Fall arrest strategy affects peak hand impact force in a forward fall

3D-printed patient-specific implants made of polylactide (PLDLLA) and β-tricalcium phosphate (β-TCP) for corrective osteotomies of the distal radius

The most common surgical procedure to manage the malunion of the bones is corrective osteotomy. The current gold standard for securing the bone segments after osteotomy is the use of titanium plates and allografts which have disadvantages such as possible allergic reaction, additional operations such as extraction of the graft from other sites and removal operation. The utilization of resorbable materials presents an opportunity to mitigate these drawbacks but has not yet been thoroughly researched in the literature. This study assesses the viability of using biodegradable, 3D-printed patient-specific implants made of Poly(-L-lactide-co-D, L-lactide) (PLDLLA) and β-Tricalcium Phosphate (β-TCP) as an alternative material in an in-vitro biomechanical study involving ex vivo biomechanical compression testing, biodegradation testing, and calorimetric measurements. These implants possess a unique shape, resembling a wedge and are fixated as a connection between the osteotomised bone using resorbable screws. Following point-of-care virtual planning, bio-mechanical compressive tests with (n = 5) ex vivo radii equipped with PLDLLA/ β-TCP implants were performed to prove sufficient stability of the connection. All PLDLLA/ β-TCP implants withstood a compressive force of at least 1'211 N which exceeds the maximum force reported in literature in case of a fall from the height of one meter. Furthermore, the results showed a consistent surface chemistry and slow degradation rate. The outcomes are encouraging, establishing the groundwork for an innovative distal radius corrective osteotomy surgical method. However, further research is necessary to thoroughly evaluate the long-term biodegradability and mechanical efficacy of the implants.

A method for simulating forward falls and controlling impact velocity

Assessment of protective arm reactions associated with forward falls are typically performed by dropping research participants from a height onto a landing surface. The impact velocity is generally modulated by controlling the total height of the fall. This contrasts with an actual fall where the fall velocity is dependent on several factors in addition to fall height and not likely predictable at the onset of the fall. A counterweight and pulley system can be used to modulate the fall velocity in simulated forward falls in a manner that is not predictable to study participants, enhancing experimental validity. However, predicting the fall velocity based on participant height and weight and counterweight mass is not straightforward. In this article, the design of the FALL simulator For Injury prevention Training and assessment (FALL FIT) system is described. A dynamic model of the FALL FIT and counterweight system is developed and model parameters are fit using nonlinear optimization and experimental data. The fitted model enables prediction of fall velocity as a function of participant height and weight and counterweight load. The method can be used to provide controllable perturbations thereby elucidating the control strategy used when protecting the body from injury in a forward fall, how the control strategy changes because of aging or dysfunction or as a method for progressive protective arm reaction training.•Construction of device to simulate forward falls with controllable impact velocity using material that are commercially available is described•A dynamic model of the FALL FIT is developed to estimate the impact velocity of a simulated forward fall using participant height and counterweight load•The dynamic model is validated using data from 3 previous studies.

Impact forces in backward falls: Subject-specific video-based rigid body simulation of backward falls

A critical missing component in the study of real-world falls is the ability to accurately determine impact forces resulting from the fall. Subject-specific rigid body dynamic (RBD) models calibrated to video captured falls can quantify impact forces and provide additional insights into injury risk factors. RBD models were developed based on five backward falls captured on surveillance video in long-term care facilities in British Columbia, Canada. Model joint stiffness and initial velocities were calibrated to match the kinematics of the fall and contact forces were calculated. The effect of joint stiffnesses (neck, lumbar spine, hip, and knee joint) on head contact forces were determined by modifying the calibrated stiffness values ±25%. Fall duration, fall trajectories, and maximum velocities showed a close match between fall events and simulations. The maximum value of pelvic velocity difference between Kinovea (an open-source software 2D digitization software) and Madymo multibody modeling was found to be 6% ± 21.58%. Our results demonstrate that neck and hip stiffness values have a non-significant yet large effect on head contact force (t(3) = 1, p = 0.387 and t(3) = 2, p = 0.138), while lower effects were observed for knee stiffness, and the effect of lumbar spine stiffness was negligible. The subject-specific fall simulations constructed from real world video captured falls allow for direct quantification of force outcomes of falls and may have applications in improving the assessment of fall-induced injury risks and injury prevention methods.

The timing and amplitude of the muscular activity of the arms preceding impact in a forward fall is modulated with fall velocity

Protective arm reactions have been shown to be an important injury avoidance mechanism in unavoidable falls. Protective arm reactions have been shown to be modulated with fall height, however it is not clear if they are modulated with impact velocity. The aim of this study was to determine if protective arm reactions are modulated in response to a forward fall with an initially unpredictable impact velocity. Forward falls were evoked via sudden release of a standing pendulum support frame with adjustable counterweight to control fall acceleration and impact velocity. Thirteen younger adults (1 female) participated in this study. Counterweight load explained more than 89% of the variation of impact velocity. Angular velocity at impact decreased (p < 0.001), drop duration increased from 601 ms to 816 ms (p < 0.001), and the maximum vertical ground reaction force decreased from 64%BW to 46%BW (p < 0.001) between the small and large counterweight. Elbow angle at impact (129 degrees extension), triceps (119 ms) and biceps (98 ms) pre-impact time, and co-activation (57%) were not significantly affected by counterweight load (p-values > 0.08). Average triceps and biceps EMG amplitude decreased from 0.26 V/V to 0.19 V/V (p = 0.004) and 0.24 V/V to 0.11 V/V (p = 0.002) with increasing counterweight respectively. Protective arm reactions were modulated with fall velocity by reducing EMG amplitude with decreasing impact velocity. This demonstrates a neuromotor control strategy for managing evolving fall conditions. Future work is needed to further understand how the CNS deals with additional unpredictability (e.g., fall direction, perturbation magnitude, etc.) when deploying protective arm reactions.

Fall arrest strategy training improves upper body response time compared to standard fall prevention exercise in older women: A randomized trial

INTRODUCTION

Exercise can decrease fall risk in older adults but less is known about training to reduce injury risk in the event a fall is unavoidable. The purpose of this study was to compare standard fall prevention exercises to novel Fall Arrest Strategy Training (FAST); exercises designed to improve upper body capacity to reduce fall-injury risk in older women.

METHOD

Forty women (mean age 74.5 years) participated in either Standard (n = 19) or FAST (n = 21) twice per week for 12 weeks. Both interventions included lower body strength, balance, walking practice, agility and education. FAST added exercises designed to enhance forward landing and descent control such as upper body strengthening, speed and practice of landing and descent on outstretched hands.

