PA OBLIQUE PROJECTION: HAND

Friday, December 16, 2011

Pathology Demonstrated:

  • Fracture and/or dislocation of the phalanges, metacarpals, and all joints of the hand are shown. Pathologic processes, such as osteoporosis and osteoarthritis, also may be demonstrated.


Technical Factor:

  • IR size - 24 x 30cm (10 x 12 inches)
  • Division of IR in half crosswise
  • Detail screen, table top
  • Digital IR - using lead masking
  • 55 to 65 kV range


Shielding:

  • Place lead shield over patient's lap to shield gonads.


Patient Position:

  • Seat patient at end of table with elbow flexed about 90degrees and hand and forearm resting on table.


Part Position:

  • Pronate hand on cassette; center and align long axis of hand with long axis of portion of IR that is being exposed.
  • Rotate entire hand and wrist laterally 45degrees and support with radiolucent wedge or step block, as shown, so that all digits are separated and parallel to IR (see exception below).


Central Ray:

  • CR perpendicular to IR, directed to third MCP joint
  • Minimum SID of 40 inches (100cm)


Collimation:

  • Collimate on four sides to hand and wrist.


Exception:

  • For a routine oblique hand, use a support block to place digits parallel to IR (fig. 5-70). This blocks prevents foreshortening of phalanges and obscuring of interphalangeal joints. If the metacarpals only are of interest, the image can be taken with thumb and fingertips touching cassette (fig. 5-71).


Radiographic Criteria:

Structure Shown:
  • Oblique projection of the entire hand and wrist and about 2.4cm (1 inch) of distal forearm are visible.


Position:
  • MCP and IP joints are open without foreshortening of midphalanges or distal phalanges, indicating that fingers are parallel to IR.
  • Long axis of hand and wrist should be align with IR


45degrees oblique is evidenced by the following: 
  • Midshafts of metacarpals should not overlap;
  • some overlap of distal heads of third, fourth, and fifth, metacarpals but no overlap of distal second and third metacarpals should occur;
  • excessive overlap of metacarpals indicates overrotation, and too much separation indicates underotation
Collimation and CR:
  • Collimation should be visible on four sides to area of affected hand.
  • CR and center of collimation field should be at third MCP joint.

Exposure Criteria:
  • Optimal density and contrast with no motion demonstrate soft tissue margins and clear, sharp bony trabecular markings.

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