Effect of soft shell hip protectors on pressure distribution to the hip during sideways falls

Effects of hip joint kinematics on the effective pelvis stiffness and hip impact force during simulated sideways falls

Improved understanding is required on how hip fracture risk is influenced by landing configuration. We examined how hip impact dynamics was affected by hip joint kinematics during simulated sideways falls. Twelve young adults (7 males, 5 females) of mean age 23.5 (SD = 1.5) years, participated in pelvis release experiments. Trials were acquired with the hip flexed 15° and 30° for each of three hip rotations: +15° ("external rotation"), 0°, and -15° ("internal rotation"). During falls, force-deformation data of the pelvis were recorded. Outcome variables included the peak hip impact force (Fexperimental) and effective stiffness of the pelvis (k1st, ksecant, and kms) determined with different methods suggested in literature, and predicted hip impact force during a fall from standing height (F1st, Fsecant and Fms). The two-way repeated-measures ANOVA was used to test whether these variables were associated with hip joint angles. The Fexperimental, ksecant and Fsecant were associated with hip rotation (F = 5.587, p = 0.005; F = 9.278, p < 0.0005; F = 5.778, p = 0.004, respectively), and 15 %, 31 % and 17 % smaller in 15° external than internal rotation (848 versus 998 N; 24.6 versus 35.6 kN/m; 2,637 versus 3,170 N, respectively). However, none of the outcome variables were associated with hip flexion (p > 0.05). Furthermore, there were no interactions between the hip rotation and flexion for all outcome variables (p > 0.05). Our results provide insights on hip impact dynamics, which may help improve a hip model to assess hip fracture risk during a fall.

Predicting soft tissue thicknesses overlying the iliac crests and greater trochanters of younger and older adults

Soft tissues overlying the hip play a critical role in protecting against fractures during fall-related hip impacts. Consequently, the development of an efficient and cost-effective method for estimating hip soft tissue thicknesses in living people may prove to be valuable for assessing an individual's injury risk and need to adopt preventative measures. The present study used multiple linear stepwise regression to generate prediction equations from participant characteristics (i.e., height, sex) and anthropometric measurements of the pelvis, trunk, and thigh to estimate soft tissue thickness at the iliac crests (IC) and greater trochanters (GT) in younger (16-35 years of age: 37 males, 37 females) and older (36-65 years of age: 38 males, 38 females) adults. Equations were validated against soft tissue thicknesses measured from full body Dual-energy X-ray Absorptiometry scans of independent samples (younger: 13 males, 13 females; older: 13 males, 12 females). Younger adult prediction equations exhibited adjusted R2 values ranging from 0.704 to 0.791, with more explained variance for soft tissue thicknesses at the GT than the IC; corresponding values for the older adult equations were higher overall and ranged from 0.819 to 0.852. Predicted and actual soft tissue thicknesses were significantly correlated for both the younger (R2 = 0.466 to 0.738) and older (R2 = 0.842 to 0.848) adults, averaging ≤ 0.75cm of error. This research demonstrates that soft tissue thicknesses overlying the GT and IC can be accurately predicted from equations using anthropometric measurements. These equations can be used by clinicians to identify individuals at higher risk of hip fractures who may benefit from the use of preventative measures.

Femur geometry and body composition influence femoral neck stresses: A combined fall simulation and beam modelling approach

Metrics of femur geometry and body composition have been linked to clinical hip fracture risk. Mechanistic explanations for these relationships have generally focused on femur strength; however, impact loading also modulates fracture risk. We evaluated the potential effects of femur geometry and body composition on femoral neck stresses during lateral impacts. Fifteen female volunteers completed low-energy sideways falls on to the hip. Additionally, participants completed ultrasound and dual-energy x-ray absorptiometry imaging to characterize trochanteric soft tissue thickness (TSTT) over the hip and six metrics of femur geometry, respectively. Subject-specific beam models were developed and utilized to calculate peak femoral neck stress (σ_Neck), utilizing experimental impact dynamics. Except for femoral neck axis length, all metrics of femur geometry were positively correlated with σ_Neck (all p < 0.05). Larger/more prominent proximal femurs were associated with increased force over the proximal femur, whereas a wider neck-shaft angle was associated with greater stress generation independent of force (all p < 0.05). Body mass index (BMI) and TSTT were negatively correlated with σ_Neck (both p < 0.05). Despite strong correlations, these metrics of body composition appear to influence femoral neck stresses through different mechanisms. Increased TSTT was associated with reduced force over the proximal femur, whereas increased BMI was associated with greater resistance to stress generation (both p < 0.05). This study provided novel insights into the mechanistic pathways through which femur geometry and body composition may modulate hip fracture risk. Our findings complement clinical findings and provide one possible explanation for incongruities in the clinical fracture risk and femur strength literature.

The Influence of Fall Direction and Hip Protector on Fracture Risk: FE Model Predictions Driven by Experimental Data

Hip fractures in older adults, which often lead to lasting impairments and an increased risk of mortality, are a major public health concern. Hip fracture risk is multi-factorial, affected by the risk of falling, the load acting on the femur, and the load the femur can withstand. This study investigates the influence of impact direction on hip fracture risk and hip protector efficacy. We simulated falls for 4 subjects, in 7 different impact directions (15° and 30° anterior, lateral, and 15°, 30°, 60°, and 90° posterior) at two different impact velocities (2.1 and 3.1 m/s), all with and without hip protector, using previously validated biofidelic finite element models. We found the highest number of fractures and highest fragility ratios in lateral and 15° posterior impacts. The hip protector attenuated femur forces by 23–49 % for slim subjects under impact directions that resulted in fractures (30° anterior to 30° posterior). The hip protector prevented all fractures (6/6) for 2.1 m/s impacts, but only 10% of fractures for 3.1 m/s impacts. Our results provide evidence that, regarding hip fracture risk, posterior-lateral impacts are as dangerous as lateral impacts, and they support the efficacy of soft-shell hip protectors for anterior- and posterior-lateral impacts.