RESULTS

Both FAST and Standard significantly improved strength, mobility, balance, and fall risk factors from pre to post-intervention. There was a significant time by group interaction effect for upper body response time where FAST improved but Standard did not (p = 0.038).

DISCUSSION

FAST resulted in similar gains in factors that reduce fall risk as a standard fall prevention program; with the additional benefit of improving speed of arm protective responses; a factor that may help enhance landing position and reduce injury risks such as head impact during a forward fall.

A Comparison of Inertial Measurement Unit and Motion Capture Measurements of Tibiofemoral Kinematics during Simulated Pivot Landings

Injuries are often associated with rapid body segment movements. We compared Certus motion capture and APDM inertial measurement unit (IMU) measurements of tibiofemoral angle and angular velocity changes during simulated pivot landings (i.e., ~70 ms peak) of nine cadaver knees dissected free of skin, subcutaneous fat, and muscle. Data from a total of 852 trials were compared using the Bland-Altman limits of agreement (LoAs): the Certus system was considered the gold standard measure for the angle change measurements, whereas the IMU was considered the gold standard for angular velocity changes. The results show that, although the mean peak IMU knee joint angle changes were slightly underestimated (2.1° for flexion, 0.2° for internal rotation, and 3.0° for valgus), the LoAs were large, ranging from 35.9% to 49.8%. In the case of the angular velocity changes, Certus had acceptable accuracy in the sagittal plane, with LoAs of ±54.9°/s and ±32.5°/s for the tibia and femur. For these rapid motions, we conclude that, even in the absence of soft tissues, the IMUs could not reliably measure these peak 3D knee angle changes; Certus measurements of peak tibiofemoral angular velocity changes depended on both the magnitude of the velocity and the plane of measurement.

Variations in Strain Distribution at Distal Radius under Different Loading Conditions

Distal radial fractures exhibit various fracture patterns. By assuming that the strain distribution at the distal radius affects the diversification of the fracture pattern, a parameter study using the finite element model of a wrist developed from computed tomography (CT) images was performed under different loading conditions. The finite element model of the wrist consisted of the radius, ulna, scaphoid, lunate, triquetrum, and major carpal ligaments. The material properties of the bone models were assigned on the basis of the Hounsfield Unit (HU) values of the CT images. An impact load was applied to the scaphoid, lunate, and triquetrum to simulate boundary conditions during fall accidents. This study considered nine different loading conditions that combine three different loading directions and three different load distribution ratios. According to the analysis results, the strain distribution at the distal radius changed with respect to the change in the loading condition. High strain concentration occurred in regions where distal radius fractures are commonly developed. The direction and distribution of the load acting on the radius were considered to be factors that may cause variations in the fracture pattern of distal radius fractures.

Test-retest reliability of the FALL FIT system for assessing and training protective arm reactions in response to a forward fall

The use of the hands and arms is an important protective mechanism in avoiding fall-related injury. The aim of this study was to evaluate the test-retest reliability of fall dynamics and evokd protective arm response kinematics and kinetics in forward falls simulated using the FALL simulator For Injury prevention Training and assessment system (FALL FIT). Fall FIT allows experimental control of the fall height and acceleration of the body during a forward fall. Two falls were simulated starting from 4 initial lean angles in Experiment 1 and with 4 different fall accelerations in Experiment 2. Fourteen younger adults (25.1±3.5 years) and 13 older adults (71.3±3.7 years) participated in Experiment 1 and 13 younger adults (31.8±5.7 years) participated in Experiment 2. Intraclass correlation coefficients (ICC) were used to the evaluate absolute agreement of single measures at each condition and averages across conditions. Average measures of fall dynamics and evoked kinematics and kinetics exhibited excellent reliability (ICC(A,4)>0.86). The reliability of single measures (ICC(A,1) > 0.59) was good to excellent, although 18% of single measures had a reliability (ICC(A,1)) between 0.00 and 0.57. The FALL FIT was shown to have good to excellent reliability for most measures. FALL FIT can produce a wide range of fall dynamics through modulation of initial lean angle and body acceleration. Additionally, the range of fall velocities and evoked kinematics and kinetics are consistent with previous fall research.•

The FALL FIT can be used to gain further insight into the control of protective arm reactions and may provide a therapeutic tool to assess and train protective arm reactions.

Age-related changes in protective arm reaction kinematics, kinetics, and neuromuscular activation during evoked forward falls

Fall related injuries in older adults are a major healthcare concern. During a fall, the hands and arms play an important role in minimizing trauma from ground impact. Although older adults are able to orient the hands and arms into a protective orientation after falling and prior to ground impact, an inability to avoid increased body impact occurs with age. Previous investigations have generally studied rapid arm movements in the pre-impact phase or absorbing energy in the post-impact phase. There are no known studies that have directly examined both the pre-impact and post-impact phase in sequence in a forward fall. The aim of this study was to identify age-related biomechanical and neuromuscular changes in evoked arm reactions in response to forward falls that may increase fall injury risk. Fourteen younger and 15 older adults participated. Falls were simulated while standing with torso and legs restrained via a moving pendulum system from 4 different initial lean angles. While there was not a significant age-related difference in the amount of energy absorbed post-impact (p = 0.68), older adults exhibited an 11% smaller maximum vertical ground reaction force when normalized to body weight (p = 0.031), and 8 degrees less elbow extension at impact (p = 0.045). A significant interaction between age and initial lean angle (p = 0.024), indicated that older adults required 54%, 54%, 41%, and 57% greater elbow angular displacement after impact at the low, medium, medium-high, and high initial lean angles compared to younger adults. These results suggested older adults may be at greater risk of increased body impact due to increased elbow flexion angular displacement after impact when the hands and arms are able to contact the ground first. Both groups exhibited robust modulation to the initial lean angle with no observed age-related differences in the initial onset timing or amplitude of muscle activation levels. There were no significant age-related differences in the EMG timing, amplitude or co-activation of muscle activation preceding impact or following impact indicating comparable neuromotor response patterns between older and younger adults. These results suggest that aging changes in muscular elements may be more implicated in the observed differences than changes in neuromuscular capacity. Future work is needed to test the efficacy of different modalities (e.g. instruction, strength, power, perturbation training, fall landing techniques) aimed at reducing fall injury risk.

In vivo soft tissue compressive properties of the human hand

Background/Purpose

Falls onto outstretched hands are the second most common sports injury and one of the leading causes of upper extremity injury. Injury risk and severity depends on forces being transmitted through the palmar surface to the upper extremity. Although the magnitude and distribution of forces depend on the soft tissue response of the palm, the in vivo properties of palmar tissue have not been characterized. The purpose of this study was to characterize the large deformation palmar soft tissue properties.

