Thumb : AP and PA Projection

Thursday, March 5, 2015

X-ray Examination of the Thumb : AP projection

AP view of the thumb is the usual projection taken by technologist, PA projection is an exemption projection when patient cannot position AP. AP and PA projection demonstrate's fractures and/or dislocations of the distal and proximal phalanges, distal metacarpal, and associated joints are demontrated. Some pathologic processes, such as osteoporosis and osteoarthritis, also may be demonstrated. (See special AP modified Robert's projection for Bennette's fracture at base of first metacarpal.)

Technical Factors:

IR size - 18 x 24 cm (8 x 10 inches)
Division in thirds crosswise
Detail screen, tabletop
Digital IR - use lead masking
50 to 60 kV range

AP Projection : Thumb

Patient and Part Position - AP View

AP Position
Seat patient facing table, arms extented in front, with hand rotated internally to supinate thumb for AP projection.
First, demonstrate this awkward position on your self, so the patient can see how it is done and better understand what is expected.
Internally rotate hand with fingers extended until posterior surface of thumb is in contact with IR ( may have to hold fingers back with other hand as shown).
Align thumb with long axis of portion of IR being exposed.
Center first MCP joint to CR and to center of portion of IR being exposed. (Remember, first metacarpal is considered part of thumb.)

Radiographic Shielding:

Place shield over patient's lap to shield gonads.

Exception - PA ( Only if Patient Cannot Position for Previous AP)

Place hand in near-lateral position and rest thumb on sponge support block that is high enough so that thumb is not rotated but is in position for a true PA projection (fig. 5-52)

Note: As a rule, the pa is not advisable because it results in loss of definition caused by increased object image receptor distance (OID).

Central Ray and Collimation:

CR perpendicular to IR, to first MCP joint
Minimum SID of 40 inches (100cm)
Collimate on four sides to area of thumb, remembering that thumb includes entire first metacarpal.

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