Thumb Projections

Patient Preparation

Explain the procedure to the patient.
Remove rings, jewelry, or any metallic objects from the hand.
Position the hand comfortably on the IR.
Use lead shielding as appropriate.

BASIC PROJECTIONS

1. Anteroposterior (AP) Projection — Thumb

Positioning:

Hand supinated (palm up) on the IR.
Thumb fully extended and slightly abducted from the hand.
Other fingers flexed away from the thumb.

Central Ray (CR):

Perpendicular to IR.
Directed to the first metacarpophalangeal (MCP) joint.

SID (Source-to-Image Distance):

100–110 cm (40–44 inches).

Collimation:

Include distal phalanx to base of first metacarpal.

Evaluation Criteria:

Phalanges, MCP joint, and first metacarpal visualized.
Open interphalangeal and MCP joints.
Sharp trabecular detail.

2. Posteroanterior (PA) Oblique Projection — Thumb

Positioning:

Hand pronated on IR.
Thumb rotated laterally 45° (external oblique).
MCP joint centered to IR.

Central Ray (CR):

Perpendicular to IR.
Directed to MCP joint.

SID:

100–110 cm (40–44 inches).

Collimation:

Include distal phalanx to base of first metacarpal.

Evaluation Criteria:

First metacarpal free of superimposition.
Open MCP joint.
Phalanges and joint spaces clearly visualized.

OTHER PROJECTIONS

3a. Lateral Projection — Thumb (Mediolateral or Lateromedial)

Positioning:

Thumb placed in true lateral with palmar (mediolateral) or dorsal (lateromedial) surface on IR.
Other fingers flexed away or supported.

Central Ray (CR):

Perpendicular to IR.
Directed to MCP joint.

SID:

100–110 cm (40–44 inches).

Collimation:

Include distal phalanx to base of first metacarpal.

Evaluation Criteria:

Thumb in true lateral.
Interphalangeal and MCP joints open.
Phalanges and first metacarpal sharply visualized.
Soft tissue margins visible.

3b. AP Axial Projection — Thumb (Modified Roberts Method)

Positioning:

Patient seated at table, hand supinated.
Thumb fully extended and slightly abducted from the hand.
CR angled 15° proximally toward wrist.
Centered at the first carpometacarpal (CMC) joint.

Central Ray (CR):

15° toward wrist, directed to CMC joint.

SID:

100–110 cm (40–44 inches).

Collimation:

Include distal phalanx, first metacarpal, and CMC joint.

Evaluation Criteria:

Trapeziometacarpal (CMC) joint well visualized.
Minimal foreshortening of first metacarpal.
Distal thumb and base clearly seen.
Sharp bony and soft tissue detail.

Image Evaluation Checklist

Entire thumb visualized from distal phalanx to first metacarpal base (and CMC joint for AP axial).
Proper positioning (AP, PA oblique, lateral, AP axial) achieved.
Sharp detail without motion.
SID maintained at 100–110 cm.
Anatomical markers correctly placed.

Common Pathologies Demonstrated

Fractures of distal, proximal phalanges, or first metacarpal.
Dislocations of interphalangeal or MCP joints.
Trapeziometacarpal (CMC) joint pathology (for AP axial).
Osteoarthritis or degenerative changes.
Soft tissue injuries or foreign bodies.