Thumb Lateral is a radiography positioning projection of the Upper Extremity. Seated, thumb abducted with its medial surface against the IR. SID 40". The centering point is located first mcp joint of the thumb.. The central ray is perpendicular to the mcp joint.. Image-quality criteria include thumb shown in true lateral with no rotation or foreshortening., 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.
- IP, MCP, and first CMC joints.
- CMC articulation.
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 the thumb fully abducted.
- Rotate the thumb so its medial surface rests against the IR and the thumbnail is perpendicular.
Position & centering point
First MCP joint of the thumb.
Central ray
Perpendicular to the MCP joint.
Exposure / technique
- kVp
- 55–65
- mAs
- 2–3
- SID
- 40" (102 cm)
- Notes
- Tabletop technique. Medial surface of the thumb against the IR, thumbnail perpendicular to it.
Image-quality criteria
- Thumb shown in true lateral with no rotation or foreshortening.
- Both thumb phalanges (proximal and distal) and the metacarpal included.
- Joint spaces open and clearly visible.
- Soft tissue and bone trabeculae sharp, no motion blur.
- Collimation: 1 inch on all sides, 1 inch proximal to CMC joint.
Common errors / ARRT traps
- 1 Hand supinated or pronated rotates thumb off true lateral.
- 2 Insufficient abduction overlaps thumb with adjacent digits.
- 3 CR off-centered clips distal phalanx or metacarpal.
- 4 Thumb flexion foreshortens phalanges.
Clinical indications
- Thumb trauma evaluation when AP view is inadequate.
- Suspected thumb joint instability or dislocation.
- Assessment of thumb soft tissue injury or edema.
- Post-operative follow-up of thumb fixation.
Aligned to the current ARRT Radiography Content Specifications.