Monday, December 12, 2011

Modified Robert's Method

This special projection is an x-ray examination of the thumb AP projection. This is best to for ruling out Bernett's fracture in the first metacarpal, it is also demonstrates fracture and/or dislocation of the first CMC joint. Some pathologic processes such as osteoarthritis may be demonstrated.

    Technical Factor and Shielding

    • IR size - 18 x 24cm (8 x 10 inches)
    • Detail screen, tabletop 
    • Digital IR - use lead masking
    • 50 - 60 kV range
    • Place lead shield over patient's lap to shield gonads.

      Patient and Part Position

      • Seat patient parallel to end of table, with hand and arm fully extented.
      • Rotate arm internally until posterior aspect of thumb rest on cassette.
      • Place thumb in center of the IR, parellel to side border of the cassette.
      • Extend fingers so soft tissue does not superimpose first CMC joint.
      • Advise patient to hold fingers aside with the other hand, if necessary.

        Central Ray and Collimation

        • CR directed 15degrees proximally (toward wrist), entering at the first CMC joint
        • Minimum SID of 40 inches (100cm)
        • Collimate on four sides to area of thumb and first CMC joint.

          Note: This projection was first describe by M. Robert in 1936 to demonstrate the first CMC joint with the use of a perpendicular CR. The projection was later modified to include a 15degrees proximal CR angle.

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