Factors that influence the distribution of impact force relative to the proximal femur during lateral falls

In-vivo fall simulations generally evaluate hip fracture risk through differences in impact force magnitude; however, the distribution of force over the hip likely modulates loading and subsequent injury risk of the underlying femur. The current study characterized impact force distribution over the hip during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulation protocols (FSP) including highly controlled vertical pelvis and more dynamic kneeling and squat releases. At the instant of peak force, percentage of impact force applied in a circular region (r = 5 cm) centered over the greater trochanter (F_GT%) was determined to characterize force localization. To assess the need for anatomically aligned pressure analysis, this process was repeated utilizing peak pressure location as a surrogate for the greater trochanter (F_PP%). F_GT% was 10.8 and 21.9% greater in pelvis release than kneeling and squat releases respectively. F_GT% was 19.1 and 30.4% greater in males and low-TSTT individuals compared to females and high-TSTT individuals. TSTT explained the most variance (43.7-55.3%) in F_GT% across all protocols, while sex explained additional variance (5.3-19.0%) during dynamic releases. In all FSP, TSTT-groups and sexes, average peak pressure location was posterior and distal to the GT. F_PP% overestimated F_GT% by an average of 15.7%, highlighting the need for anatomically aligned pressure analysis. This overestimation was FSP and sex dependent, minimized during pelvis release and in males. The data have important implications from clinical and methodological perspectives, and for implementation in tissue-level computational models.

The effect of the hip impact configuration on the energy absorption provided by the femoral soft tissue during sideways falls

The femoral soft tissue (i.e., skin, muscle, fat) may play a key role in preventing hip fractures during a fall by absorbing the impact energy. We measured the femoral soft tissue deformation and associated compressive force during simulated sideways falls to estimate the energy absorbed by the soft tissue, and then examined how this was affected by the hip impact configuration and gender. Eighteen young adults (9 males and 9 females) participated in the pelvis release experiment. The pelvis was raised through a rope attached to an electromagnet on the ceiling, so the skin surface barely touches the ultrasound probe, which flush to a Plexiglas plate placed on a force plate. The electromagnet was turned off to cause a fall while the soft tissue deformation and associated compressive force were being recorded. Trials were acquired with three hip impact configurations. An outcome variable included the energy absorbed by the femoral soft tissue during a fall. The energy absorbed by the femoral soft tissue ranged from 0.03 to 3.05 J. Furthermore, the energy absorption was associated with the hip impact configuration (F = 4.69, p = 0.016). On average, the absorbed energy was 62% greater in posteriolateral than anteriolateral impact (0.92 versus 0.57 J). However, the energy absorption did not differ between male and female (F = 0.91, p = 0.36). The force-deflection behavior of the femoral soft tissue during a fall has been recorded, providing insights on the potential protective benefits of the soft tissue covering during a fall.

Hip protectors are cost-effective in the prevention of hip fractures in patients with high fracture risk

Cost-effective preventive interventions are necessary for tackling the increasing number of hip fractures, which are frequently occuring as a serious consequence of osteoporosis. Several interventions have been available for preventing and treating osteoporosis. The aim of this study was to systematically review and critically appraise studies that assessed cost-effectiveness of hip protectors for the prevention of hip fractures and to investigate the effects of age, gender and residence situation on cost-effectiveness. A systematic review was conducted in order to identify economic evaluation studies examining the hip protector solely or compared to no treatment according to the Preferred Reported Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Synthesis of results was performed to observe trends between the studies. Methodological quality of the studies was assessed by the use of the Quality of Health Economic Studies (QHES) instrument. A total of 15 economic evaluation studies were included for analysis. The methodological quality was high in most studies (13/15). The hip protector was solely evaluated in three studies and within 12 other studies compared with no intervention. All studies that investigated the cost-effectiveness in long-term care facilities revealed that hip protector use is a cost-effective strategy for the prevention of hip fractures in elderly. Cost-effectiveness was also observed in two studies that provided hip protectors in a geriatric hospital ward. Four studies included both community-dwelling residents and residents living in a long-term care facility in their study. These studies showed more variability regarding cost-effectiveness. One study did not report information regarding the residence situation of their cohort, but also observed cost-effectiveness. In conclusion, this review suggests that hip protectors are a cost-effective approach in the prevention of hip fractures in populations with high risk of hip fractures especially in long-term care facilities and a geriatric ward in a hospital.

The association between anterior femoroacetabular impingement and femoral neck fractures: An observational study

The impact between acetabulum and femoral neck is another possible mechanism of femoral neck fracture.Direct trauma of the greater trochanter may not be able to fully explain the mechanism underlying femoral neck fracture. In this study, we sought to investigate whether anterior femoroacetabular impingement are associated with femoral neck fractures.A total of 36 patients with femoral neck fracture who had undergone total hip arthroplasty or hemiarthroplasty were included in this study. These patients were divided into 2 groups: labrum tear group and normal labrum group. Patients' age, gender, body mass index, muscle injury, injury pattern, trauma severity, femoral head-neck offset, femoral head-neck ratio, Cam deformity alpha angle, acetabular anteversion, femoral head diameter, acetabular index, cortical index, hip axis length, and neck stem angle were recorded and analyzed. SPSS 18.0 software was used for statistical analyses.According to intraoperative findings, 22 patients exhibited a labrum tear. Magnetic resonance imaging examination revealed bone contusion on the anterolateral margin of the acetabulum with muscle damage surrounding the hip. Among 14 cases without a labrum tear, no bone contusion and obvious muscle injury were found on the anterolateral margin of the acetabulum. Notably, muscle injury, injury pattern, trauma severity and femoral head-neck offset differed significantly (P < .05) between labrum tear and normal labrum groups.Previous studies have focused more on direct lateral trauma. In this study, the impact between acetabulum and femoral neck is another possible mechanism besides lateral impact. Specifically, the abnormal anatomy of the hip, such as femoral head-neck offset, may promote the fracturing process.

