Thumb - PA

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Radiographic Positioning

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Name of projection Thumb - PA or AP
Area Covered Distal and proximal phalanx, carpometacarpal joint, metacarpal, trapezium
Pathology shown Fracture, dislocation, foreign body, infection, tumour, arthritis
Radiographic Anatomy Hand Radiographic Anatomy
IR Size & Orientation 18 x 24cm
Landscape, divided for multiple thumb images, use lead masking for unused area
Film / Screen Combination Detail
(CR and DR as recommended by manufacturer)
Bucky / Grid No
Filter No
Exposure 50 kVp
2.5 mAs
FFD / SID 100cm
Central Ray Directed to thumbs metacarpophalngeal joint
Perpendicular to the IR
Collimation Centre: Metacarpophalngeal joint
Shutter A: Distal phalanx to carpometacarpal joint
Shutter B: To include soft tissues
Markers Distal and Lateral
Marker orientation AP
Shielding Gonadal (check your department's policy guidelines)
Respiration Not applicable
  • Patient seated at end of table
For AP:
  • Rotate arm and hand internally until thumb is AP
  • Thumbnail and thumb flat against IR
For PA:
  • Raise thumb until in the PA position (may use sponge support)
For both:
  • Long axis of thumb in centre line of IR
  • Metacarpophalangeal joint in centre of IR
  • Other digits held back out of the way
  • Support elbow if it is elevated

  • No rotation of the digit demonstrated by
    • equal concavity of phalangeal and metacarpal shafts
    • equal amount of soft tissue on both sides of phalanges
    • Thumbnail, if visualised, will be centred
  • Long axis of digit is aligned with long axis of IR
AP position:
  • Soft tissue overlap of palm over midshaft of first metacarpal and carpometacarpal joint
  • Following joint spaces are open: metacarpophalangeal, interphalangeal, carpometacarpal
PA position:
  • Palm soft tissue does not overlap metacarpal and carpometacarpal joint
  • Carpometacarpal joint is closed
Area Covered
  • Distal and proximal first phalanx, carpometacarpal joint, first metacarpal and trapezium
  • Centred at metacarpophalangeal joint
  • Opened to include distal phalanx to trapezium
  • Opened to include soft tissue
  • Bony trabecular patterns and cortical outlines are sharply defined
  • Soft tissues are visualised
Special Notes