Normal Ulnar Variance Size on Radiography
Ulnar variance describes the relative length difference between the distal articular surfaces of the ulna and radius, measured on a posteroanterior (PA) wrist radiograph. Accurate assessment is clinically important because abnormal variance is strongly associated with a spectrum of wrist disorders, including ulnar impaction syndrome, TFCC tears, and Kienböck disease.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Posteroanterior | -2-2 mm |
Clinical Significance
Normal ulnar variance falls between -2 mm and +2 mm on a standard PA radiograph. A value within this range is considered neutral variance. Deviation beyond these thresholds is associated with distinct pathological conditions.
Positive ulnar variance (ulna longer than radius, >+2 mm) increases load transmission through the ulnocarpal joint, predisposing to ulnar impaction syndrome, triangular fibrocartilage complex (TFCC) degeneration, and lunotriquetral ligament tears. Negative ulnar variance (ulna shorter than radius, <-2 mm) is classically linked to Kienböck disease (avascular necrosis of the lunate), thought to result from altered vascular supply and increased radial loading of the lunate.
- Ulnar impaction syndrome (positive variance)
- Kienböck disease / lunate avascular necrosis (negative variance)
- TFCC tears (positive variance)
- Lunotriquetral ligament pathology (positive variance)
- Post-traumatic variance change following distal radius fracture malunion
Reference: Cooney WP. The Wrist, Diagnosis and Operative Treatment. Lippincott Williams & Wilkins. (2010).
Imaging Notes
Ulnar variance is measured on a true posteroanterior radiograph with the shoulder abducted 90°, elbow flexed 90°, and the forearm in neutral rotation. Forearm pronation artificially increases positive variance, while supination decreases it; strict neutral positioning is therefore essential for reproducibility. The measurement is taken as the perpendicular distance between a line drawn across the distal radial articular surface and a parallel line tangent to the distal ulnar articular surface.
Dynamic or grip-view radiographs may be obtained to unmask variance changes under load, which can be relevant in athletes or patients with activity-related ulnar-sided wrist pain. Comparison with the contralateral wrist is recommended when subtle asymmetry is suspected.