Test systems for the biomechanical evaluation of hip protectors: a systematic review

Various mechanical and biomechanical test systems to evaluate the effectiveness of hip protectors designed to prevent hip fracture as a result of falls were examined in this review. The articles considered were selected systematically. The effect of differences in design criteria was demonstrated, and it was observed that the impact energy employed during testing dramatically affects the performance of the hip protector. Over the past three decades, researchers have continuously experimented with various systems to determine the efficacy of various hip protectors. The primary aim has been to make informed decisions in optimizing hip protector design. This article provides a systematic review of various test systems employed in the determination of the biomechanical efficacy of hip protectors. A systematic literature search was carried out, and 28 relevant articles were included to demonstrate the effect of test systems in the evaluation of the biomechanical effectiveness of hip protectors. Methodological studies illustrated the appropriate use of impact testing systems for the simulation of hip anatomy and fall dynamics in evaluating the effectiveness of hip protectors in preventing a hip fracture. This systematic review has demonstrated the effect of the variability of test systems on the evaluation of impact attenuation by various hip protectors. The lack of standardized test systems accounts for the inconsistencies in the test results of the efficacy of hip protectors. This has been a major challenge in the efforts of researchers to optimize the interventions. The standardization of test systems may require needed improvements immediately as opposed to the development of new interventions in order to ensure that only hip protectors with adequately proven efficacies are deployed for clinical trials or for the protection of the hips of vulnerable individuals from sideways impact.

Developing Fall-impact Protection Pad with 3D Mesh Curved Surface Structure using 3D Printing Technology

In this study, we present the development of fall-impact protection pads for elderly people using three-dimensional (3D) printing technology. To develop fall-impact protection clothing, it is important to maintain the functionality of the protection pad while ensuring that its effectiveness and appearance remain optimal in the process of inserting it. Therefore, this study explores the benefit of exploiting 3D scan data of the human body using 3D printing technology to develop a fall-impact protection pad that is highly suited to the human body shape. The purpose of this study was to present a 3D modeling process for creating curved protective pads comprising a hexagonal mesh with a spacer fabric structure and to verify the impact protection performance by printing curved pads. To this end, we set up a section that includes pads in the 3D human body scan data and extracted body surface information to be applied in the generation of the pad surface. The sheet-shaped hexagonal mesh structure was cut and separated according to the pad outline, and then deformed according to the curved surface of the human body. The pads were printed, and their protection performance was evaluated; a 79.2–81.8% reduction in impact force was observed compared to similar cases in which the pads were not used.

Development and Evaluation of Fall Impact Protection Pads Using Additive Manufacturing

This paper presents the development and evaluation of fall-impact protection pants for elderly women using additive manufacturing. The protective pants were designed incorporating a protective pad in the hip area to reduce the impact of falls on the human body. The protective pad is a 3D mesh structure with a curved surface to fit the human body. Pads printed with flexible thermoplastic polyurethane were combined with foam to create the final pad. The impact-absorbing performance of the pad was verified through physical impact experiments. When dropping a bowling ball onto the protective pad from heights of 15, 20, and 25 cm, the protective pad was found to reduce the impact force by more than 82% in all cases. The impact force was less than the average fracture threshold of 3472 N. A subject group and an expert group evaluated the appearance, pad characteristics, motion functionality, and the wearability of the protection pants. Despite the insertion of a pad, the pants appeared natural and had a good fit. The pads were evaluated as being well-designed in terms of their position, shape, area, thickness, weight, flexibility, ease of insertion, and ease of use. Users were comfortable performing various motions when wearing the designed protective clothing. Therefore, this work can be considered to have developed protective clothing that provides satisfactory impact-protection performance and comfort thereby advancing the possibility of applying additive manufacturing to the creation of functional garments.

Force, impulse and energy during falling with and without knee protection: an in-vitro study

The mechanics of protective knee padding mitigating injury from a high-force fall have not been investigated in real-life scenarios to date. This study compares the effect of wearing knee pads to unprotected impact on a hard surface. We hypothesized that knee pads reduce the force and energy transmitted to the bony structures of the knee cap compared with unprotected conditions. Eight human knee cadaver specimens were embedded and fixed with a flexion angle of 100 degrees in a custom-made drop testing device (75 kg including the knee). The usage of a knee pad led to an average peak force attenuation on impact of 15% (no pad: 5932 N SD: 2472 N; pad: 4210 N SD: 2199 N; p < 0.001). Contact time on the plate was higher with a knee pad (no pad: 0.015 s SD: 0.009 s; pad: 0.028 s SD: 0.014 s; p < 0.001). Therefore, the observed impulse was also increased (no pad: 62.2 Ns SD: 17.8 Ns; pad: 74.6 Ns SD: 18.6 Ns; p < 0.001). This effect diminished as drop height was increased. Energy dissipation, defined as the difference between kinetic energy pre-impact and peak potential energy post-impact, was higher without a knee pad (no pad: 10.5 J SD: 6.2 J; pad: 4.2 J SD: 5.0 J; p < 0.001). The results from this study illustrate the magnitude of influence that knee pads have on peak forces, transmitted impulse, and energy transfer from a high-force impact in real-life scenarios. Contrary to expectations, the knee pad did not act as a mechanical damper. The mechanical behavior more closely resembled a spring that temporarily stores energy and consequentially reduces peak forces upon impact. Based on this study, future developments in padding might benefit from focusing on the aspect of energy storage and temporarily delayed energy dissipation.

