PA Wrist:
The PA Wrist is the starting point for every wrist series. Because the carpal bones are small and tightly packed, the goal of this view is to spread them out as much as possible. A common mistake is leaving the fingers straight, which creates a natural arch in the wrist and obscures the very joint spaces we need to see. Mastering the PA wrist is about achieving a “flat” anatomy for a clear, diagnostic window into the carpus.
The Goal
To demonstrate the carpal bones, distal radius, and ulna, and the proximal metacarpals in a true PA projection with open radiocarpal and intercarpal joint spaces.
Patient Positioning
- The Setup: Seat the patient at the end of the table with the shoulder, elbow, and wrist all at the same height. This ensures the joint is level and prevents distortion.
- The Hand: Place the palm flat on the IR.
- The Richie “Arch” Trick: Instruct the patient to slightly arch their hand or flex their fingers into a loose fist.
- Why: Flexing the fingers into a fist pulls the wrist downward, placing the carpal bones in direct, flat contact with the IR. This opens the joint spaces and reduces magnification.
- Pro-Tip: Ensure the patient’s forearm is straight on the table. If the arm is angled, the radius and ulna will appear rotated, even if the hand looks flat.
Technical Factors
- Central Ray (CR): Perpendicular to the mid-carpal area (the center of the wrist).
- SID: 40″.
- Collimation: Include the mid-forearm (distal radius/ulna) and the proximal half of the metacarpals.
Image Evaluation Criteria (The “Richie” Checklist)
A professional PA Wrist must meet these essential standards:
- Proper Alignment: The distal radius and ulna should be seen without excessive rotation.
- Open Joint Spaces: The radiocarpal (wrist) joint and the spaces between the carpal bones should be as clear as possible.
- Complete Anatomy: You must include the proximal metacarpals and the distal 1/3 of the forearm.
- Sharp Detail: Sharp trabecular markings should be visible throughout the scaphoid, lunate, and other carpals.
- Correct Marker: Your physical R/L marker must be visible within the collimation, placed on the lateral side of the wrist.
Why the PA Matters
The PA view is our primary “map” of the wrist. It allows the provider to check for carpal alignment and “Gilula’s Lines” (the three smooth arcs formed by the carpal bones). If the wrist is not flat, these lines will appear broken, which could lead to a misdiagnosis of a ligament tear or dislocation.
Richie’s Pro-Tips for Wrist Imaging
Patient Comfort: Keep the room dim but never dark. Explain the importance of staying motionless to avoid “fuzziness” in the image, as a sharp image is the only way to ensure a correct diagnosis.
Watch the Fingers: If the patient’s fingers are extended straight out, the carpus will “tilt” anteriorly. Always remember: Fingers flexed = Wrist flat.
Physical Markers: Never use a digital marker for a wrist exam. Because these images are used for fine-detail orthopedic work, the legal and medical standard requires a physical marker placed at the time of exposure.