Methods

In vivo dynamic indentations were conducted on 15 young adults (21–29 years) to quantify the soft tissue characteristics of over the trapezium. The effects of loading rate, joint position, tissue thickness and sex on soft tissue responses were assessed.

Results

Energy absorbed by the soft tissue and peak force were affected by loading rate and joint angle. Energy absorbed was 1.7–2.8 times higher and the peak force was 2–2.75 times higher at high rate loading than quasistatic rates. Males had greater energy absorbed than females but not at all wrist positions. Damping characteristics were the highest in the group with the thickest soft tissue while damping characteristics were the lowest in group with the thinnest soft tissues.

Conclusion

Palmar tissue response changes with joint position, loading rate, sex, and tissue thickness. Accurately capturing these tissue responses is important for developing effective simulations of fall and injury biomechanics and assessing the effectiveness of injury prevention strategies.

Human inspired fall arrest strategy for humanoid robots based on stiffness ellipsoid optimisation

Falls are a common risk and impose severe threats to both humans and humanoid robots as a product of bipedal locomotion. Inspired by human fall arrest, we present a novel humanoid robot fall prevention strategy by using arms to make contact with environmental objects. Firstly, the capture point method is used to detect falling. Once the fall is inevitable, the arm of the robot will be actuated to gain contact with an environmental object to prevent falling. We propose a hypothesis that humans naturally favour to select a pose that can generate a suitable Cartesian stiffness of the arm end-effector. Based on this principle, a configuration optimiser is designed to choose a pose of the arm that maximises the value of the stiffness ellipsoid of the endpoint along the impact force direction. During contact, the upper limb acts as an adjustable active spring-damper and absorbs impact shock to steady itself. To validate the proposed strategy, several simulations are performed in MATLAB & Simulink by having the humanoid robot confront a wall as a case study in which the strategy is proved to be effective and feasible. The results show that using the proposed strategy can reduce the joint torque during impact when the arms are used to arrest the fall.

The Role of Fall Biomechanics in the Cause and Prevention of Bone Fractures in Older Adults

PURPOSE OF REVIEW

Adults over age 65 experience the highest rates of bone fracture, and 90% of fractures in older adults are caused by falls from standing height or lower. Advances in fracture prevention rely on our ability to prevent falls, reduce the severity of falls, and enhance the resistance of bone to trauma. To help guide these efforts, we need improved understanding on the types of falls that cause fractures.

RECENT FINDINGS

In this review, we describe recent evidence on how the mechanics of falls in older adults influence the risk for fractures to the hip, wrist, vertebrae, and humerus. We discuss how fracture risk depends on fall height, fall direction, and landing configuration. We also review the benefits of exercise, wearable protective gear, and environmental modifications in preventing fractures in older adults. Our findings highlight promising new directions in fracture prevention, and the need for collaboration between the bone and falls research communities to implement proven strategies and generate new solutions.

On challenges in clinical assessment of hip fracture risk using image-based biomechanical modelling: a critical review

INTRODUCTION

Hip fracture is a common health risk among elderly people, due to the prevalence of osteoporosis and accidental fall in the population. Accurate assessment of fracture risk is a crucial step for clinicians to consider patient-by-patient optimal treatments for effective prevention of fractures. Image-based biomechanical modeling has shown promising progress in assessment of fracture risk, and there is still a great possibility for improvement. The purpose of this paper is to identify key issues that need be addressed to improve image-based biomechanical modeling.

MATERIALS AND METHODS

We critically examined issues in consideration and determination of the four biomechanical variables, i.e., risk of fall, fall-induced impact force, bone geometry and bone material quality, which are essential for prediction of hip fracture risk. We closely inspected: limitations introduced by assumptions that are adopted in existing models; deficiencies in methods for construction of biomechanical models, especially for determination of bone material properties from bone images; problems caused by separate use of the variables in clinical study of hip fracture risk; availability of clinical information that are required for validation of biomechanical models.

RESULTS AND CONCLUSIONS

A number of critical issues and gaps were identified. Strategies for effectively addressing the issues were discussed.

Can a simple fall cause a rotator cuff tear? Literature review and biomechanical considerations

PURPOSE

A simple fall on the shoulder is often referred to as minor trauma that cannot cause a tendon tear but at best reveal a pre-existing rotator cuff pathology. We wanted to know whether this statement was true. The purpose of our study was therefore to summarize the causes of acute rotator cuff tears reported in the literature and provide a biomechanical explanation for tendon tears diagnosed after a fall.

METHOD

We searched PubMed and included studies reporting rotator cuff tears occurring due to a trauma. The number of cases, the tendons involved, the age of the patients, and the nature of trauma were summarized. In addition, we noted any information provided by the authors on the pathogenesis of acute tendon ruptures.

RESULTS

Sixty-seven articles with a total of 4061 traumatic rotator cuff tears met the inclusion criteria. A simple fall was the most common cause (725 cases) and the supraspinatus tendon was most frequently affected. The postulated pathomechanism is a sudden stretch of the tendon-muscle unit while contracting (eccentric loading).

CONCLUSION

A simple fall can cause an acute rotator cuff tear and fall-related tears are not restricted to young individuals. They can affect patients of any age. The stresses occurring within the rotator cuff during an attempt to cushion a fall may locally exceed the tensile strength of the tendon fibers and cause a partial or full-thickness tear.

Motion and Strength Analysis of 2-Tine Staple and K-Wire Fixation in Scapholunate Ligament Stabilization in a Cadaver Model

Purpose

Previous studies have demonstrated the benefits of 2- and 4-tine staple fixation in scapholunate interosseous ligament (SLIL) reconstruction, including improved rotational control and avoidance of the articular surface. This study compared scaphoid and lunate kinematics after SLIL fixation with traditional Kirschner wire (K-wire) fixation or 2-tine staple fixation.

Methods

Eight fresh frozen cadaver arms with normal scapholunate (SL) intervals were included. Infrared motion capture was used to assess kinematics between the scaphoid and lunate as the wrists were moved through a simulated dart-throw motion. Kinematic data were recorded for each wrist in 4 states: SLIL intact, SLIL sectioned, K-wire fixation across SL interval and scaphocapitate joint, and 2-tine Nitinol staple fixation across SL interval. Strength of the SL staple fixation was evaluated using an axial load machine to assess load to failure of the staple construct.

Results

Range of motion of the scaphoid and lunate with SLIL intact and SLIL sectioned were similar. K-wire fixation across the SL interval significantly decreased the overall wrist range of motion as well as scaphoid and lunate motion in all planes except for scaphoid flexion. Conversely, scaphoid and lunate motion after staple fixation was similar to that in normal wrists, except for a significant decrease in scaphoid extension. Under axial load simulating a ground-level fall, 3 of 8 arms demonstrated no failure, and none of the failures was due to direct failure of the 2-tine staple.

