Documentation:FIB book/Foosh Injury Biomechanics

Introduction

Falls are an ever-present threat to the well-being of individuals across the globe, and their repercussions are both far-reaching and profound. In Canada, falls represent the most common source of injury in older adults , and they have remained a subject of persistent concern in the field of injury biomechanics. Falls make up over 85% of hospital-related visits in seniors, with related healthcare costs totaling over $2 billion a year .

Infographic on Falls for Canadians over 65

Within this expansive landscape of fall-related injuries, it is crucial to focus on a particular aspect that has often been overshadowed by more severe outcomes: injuries to the distal upper extremities, specifically those afflicting the hand and wrist. While such injuries may not pose a direct threat to one's life, they wield a profound impact on the quality of life for those affected. This subset of injuries, known as “Falls on Outstretched Hands” (FOOSH), is frequently encountered among individuals who instinctively reach out to break their falls. Not only is this mechanism of injury exceedingly common, but it is also notably challenging to diagnose and manage, primarily due to the intricate anatomy of the wrist and the limited vascularity of its constituent parts .

This photo is a depiction of a human hand and wrist with labeled bones

The wrist forms a remarkably intricate assembly, made up of the distal ends of the radius and ulna, along with eight carpal bones interconnected by ligaments and cartilaginous structures . FOOSH injuries predominantly impact the proximal carpal row of the wrist, which includes the lunate, triquetral, and scaphoid bones . Individuals' vulnerability to injury, coupled with the intricate interplay of anatomical components, makes the wrist an exceptionally challenging area to collect data on, understand, and ultimately prevent injuries within.

It is evident that comprehending the forces experienced by different parts of the hand and wrist during falls, particularly FOOSH injuries, holds immense significance in the pursuit of understanding injury mechanisms. This knowledge is key for the development of effective preventive measures and treatments aimed at mitigating the physical and psychological burdens borne by individuals afflicted by FOOSH-related injuries.

This research seeks to delve into the world of FOOSH injuries and the forces exerted on the hand and wrist during these falls, employing a multifaceted approach that combines experimental and theoretical techniques. An exploration of the available media information, including research articles and online resources, will be further analyzed in this paper. In the following sections, a detailed analysis of existing studies addressing these critical facets will be explored. This will offer valuable insight into the methodologies they have employed to dissect the intricacies of FOOSH injuries. This paper aims to contribute to the body of knowledge on this underrepresented issue and advance the understanding of the biomechanical underpinnings that govern FOOSH injuries, with the ultimate goal of enhancing injury prevention.

Previously Conducted FOOSH Injury Biomechanics Research

Distal Radius Fractures: An Epidemiological Review

The study conducted by Koo et al. delves into the characteristics of distal radius fractures, which are recognized as one of the most prevalent fracture types. While extensive research has been conducted in Western populations, this study fills a notable gap by providing specific data pertaining to an Asian population, with a focus on cases in Singapore. The primary objectives were to comprehensively analyze the demographics and clinical attributes associated with distal radius fractures, encompassing aspects such as age distribution, gender disparities, fracture classification based on the AO system, mechanisms of injury, presence of associated injuries, and the preferred modalities of treatment. This study revealed that the highest prevalence of FOOSH injuries was amongst 3-50 year old males and 50-60 year old females. The majority of fractures were categorized as type A (extra-articular), with falls on outstretched hands (FOOSH) constituting the predominant mechanism of injury. The study also highlighted patients over 60 were more likely to receive  a more conservative form of treatment that was non-surgical , contrasting with their younger counterparts. Moreover, the study underscored a prevalence of associated ulnar styloid fractures and elucidated the absence of a significant correlation between hand dominance and the location of fractures. This study offers crucial insights into fracture patterns, mechanisms of injury, and treatment preferences, particularly for an Asian population. This is very useful as Asian immigrants are the largest and fastest growing group in Canada (ref).  By understanding these distinctive characteristics, researchers can refine strategies for injury prevention and tailor treatment approaches more effectively, ultimately enhancing patient outcomes in cases related to FOOSH-induced acute injuries.

