Radial Shortening: Definition and Measurement
Radial shortening is measured as the distance from the distal radial articular surface to the distal ulnar articular surface on a posteroanterior (PA) radiograph, and a measurement >3mm post-reduction is a threshold for considering operative fixation in non-geriatric patients with distal radius fractures 1.
What is Radial Shortening?
Radial shortening represents the loss of normal radial length relative to the ulna following a distal radius fracture. This parameter is critical because it directly impacts functional outcomes and guides treatment decisions. The term is often confused with "radial height" or "radial length," but these should be distinguished 2.
How to Measure Radial Shortening
The Correct Measurement Technique
Measure the perpendicular distance from the distal radial articular surface to the distal ulnar articular surface on a PA wrist radiograph 2, 3. This is the only measurement method that has been validated to correlate with functional outcomes 3.
Key Technical Points:
- Obtain a true PA radiograph of the wrist
- Draw a line perpendicular to the long axis of the radius
- Measure from the tip of the radial styloid to the distal ulnar articular surface
- Normal radial length is approximately 11-12mm (the radius is typically longer than the ulna)
- Radial shortening >3mm indicates significant displacement 1
Common Pitfalls to Avoid
Nearly half (47.5%) of published studies fail to define how they measure radial height/shortening 2, leading to confusion and inconsistent treatment decisions. The literature shows three different measurement approaches:
- 50.9% measure from radial styloid to distal ulna (correct method)
- 10.9% measure from radial styloid to distal radius (incorrect)
- 29.2% use other undefined methods (problematic)
Only the first method (radial styloid to distal ulnar surface) has been shown to correlate with functional outcomes 3.
Clinical Significance
Treatment Thresholds
According to the 2022 AAOS/ASSH guidelines, for patients under 65 years of age, post-reduction radial shortening >3mm is an indication for operative fixation 1. This threshold is based on moderate evidence from one high-quality and 26 moderate-quality studies demonstrating improved radiographic and patient-reported outcomes with surgical treatment.
Prognostic Value
Radial shortening of ≥2mm has been associated with worse functional outcomes 4. In elderly patients with osteoporotic bone treated with K-wire fixation, 56.8% demonstrated radial shortening of 2mm or more at final follow-up, suggesting this fixation method may be inadequate for maintaining radial length 4.
Terminology Clarification
Radial shortening requires comparison with a reference value (either the contralateral wrist or expected normal anatomy), while radial height/length is an absolute measurement 2. The standardized terminology should be:
- Radial length/height: Absolute measurement from radial styloid to distal ulnar surface
- Radial shortening: Loss of radial length compared to normal or pre-injury state
- Ulnar variance: Related but distinct measurement of ulnar length relative to radius