Forearm AP is a radiography positioning projection of the Upper Extremity. Seated, forearm extended on IR, palm supinated. SID 40". The centering point is located at the midpoint of the forearm, midway between the wrist and elbow joints. The central ray is perpendicular to the IR at the midpoint of the forearm, midway between the wrist and elbow joints. Image-quality criteria include entire radius and ulna visible from wrist to elbow, no rotation: humeral epicondyles in profile, radial head, neck and tuberosity slightly superimposed by the ulna. A sample technique is 70 kVp with DR 1.25 or CR 2.2 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Entire radius from styloid process to head.
- Entire ulna from styloid to olecranon process.
- Open radioulnar space.
- Proximal row of carpal bones, with the wrist and elbow joint spaces only partially open.
- Distal humerus and wrist anatomy.
Patient preparation
- WARNING: with possible spinal injury or severe trauma, do not attempt to move the patient; do not rotate a severely injured part or remove splints (Bontrager). Merrill's: do not attempt true AP or lateral positioning of a severely injured limb; take two projections 90 degrees apart, moving it as little as possible, and move the IR and tube if the patient cannot reach the position.
- Verify patient identity using two identifiers.
- Remove watches, bracelets, and radiopaque items from the arm.
- Seat the patient at the end of the table.
- Extend the forearm fully on the IR with palm facing up.
- Adjust table height so the entire forearm rests in the same plane.
Position & centering point
At the midpoint of the forearm, midway between the wrist and elbow joints.
Central ray
Perpendicular to the IR at the midpoint of the forearm, midway between the wrist and elbow joints.
Exposure / technique
- kVp
- 70
- mAs
- DR 1.25 / CR 2.2
- SID
- 40" (102 cm)
- Notes
- Tabletop technique. Include both wrist and elbow joints. Sample technique: DR 1.25 / CR 2.2 mAs at 70 kVp, 40 in SID, for a 7 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Entire radius and ulna visible from wrist to elbow.
- No rotation: humeral epicondyles in profile, radial head, neck and tuberosity slightly superimposed by the ulna.
- Wrist and elbow joints included in the collimation.
- Minimal superimposition of proximal radius and ulna.
- Bone trabeculae sharp, no motion blur.
- Collimation: sides to the forearm; include at least 1 to 1 1/2 inches (3 to 4 cm) past both joints (Bontrager) or 2 inches (5 cm) (Merrill's).
Common errors
- 1 Incomplete supination rotates the radius over the ulna.
- 2 Shoulder not dropped, so the upper limb is not on one horizontal plane.
- 3 Field too tight at the ends: beam divergence can cut off a joint.
- 4 Motion blur from patient movement during exposure.
Clinical indications
- Trauma evaluation for radius or ulna fracture.
- Pathologic processes such as osteomyelitis or arthritis.