Biomechanical testing of hip protectors following the Canadian Standards Association express document

A variety of hip protectors are available, but it is not clear which is the most effective and there is no standard test to evaluate their performance. This is the first study that uses a standard mechanical test on hip protectors. Some protectors perform well but others are almost ineffective, providing little to no protection to the wearer during a fall.

INTRODUCTION

Each year, over 70,000 patients are admitted to hospital in the UK with hip fractures. There are a variety of commercial hip protectors currently available. However, it is not explicitly clear which is the most effective with regard to maximum force attenuation, whilst still being both comfortable for the user and providing reasonable force reduction if misplaced from the intended position. The numerous test methods reported in the literature have given conflicting results, making objective comparison difficult for users, researchers, and manufacturers alike. The Canadian Standards Association (CSA) has therefore published an express document (EXP-08-17) with a draft standard test method. This paper presents initial results for a range of hip protectors.

METHODS

Eighteen commercially available hip protectors were tested according to EXP-08-17. Each hip protector was impacted five times in correct anatomical alignment over the greater trochanter and once at 50 mm displacements in the anterior, posterior, and lateral directions.

RESULTS

Considerable differences were identified between individual hip protectors in their ability to reduce impact forces on the femur (between 3% and 36% reduction in peak force). The performance was reduced when misplaced in many cases (maximum reduction only 20%).

CONCLUSIONS

This is the first study that uses a standard mechanical test on hip protectors. Previous studies have used a variety of methods, making it difficult to interpret results. We hope that these results using a standard test method will facilitate the effective comparison of results, as well as providing useful data for clinicians, users, and purchasers.

Study on buffer characteristics of air cushion used as hip protector

INTRODUCTION

In order to develop a good hip protector to prevent in the elderly hip fracture as a result of a fall, we studied the buffer characteristics of sponges and air cushions.

METHODS

The buffer rate of material was defined, and the absorption ability of the material to instantaneous impact was evaluated. An experimental device was developed and used to measure the buffer rates of sponges and leak-allowed air cushions with orifice(s).

RESULTS

According to the experimental results, the buffer rate largely depended on the hardness of the sponge materials, and on the total area of the orifice(s) for the leak-allowed air cushions. Compared with the sponge with correct hardness and thickness, the buffer characteristic of the air cushion seems slightly inferior.

CONCLUSIONS

Nevertheless, the air cushion's overall performance, including the better buffer rate, ultra-lightness, flexibility, and low cost, makes it a potentially useful material for hip protectors and other sport protectors.

Determinants of staff commitment to hip protectors in long-term care: A cross-sectional survey

BACKGROUND

If worn, certain models of hip protectors are highly effective at preventing hip fractures from falls in residents of long-term care, but modest acceptance and adherence have limited the effectiveness of hip protectors. Residents of long-term care are more likely to accept the initial offer of hip protectors and to adhere to recommendations concerning the use of hip protectors when staff are committed to supporting the application of hip protectors. Yet, we know very little about the nature of and factors associated with staff commitment to hip protectors in long-term care.

OBJECTIVE

To identify factors associated with staff commitment to hip protectors in long-term care.

DESIGN

A cross-sectional survey.

SETTING

Thirteen long-term care homes (total beds = 1816) from a single regional health district in British Columbia, Canada.

PARTICIPANTS

A convenience sample of 535 paid staff who worked most of their time (>50% of work hours) at a participating long-term care home, for at least one month, and for at least 8 h per week. We excluded six (1.1%) respondents who were unaware of hip protectors. Of the remaining 529 respondents, 90% were female and 55% were health care assistants.

METHODS

Respondents completed the Commitment to Hip Protectors Index to indicate their commitment to hip protectors. We used Bayesian Model Averaging logistic regression to model staff commitment as a function of personal variables, experiences with hip protectors, intraorganizational communication and influence, and organizational context.

RESULTS

Staff commitment was negatively related to organizational tenure >20 years (posterior probability = 97%; logistic regression coefficient = -0.28; 95% confidence interval = -0.48, -0.08), and awareness of a padded hip fracture (100%; -0.57; -0.69, -0.44). Staff commitment was positively related to the existence of a champion of hip protectors within the home (100%; 0.24; 0.17, 0.31), perceived quality of intraorganizational communication (100%; 0.04; 0.02, 0.05), extent of mutual respect between residents and staff and perceived contribution to quality of life of the residents they serve (100%; 0.10; 0.05, 0.15), and frequency of transformational leadership practices by respondents' primary supervisors (100%; 0.01; 0.01, 0.02).

CONCLUSIONS

We provide novel insight into the factors governing staff commitment to hip protectors in long-term care. Targeting of these factors could improve acceptance and adherence with hip protectors, thereby contributing to enhanced effectiveness of hip protectors to prevent hip fractures in long-term care.

Sideways fall-induced impact force and its effect on hip fracture risk: a review

Osteoporotic hip fracture, mostly induced in falls among the elderly, is a major health burden over the world. The impact force applied to the hip is an important factor in determining the risk of hip fracture. However, biomechanical researches have yielded conflicting conclusions about whether the fall-induced impact force can be accurately predicted by the available models. It also has been debated whether or not the effect of impact force has been considered appropriately in hip fracture risk assessment tools. This study aimed to provide a state-of-the-art review of the available methods for predicting the impact force, investigate their strengths/limitations, and suggest further improvements in modeling of human body falling.

METHODS

We divided the effective parameters on impact force to two categories: (1) the parameters that can be determined subject-specifically and (2) the parameters that may significantly vary from fall to fall for an individual and cannot be considered subject-specifically.

RESULTS

The parameters in the first category can be investigated in human body fall experiments. Video capture of real-life falls was reported as a valuable method to investigate the parameters in the second category that significantly affect the impact force and cannot be determined in human body fall experiments.

