PA OBLIQUE WRIST - Specialized Oblique Projection

PA Oblique Wrist Projection

Oblique Positioning Diagram

SPECIALTY OF THIS PROJECTION

The PA oblique wrist projection is specifically designed to:

Visualize carpal bones on the lateral side of the wrist
Evaluate trapezium and scaphoid without superimposition
Address the limitation of the direct PA projection where the scaphoid superimposes on itself
Visualize the trapezio-trapezoid and scapho-trapezial joint spaces
Provide a profile view of lateral structures of the carpus

Exposure Factors

Kilovoltage (kV)

Optimal for bone contrast

Milliampere-seconds (mAs)

Moderate exposure

Fine Focus

Focal Spot Type

105-115 cm

SID (Source-to-Image Distance)

No Bucky

Configuration

Standard parameters: Similar to lateral projection for consistency in comparative studies

Visible Anatomical Structures

In a 45° PA oblique projection, the following should be observed:

Trapezium and distal half of the scaphoid well visualized
Distal radius and ulna
Full carpus and proximal half of metacarpals
Trapezio-trapezoid and scapho-trapezial joint spaces open
Small interosseous space between shafts of 3-4 and 4-5 metacarpals
Slight overlapping of distal radius and ulna
Soft tissues and bony trabeculation preserved
Lateral side carpal bones without superimposition

Radiographic Plate Configuration

18 × 24 cm divided longitudinally into 2 portions

Purpose: Perform 2 projections on the same plate
Projection 1: PA wrist (first third)
Projection 2: PA oblique wrist (this technique, second third)
Alternative: Can also be used for AP projection
Advantage: Resource efficiency and direct comparison
Technique: Use cone or diaphragm to limit beam to the corresponding portion

Patient Positioning

Seat the patient at the end of the radiographic table, with axilla in contact with the table

Place the palmar surface of the wrist on the image receptor

Adjust the IR so its center point is under the scaphoid

From the pronation position, rotate the wrist laterally (externally) 45°

Place a 45° foam wedge under the elevated side for precision and reproducibility

Slightly extend the wrist

If fingers do not touch the table, place additional support

For specific scaphoid studies, adjust the wrist in ulnar deviation

Place a sandbag over the forearm for immobilization

IMPORTANCE OF THE 45° FOAM WEDGE

The 45° foam wedge serves critical functions in this projection:

Angular Precision: Ensures exact 45° rotation
Reproducibility: Allows for exact comparison in serial controls
Comfort: Improves patient tolerance of positioning
Stability: Prevents movement during exposure
Standardization: Technical uniformity between different operators

Note: The wedge should be placed under the elevated side of the wrist (thumb side)

Central Ray

Perpendicular to the mid-carpal area

Enters immediately distal to the radius

Specific characteristics:

Direction: Perpendicular to the plate
Target: Mid-carpal area
Entry point: Immediately distal to the radius
Angulation: 0° (no vertical angulation)
Purpose: Optimal centering for lateral carpal visualization

ADVANTAGE OVER DIRECT PA PROJECTION

Problem in Direct PA: The scaphoid superimposes on itself

Solution in PA Oblique: 45° rotation allows for:

Full visualization of the scaphoid without superimposition
Evaluation of scaphoid fractures not visible in PA
Visualization of the scapho-trapezial joint
Detail of trapezium and trapezoid
Open lateral joint spaces

Optimal Image Criteria

Key Structures

Trapezium and scaphoid visible

Joint spaces open

No critical superimposition

Correct Rotation

Exact 45° rotation

Lateral carpus in profile

Metacarpals in position

Full Inclusion

Distal radius and ulna

Full carpus

Proximal metacarpals

Patient Instructions

"Remain still during the examination"

Maintain the 45° oblique position without moving during the radiographic exposure

Normal breathing, but hands and fingers must remain completely still

Specific Clinical Indications

Suspected scaphoid fracture

Lateral carpal trauma

Trapezio-metacarpal pain

Trapezium arthrosis evaluation

Common Technical Challenges

Frequent problems in PA oblique wrist projection:

Incorrect rotation (not exactly 45°)
Lack of foam wedge causing variability
Movement during exposure
Misplacement on divided plate
Incorrect centering of the beam
Insufficient ulnar deviation for scaphoid study
Patient discomfort in maintained position
Persistent superimposition of structures

Solution: Always use a 45° foam wedge to guarantee the exact angle and reproducibility

COMPARISON WITH OTHER WRIST PROJECTIONS

Specific advantages of PA Oblique:

Vs. Direct PA: Better visualization of scaphoid and trapezium
Vs. Lateral: Better evaluation of lateral carpus
Vs. Carpal Tunnel: Focus on lateral bony structures
Vs. Scaphoid specific: Less angulation, more natural position

Limitations: Does not replace Direct PA projection for global carpal evaluation

Ideal as a supplement following standard PA and lateral when lateral pathology is suspected.

PA OBLIQUE WRIST PROJECTION