Influence of nonlinear soft tissue modeling on the external and internal forces during lateral hip impacts

Advancing Osteoporosis Assessment Through a Numerical Study Utilizing Ultrasonic Waves in Femur Bone Evaluation

OBJECTIVE

Osteoporosis, a musculoskeletal condition characterized by bone density loss, significantly heightens the risk of fractures. Early detection of this condition is paramount in both its prevention and effective treatment. Traditionally, osteoporosis diagnosis relies heavily on dual X-ray absorptiometry. However, this research demonstrates an initiative by utilizing quantitative ultrasound as a cost-effective, noninvasive alternative, particularly advantageous in certain scenarios.

METHODS

By applying the finite element method, we simulate ultrasound propagation within intricate femur head models, incorporating both healthy and osteoporotic conditions. Through meticulous analysis, we unveil novel speed-based and amplitude-based indices derived from ultrasound signals, offering insights of high resolution into bone evaluation.

RESULTS

Our findings illuminate a paradigm shift: as osteoporosis advances, there is a discernible decrease in speed of sound values, while ultrasound amplitude exhibits intriguing fluctuations, dependent on intricate tissue interactions such as diverse acoustic impedance at tissues' interface and echo reflections within the bone models.

CONCLUSIONS

The approach used in this study promises to reshape osteoporosis assessment, paving the way to revolutionize prevention and treatment strategies. The associated results of our study also could open up new avenues for investigating ultrasound propagation in three-dimensional bone models.

Sex differences in in vivo soft tissue compressive properties of the human hip in young adults: a comparison between passive vs active state

Hip injuries are a frequent outcome of falls. Studying the biomechanics of hip injuries requires a comprehensive understanding of soft tissue properties and their responses to external loads. Particularly, muscle activity is crucial in arresting a fall and is likely to affect soft tissue properties. Failing to consider muscle activation might result in incorrect conclusions regarding the processes underlying injuries and the efficacy of preventive strategies. Soft tissue response is also affected by loading rate, sex, and mechanical testing protocols, highlighting the need for precise experimental design and interpretation. Forty individuals (age = 25.53 ± 3.41 years) were recruited (20 males and 20 females) to investigate the hip soft tissue response during a high-speed cyclic indentation testing. Muscle activity was recorded using electromyography (EMG) and soft tissue thickness was measured using ultrasound imaging. Peak force, energy, and tissue stiffness were measured using tissue indentation. The hip soft tissue exhibited hysteresis and was nonlinear during loading. Sex differences in trochanteric soft tissue stiffness resulted in males having 38% higher peak force than females and absorbed energy was 32% higher in the active state than the passive state (in combined participants). Characterizing the range of tissue responses for in vivo hip soft tissues emphasizes the natural variability in healthy human tissues and the need to consider the range of tissue behaviors in models, not just the average response. Both sex and muscle activation increased tissue mechanical variability and need to be considered in future physical and computational models of hip impact.

Infant skull fractures align with the direction of bone mineralization

The geometry and mechanical properties of infant skull bones differ significantly from those of adults. Over the past decades, debates surrounding whether fractures in infants come from deliberate abuse or accidents have generated significant impacts in both legal and societal contexts. However, the etiology of infant skull fractures remains unclear, which motivates this study with two main components of work. Firstly, we present and implement a progressive unidirectional fabric composite damage model for infant cranial vaults to represent ductile and anisotropic properties-two typical mechanical characteristics of infant skulls. Secondly, we hypothesize that these intrinsic material properties cause injuries perpendicular to the fiber direction to dominate infant skull fractures, resulting in fracture lines that align with the direction of mineralization in the infant skull. The material model and the finite element (FE) model were verified hierarchically, and this hypothesis was verified by reconstructing two legal cases with known fall heights and implementing the above damage model into CT-based subject-specific infant FE head models. We discovered that the infant skull is more susceptible to injuries within planes perpendicular to the mineralization direction because of the anisotropic mechanical property caused by the direction of mineralization, leading to infant skull fractures aligning with the mineralization direction. Our findings corroborated the several previously reported observations of fractures on cranial vaults, demonstrating that these fractures were closely associated with sutures and oriented along the mineralization direction, and revealed the underlying mechanisms of infant skull fracture pattern. The modeling methods and results of this study will serve as an anchor point for more rigorous investigations of infant skull fractures, ultimately aiming to provide convincing biomechanical evidence to aid forensic diagnoses of abusive head trauma.

Effectiveness of energy absorbing floors in reducing hip fractures risk among elderly women during sideways falls

Falls among the elderly cause a huge number of hip fractures worldwide. Energy absorbing floors (EAFs) represent a promising strategy to decrease impact force and hip fracture risk during falls. Femoral neck force is an effective predictor of hip injury. However, the biomechanical effectiveness of EAFs in terms of mitigating femoral neck force remains largely unknown. To address this, a whole-body computational model representing a small-size elderly woman with a biofidelic representation of the soft tissue near the hip region was employed in this study, to measure the attenuation in femoral neck force provided by four commercially available EAFs (Igelkott, Kradal, SmartCells, and OmniSports). The body was positioned with the highest hip force with a -10∘ trunk angle and +10∘ anterior pelvis rotation. At a pelvis impact velocity of 3 m/s, the peak force attenuation provided by four EAFs ranged from 5% to 19%. The risk of hip fractures also demonstrates a similar attenuation range. The results also exhibited that floors had more energy transferred to their internal energy demonstrated greater force attenuation during sideways falls. By comparing the biomechanical effectiveness of existing EAFs, these results can improve the floor design that offers better protection performance in high-fall-risk environments for the elderly.

