[Palmar Displacement in Distal Radius Fractures following Extension Injuries of the Wrist].

Background: Fractures of the distal radius have been traditionally classified based on the suspected mechanism of injury. Among clinicians, the terms "Colles" and "Smith" fractures are commonly used to refer to a distal radius fracture that is either displaced to the dorsal (Colles) or palmar (Smith) side of the radius. When analysing x-rays, it is not uncommon for a Smith fracture to be detected in cases where patients describe a fall on the wrist in an extended position. Thus, the question arises how a flexion-type fracture can occur after an extension injury. So far, only little research has been conducted into this subject.

Material and methods: The aim of this study was to analyse the mechanisms of injury that lead to various types of distal radius fractures. Particular emphasis was placed on "Smith" fractures and on the biomechanical, physiological and anatomical characteristics that contribute to their occurrence. To assess these relationships, data of fractures were collected following a life-like fracture simulation using a "drop-bench" in non-formalin fixated human specimens. These fractures were produced between January 2016 and December 2021. Biographic data of all specimens used were available. Additionally, all biomechanical and physical characteristics of the fracture simulation were fully documented.

Results: Of the 122 specimens with a full data set, 17 (13.9%) fractures were determined to be Smith fractures based on their radiological appearance. In 10 of these flexion fractures, the wrist was set in dorsal extension. The mean angle of extension was 86.3 degrees for flexion fractures compared to 90.5 degrees for extension fractures. Six out of 10 Smith-type fractures that were set in dorsal extension were also exposed to pronation, whereas only one was exposed to supination. The mean potential energy for fracture creation was 168.0 joules for Smith fractures in dorsal extension, whereas all other fractures showed a mean of 185.2 joules.

Conclusions: It can be concluded that a Smith fracture is not limited to being the result of a fall on the wrist in a flexed position. The same fracture may also be the result of a fall with the wrist in an extended position if certain physical factors are applicable.