Conclusions

This study demonstrates 2-tine staple fixation across the SL interval is effective in providing initial stability and maintaining physiologic motion of the scaphoid and lunate compared with K-wire fixation after SLIL injury.

Clinical relevance

This study demonstrates an alternate technique for the stabilization of the SL interval in repair of acute SLIL injuries using 2-tine staple fixation, which maintains near physiologic motion of the scaphoid and lunate after SLIL injury.

Mechanical performance comparison of two surgical constructs for wrist four-corner arthrodesis via dorsal and radial approaches

BACKGROUND

Four-corner arthrodesis, which involves fusing four carpal bones while removing the scaphoid bone, is a standard surgery for the treatment of advanced stages of wrist arthritis. Nowadays, it can be performed using a dorsal approach by fixing a plate to the bones and a new radial approach is in development. To date, there is no consensus on the biomechanically optimal and most reliable surgical construct for four-corner arthrodesis.

METHODS

To evaluate them biomechanically and thus assist the surgeon in choosing the best implant orientation, radial or dorsal, the two different four-corner arthrodesis surgical constructs were virtually simulated on a 3D finite element model representing all major structures of the wrist. Two different realistic load sets were applied to the model, representing common tasks for the elderly.

FINDINGS

Results consistency was assessed by comparing with the literature the force magnitude computed on the carpal bones. The Von Mises stress distribution in the radial and dorsal plates were calculated. Stress concentration was located at the plate-screw interface for both surgical constructs, with a maximum stress value of 413 MPa for the dorsal plate compared to 326 MPa for the radial plate, meaning that the stress levels are more unfavourable in the dorsal approach.

INTERPRETATION

Although some bending stress was found in one load case, the radial plate was mechanically more robust in the other load case. Despite some limitations, this study provides, for the first time, quantified evidence that the newly developed radial surgical construct is mechanically as efficient as the dorsal surgical construct.

A systematic review of upper extremity responses during reactive balance perturbations in aging

BACKGROUND

Balance responses to perturbations often involve the arms in an attempt to either restore balance or protect against impact. Although a majority of research has been dedicated to understanding age-related changes in lower limb balance responses, there is a growing body of evidence supporting age-related changes in arm responses. This systematic review aimed to summarize differences in arm responses between older and younger adults under conditions requiring counterbalancing, reaching to grasping, and protection against impact.

METHODS

Following a systematic review and critical appraisal of the literature, data regarding the arm response in studies comparing young and older adults was extracted. The resulting articles were also assessed for quality to determine risk of bias.

RESULTS

Fifteen high quality studies were identified. The majority of these studies reported delayed onsets in muscle activation, differences in arm movement strategies, delayed movement timing, increased impact forces, and greater grasp errors in older compared to young adults. These differences were also identified under varied visual and cognitive conditions.

CONCLUSIONS

The studies included in this review demonstrate age-related differences in arm responses regardless of the direction and nature of the perturbation. These differences could provide insight into developing more targeted rehabilitation and fall prevention strategies. More research is needed to assess whether the identified age-related differences are a necessary compensation or a contributory factor to balance impairments and fall risk in older adults.

Current and Emerging Trends in the Management of Fall Risk in People with Lower Limb Amputation

Purpose of Review

People living with lower limb amputation are at an increased risk of falling compared with the healthy geriatric population. Factors of increased age and increased number of comorbidities could compound the already increased risk. The purpose of this article is to highlight recent research associated with fall risk in amputees and provide the reader with evidence to help guide clinical interventions.

Recent Findings

Though research on the topic of falls in people with amputation is becoming more common, there is still a dearth of evidence regarding what contributes to increased fall risk and how to address it in this population. There are recent studies that have examined therapy and prosthetic interventions that could mitigate fall risk in people with amputation, yet there is not enough evidence to develop a consensus on the topic. More research is required to determine what contributes to increased fall rates in people with amputation, and what detriments to an amputee's function or psyche may result after incurring a fall.

Summary

Borrowing from what is known about geriatric fall risk and combining the information with novel and existing approaches to fall mitigation in amputees can offer clinicians the opportunity to develop evidence-based programs to address fall risk in their patients with lower limb amputation.

Effect of Holding Objects on the Occurrence of Head Impact in Falls by Older Adults: Evidence From Real-Life Falls in Long-Term Care

BACKGROUND

Falls cause approximately 80% of traumatic brain injuries in older adults, and nearly one third of falls by residents in long-term care (LTC) result in head impact. Holding objects during falls, such as mobility aids, may affect the ability of LTC residents to avoid head impact by arresting the fall with their upper limbs. We examined the prevalence of holding objects and their effect on risk for head impact during real-life falls in older adults living in LTC.

METHODS

We analyzed videos of 1105 real-life falls from standing height by 425 LTC residents, using a validated questionnaire to characterize the occurrence of head impact and whether the resident held objects during descent and impact. We classified objects as either "weight-bearing" (via contact to the fixed environment, eg, chairs and walkers) or "non-weight-bearing" (eg, cups) and tested their effect on odds for head impact with generalized estimating equations.

RESULTS

Residents held objects in more than 60% of falls. The odds for head impact were reduced for falls where weight-bearing objects were held or grasped during descent (odds ratio = 0.52; 95% confidence interval = 0.39-0.70) or maintained throughout the fall (odds ratio = 0.34; 95% confidence interval = 0.23-0.49). The most commonly held objects were chairs/wheelchairs (23% of cases), tables/counters (10% of cases), and walkers/rollators (22% of cases); all reduced the odds of head impact when held during descent. Holding non-weight-bearing objects did not affect the odds of head impact (odds ratio = 1.00; 95% confidence interval = 0.64-1.55).

CONCLUSION

Our results show that older adults in LTC use held, weight-bearing objects to reduce their risk for head impact during falls.

Protective arm movements are modulated with fall height

Protective arm reactions were evoked in 14 younger adults to determine the effect of fall height on protective arm reaction biomechanics. Participants were supported in a forward-leaning position on top of an inverted pendulum that isolated arm reaction by preventing any fall arresting contribution that may come from the ankle, knees, or hip. At an unpredictable time, the pendulum was released requiring participants to rapidly orient their arms to protect the head and body. Vertical ground reaction force (vGRF), arm kinematics, and electromyographic (EMG) measures of the biceps and triceps were compared at four initial lean angles. The time following perturbation onset and prior to impact consisted of two phases: rapid extension of the elbows and co-activation of the biceps and triceps in preparation for impact. The rapid orientation phase was modulated with fall height while the co-activation of the biceps and triceps in preparation for landing was minimally affected. Larger lean angles resulted in increased vGRF, increased elbow extension at impact, decreased elbow angular extension velocity at impact, and increased neck velocity at impact while hand velocity at impact was not significantly affected. The neuromuscular control strategy appears to optimize elbow extension angle/angular velocity prior to co-activation of the biceps and triceps that occurs about 100 ms prior to impact. Future work should investigate how the neuromuscular control strategy handles delayed deployment of protective arm reactions.

