AP MORTISE PROJECTION - 15 TO 20 DEGREE MEDIAL ROTATION : ANKLE

Wednesday, September 19, 2012


 Pathology Demonstrated:

  • This projection is particular useful for evaluation pathology involving the entire ankle mortise and the proximal fifth metatasals, a common fracture site.


Technical Factors:

  • IR size - 24 x 30 cm (10 x 12 inches)
  • Divide in half, crosswise
  • Detail screen
  • Digital IR - use lead masking
  • 60 +- kV range
  • mAs 6


Shielding:

  • Place leas shield over pelvic area.


Patient Position:

  • Take radiograph with patient in the supine position; place pillow under head; legs should be fully extended.


Part Position:

AP mortise 15-20 degree medial rotation
  • Center and align ankle joint to CR and to long axis of portion of IR being exposed.
  • Do not dorsiflex foot, but allow to remain in natural extended (plantar flexed) position (allows for visualization of base of fifth metatasal - a common fracture site).
  • Internally rotate entire leg and foot about 15 to 20 degrees until intermalleolar line is parallel to IR.
  • Place support against foot if needed to prevent motion.


Central Ray:

  • CR perpendicular to IR, directed midway between malleoli
  • Minimum SID of 40 inches (100 cm)


Collimation:

  • Collimate to lateral skin margins, including proximal matatasals and distal tibia-fibula.


CR and DR:

  • Close collimation and lead masking are important over unused portions of image plate.


Notes: This position should not be a substitute for either the AP projection or the oblique ankle position but rather be a separate projection of the ankle that is taken routinely when potential trauma or sprains of the ankle joint are involved.
This is also a common projection taken during open reduction surgery of the ankle.

Radiographic Criteria:

Structure Shown:


AP mortise 15-20 degree medial rotation
  • Distal one-third of the tibia and fibula, the tibia platfond involving the epiphysis if present, the lateral and medial malleoli, the talus, and the proximal half of the metatasals should be demonstrated.
  • The entire ankle mortise should be open and well visualized ( 3 to 4 mm space over entire talar surface is normal; an extra 2 mm widening is abnormal).


Position:

  • Proper obliquity for the mortise joint is evidenced by demonstration of open lateral and medial mortise joints with the malleoli demonstrated in profile.
  • Only minimal superimposition should exist at the distal tibiofibular joint.


Collimation and CR:

  • The center of four-sided collimation (CR) should be to mid-ankle joint with the distal one-third of the lower leg to the proximal half of the metatasals included.
  • All soft tissue structures also should be demonstrated.


Exposure Criteria:

  • No motion as demonstrated by sharp bony outlines and trabecular markings.
  • Optimal exposure should demonstrate soft tissue structure and sufficient density for talus and distal tibia and fibula.

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