Failure characteristics of the isolated distal radius in response to dynamic impact loading

Abstract

We examined the mechanical response of the distal radius pre-fracture and at fracture under dynamic impact loads. The distal third of eight human cadaveric radii were potted and placed in a custom designed pneumatic impact system. The distal intraarticular surface of the radius rested against a model scaphoid and lunate, simulating 458 of wrist extension. The scaphoid and lunate were attached to a load cell that in turn was attached to an impact plate. Impulsive impacts were applied at increasing energy levels, in 10 J increments, until fracture occurred. Three 458 stacked strain gauge rosettes were affixed along the length of the radius quantifying the bone strains. The mean (SD) fracture energy was 45.5 (16) J. The mean (SD) resultant impact reaction force (IRFr) at failure was 2,142 (1,229) N, resulting in high compressive strains at the distal (2,718 (1,698) me) and proximal radius (3,664 (1,890) me). We successfully reproduced consistent fracture patterns in response to dynamic loads. The fracture energy and forces reported here are lower and the strains are higher than those previously reported and can likely be attributed to the controlled, incremental, dynamic nature of the applied loads. Keywords: radius; impact; fracture; forward fall; injury criteriaThe distal radius is a common fracture site, often resulting from a forward fall. Nevitt and Cummings 1 reported that, of 337 forward falls, 39% resulted in a wrist fracture, with more than 60% requiring some form of surgical intervention. 2,3 This has lead to these injuries being identified as a major health problem, 4 and the World Health Organization has listed fracture prevention among healthcare priorities. 5 Nonetheless, fracture frequency remains high ($164,000 emergency room visits/year from 1991 to 2009 in the US alone 6 ), and researchers have been unable to determine optimal treatment strategies for various patterns and severities of wrist fractures. 7 Although general consensus exists regarding risk factors for distal radius fractures, 8 prevention of these injuries requires a more thorough understanding of the injury mechanisms. The injury mechanism is one of the most important elements of the history, 7 as this information can help discern the degree of damage to the bone and the surrounding soft tissues. Beardley et al. 9 identified the importance of understanding the energy involved in a fracture as it generally determines the degree of comminution, thus affecting the treatment protocol.An accurate understanding of the injury mechanisms (e.g., kinetic energy involved and direction of loading) can be accomplished by improving our knowledge of the input parameters and the bones' response to dynamic loading through valid laboratory studies. 10 Many researchers mechanically loaded human cadaver specimens to determine the maximal strength of the distal radius, 10-22 but methodological inconsistencies have led to variability in results. Researchers studied the response to dynamic impact loads 10,[17][18][19] to better simulate real-worl...

An ex vivo experiment to reproduce a forward fall leading to fractured and non-fractured radii

“…Previous studies loaded radii until failure in all cases, with some under quasi-static conditions 65 one using fall conditions (Burkhart et al, 2012). In this context, the aim of this study is to 67…”

Development and validation of a distal radius finite element model to simulate impact loading indicative of a forward fall

“…Each specimen was subjected to a mean (standard deviation (SD)) of 3.5 (1.2) and 4.2 (1.7) impacts to experience a crack and fracture event, respectively. 20 Prior to experimental testing, the locations of three strain gauge rosettes (Vishay Micro-Measurements, Vishay Precision Group, Malvern, PA, USA; grid resistance = 350 Ω; gauge factor = +1.3%) and two accelerometers (MMA220KEG (x- and y-axes) and MMA1210 (z-axis); Freescale Semiconductor, Ottawa, ON, Canada) were identified on each of the specimens by digitizing the center of each transducer (Microscribe G2X; Immersion Corporation, San Jose, CA, USA). Three screw holes placed in the PVC pipe potting device were also digitized to create a local coordinate system.…”

“…These models have also not considered the kinematics of a forward fall, such as the angle the forearm makes with the ground or the angle of the wrist at impact. 20…”

Quantifying Forearm Soft Tissue Motion from Massless Skin Markers following Forward Fall Hand Impacts

“…Across all impact trials, a distance of approximately 30 cm was maintained between the thenar regions of participants' palms and two force plates, which were mounted rigidly to a vertical steel structure attached to the steel framing of the laboratory wall. The force plates were positioned side-by-side at a 20° angle from vertical to simulate the positions of the wrist (~45° extension) and forearm (~75° with respect to the ground), characteristic of a forward fall (Myers et al, 1991;Greenwald, Janes, Swanson & McDonald, 1998;Burkhart et al, 2012;Burkhart, Quenneville, Dunning & Andrews, 2014). Targets were also outlined on the force plates to help standardize the impact postures for each participant.…”

“…Impacts to the hands and wrists resulting from forward falls, whether accidental in nature or due to recreational sporting activities, are problematic in both young and older adult populations because of the high incidence of upper extremity injuries (e.g., sprains, dislocations, fractures) associated with them (Nevitt & Cummings, 1993;Idzikowski, Janes & Abbott, 2000;Palvanen et al, 2000;Mirhadi, Ashwood & Karagkevrekis, 2015). Research concerning the injury mechanisms of a forward fall onto the hands of outstretched arms has largely focused on the in vitro impact response of the distal radius and its ability to dissipate high levels of mechanical energy (Myers et al, 1991;Muller, Webber & Bouxsein, 2003;Burkhart, Andrews & Dunning, 2012). However, the movement of soft tissue masses (muscle, fat, skin) relative to bone also plays a protective role in mitigating the injurious effects of impact through shock attenua-2 IJKSS 6(3): 1-11 2007;Akbarshahi et al, 2010;Kuo et al, 2011).…”