In vivo soft tissue compressive properties of the human hand:

This research paper presents an in-depth investigation into the in vivo compressive properties of palmar soft tissue in the human hand, with a specific focus on understanding the mechanisms involved in falls onto FOOSH, a common cause of upper extremity injuries, often occurring during activities such as skiing, snowboarding, and various sports. Therefore, comprehending the mechanical behavior of palmar soft tissues is crucial for both injury prevention and the development of accurate simulation models. The primary objectives of this study encompassed two key aspects. Firstly, the research aimed to characterize the response of in vivo palmar soft tissues to indentation testing, providing valuable insights into their behavior under compression. Secondly, the study sought to determine the influence of several critical factors on tissue mechanics, including loading rate, joint angle, sex, and tissue thickness. Overall, the findings uncovered several important aspects of palmar soft tissue mechanics. Notably, it revealed the nonlinearity of tissue response and its significant dependence on loading rate, underlining the need for sophisticated modeling to accurately simulate fall scenarios. Although wrist position introduced some variability in the results, it did not consistently affect tissue mechanics. Furthermore, gender differences in tissue response were minimal, and the influence of tissue thickness on peak force and energy absorption was most pronounced during extreme wrist extension and at high loading frequencies. Consequently, this research contributes significantly to our understanding of FOOSH injuries by providing detailed insights into the complex mechanics of palmar soft tissues. It highlights the necessity for comprehensive and precise models to faithfully replicate fall scenarios and, in turn, informs more effective injury prevention strategies.

Prediction of upper extremity impact forces during falls on the outstretched hand:

This study delves into how fractures to the upper extremities occur, focusing on the biomechanics of falls on the outstretched hand. The main purpose of this study was to answer two main research questions:

1) What are the peak forces, displacements, and energies applied to the upper extremity during falls on the outstretched hand?

2) How do these vary with descent distance and the mass and height of the individual?

Schematics and results of FOOSH laboratory simulation

In order to investigate these research questions, human subjects were used to measure impact forces on the hand during low height falls ranging from 0-5 cm, onto a single hand with a fully extended elbow. 8 male and 8 female subjects between the ages of 20-35, and with varying body masses were selected to participate. The study indicated clear findings on the pattern of forces experienced by the wrist of the subject. These patterns were governed by an initial high-frequency force peak which occurred around 20 ms after impact. This was followed by a second, lower-frequency oscillation which occurred around 110 ms after impact. Various factors affected the magnitude of these peaks in different ways. Increasing fall height more closely affected the initial high frequency peak but, increasing body mass more closely affected the second low frequency peak. The magnitude of this first peak was larger than the second peak in all recorded cases, except for very low fall heights.

Using the data from these low height falls, the researchers were able to create mathematical models to predict the forces experienced during falls from larger heights. The model they used consisted of masses to represent the upper extremity and torso, as well as parameters to mimic the stiffness and damping of both the wrist/palmar soft tissues and the shoulder/torso. This model allowed for the prediction of wrist contact force and shoulder contact forces.

When analyzing data from fall heights of 1cm, 3cm, and 5cm, it was found that wrist damping remains fairly constant in each case, which explains why the first peak increases in magnitude with increasing height. Additionally, shoulder stiffness was found to decrease with increasing height, which resulted in the magnitude of the second peak increasing less significantly as height increased. However, all stiffness and damping values showed to increase linearly with increases in height, which suggest the model could be accurately used to assess higher falls.

Once this data was used to quantify and reassess the parameter values in the mathematical model, it was used to predict forces in FOOSH falls between 0-2m. The findings show that the peak force experienced by the wrist, in the initial high frequency peak,  reaches 4.2kN when falling from 2m. This value greatly surpasses the mean fracture force of 2.27kN +/- 0.88kN (S.D.), which was deemed through other previous studies . The data thus indicated that any fall from a height of greater than 0.6m results in significant risk of wrist fracture.

