Measuring Instability in the Distal Radius Fracture
The same wrist fracture can go in a cast or under the knife depending on 3 numbers measured off the film.
Takeaways
- Distal radius fracture is bimodal by age and mechanism. Young patients fracture from high-energy trauma and older patients, mostly women, fracture from a low-energy fall onto osteoporotic bone. Incidence in women over 50 runs roughly 4x higher than in age-matched men. (Diamantopoulos et al, PLoS ONE 2012)
- 3 measurements describe the normal distal radius on plain film. Radial inclination averages 22°, volar tilt 11°, and radial height 11-12mm, with ulnar variance near neutral. Population studies show a wider spread (radial inclination 13-30°), so treat these as reference values rather than a hard cutoff. (Nana, Joshi & Lichtman, J Am Acad Orthop Surg 2005;13:159-171)
- 3 numbers separate a stable reduction from one that needs surgery. The AAOS/ASSH 2020 guideline favors operative fixation over casting once post-reduction radial shortening exceeds 3mm, dorsal tilt exceeds 10°, or intra-articular step-off exceeds 2mm, in patients under 65 (moderate strength of recommendation). (AAOS/ASSH CPG, Management of Distal Radius Fractures, 2020)
- Lafontaine's 5 criteria predict instability and perform only moderately. Age over 60, initial dorsal angulation over 20°, dorsal comminution, intra-articular extension, and an associated ulnar fracture each count, and 3 or more predicts an unstable fracture. A 2025 validation of 274 patients found an AUROC of only 0.65 and redisplacement in 39% despite closed reduction. (Lafontaine et al, Injury 1989;20:208-210; Dissaneewate et al, J Orthop Surg Res 2025, PMID 39920836)
- Acute carpal tunnel syndrome complicates about 1 in 20 distal radius fractures. Leow found acute carpal tunnel syndrome in 51 of 1189 distal radius fractures (4.3%), median onset at 1 week, more common with comminuted intra-articular patterns. Document median nerve function before and after every reduction. (Leow et al, Eur J Orthop Surg Traumatol 2021;31:981-987, PMID 33891155)
- 4 eponyms describe the direction and pattern of displacement. Colles is extra-articular with dorsal displacement and the classic dinner fork deformity. Smith is its mirror image with volar displacement. Barton is an intra-articular fracture-dislocation where a dorsal or volar rim fragment carries the carpus with it, and Chauffeur's (Hutchinson) is an isolated intra-articular radial styloid fragment. (StatPearls NBK553071, NBK547714, NBK499906)
- Distal radius fractures rarely arrive alone. Arthroscopic series find scapholunate ligament injury in 35.3% and lunotriquetral injury in 18.2% of wrists, and DRUJ instability in roughly 34% at 6 months after volar plating. TFCC injury rates vary widely by series, up to 90% on arthroscopy, and are not yet standardized. (Begum et al, J Hand Surg Asian Pac Vol 2022;27:935-944, PMID 36476085)
- Surgery does not beat casting for most patients over 65. The AAOS 2020 guideline found strong evidence that operative fixation does not improve outcomes past that age, and the WRIST trial found a clear short-term benefit only in high-activity, low-comorbidity older adults. Fixation technique (K-wire vs volar plate) made no difference to patient-reported outcome in DRAFFT. (AAOS/ASSH CPG 2020; Costa et al, BMJ 2014;349:g4807, PMID 25096595)