CONCLUSIONS

The analysis of the gathered data revealed that there is a need to develop modified biomechanical models for more accurate prediction of the impact force and appropriately adopt them in hip fracture risk assessment tools in order to achieve a better precision in identifying high-risk patients. Graphical abstract Impact force to the hip induced in sideways falls is affected by many parameters and may remarkably vary from subject to subject.

Validation and psychometric properties of the commitment to hip protectors (C-HiP) index in long-term care providers of British Columbia, Canada: a cross-sectional survey

BACKGROUND

If worn during a fall, hip protectors substantially reduce risk for hip fracture. However, a major barrier to their clinical efficacy is poor user adherence. In long-term care, adherence likely depends on how committed care providers are to hip protectors, but empirical evidence is lacking due to the absence of a psychometrically valid assessment tool.

METHODS

We conducted a cross-sectional survey in a convenience sample of 529 paid care providers. We developed the 15-item C-HiP Index to measure commitment, comprised of three subscales: affective, cognitive and behavioural. Responses were subjected to hierarchical factor analysis and internal consistency testing. Eleven experts rated the relevance and clarity of items on 4-point Likert scales. We performed simple linear regression to determine whether C-HiP Index scores were positively related to the question, "Do you think of yourself as a champion of hip protectors", rated on a 5-point Likert scale. We examined whether the C-HiP Index could differentiate respondents: (i) who were aware of a protected fall causing hip fracture from those who were unaware; (ii) who agreed in the existence of a champion of hip protectors within their home from those who didn't.

RESULTS

Hierarchical factor analysis yielded two lower-order factors and a single higher-order factor, representing the overarching concept of commitment to hip protectors. Items from affective and cognitive subscales loaded highest on the first lower-order factor, while items from the behavioural subscale loaded highest on the second. We eliminated one item due to low factor matrix coefficients, and poor expert evaluation. The C-HiP Index had a Cronbach's alpha of 0.96. A one-unit increase in championing was associated with a 5.2-point (p < 0.01) increase in C-HiP Index score. Median C-HiP Index scores were 4.3-points lower (p < 0.01) among respondents aware of a protected fall causing hip fracture, and 7.0-points higher (p < 0.01) among respondents who agreed in the existence of a champion of hip protectors within their home.

CONCLUSIONS

We offer evidence of the psychometric properties of the C-HiP Index. The development of a valid and reliable assessment tool is crucial to understanding the factors that govern adherence to hip protectors in long-term care.

The dynamics of electric powered wheelchair sideways tips and falls: experimental and computational analysis of impact forces and injury

Background

To reduce the occurrence of wheelchair falls and to develop effective protection systems, we aimed to quantify sideways tip and fall dynamics of electric power wheelchairs (EPWs). We hypothesized that driving speed, curb height and angle of approach would affect impact forces and head injury risk for wheelchair riders. We further expected that fall dynamics and head injury risk would be greater for unrestrained riders compared to restrained riders.

Methods

Sideways wheelchair tip and fall dynamics were reconstructed using a remotely operated rear wheel drive EPW and a Hybrid III test dummy driving at different approach angles (5 to 63°) over an adjustable height curb (0.30 to 0.41 m) at speeds of 0.6–1.5 m/s. Rigid body dynamics models (Madymo, TASS International, Livonia, MI) were developed in parallel with the experiments to systematically study and quantify the impact forces and the sideways tip or fall of an EPW user in different driving conditions.

Results

Shallower approach angles (25°) (p < 0.05) and higher curbs (0.4 m) (p < 0.05) were the most significant predictors of tipping for restrained passengers. Unrestrained passengers were most affected by higher curbs (0.4 m) (p < 0.005) and fell forward from the upright wheelchair when the approach angle was 60°. Head impact forces were greater in unrestrained users (6181 ± 2372 N) than restrained users (1336 ± 827 N) (p = 0.00053). Unrestrained users had significantly greater head impact severities than restrained users (HIC = 610 ± 634 vs HIC = 29 ± 38, p = 0.00013) and several tip events resulted in HICs > 1000 (severe head injury) in unrestrained users.

Conclusions

Sideways tips and forward falls from wheelchairs were most sensitive to curb height and approach angle but were not affected by driving speed. Sideways tips and falls resulted in impact forces that could result in concussions or traumatic brain injury and require injury prevention strategies. Seat belts eliminated the risk of falling from an upright chair and reduced head impact forces in sideways wheelchair tips in this study; however, their use must be considered within the ethical and legal definitions of restraints.

The effects of body mass index and sex on impact force and effective pelvic stiffness during simulated lateral falls

BACKGROUND

The incidence of hip fractures is highest for underweight females with low body mass index (BMI). However, it is unknown how these factors influence impact dynamics during in-vivo lateral hip impacts.We used a pelvis release paradigm to compare: (1) absolute and normalized forces applied to the femur-pelvis system across sex and BMI groups; (2) the force-prediction accuracy of vibration-based versus force-deflection-based estimates of effective pelvic stiffness; and (3) effective pelvic stiffness between BMI and sex groups.

METHODS

Twenty-eight persons participated (7 low-BMI females, 7 low-BMI males, 7 high-BMI females, 7 high-BMI males,with BMI criteria of <22.5 and >28 for low- and high-BMI groups respectively). The participant's pelvis was released from heights of 0 to 5 cm. A force plate measured impact loads, while a motion capture system measured pelvic deflection.

FINDINGS

Peak impact forces were 22.6% higher, while normalized peak forces were 31.2% lower, for high- compared to low-BMI participants. Accuracy of peak force predictions improved by 25% for the force-deflection versus the vibration-based stiffness estimation method. Effective pelvic stiffness was greater for males than females, but no significant differences were observed between BMI groups.