Simultaneous ORIF for bilateral comminuted proximal humerus fractures: Case report in an elderly patient

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Rare case of traumatic bilateral proximal humerus fractures.

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Simultaneous bilateral open reduction and internal fixation showed good recovery.

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Post op care is of great importance for patient recovery and return to daily activities.

Introduction

Bilateral proximal humerus fractures are rather rare and occur due to high energetic traumas in young patients and even low energetic traumas in older patients having osteoporosis. Open reduction and internal fixation (ORIF) is the most popular treatment for this type of fracture while other types of treatment such as arthroplasty or conservative treatment are also, but less commonly used.

Presentation of case

This report presents the case of an 80 years old female patient with bilateral proximal humerus fractures and a history of hypothyroidism. The patient was treated with simultaneous open reduction and internal fixation and presented a normal and full-range motion in both shoulders after follow-up.

Discussion

Frequency of proximal humerus fractures has increased with the increase in life expectancy. Osteoporotic people are at higher risk. Around five percent of all extremity fractures are humerus proximal end fractures for people below 40 years old and 76 % for cases of people over 40 years old, with females being more susceptible. ORIF is the treatment of choice for such fractures. Replacement arthroplasty, minimally invasive techniques and conservative management are other options depending on fracture characteristics.

Conclusion

This is an interesting rare case of simultaneous bilateral proximal humerus fractures in an elderly female patient, treated operatively with satisfactory results on follow up.

Biomechanical and physiological age differences in a simulated forward fall on outstretched hands in women

BACKGROUND

Falling on the outstretched hands, a protective mechanism to arrest the body and avoid injury, requires upper limb and trunk motor control for effective body descent. Older women are particularly susceptible to injury from a forward fall, but the biomechanical and physiological (e.g., muscle strength) factors related to this increased risk are poorly understood. Determining age differences in the modifiable neuromuscular factors related to a forward fall landing and descent could help to inform injury prevention strategies. The purpose was to investigate age related differences in upper extremity strength and fall arrest strategy differences during a simulated fall and to evaluate the relationships between muscle strength and biomechanical variables.

METHODS

Nineteen younger (mean age 23.0 yrs., SD 3.8) and 16 older (mean age 68.2 yrs., SD 5.3) women performed five trials of simulated falls. Biomechanical measures and electromyographic muscle activity were recorded during the descents. Concentric, isometric and eccentric strength of the non-dominant upper limb was measured via a dynamometer using a customized protocol.

FINDINGS

Older women demonstrated lower concentric elbow extension strength compared to younger women (p = 0.002). Landing strategies differed where younger women had significantly greater elbow joint angle (p = 0.006) and velocity (p = 0.02) at impact. Older women demonstrated diminished capacity to absorb energy and control descent on outstretched hands compared to younger women (p = 0.001).

INTERPRETATION

The landing strategy used by older women along with decreased energy absorption may increase risk of fall-related injury and increase the likelihood of trunk or head impact with the ground.

Does Fall Arrest Strategy Training Added to a Fall Prevention Programme Improve Balance, Strength, and Agility in Older Women? A Pilot Study

Purpose: The purpose of this study was to determine the effect of a unique exercise programme (Fall Arrest Strategy Training, or FAST) on upper body strength, range of motion (ROM), and fall risk in older women. FAST was designed to improve upper body capacity to prevent injury when a fall cannot be avoided. Method: A quasi-randomized site design included 71 older women (aged 67-95 y, mean age 83 years), who participated either in a standard fall prevention programme (Staying on Your Feet, or SOYF; n=29) or in SOYF combined with FAST (n=42). The women were measured three times-at baseline, after the 12-week intervention, and again 12 weeks later-for upper body strength, ROM, and fall risk factors (fall risk questionnaire, balance, mobility, and leg strength). Results: No significant differences were found in age, physical activity, or cognitive or functional status between the SOYF-standard and the SOYF-FAST groups. Both groups improved their fall risk status after the intervention, with no significant differences between them; however, the SOYF-FAST group showed greater improvements in upper extremity strength and ROM (p=0.007). Conclusion: FAST can feasibly be integrated into fall prevention programming, with additional gains in upper body strength and ROM in older women.

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.

Female Age-Related Differences in Biomechanics and Muscle Activity During Descents on the Outstretched Arms

The purposes of this study were to examine female age differences in: (1) upper extremity (UE) and trunk muscle activity, elbow joint moment, loading force, and UE energy absorption during a controlled forward body descent; and (2) UE muscle strength. Twenty young (mean 24.8 ± 3.4 years) and 20 older (68.4 ± 5.7 years) women were assessed via dynamometry for isometric, concentric, and eccentric UE strength and performed forward descents on force plates at three body lean angles (60°, 45°, and 30° from horizontal). Significant differences (p < .05) were found for muscle strength, biomechanics, and muscle activity. Concentric UE strength averaged 15% lower in older women. At 30° body lean, older women absorbed less energy. Older women had greater biceps brachii activation and less external oblique activation at all body lean angles. Age differences in muscle strength, activation, and energy absorption may contribute to fall-related injury risk.

Can Recovery Foot Placement Affect Older Adults' Slip-Fall Severity?

Following a slip occurred in the overground walking, a fall can be classified into two exclusive categories: feet-forward fall or split fall. The purposes of this study were to investigate whether the placement of the recovery foot would determine the slip types, the likelihood of fall, and the severity associated with each fall. The fall severity was estimated based on the impact velocity of body segments or trunk orientation upon fall arrest. One hundred ninety-five participants experienced a novel, unannounced slip while walking on a 7-m walkway. Kinematics of a full-body marker set was collected by a motion capture system which was synchronized with the force plates and loadcell. The results showed that the recovery foot landing position relative to the projected center of mass position at the recovery foot touchdown determined the slip type by 90.8%. Feet-forward slips led to significantly lower rate of falls than did split slips (47.6 vs. 67.8%, p < 0.01). Yet, feet-forward falls were much more dangerous because they were associated with significantly greater estimated maximum hip impact velocity (p < 0.001) and trunk backward leaning angle (p < 0.001) in comparison to split falls.

