm) to reduce divergence of x-ray beam and to include more of body part (increase mAs accordingly)


Collimation:

  • Collimate on both sides to skin to skin margins, with full collimation at ends of IR borders to include maximum knee and ankle joints.


Alternative follow-up exam routine:

  • The routine for follow-up exams of lone bones in some departments is to nclude only the joint that is nearest the siteof injury and to place this joint a minimum of 2 inches (5 cm) from the end of the IR for better demonstration of this joint. However, for initial exams, it is important, especially when the injury site is at the distal leg, to also include the proximal tibiofibular joint area because it is common to have a second fracture at this site. For very large patients, a second AP projection of the knee and proximal leg may be needed on a  smaller IR.


Radiographic Criteria:

Structures Shown:

AP fractured Leg
  • The entire tibia and fibula should be included with both the ankle and knee joints demonstrated on one (or two if needed) IR(s). (The exeption is alternate routine on follow-up exams.)


Position:

  • No rotation as evidenced be demonstration of the femoral and tibial condyles in profile with the intercondylar eminence centered within the intercondylar fossa.
  • Some overlap of the fibula and tibia will be visible at both proximal and distal ends.


Collimation and CR:

  • Close collimation borders should be visible, but only minimal (if any) borders should be visible at the ends to maximize visualization of both joints.
  • Divergence of the beam will cause the knee and ankle joint spaces to be mostly closed.


Exposure Critetia:

  • Correct use of the anode heel effect will result in an image with nearer equal density at both ends of the IR.
  • No motion is present, as is evidenced by sharp cortical margins and trabecular patterns.
  • Contrast should be sufficient to visualize soft tissue and bony trabecular markings at both ends of tibia.

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