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.