The effect of asymmetrical body orientation during simulated forward falls on the distal upper extremity impact response of healthy people

The occurrence of distal upper extremity injuries resulting from forward falls (approximately 165,000 per year) has remained relatively constant for over 20years. Previous work has provided valuable insight into fall arrest strategies, but only symmetric falls in body postures that do not represent actual fall scenarios closely have been evaluated. This study quantified the effect of asymmetric loading and body postures on distal upper extremity response to simulated forward falls. Twenty participants were suspended from the Propelled Upper Limb fall ARest Impact System (PULARIS) in different torso and leg postures relative to the ground and to the sagittal plane (0°, 30° and 45°). When released from PULARIS (hands 10cm above surface, velocity 1m/s), participants landed on two force platforms, one for each hand. Right forearm impact response was measured with distal (radial styloid) and proximal (olecranon) tri-axial accelerometers and bipolar EMG from seven muscles. Overall, the relative height of the torso and legs had little effect on the forces, or forearm response variables. Muscle activation patterns consistently increased from the start to the peak activation levels after impact for all muscles, followed by a rapid decline after peak. The impact forces and accelerations suggest that the distal upper extremity is loaded more medial-laterally during asymmetric falls than symmetric falls. Altering the direction of the impact force in this way (volar-dorsal to medial-lateral) may help reduce distal extremity injuries caused when landing occurs symmetrically in the sagittal plane as it has been shown that volar-dorsal forces increase the risk of injury.

Injury tolerance of the wrist and distal forearm to impact loading onto outstretched hands

BACKGROUND

The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tolerance of the wrist is poorly understood. This study sought to quantify the injury tolerance of the adult male forearm-wrist complex under loading simulating axial impact to an outstretched hand.

METHODS

Fifteen isolated cadaveric forearm/wrist specimens were tested. Loading was applied via an instrumented drop tower device designed to impact the palmar surface of the hand with the wrist extended to approximately 90 degrees. Impact severity was modulated by adjusting the boundary condition of the elbow. Elbow reaction force and deformation of the specimen (deflection of the palmar surface of the hand toward the elbow) were measured. Bone-implanted strain gauges were used to detect the time of fracture. Injury risk functions were developed using parametric survival analysis with a cumulative Weibull distribution.

RESULTS

Of 14 specimens, 10 exhibited a fracture to the wrist or forearm after test (one specimen was excluded from the analysis). Injury severities varied from nondisplaced fractures of the radius to severely displaced fractures and/or fracture-dislocations of the carpal bones. Of the potential predictors studied, the specimen deflection expressed as a percentage of the initial specimen length produced the injury risk model of best fit (50% risk of fracture at 1.69% deflection; 95% confidence interval, 1.38-2.07% deflection). The value of the elbow reaction force corresponding to a 50% risk of injury was 4.34 kN (3.80-4.97 kN).

CONCLUSION

These results provide information for the prediction of wrist and forearm injury in biomechanical models simulating impacts in the field and provide tolerance information for the development of injury mitigation countermeasures.

Effects of Age, Gender and Level of Co-contraction on Elbow and Shoulder Rotational Stiffness and Damping in the Impulsively End-Loaded Upper Extremity

Whether an arm will buckle under an impulsive end-load should partly depend on the elastic and viscous properties of the pretensed arm muscles. In measuring these properties we hypothesized that neither age, gender, nor muscle pre-contraction level would affect the bilinear elbow or shoulder lumped rotational stiffness or damping parameters in the impulsively end-loaded upper extremity of 38 healthy men and women. Subjects were instructed to preactivate triceps to either 25, 50 or 75% of maximum myoelectric activity levels. Then a standardized impulsive end-load was applied via a 6-axis load cell to the wrist of the slightly flexed arm in the prone posture. Arm kinematic responses were acquired at 280 Hz and an inverse dynamics analysis was used to estimate the bilinear rotational stiffnesses and damping parameters at the elbow and shoulder. The results show that pre-contraction level affected normalized joint rotational stiffness and damping coefficients (p < 0.02). Age affected the initial stiffness for the elbow (p < 0.05), and gender affected that of the shoulder in the sagittal plane (p < 0.006). Arm muscle strength was positively related to normalized stiffness at the elbow, but not the shoulder. We conclude that age, gender and pre-contraction level each affect the viscoelastic behavior of the end-loaded upper extremity in healthy adults.

Contact areas of the scaphoid and lunate with the distal radius in neutral and extension: correlation of falling strategies and distal radial anatomy

The functional neutral of wrist movement is about 10° extension yet the distal radius has a volar tilt. This has not previously been explained. Assuming that the contact area between the carpus and the distal radius increased in wrist extension this would also help stabilize the carpus on the distal radius in positions where typically there is greater loading. To test this hypothesis we reconstructed three-dimensional structures of the carpal bones and distal radius using computed tomography scans of 13 normal wrists. The contact areas of the scaphoid with the distal radius were measured and were found progressively increased from flexion 20°, neutral, extension 20°, to extension 40°. The maximal increases in the contact area of the scaphoid and the distal radius was at full wrist extension. No significant changes in the contact areas of the lunate with the distal radius were found between the different positions. The contact characteristics provide greater stability to the carpus on the distal radius, and to help spread forces from impact to the wrist reducing the transmitted peak forces and thus the risk of distal radius and carpal injuries.

Measurement of the Effect of Playground Surface Materials on Hand Impact Forces During Upper Limb Fall Arrests

Distal radius fractures are common on playgrounds. Yet current guidelines for the selection of playground surface materials are based only on protection against fall-related head injuries. We conducted “torso release” experiments to determine how common playground surface materials affect impact force applied to the hand during upper limb fall arrests. Trials were acquired for falls onto a rigid surface, and onto five common playground surface materials: engineered wood fiber, gravel, mulch, rubber tile, and sand. Measures were acquired for arm angles of 20 and 40 degrees from the vertical. Playground surface materials influenced the peak resultant and vertical force (P< .001), but not the peak horizontal force (P= .159). When compared with the rigid condition, peak resultant force was reduced 17% by sand (from 1039 to 864 N), 16% by gravel, 7% by mulch, 5% by engineered wood fiber, and 2% by rubber tile. The best performing surface provided only a 17% reduction in peak resultant force. These results help to explain the lack of convincing evidence from clinical studies on the effectiveness of playground surface materials in preventing distal radius fractures during playground falls, and highlight the need to develop playground surface materials that provide improved protection against these injuries.