INTERPRETATION

This study adds to clinical understanding of the effects of sex and BMI on impact dynamics during falls on the hip, and raises questions about the biomechanical mechanisms underlying the protective role of high BMI on hip fracture risk. Understanding the relationship between impact mechanics and faller characteristics should lead to more effective prevention of hip fractures.

Multi-body simulation of various falling scenarios for determining resulting loads at the prosthesis interface of transfemoral amputees with osseointegrated fixation

Conventionally, transfemoral amputees are treated with a shaft prosthesis fitted over the residual limb. To improve the quality of life of such patients, in particular those with complications relating to conventional attachment (e.g., skin irritation, stump ulcers, and poor motor-control with short stumps), osseointegrated prosthesis fixation implants have been developed and implanted in a limited population of patients. To assess possible damage to the implant/prosthesis during falling scenarios, the loads in high-risk situations were estimated using a multi-body simulation of motion. Five falling scenarios were identified and performed by healthy volunteer wearing safety equipment. Kinematic data and ground reaction forces were captured as input for the inverse-dynamics-based simulations, from which the forces and moments at a typical implant-prosthesis interface location were computed. The estimated peak loads in all five scenarios were of a magnitude that could lead to bone fracture. The largest peak force observed was 3274 ± 519 N, with an associated resultant moment of 176 ± 55 Nm on the prosthesis-implant interface. A typical femur is prone to fracture under this load, thus illustrating the need for a safety-release element in osseointegrated prosthesis fixation.

Osteoporosis diagnosis and medical treatment

Osteoporosis, the presence of either low bone mineral density or a history of a fragility fracture, is known to be associated with an increased risk of future fracture. Fracture prevention is possible through use of both nonpharmacologic and prescription treatments. Despite recent controversy regarding the safety of calcium supplementation and the appropriate dosing of calcium and vitamin D, calcium and vitamin D remain an important part of bone health. However, prescription osteoporosis treatments should be considered for those at higher risk for fracture, and there are currently several treatment options available.

The influence of body mass index and gender on the impact attenuation properties of flooring systems

The biomechanical effectiveness of safety floors has never been assessed during sideways falls with human volunteers. Furthermore, the influence of body mass index (BMI) and gender on the protective capacity of safety floors is unknown. The purpose of this study was to test whether safety floors provide greater impact attenuation compared with traditional flooring, and whether BMI and gender modify their impact attenuation properties. Thirty participants (7 men and 7 women of low BMI; 7 men and 9 women of high BMI) underwent lateral pelvis release trials on 2 common floors and 4 safety floors. As a group, the safety floors reduced peak force (by up to 11.7%), and increased the time to peak force (by up to 25.5%) compared with a traditional institutional grade floor. Force attenuation was significantly higher for the low BMI group, and for males. Force attenuation was greatest for the low BMI males, averaging 26.5% (SD = 3.0) across the safety floors. These findings demonstrate an overall protective effect of safety floors during lateral falls on the pelvis, but also suggest augmented benefits for frail older adults (often with low body mass) who are at an increased risk of hip fracture.

Transmission of force in the lumbosacral spine during backward falls

STUDY DESIGN

Mathematical model, combined with and verified using human subject data.

OBJECTIVE

(1) To develop and verify a lumped-parameter mathematical model for prediction of spine forces during backward falls; (2) to use this model to evaluate the effect of floor stiffness on spine forces during falls; and (3) to compare predicted impact forces with forces previously measured to fracture the spine.

SUMMARY OF BACKGROUND DATA

Vertebral fractures are the most common osteoporotic fractures and commonly result from falls from standing height. Compliant flooring reduces the force at the ground during a backward fall from standing; however, the effect on spine forces is unknown.

METHODS

A 6-df model of the body was developed and verified using data from 10 human subjects falling from standing onto 3 types of compliant floors (soft: 59 kN/m, medium: 67 kN/m, and firm: 95 kN/m). The simulated ground forces were compared with those measured experimentally. The model was also used to assess the effect of floor stiffness on spine forces at various intervertebral levels.

RESULTS

There was less than 14% difference between model predictions and experimentally measured peak ground reaction forces, when averaged over all floor conditions. When compared with the rigid floor, average peak spine force attenuations of 46%, 43%, and 41% were achieved with the soft, medium, and firm floors, respectively (3.7, 3.9, 4.1 kN vs. 6.9 kN at L4/L5). Spine forces were lower than those at the ground and decreased cranially (4.9, 3.9, 3.7, 3.5 kN at the ground, L5/S1, L4/L5, and L3/L4, respectively, for the soft floor).

CONCLUSION

Lowering the floor stiffness (from 400 to 59 kN/m) can attenuate peak lumbosacral spine forces in a backward fall onto the buttocks from standing by 46% (average peak from 6.9 to 3.7 kN at L4/L5) to values closer to the average tolerance of the spine to fracture (3.4 kN).

The effects of pad geometry and material properties on the biomechanical effectiveness of 26 commercially available hip protectors

Wearable hip protectors (padded garments) represent a promising strategy to decrease impact force and hip fracture risk during falls, and a wide range of products are currently marketed. However, little is known about how design features of hip protectors influence biomechanical effectiveness. We used a mechanical test system (simulating sideways falls) to measure the attenuation in femoral neck force provided by 26 commercially available hip protectors at three impact velocities (2, 3, and 4m/s). We also used a materials testing machine to characterize the force-deflection properties of each device. Regression analyses were performed to determine which geometric (e.g., height, width, thickness, volume) and force-deflection properties were associated with force attenuation. At an impact velocity of 3m/s, the force attenuation provided by the various hip protectors ranged between 2.5% and 40%. Hip protectors with lower stiffness (measured at 500N) provided greater force attenuation at all velocities. Protectors that absorbed more energy demonstrated greater force attenuation at the higher impact velocities (3 and 4m/s conditions), while protectors that did not directly contact (but instead bridged) the skin overlying the greater trochanter attenuated more force at velocities of 2 and 3m/s. At these lower velocities, the force attenuation provided by protectors that contacted the skin overlying the greater trochanter increased with increasing pad width, thickness, and energy dissipation. By providing a comparison of the protective value of a large range of existing hip protectors, these results can help to guide consumers and researchers in selecting hip protectors, and in interpreting the results of previous clinical trials. Furthermore, by determining geometric and material parameters that influence biomechanical performance, our results should assist manufacturers in designing devices that offer improved performance and clinical effectiveness.

