Thumb PA Oblique is a radiography positioning projection of the Upper Extremity. Seated, hand pronated, thumb obliqued 45 degrees. SID 40". The centering point is located mcp joint, 1 inch on ulnar side of ir.. The central ray is perpendicular to the mcp joint.. Image-quality criteria include thumb shown in 45-degree oblique with minimal overlap of digits., both thumb phalanges (proximal and distal) and the metacarpal included.. Standard exposure ranges from 55 to 65 kVp, 2 to 3 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Distal and proximal phalanges (the thumb has only two).
- First metacarpal.
- DIP, PIP, and MCP articulations.
- CMC joint region.
Patient preparation
- Verify patient identity using two identifiers.
- Remove rings, bracelets, and radiopaque items from the hand.
- Seat the patient at the end of the table.
- Extend the arm with hand pronated (palm down).
- Abduct the thumb to place distal aspect at 45-degree angle.
Position & centering point
MCP joint, 1 inch on ulnar side of IR.
Central ray
Perpendicular to the MCP joint.
Exposure / technique
- kVp
- 55–65
- mAs
- 2–3
- SID
- 40" (102 cm)
- Notes
- Tabletop technique. Palm facing down (pronated hand).
Image-quality criteria
- Thumb shown in 45-degree oblique with minimal overlap of digits.
- Both thumb phalanges (proximal and distal) and the metacarpal included.
- Joint spaces open and clearly visible.
- Bone trabeculae and soft tissue sharp, no motion blur.
- Collimation: 1 inch on all sides, 1 inch proximal to CMC joint.
Common errors / ARRT traps
- 1 Angle of thumb less than 45 degrees rotates it off-axis.
- 2 Supinated hand negates the oblique positioning.
- 3 CR off-centered clips phalanges or metacarpal.
- 4 Excessive flexion foreshortens the thumb.
Clinical indications
- Thumb trauma when AP projection cannot be obtained.
- Suspected thumb joint arthrosis or degenerative disease.
- Evaluation of thumb soft tissue injury or swelling.
- Post-operative follow-up with hardware assessment.
Aligned to the 2025 ARRT Content Specifications.