This study also considered the energy absorption of the fall, and how it is related to the stiffnesses of the wrist and shoulder joints. As the shoulder joint was found to be much less stiff than the wrist joint, it underwent more deflection and absorbed the majority of the energy of the fall. The researchers acknowledge that if the fracture risk were to depend more on peak displacement and energy absorption: the second low-frequency oscillation may be a clearer indicator of injury risk as the peaks of both of these values are experienced in this second region. However, they speculate that the energy absorption values would be more predictive of related soft tissue injuries as opposed to fracture.

Surface stiffness affects impact forces during a fall on the outstretched hand:

This study investigated the role of surface stiffness modifications affected the forces experienced in upper extremities during  FOOSH. Modifying surface stiffnesses is often thought of as a simple interventional tools to limit the forces of impact in falls, but the magnitude in which they reduce force in this type of fall has not been previously well documented. This study expanded upon research conducted in the previous one (above), and determined how different surface stiffnesses affected the initial high frequency peak, and the latter low frequency oscillation. It was found that decreases in surface stiffness significantly reduce the magnitude of the first peak but not the second peak. The reason for decrease of the first peak can be attributed to the soft surface’s ability to reduce the velocity experienced by the wrist damping elements at impact. The second peak remains fairly constant because the peak deflection of the shoulder joint is fairly unchanged.

These findings suggest that soft surfaces may reduce the risk of fracture occurring from large initial collision forces experienced by the wrist due to the attenuation and delay of the first peak. However, surface stiffness must be reduced to an impractical level to reduce shoulder deformation,  low frequency force oscillations, and their related injuries.

Age differences in upper extremity joint moments and strength during a laboratory-based tether-release forward fall arrest in older women:

This study conducts an in-depth analysis of age-related disparities in upper extremity joint moments and muscular strength within the context of controlled laboratory simulations of tether-release forward fall arrests. The research primarily centers on older women, with the primary objective of uncovering discrepancies in joint moments and strength between younger and older individuals, particularly concerning fall-related scenarios. The research method involves subjecting older women to controlled laboratory simulations of tether-release forward falls, a scenario with direct relevance to FOOSH. This approach facilitates the assessment of joint moments and muscular strength in the upper extremities, crucial factors in mitigating fall-related injuries, including FOOSH incidents. During the simulations, specific findings revealed notable variations in joint moments and muscular strength between the younger and older female participants. These differences illuminate the age-related distinctions in the biomechanics of fall arrests, providing valuable insights into the vulnerabilities of older individuals to FOOSH injuries. By examining the impact of age on joint moments and strength during fall arrest, it provides valuable insights into the vulnerability of older individuals to FOOSH injuries. Furthermore, the findings carry practical implications for designing tailored fall prevention strategies and safety measures that consider the unique biomechanical challenges faced by older populations, ultimately contributing to a reduction in the frequency and severity of FOOSH injuries among older women.

Strengths and Weaknesses

The collection of research papers provides a multifaceted insight into the epidemiology and biomechanics of falls on outstretched hands (FOOSH), offering several strengths and some overarching weaknesses. The strengths of this body of work are notably diverse. Koo et al.'s epidemiological study addresses a substantial gap by examining distal radius fractures in an Asian population , a region that has been underrepresented in previous research. Their findings offer valuable insights into the unique characteristics of these fractures, particularly age-related prevalence and treatment preferences, with relevance to areas experiencing an influx of Asian immigrants into Canada. Spartacus et al.'s investigation into the compressive properties of palmar soft tissues deepens our understanding of FOOSH biomechanics, emphasizing the nonlinear tissue behavior and its dependence on loading rates, an important consideration for both modeling and injury prevention. Furthermore, Chiu and Robinovitch's research predicts upper extremity impact forces during FOOSH falls, revealing significant fracture risks, even in low-height falls, and provides mathematical models for assessing fracture risk.