Increasing adherence with the use of hip protectors for older people living in the community

For people at high risk of hip fracture living in community settings, providing hip protectors at no cost increased adherence, but the additional effect of an educational programme was limited. Overall, the level of adherence was modest.

INTRODUCTION

The objective of the study was to increase adherence with hip protector use by older people at high risk of hip fracture. The study included two randomised controlled trials with 308 older people recruited from three hospital rehabilitation wards and 171 older people recruited from the community.

METHODS

Participants were randomised into three groups. The control group received a brochure about hip protectors. The no cost group were fitted with free hip protectors and asked to use them. The combined group received free hip protectors and education sessions about their use. Adherence with the use of hip protectors at 3 and 6 months after recruitment was measured. Secondary outcomes were falls, fractures and hospitalisations.

RESULTS

Very few participants in the two control groups bought a hip protector. Overall adherence in the four intervention groups was modest, but higher in the community recruitment setting (49%) than in the hospital recruitment setting (36%) at 6 months. In the community recruitment group, at 3 months of follow-up, a significantly higher number of participants in the combined group (62%) were wearing hip protectors compared to the no cost group (43%, p=0.04). Five hip fractures occurred during the study, with four sustained whilst not wearing the hip protectors.

CONCLUSION

Providing hip protectors at no cost to community living older people at high risk of hip fractures modestly increases initial acceptance and adherence with hip protector use. Additional education may further increase hip protector use in people living in the community in the short term.

Load on osseointegrated fixation of a transfemoral amputee during a fall: Determination of the time and duration of descent

Mitigation of fall-related injuries for populations of transfemoral amputees fitted with a socket or an osseointegrated fixation is challenging. Wearing a protective device fitted within the prosthesis might be a possible solution, provided that issues with automated fall detection and time of deployment of the protective mechanism are solved. The first objective of this study was to give some examples of the times and durations of descent during a real forward fall of a transfemoral amputee that occurred inadvertently while attending a gait measurement session to assess the load applied on the residuum. The second objective was to present five semi-automated methods of detection of the time of descent using the load data. The load was measured directly at 200 Hz using a six-channel transducer. The average time and duration of descent were 242 ± 42 ms (145-310 ms) and 619 ± 42 ms (550-715 ms), respectively. This study demonstrated that the transition between walking and falling was characterized by times of descent that occurred sequentially. The sensitivity and specificity of an automated algorithm might be improved by combining several methods of detection based on the deviation of the loads measured from their own trends and from a template previously established.

Characterizing the effective stiffness of the pelvis during sideways falls on the hip

The force applied to the proximal femur during a fall, and thus hip fracture risk, is dependent on the effective stiffness of the body during impact. Accurate estimates of pelvis stiffness are required to predict fracture risk in a fall. However, the dynamic force-deflection properties of the human pelvis have never been measured in-vivo. Our objectives were to (1) measure the force-deflection properties of the pelvis during lateral impact to the hip, and (2) determine whether the accuracy of a mass-spring model of impact in predicting peak force depends on the characterization of non-linearities in stiffness. We used a sling and electromagnet to release the participant's pelvis from heights up to 5 cm, simulating low-severity sideways falls. We measured applied loads with a force plate, and pelvis deformation with a motion capture system. In the 5 cm trials peak force averaged 1004 (SD 115)N and peak deflection averaged 26.3 (5.1)mm. We observed minimal non-linearities in pelvic force-deflection properties characterized by an 8% increase in the coefficient of determination for non-linear compared to linear regression equations fit to the data. Our model consistently overestimated peak force (by 49%) when using a non-linear stiffness equation, while a piece-wise non-linear fit (non-linear for low forces, linear for loads exceeding 300 N) predicted peak force to within 1% at our highest drop height. This study has important implications for mathematical and physical models of falls, including mechanical systems that assess the biomechanical effectiveness of protective devices aimed at reducing hip fracture risk.

Load on osseointegrated fixation of a transfemoral amputee during a fall: loading, descent, impact and recovery analysis

Falling represents a health risk for lower limb amputees fitted with an osseointegrated fixation mainly because of the potential damage to the fixation. The purpose of this study was to characterize a real forward fall that occurred inadvertently to a transfemoral amputee fitted with an osseointegrated fixation while attending a gait measurement session to assess the load applied on the residuum. The objective was to analyze the load applied on the fixation with an emphasis on the sequence of events, the pattern and the magnitude of the forces and moments. The load was measured directly at 200 Hz using a six-channel transducer. Complementary video footage was also studied. The fall was divided into four phases: Loading (240 ms), descent (620 ms), impact (365 ms) and recovery (2495 ms). The main impact forces and moments occurred 870 ms and 915 ms after the heel contact, and corresponded to 133% BW and 17 % BWm, or 1.2 and 11.2 times the maximum forces and moments applied during the previous steps of the participant, respectively. This study provided key information to engineers and clinicians facing the challenge to design equipment, and rehabilitation and exercise programs to restore safely the locomotion of lower limb amputees.

