Elbow AP Oblique (Lateral Rotation) is a radiography positioning projection of the Upper Extremity. Arm extended, rotated 45 degrees laterally until 1st/2nd digits touch the table. The centering point is located mid-elbow joint, about 3/4 inch (2 cm) distal to the midpoint of the line between the epicondyles, with the arm rotated 45 degrees laterally from a true AP position. The central ray is perpendicular to the mid-elbow joint. Image-quality criteria include radial head, neck, and tuberosity free of superimposition by the ulna, capitulum visible in profile. The SID is 40 inches (102 cm).
Anatomy demonstrated
- Radial head, neck, and tuberosity.
- Capitulum of the humerus in profile.
- Radius and ulna separated.
- Distal humerus.
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 arm over the IR, palm up, in true AP first.
- Rotate the entire arm 45 degrees laterally until 1st and 2nd digits touch the table.
Position & centering point
Mid-elbow joint, about 3/4 inch (2 cm) distal to the midpoint of the line between the epicondyles, with the arm rotated 45 degrees laterally from a true AP position.
Central ray
Perpendicular to the mid-elbow joint.
Exposure / technique
- kVp
- N/A
- mAs
- N/A
- SID
- 40" (102 cm)
- Notes
- Lateral rotation separates the radius and ulna and frees the radial head. If the patient cannot fully extend the elbow, Bontrager points to the Coyle axial laterals. Bontrager digital range: 65 to 75 kV. Merrill's chart has no separate row for this oblique, so no mAs is given.
Image-quality criteria
- Radial head, neck, and tuberosity free of superimposition by the ulna.
- Capitulum visible in profile.
- Lateral epicondyle elongated and in profile.
- Distal humerus and proximal forearm both included.
- Bone trabeculae sharp, no motion blur.
- Collimation: 3 inches proximal and distal to the joint.
Common errors
- 1 Interepicondylar plane not about 45 degrees to the IR, so the radial head overlaps the ulna.
- 2 Failure to keep the digits touching the table tells you the rotation is short.
- 3 Shoulder not lowered onto the same horizontal plane as the elbow.
Clinical indications
- Suspected radial head or radial neck fracture.
- Pathologic processes such as osteomyelitis and arthritis.