Robert, Lewis and Long and Rafert Method - Thumb Xray

Tuesday, April 10, 2018

First Carpometacarpal joint - AP Projection

  Robert first describe the radiographic projection of the first CMC joint in 1936. Lewis modified the central ray for this projection in 1988, and long and Rafert further modified the central ray in 1995. This projection is commonly performed to demonstrate arthritic changers, Fractures, displacement of the first CMC joint and Bennett’s fracture. The Robert method does not replace the initial AP or PA thumb projection.

Image Receptor : 8 X 10 inches. Lengthwise.

Patient Position:

   The patient is positioned sideways at the end of the radiographic table. The patient should be positioned low enough to place the shoulder, elbow and wrist on the same plane. The entire limb must be on the same plane to prevent elevation of the carpal bones and closing of the CMC joint.

Part Position:

  • Extend the limb straight out on the radiographic table.
  • Rotate the arm internally to place the posterior aspect of the thumb on the IR with the thumbnail down.
  • Place the thumb in the center of the IR.
  • Hyperextend the hand so that the soft tissue over the ulnar aspect does not obscure the first CMC joint, and ensure that the thumb is not oblique.
  • Long and Rafert state that the patient may hold the fingers back with the other hand.
  • Steady the hand on a sponge if necessary.
  • Shield gonalds.

Central Ray:

Robert Method
  • Central is perpendicular entering at the first CMC joint.

Long and Rafert modification
  • Angled 15 degrees proximally along the long axis of the thumb and entering the first CMC joint
  • Collimate to include the entire thumb.

Lewis modification
  • Central ray is angled 10 to 15 degrees proximally along the long axis of the thumb and entering the first MCP joint.

Angulation of the central ray serves two purposes:
  • It may help project the soft tissue of the hands away from the first CMC joint.
  • It can help open the joint space when the space in not shown with a perpendicular central ray.

Structure shown:

This projection demonstrate the first CMC joint free of superimposition of the soft tissue of the hands.

Evaluation Criteria:

  • The following should be clearly demonstrated:
  • First CMC joint free of superimposition of the hand and other bony structures.
  • First metacarpal with the base in convex profile.
  • Traperzium is clearly demonstrated.

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