Abstract
Purpose
Fractures to the distal radius are costly and debilitating injuries. While it is generally accepted that the leading cause of these injuries is a fall onto an outstretched arm, the mechanics of the injury are less well understood. The main limitations of past research are the use of unrealistic loading rates or uncontrolled loading protocols. Therefore, the purpose of this research was to examine the mechanical response of the distal radius pre-fracture and at fracture, under dynamic loads indicative of a forward fall.
Method
Eight cadaveric radius specimens were cleaned of all soft tissues and potted at a 75o angle (representative of the angle between the volar radius and the ground) up to the distal third of the radius. A custom designed pneumatic impact system was used to apply impulsive impacts to the specimen at increasing energy levels until failure occurred. The intra-articular surface of the radius rested against a model scaphoid and lunate made from high density polyethylene (Sawbones) attached to a 5 degree of freedom load cell that in turn was attached to an impact plate. The position of the carpals within the intra-articular surface simulated 45o of wrist extension. Following failure (defined as the specimen being fractured into at least 2 distinct pieces), the specimens were removed from the testing apparatus and the location, type, pattern and severity of injury was noted and classified using the Frykman and Melone classification systems. Energy input and force variables were also collected at failure.
Results
All specimens fractured in the ultra distal region of the radius. Six sustained damage to the dorsal aspect, three had fractures in the volar region (one specimen had both volar and dorsal fracture) and all specimens showed signs of intra-articular damage. The mean (SD) resultant impulse and energy at fracture were 30.6 (9.3) N∗s and 45.3 (12.6) J, respectively. The mean (SD) peak resultant fracture force was 2.5 (1.3) kN at a rate of 703.1(663.4) kN/s and was highly influenced by the axial force (2.4 (1.2) kN; 672.3 (653.3) kN/s).
Conclusion
This study was successful in reproducing fractures to the distal radius in response to dynamic loads. The fracture energy reported here is significantly lower than those previously reported and can be attributed to the controlled incremental nature of the applied loads. While the fracture forces tended to fall within the range of previously reported values, only the resultant values have been reported here, and is suspected that an analysis of the individual force components will provide more information regarding the fracture mechanism. To the authors knowledge, this is the first study to systematically apply dynamic loads to the distal radius under conditions that best represent a forward fall. These findings are important, as successful prevention, treatment and rehabilitation of distal radius fractures are dependent on a thorough understanding of the injury mechanisms.