Effect of hip protectors, falling angle and body mass index on pressure distribution over the hip during simulated falls

BACKGROUND

We examined how a soft shell hip protector affects the magnitude and distribution of force to the hip during simulated falls, and how the protective effect depends on the fall direction and the amount of soft tissue padding over the hip.

METHODS

Fourteen young women with either high or low body mass index participated in a "pelvis release experiment" that simulated falls resulting in either lateral, anterolateral or posterolateral impact to the pelvis with/without a soft shell hip protector. Outcome variables were the magnitude and location of peak pressure (d, theta) with respect to the greater trochanter, total impact force, and percent force applied to four defined hip regions.

FINDINGS

The soft shell hip protector reduced peak pressure by 70%. The effect was two times greater in low than high body mass index individuals. The protector shunted the peak pressure distally along the shaft of the femur (d=52 mm (SD 22), theta=-21 degrees (SD 49) in the unpadded trials versus d=81 mm (SD 23), theta=-10 degrees (SD 35) in the padded trials). Peak force averaged 12% greater in posterolateral and 17% lower in anterolateral than lateral falls.

INTERPRETATION

Our results indicate that the hip protector we tested had a much stronger protective benefit for low than high body mass index individuals. Next generation protectors might be developed for improved shunting of pressure away from the femur, improved protection during posterolateral falls, and greater force attenuation for low body mass index individuals.

Management of osteoporosis among home health and long-term care patients with a prior fracture

Osteoporosis is a growing health concern as the number of senior adults continues to increase worldwide. Falls and fractures are very common among frail older adults requiring home health and long-term care. Preventative strategies for reducing falls have been identified and many therapies (both prescription and nonprescription) with proven efficacy for reducing fracture risk are available. However, many practitioners overlook the fact that a fragility fracture is diagnostic for osteoporosis even without knowledge of bone mineral density testing. As a result, osteoporosis is infrequently diagnosed and treated in the elderly after a fracture. Based on existing literature, we have developed an algorithm for the assessment and treatment of osteoporosis among persons with known prior fracture(s) living in long-term care facilities or receiving home health care based on the data available in the literature.

Low stiffness floors can attenuate fall-related femoral impact forces by up to 50% without substantially impairing balance in older women

Low stiffness floors such as carpet appear to decrease hip fracture risk by providing a modest degree of force attenuation during falls without impairing balance. It is unknown whether other compliant floors can more effectively reduce impact loads without coincident increases in fall risk. We used a hip impact simulator to assess femoral neck force for four energy-absorbing floors (SmartCell, SofTile, Firm Foam, Soft Foam) compared to a rigid floor. We also assessed the influence of these floors on balance/mobility in 15 elderly women. We observed differences in the mean attenuation in peak femoral neck force provided by the SmartCell (24.5%), SofTile (47.2%), Firm Foam (76.6%), and Soft Foam (52.4%) floors. As impact velocity increased from 2 to 4m/s, force attenuation increased for SmartCell (from 17.3% to 33.7%) and SofTile (from 44.9% to 51.2%), but decreased for the Firm Foam (from 87.0% to 64.5%) and Soft Foam (from 66.1% to 37.9%) conditions. Regarding balance, there were no significant differences between the rigid, SmartCell, and SofTile floors in proportion of successful trials, Get Up and Go time, balance confidence or utility ratings. SofTile, Firm Foam, and Soft Foam caused significant increases (when compared to the rigid floor) in postural sway in the anterior-posterior and medial-lateral directions during standing. However, SmartCell increased sway only in the anterior-posterior direction. This study demonstrates that two commercially available compliant floors can attenuate femoral impact force by up to 50% while having only limited influence on balance in older women, and supports development of clinical trials to test their effectiveness in high-risk settings.

The force attenuation provided by hip protectors depends on impact velocity, pelvic size, and soft tissue stiffness

Wearable hip protectors represent a promising strategy for preventing hip fractures. However, there is lack of agreement on biomechanical testing standards and subsequent uncertainty about the ability of hip protectors to attenuate impact force during a fall. To address this issue, we designed a fall impact simulator that incorporated a "biofidelic" surrogate pelvis, which matched the surface geometry and soft tissue stiffness measured in elderly women (n=15). We then used this system to measure the attenuation in peak femoral neck force provided by two commercially available soft shell protectors (Safehip Soft and Hipsaver) and one rigid shell protector (Safehip Classic). Finally, we examined how the force attenuation provided by each protector was influenced by systematic changes in fall severity (impact velocity), body size (pelvis size), and soft tissue stiffness. With the biofidelic pelvis, the force attenuation averaged over all impact velocities was 27% for Safehip Soft, 17% for Safehip Classic, and 19% for Hipsaver. However, the rank order of hip protectors (and especially the performance of Safehip Classic) varied with the test conditions. Safehip Classic attenuated force by 33% during a low velocity (1 ms) fall, but only by 8% for a high velocity (4 ms) fall. In the latter condition, improved attenuation was provided by the soft shell hip protectors (19% by Safehip Soft and 21% by Hipsaver). As soft tissue stiffness increased from softest to most rigid, the attenuation provided by Safehip Classic increased 2.9-fold (from 26% to 76%), while Safehip Soft increased 1.7-fold (from 36% to 60%) and Hipsaver increased 1.1-fold (from 36% to 38%). As pelvis size decreased from largest to smallest, the attenuation provided by Safehip Classic increased 8-fold, but for a high velocity fall and moderate tissue stiffness, never exceeded that provided by Safehip Soft and Hipsaver. Our results indicate that, under biofidelic testing conditions, the soft shell hip protectors we examined generally provided greater force attenuation (averaging up to 27%) than the hard shell protector. Measured values of force attenuation were highly sensitive to variations in impact velocity, pelvic size, and pelvic soft tissue stiffness. This indicates the need to develop international testing standards to guide market approval, the selection of protectors for clinical trials, and the design of improved hip protectors.