Age and gender effects on the proximal propagation of an impulsive force along the adult human upper extremity

We tested the null hypotheses that neither age, gender nor muscle pre-cocontraction state affect the latencies of changes in upper extremity kinematics or elbow muscle activity following an impulsive force to the hand. Thirty-eight healthy young and older adult volunteers lay prone on an apparatus with shoulders flexed 75° and arms slightly flexed. The non-dominant hand was subjected to three trials of impulsive loading with arm muscles precontracted to 25, 50, or 75% of maximum pre-cocontraction levels. Limb kinematic data and upper extremity electromyographic (EMG) activity were acquired. The results showed that pre-cocontraction muscle level (p < 0.001) and gender (p < 0.05 for wrist and shoulder) affected joint displacement onset times and age affected EMG onset times (p < 0.05). The peak applied force (F1) occurred a mean (± SD) 27 (± 2) ms after impact. The latencies for the wrist, elbow, and shoulder displacements were 21 ± 3, 29 ± 5, and 34 ± 7 ms, respectively. Because the latencies for elbow flexion and lateral triceps EMG were 23 ± 5 and 84 ± 8 ms, respectively, muscle pre-activation rather than stretch reflexes prevent arm buckling under impulsive end loads.

Stiffness and ultimate load of osseointegrated prosthesis fixations in the upper and lower extremity

Background

Techniques for the skeletal attachment of amputation-prostheses have been developed over recent decades. This type of attachment has only been performed on a small number of patients. It poses various potential advantages compared to conventional treatment with a socket, but is also associated with an increased risk of bone or implant-bone interface fracture in the case of a fall. We therefore investigated the bending stiffness and ultimate bending moment of such devices implanted in human and synthetic bones.

Methods

Eight human specimens and 16 synthetic models of the proximal femora were implanted with lower extremity prostheses and eight human specimens and six synthetic humeri were implanted with upper extremity prostheses. They were dissected according to typical amputation levels and underwent loading in a material testing machine in a four-point bending setup. Bending stiffness, ultimate bending moment and fracture modes were determined in a load to failure experiment. Additionally, axial pull-out was performed on eight synthetic specimens of the lower extremity.

Results

Maximum bending moment of the synthetic femora was 160.6±27.5 Nm, the flexural rigidity of the synthetic femora was 189.0±22.6 Nm². Maximum bending moment of the human femora was 100.4±38.5 Nm, and the flexural rigidity was 137.8±29.4 Nm². The maximum bending moment of the six synthetic humeri was 104.9±19.0 Nm, and the flexural rigidity was 63.7±3.6 Nm². For the human humeri the maximum bending moment was 36.7±11.0 Nm, and the flexural rigidity at was 43.7±10.5 Nm². The maximum pull-out force for the eight synthetic femora was 3571±919 N.

Conclusion

Significant differences were found between human and synthetic specimens of the lower and upper extremity regarding maximum bending moment, bending displacement and flexural rigidity. The results of this study are relevant with respect to previous finding regarding the load at the interfaces of osseointegrated prosthesis fixation devices and are crucial for the development of safety devices intended to protect the bone-implant interface from damaging loadings.

Prevention of fall-related injuries in 7-year-old to 12-year-old children: a cluster randomised controlled trial

INTRODUCTION

To counteract the recently observed increase in forearm fractures in children worldwide, an educational programme to improve fall skills was developed. In this 8-week programme children learned basic martial arts falling techniques in their physical education classes. In this study, the effectiveness of this educational programme to improve fall skills was evaluated.

METHODS

A cluster randomised controlled trial was conducted in 33 primary schools. The intervention group received the educational programme to improve falling skills during their physical education (PE) classes whereas the control group received their regular PE curriculum. At baseline (October 2009) and follow-up (May 2010), a questionnaire was completed by the children about their physical activity behaviours. Furthermore, fall-related injuries were registered continuously during an entire school-year.

RESULTS

A total of 36 incident injuries was reported in the intervention group, equalling an injury incidence density (IID) of 0.14 fall-related injuries per 1000 h of physical activity (95% CI 0.09 to 0.18). In contrast, 96 injuries were reported by the control group corresponding to an IID of 0.26 (95% CI 0.21 to 0.32). However, because intracluster correlation was high (ICC=0.46), differences in injury incidence were not statistically significant. When activity level was taken into account, a trend was shown suggesting that the 'falling is a sport' programme was effective in decreasing falling-related injury risk, but only in the least active children.

DISCUSSION AND CONCLUSION

Although results did not reach significance because of strong clustering effects, a trend was found suggesting that a school-based educational programme to improve falling skills may be more beneficial for the prevention of falling-related injuries in children with low levels of habitual physical activity.

ENERGY ANALYSIS OF DIFFERENT TRUNK TILTING ANGLES ON JOINT LOADING DURING FALL ON AN OUTSTRETCHED HAND

From previous researches, studies on the forward fall had focused on the relationship between the joint loading and position of the forearm and elbow. Previous studies also stressed the importance of energy absorption by the shoulder and elbow during the forward fall. However, the effects of different tilting angles on joint loading of the upper extremity had not been presented. This study investigated the effects of different tilting angles on joint loading of the upper extremity during fall on an outstretched hand. The absorbed energy at Ts, T1, T2 and Te were analyzed. Ten healthy young males were selected in this study. Subjects were adjusted to different trunk tilting angles of 0°, 10°, 20° and 30°with a custom-made suspension system with an outstretched hand of 5 cm height above the ground. The expert vision motion system with 6 CCD cameras and one force plate were used to collect kinetics and kinematics data. The results showed that shoulder would absorb the most impact energy and followed by wrist and elbow. The time period at T2 to Te absorbed more energy in every joint.

Characterizing the mechanical parameters of forward and backward falls as experienced in snowboarding

Wrist injuries are frequently observed after falls in snowboarding. In this study, laboratory experiments mimicking forward and backward falls were analysed. In six different falling scenarios, participants self-initiated falls from a static initial position. Eighteen volunteers conducted a total of 741 trials. Measurements were taken for basic parameters describing the kinematics as well as the biomechanical loading during impact, such as impact force, impact acceleration, and velocity. The effective mass affecting the wrist in a fall also was determined. The elbow angle at impact showed a more extended arm in backward falls compared to forward falls, whereas the wrist angle at impact remained similar in forward and backward falls. The study results suggest a new performance standard for wrist guards, indicating the following parameters to characterize an impact: an effective mass acting on one wrist of 3-5 kg, an impact angle of 75 degrees of the forearm relative to the ground, and an impact velocity of 3 m/s.

Non-elite gymnastics participation is associated with greater bone strength, muscle size, and function in pre- and early pubertal girls

Recent reports indicate an increase in forearm fractures in children. Bone geometric properties are an important determinant of bone strength and therefore fracture risk. Participation in non-elite gymnastics appears to contribute to improving young girls' musculoskeletal health, more specifically in the upper body.

INTRODUCTION

The primary aim of this study was to determine the association between non-elite gymnastics participation and upper limb bone mass, geometry, and strength in addition to muscle size and function in young girls.

