Normal Radioulnar Angle Size on Wrist Radiography
The radioulnar angle, also known as the radial inclination, describes the tilt of the distal radial articular surface relative to the long axis of the radius on a posteroanterior (PA) wrist radiograph. Accurate measurement is essential for evaluating distal radius fractures, congenital deformities, and post-surgical outcomes, as alterations in this angle directly affect load distribution across the radiocarpal and distal radioulnar joints.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Posteroanterior | 72-95¡ |
Clinical Significance
A normal radioulnar angle of 72–95° on PA projection reflects the ulnar tilt of the distal radius articular surface. Values outside this range suggest pathological processes or post-traumatic deformity. Reduced radial inclination (angle approaching 90° or beyond, indicating a more horizontal or reversed tilt) is commonly seen following malunited distal radius fractures and can result in altered wrist kinematics, ulnar impaction syndrome, and chronic wrist pain.
Increased inclination beyond the upper normal limit is less common but may indicate developmental variants or ligamentous laxity conditions. Surgeons use this measurement to guide reduction targets in acute fracture management and to plan corrective osteotomy in malunion cases. It should always be interpreted alongside radial height and volar tilt measurements for a complete assessment of distal radius alignment.
- Distal radius fracture malunion (most common cause of reduced inclination)
- Ulnar impaction syndrome secondary to altered load distribution
- Madelung deformity (abnormal radial inclination from physeal arrest)
- Postoperative assessment following volar plate fixation
- Rheumatoid arthritis with progressive radiocarpal destruction
Reference: Müller TB. Normal Findings in Radiology. Thieme. (2000).
Imaging Notes
The radioulnar angle is measured on a true PA wrist radiograph obtained with the shoulder abducted 90°, elbow flexed 90°, and the wrist in neutral rotation resting flat on the cassette. A line is drawn along the distal radial articular surface, and a second line is drawn perpendicular to the long axis of the radius; the angle between these two lines represents the radioulnar angle. Forearm rotation significantly affects the measured value — supination artificially reduces apparent inclination while pronation increases it — so strict neutral positioning is mandatory for reproducible measurements.
Ensure the PA projection is truly orthogonal; obliquity of even 10° can introduce measurable error. Digital systems allow on-screen goniometric tools that improve reproducibility compared to manual protractor measurement on plain film.