Finite element analysis of hip fracture risk in elderly female: The effects of soft tissue shape, fall direction, and interventions

This study investigates the effects of fall configurations on hip fracture risk with a focus on pelvic soft tissue shape. This was done by employing a whole-body finite element (FE) model. Soft tissue thickness around the pelvis was measured using a standing CT system, revealing a trend of increased trochanteric soft tissue thickness with higher BMI and younger age. In the lateroposterior region from the greater trochanter, the soft tissues of elderly females were thin with a concave shape. Based on the THUMS 5F model, an elderly female FE model with a low BMI was developed by morphing the soft tissue shape around the pelvis based on the CT data. FE simulation results indicated that the lateroposterior fall led to a higher femoral neck force for the elderly female model compared to the lateral fall. One reason may be related to the thin soft tissue of the pelvis in the lateroposterior region. Additionally, the effectiveness of interventions that can help mitigating hip fractures in lateroposterior falls on the thigh-hip and hip region was assessed using the elderly female model. The attenuation rate of the femoral neck force by the hip protector was close to zero in the thigh-hip fall and high in the hip fall, whereas the attenuation rate of the compliant floor was high in both falls. This study highlights age-related changes in the soft tissue shape of the pelvis in females, particularly in the lateroposterior regions, which may influence force mitigation for the hip joint during lateroposterior falls.

Evaluation of injury threshold from the number of rib fracture for predicting pulmonary injuries in blunt chest trauma

Background

Blunt chest trauma is a common presentation in emergency departments. The relationship between bone fractures and organ injuries has not been studied in detail. The purpose of this study was to examine the degree of external force represented by the number of rib fractures that causes lung injury in blunt chest trauma.

Patients and methods

This study was performed retrospectively using trauma patients who received medical examinations in a single university hospital emergency center between April 2015 and March 2020. We examined the association between the number of rib fractures and pulmonary damage using multivariable regression analysis and considered the relationship between rib fracture location and each type of lung injury.

Results

A total of 317 patients were included. The mean age was 63.1 years, 65.0% were male, and traffic accidents were the most common mechanism of injury (55.8%). The number of mean rib fractures was 4.0, and the mean Injury Severity Score was 11.3. The number of rib fractures was associated with an increased risk of pulmonary injuries: pulmonary contusion (odds ratio [OR] 1.30, 95% confidence interval [CI] 1.14-1.48, p < 0.05); hemothorax (OR 1.22, 95% CI 1.08-1.38, p < 0.05); pneumothorax (OR 1.15, 95% CI 1.02-1.30, p < 0.05); and hemopneumothorax (OR 1.14, 95% CI 1.01-1.28, p < 0.05). In addition, bilateral rib fractures were associated with fractures of the superior ribs more often and more severely, but were not associated with the occurrence of each type of lung injury.

Conclusion

The number of rib fractures was associated with an increased risk of pulmonary injuries. In addition, the type of pulmonary injury could be predicted from the number of rib fractures in blunt chest trauma.

Upright trunk and lateral or slight anterior rotation of the pelvis cause the highest proximal femur forces during sideways falls

Whole-body models are historically developed for traffic injury prevention, and they are positioned accordingly in the standing or sitting configuration representing pedestrian or occupant postures. Those configurations are appropriate for vehicle accidents or pedestrian-vehicle accidents; however, they are uncommon body posture during a fall accident to the ground. This study aims to investigate the influence of trunk and pelvis angles on the proximal femur forces during sideways falls. For this purpose, a previously developed whole-body model was positioned into different fall configurations varying the trunk and pelvis angles. The trunk angle was varied in steps of 10° from 10 to 80°, and the pelvis rotation was changed every 5° from -20° (rotation toward posterior) to +20° (rotation toward anterior). The simulations were performed on a medium-size male (177 cm, 76 kg) and a small-size female (156 cm, 55 kg), representative for elderly men and women, respectively. The results demonstrated that the highest proximal femur force measured on the femoral head was reached when either male or female model had a 10-degree trunk angle and +10° anterior pelvis rotation.

Analysis of loading to the hip joint in fall using whole-body FE model

Hip fractures caused by falls are important health problems for the elderly. Many studies used finite element (FE) models of the femur and its surroundings to evaluate the hip fracture risk during the impact phase in a fall. In this study, the whole-body human FE model (THUMS) of a small female was applied from the descent to the impact phase in a fall to understand the effect of the whole body. Brosh's material model was used for the soft tissue of the hip. A low-BMI and high-BMI model were developed based on THUMS (middle-BMI). For the middle-BMI model, the torso angle and the pelvis impact velocity were 45.2° and 2.62 m/s at the time of pelvis impact. The effective mass changed with time, and was 18.3 kg when the femoral neck force was maximum. The femoral neck force was 2.11 kN for the low-BMI model. The femoral neck forces when wearing a soft and a hard hip protector, and when falling on an energy-absorbing floor were compared for the FE models of human and a hip protector testing system. Though the force attenuation of the protective devices was 32.0-44.3 % in the testing system, the force attenuation in the middle-BMI was 0.1-22.2 %. In the low-BMI model, the attenuation of the soft protector was limited (4.2 %) because the hip protector protruded from the outer surface, so the contact force was concentrated at the hip region. This research suggests the importance of including the whole body to evaluate the hip fracture risk.