However, some overarching weaknesses are evident in these studies. The potential limitations across the collection of papers include the reliance on human subjects for experimentation, which poses ethical and practical constraints. Additionally, the focus on specific populations, such as older women or Asian populations, may limit the generalizability of the findings to broader demographics. Furthermore, the predominantly laboratory-based simulations may not fully encapsulate the complexities of real-world FOOSH scenarios. While the papers provide critical insights into fracture risks and tissue mechanics, the scope of FOOSH-related injuries, including soft tissue injuries, and variations in fall conditions are not comprehensively addressed.

In summary, this collection of research papers represents a valuable contribution to understanding FOOSH-related acute injuries from epidemiological and biomechanical perspectives. The strengths lie in their specific focus on previously understudied populations, insights into tissue behavior, prediction of fracture risk, and potential interventions to mitigate FOOSH forces. However, the limitations encompass the experimental constraints, limited demographic representation, and the gap in considering a broader range of FOOSH-related injuries and real-world conditions. These studies collectively enhance the knowledge of FOOSH injuries, offering a foundation for further research as seen in the next section.

Controversy

FOOSH From Short Distances

An important controversy surrounding FOOSH revolves around the degree of predictive accuracy and the practical implications of biomechanical models for assessing fracture risk. The study by Chiu and Robinovitch strives to predict upper extremity impact forces during FOOSH falls, providing crucial insights into the significant fracture risk associated with FOOSH incidents. However, it raises questions about the practical utility of these findings, particularly concerning how this controversy has influenced current knowledge or practice in the field. The specific controversy pertains to the 0.6m threshold identified for significant wrist fracture risk. This finding implies that even low-height falls may result in substantial injury, challenging the conventional wisdom that only higher falls present a risk. The practical implications of this controversy are substantial, as it necessitates a reevaluation of fall prevention strategies and safety measures, with a focus on lower-height falls, which are more common in daily life. Researchers and clinicians must address whether the established fracture risk threshold can be effectively incorporated into real-world injury prevention practices, considering the broader impact on current practices and guidelines in the field of FOOSH injury biomechanics.

Future Work

Assessing the effectiveness of preventive measures in the context of FOOSH is a critical research area that's still yet to be discovered. Future research should evaluate the real-world impact of various preventive measures, considering their cost, complexity, and context-specific utility. Understanding the effectiveness of these measures through controlled experiments and data analysis is vital for evidence-based injury prevention strategies. It can then be used to inform the development of targeted programs and policies, enhancing individual well-being and public health outcomes while reducing the incidence and severity of FOOSH-related injuries.

Falls on Outstretched Hands can occur in diverse scenarios, such as car accidents, occupations, sports, and recreational activities. While the fundamental FOOSH mechanism remains consistent, the specific biomechanical factors and risk elements may vary considerably between these contexts. Future research should focus on dissecting the biomechanics of FOOSH injuries in different scenarios to identify scenario-specific risk factors and injury patterns. This approach can enable the development of tailored injury prevention strategies for each context. By understanding how the mechanics of FOOSH differ in, for example, a skiing accident versus a workplace fall, researchers can provide valuable insights about the unique challenges and interventions relevant to the specific situations.

In addition, the long-term outcomes of FOOSH injuries, particularly distal radius fractures, is another critical area for research. While there is a substantial body of research focused on initial diagnosis and short-term recovery, there is a relative scarcity of studies examining the extended consequences of FOOSH injuries. Investigating the risk of post-traumatic osteoarthritis in the wrist, for instance, can provide essential information regarding the lasting impact of these injuries on joint health. Such long-term outcome studies can inform clinical decision-making, rehabilitation planning, and patient counseling. More importantly, understanding the trajectory of FOOSH-related injuries over time, including potential late-onset complications and functional limitations, is vital for the development of comprehensive treatment guidelines.