Reading the Five Measurements of the Distal Radius
A distal radius that heals short or tilted can leave a weak, stiff and painful wrist, and the post-reduction film decides who needs surgery.
Key terminology
- Colles fracture
- This distal radius fracture has the broken end tipped and shifted toward the back of the hand. It gives the dinner fork deformity after a fall on an outstretched hand.
- Smith fracture
- This distal radius fracture has the broken end tipped toward the palm. It is the reverse Colles pattern and usually follows a fall on a flexed wrist.
- Radial inclination
- This angle on the PA view shows how steeply the radial joint surface slopes up toward the radial styloid. Collapse of the styloid flattens it.
- Radial height
- This length on the PA view runs from the ulnar corner of the radial joint surface up to the tip of the radial styloid. It drops when the radius shortens.
- Ulnar variance
- This measure on the PA view compares where the end of the ulna sits against the end of the radius. A longer ulna reads as positive variance.
- Volar tilt
- This angle on the lateral view shows which way the radial joint surface faces. Normally it faces slightly toward the palm, and a Colles pattern reverses it.
- Articular step-off
- This is a stair or gap in the cartilage surface of the radius where a fracture enters the joint. A large step raises the risk of wrist arthritis.
Takeaways
- A Colles fracture tilts the distal radius fragment dorsally and a Smith fracture tilts it volarly. Colles follows a fall on an outstretched hand with the wrist extended and classically has dorsal angulation, dorsal displacement, radial shortening and often an ulnar styloid fracture. Smith is the reverse Colles, typically from a fall on a flexed wrist or a blow to the back of the hand. The lateral film tells them apart (StatPearls, Colles Fracture, NBK553071, PMID 31971712; StatPearls, Smith Fracture, PMID 31613494).
- Every distal radius film is checked against 5 standard measurements on the PA and lateral views. Radial inclination, radial height and ulnar variance come from the PA view. Volar tilt comes from the lateral, and articular step-off is read wherever the joint surface shows best. Abnormal wrist anatomy after fracture has been linked to weak grip, stiffness, pain, distal radioulnar joint instability and ulnocarpal impaction (Mignemi et al, J Hand Surg Am 2013;38:40-48, PMID 23218558).
- Volar tilt is read on the true lateral, and the normal joint surface faces slightly toward the palm. Normal volar tilt is about 11°. A Colles pattern reverses it into dorsal tilt. The AAOS guideline recommends a true lateral after reduction to check alignment of the distal radioulnar joint (moderate strength) (Mignemi et al, J Hand Surg Am 2013;38:40-48, PMID 23218558; Lichtman et al, J Am Acad Orthop Surg 2010;18:180-189, PMID 20190108).
- Radial inclination and radial height both measure how far the radial styloid stands above the ulnar side of the joint. On the PA view, normal radial inclination is about 22°, the angle of the joint surface against a line perpendicular to the shaft. Radial height expresses the same rise as a length, with a normal standard of 14 ± 1 mm in one series (published norms vary). A fracture that collapses the styloid can lose both (Mignemi et al, J Hand Surg Am 2013;38:40-48, PMID 23218558).
- Ulnar variance compares the length of the ulna with the radius at the wrist and is normally close to neutral. Healthy volunteers averaged +0.74 mm in neutral rotation, and 26% had negative variance. Gripping in pronation made the ulna read longer, so variance is measured on a neutral-rotation PA view. A fracture that shortens the radius turns variance positive, which is associated with ulnocarpal impaction (Jung et al, J Bone Joint Surg Br 2001;83:1029-1033, PMID 11603517; Mignemi et al, J Hand Surg Am 2013;38:40-48, PMID 23218558).
- In patients under 65, shortening over 3 mm, dorsal tilt over 10° or step-off over 2 mm after reduction favors surgery. The 2020 AAOS/ASSH guideline rates this evidence moderate. Malunion after a Colles fracture left a weak, stiff wrist in a small series. A meta-analysis found a DASH benefit from surgery in mixed-age studies and none in studies of patients 60 or older (Kamal and Shapiro, J Am Acad Orthop Surg 2022;30:e480-e486, PMID 35143462; McQueen and Caspers, J Bone Joint Surg Br 1988;70:649-651, PMID 3403617; Ochen et al, JAMA Netw Open 2020;3:e203497, PMID 32324239).
- In older adults, a distal radius that heals crooked on film can still give a good wrist. In an RCT of patients 65 and older, volar plating gave better alignment and grip, and DASH and PRWE matched casting at 1 year, with 13 vs 5 complications. In WRIST (age 60 and older), malunion was 59.1% after casting vs 8.0% after plating, with no meaningful difference at 24 months (Arora et al, J Bone Joint Surg Am 2011;93:2146-2153, PMID 22159849; Chung et al, JAMA Netw Open 2021;4:e2112710, PMID 34137830; Kamal and Shapiro, J Am Acad Orthop Surg 2022;30:e480-e486, PMID 35143462).
- Distal radius fractures are among the most common fractures and peak in children and older adults. They make up about 25% of pediatric fractures and about 18% of fractures after 65, with over 640,000 US cases a year. Younger patients break the wrist in sports or car crashes, and older patients fall from standing onto an outstretched hand (Kamal and Shapiro, J Am Acad Orthop Surg 2022;30:e480-e486, PMID 35143462; Nellans et al, Hand Clin 2012;28:113-125, PMID 22554654).