METHODS

Eighty-eight pre- and early pubertal girls (30 high-training gymnasts [HGYM, 6-16 hr/ wk], 29 low-training gymnasts [LGYM, 1-5 h r/wk] and 29 non-gymnasts [NONGYM]), aged 6-11 years were recruited. Upper limb lean mass, BMD and BMC were derived from a whole body DXA scan. Forearm volumetric BMD, bone geometry, estimated strength, and muscle CSA were determined using peripheral QCT. Upper body muscle function was investigated with muscle strength, explosive power, and muscle endurance tasks.

RESULTS

HGYM showed greater forearm bone strength compared with NGYM, as well as greater arm lean mass, BMC, and muscle function (+5% to +103%, p < 0.05). LGYM displayed greater arm lean mass, BMC, muscle power, and endurance than NGYM (+4% to +46%, p < 0.05); however, the difference in bone strength did not reach significance. Estimated fracture risk at the distal radius, which accounted for body weight, was lower in both groups of gymnasts. Compared with NONGYM, HGYM tended to show larger skeletal differences than LGYM; yet, the two groups of gymnasts only differed for arm lean mass and muscle CSA.

CONCLUSION

Non-elite gymnastics participation was associated with musculoskeletal benefits in upper limb bone geometry, strength and muscle function. Differences between the two gymnastic groups emerged for arm lean mass and muscle CSA, but not for bone strength.

Reliability of Impact Forces, Hip Angles and Velocities during Simulated Forward Falls Using a Novel Propelled Upper Limb Fall ARrest Impact System (PULARIS)

Previous forward fall simulation methods have provided good kinematic and kinetic data, but are limited in that they have started the falls from a stationary position and have primarily simulated uni-directional motion. Therefore, a novel Propelled Upper Limb fall ARest Impact System (PULARIS) was designed to address these issues during assessments of a variety of fall scenarios. The purpose of this study was to present PULARIS and evaluate its ability to impact the upper extremities of participants with repeatable velocities, hand forces and hip angles in postures and with vertical and horizontal motion consistent with forward fall arrest. PULARIS consists of four steel tubing crossbars in a scissor-like arrangement that ride on metal trolleys within c-channel tracks in the ceiling. Participants are suspended beneath PULARIS by the legs and torso in a prone position and propelled horizontally via a motor and chain drive until they are quick released, and then impact floor-mounted force platforms with both hands. PULARIS velocity, hip angles and velocities and impact hand forces of ten participants (five male, five female) were collected during three fall types (straight-arm, self-selected and bent-arm) and two fall heights (0.05 m and 0.10 m) to assess the reliability of the impact conditions provided by the system. PULARIS and participant hip velocities were found to be quite repeatable (mean ICC = 0.81) with small between trial errors (mean = 0.03 m/s). The ratio of horizontal to vertical hip velocity components (∼0.75) agreed well with previously reported data (0.70-0.80). Peak vertical hand impact forces were also found to be relatively consistent between trials with a mean ICC of 0.73 and mean between trial error of 13.4 N. Up to 83% of the horizontal hand impact forces displayed good to excellent reliability (ICC > 0.6) with small between trial differences. Finally, the ICCs for between trial hip angles were all classified as good to excellent. Overall, PULARIS is a reliable method and is appropriate for studying the response of the distal upper extremity to impact loading during non-stationary, multi-directional movements indicative of a forward fall. This system performed well at different fall heights, and allows for a variety of upper and lower extremity, and hip postures to be tested successfully in different landing scenarios consistent with elderly and sport-related falls.

The relationship between anterior tibial acceleration, tibial slope, and ACL strain during a simulated jump landing task

BACKGROUND

Knee joint morphology contributions to anterior cruciate ligament (ACL) loading are rarely considered in the injury prevention model. This may be problematic as the knee mechanical response may be influenced by these underlying morphological factors. The goal of the present study was to explore the relationship between posterior tibial slope (which has been recently postulated to influence knee and ACL loading), impact-induced anterior tibial acceleration, and resultant ACL strain during a simulated single-leg landing.

METHODS

Eleven lower limb cadaveric specimens from female donors who had had a mean age (and standard deviation) of 65 ± 10.5 years at the time of death were mounted in a testing apparatus to simulate single-limb landings in the presence of pre-impact knee muscle forces. After preconditioning, specimens underwent five impact trials (mean impact force, 1297.9 ± 210.6 N) while synchronous three-dimensional joint kinetics, kinematics, and relative anteromedial bundle strain data were recorded. Mean peak tibial acceleration and anteromedial bundle strain were quantified over the first 200 ms after impact. These values, along with radiographically defined posterior tibial slope measurements, were submitted to individual and stepwise linear regression analyses.

RESULTS

The mean peak anteromedial bundle strain (3.35% ± 1.71%) was significantly correlated (r = 0.79; p = 0.004; ß = 0.791) with anterior tibial acceleration (8.31 ± 2.77 m/s-2), with the times to respective peaks (66 ± 7 ms and 66 ± 4 ms) also being significantly correlated (r = 0.82; p = 0.001; ß = 0.818). Posterior tibial slope (mean, 7.6° ± 2.1°) was significantly correlated with both peak anterior tibial acceleration (r = 0.75; p = 0.004; ß = 0.786) and peak anteromedial bundle strain (r = 0.76; p = 0.007; ß = 0.759).

CONCLUSIONS

Impact-induced ACL strain is directly proportional to anterior tibial acceleration, with this relationship being moderately dependent on the posterior slope of the tibial plateau.

The effects of gender, level of co-contraction, and initial angle on elbow extensor muscle stiffness and damping under a step increase in elbow flexion moment

Flexion buckling of an arm under the large ground reaction loads associated with arresting a fall to the ground increases the risk for head and thorax injuries. Yet, the factors that determine the arm buckling load remain poorly understood. We tested the hypothesis in 18 healthy young adults that neither gender, triceps co-contraction level (i.e., 25, 50, or 75% MVC) nor elbow angle would affect the rotational stiffness and damping resistance to step changes in elbow flexion loading. Data on the step response were gathered using optoelectronic markers (150 Hz) and myoelectric activity measurements (2 kHz), and an inverse dynamics analysis was used to estimate elbow extensor stiffness and damping coefficients. A repeated-measures analysis of variance showed that gender (p = 0.032), elbow flexion angle and co-contraction level (both p < 0.001) affected stiffness, but only the latter affected the damping coefficient (p = 0.035). At 25° of initial elbow flexion angle and maximum co-contraction, female stiffness and damping coefficients were 18 and 30% less, respectively, than male values after normalization by body height and weight. We conclude that the maximum extensor rotational stiffness and damping at the elbow is lower in women than in men of the same body size, and varies with triceps co-contraction level and initial elbow angle.