A Finite Element Model of the Foot/Ankle to Evaluate Injury Risk in Various Postures

A finite element model of human hindfoot and its application in supramalleolar osteotomy

BACKGROUND

The majority of the ankle osteoarthritis cases are posttraumatic and affect younger patients with a longer projected life span. Hence, joint-preserving surgery, such as supramalleolar osteotomy becomes popular among young patients, especially those with asymmetric arthritis due to alignment deformities. However, there is a lack of biomechanical studies on postoperative evaluation of stress at ankle joints. We aimed to construct a verifiable finite element model of the human hindfoot, and to explore the effect of different osteotomy parameters on the treatment of varus ankle arthritis.

METHODS

The bones of the hindfoot are reconstructed using normal CT tomography data from healthy volunteers, while the cartilages and ligaments are determined from the literature. The finite element calculation results are compared with the weight-bearing CT (WBCT) data to validate the model. By setting different model parameters, such as the osteotomy height (L) and the osteotomy distraction distance (h), the effects of different surgical parameters on the contact stress of the ankle joint surface are compared.

FINDINGS

The alignment and the deformation of hindfoot bones as determined by the finite element analysis aligns closely with the data obtained from WBCT. The maximum contact stress of the ankle joint surface calculated by this model increases with the increase of the varus angle. The maximum contact stresses as a function of the L and h of the ankle joint surface are determined.

INTERPRETATION

The relationship between surgical parameters and stress at the ankle joint in our study could further help guiding the planning of the supramalleolar osteotomy according to the varus/valgus alignment of the patients.

Single-cell RNA sequencing reveals differences between force application and bearing in ankle cartilage

Chondrocytes are the major functional elements of articular cartilage. Force has been demonstrated to influence the structure and function of articular cartilage and chondrocytes. Therefore, it is necessary to evaluate chondrocytes under different force conditions to gain deep insight into chondrocyte function. Six cartilage tissues from the distal tibia (referred to as the AT group) and five cartilage tissues from the trochlear surface of the talus (referred to as the ATa group) were obtained from 6 donors who had experienced fatal accidents. Single-cell RNA sequencing was used on these samples. A total of 149,816 cells were analyzed. Nine chondrocyte subsets were ultimately identified. Pseudotime analyses, enrichment analyses, cell-cell interaction studies, and single-cell regulatory network inference and clustering were performed for each cell type, and the differences between the AT and ATa groups were analyzed. Immunohistochemical staining was used to verify the existence of each chondrocyte subset and its distribution. The results suggested that reactive oxygen species related processes were active in the force-applied region, while tissue repair processes were common in the force-bearing region. Although the number of prehypertrophic chondrocytes was small, these chondrocytes seemed to play an important role in the ankle.

Clinically useful finite element models of the natural ankle - A review

BACKGROUND

Biomechanical simulation of the foot and ankle complex is a growing research area but compared to simulation of joints such as hip and knee, it has been under investigated and lacks consistency in research methodology. The methodology is variable, data is heterogenous and there are no clear output criteria. Therefore, it is very difficult to correlate clinically and draw meaningful inferences.

METHODS

The focus of this review is finite element simulation of the native ankle joint and we will explore: the different research questions asked, the model designs used, ways the model rigour has been ensured, the different output parameters of interest and the clinical impact and relevance of these studies.

FINDINGS

The 72 published studies explored in this review demonstrate wide variability in approach. Many studies demonstrated a preference for simplicity when representing different tissues, with the majority using linear isotropic material properties to represent the bone, cartilage and ligaments; this allows the models to be complex in another way such as to include more bones or complex loading. Most studies were validated against experimental or in vivo data, but a large proportion (40%) of studies were not validated at all, which is an area of concern.

INTERPRETATION

Finite element simulation of the ankle shows promise as a clinical tool for improving outcomes. Standardisation of model creation and standardisation of reporting would increase trust, and enable independent validation, through which successful clinical application of the research could be realised.

Biomechanical Analysis of Foot–Ankle Complex during Jogging with Rearfoot Strike versus Forefoot Strike

Background and Aim. In order to reduce foot and ankle injuries induced by jogging, two-foot strike patterns, rearfoot strike (RFS), and forefoot strike (FFS), were adopted and compared. First, RFS jogging and FFS jogging were experimentally studied, so as to acquire kinematic and kinetic data, including foot strike angle, knee flexion angle, and ground reaction force (GRF). Then, a 3D finite element model of foot–ankle complex was reconstructed from the scanned 2D-stacked images. Biomechanical characteristics, including plantar pressure, stress of metatarsals, midfoot bone, calcaneus and cartilage, and tensile force of plantar fascia and ligaments, were obtained. The results showed that RFS jogging and FFS jogging had a similar change trend and a close peak value of GRF. Since possessing more momentum in the push stage and less momentum in the brake stage, FFS jogging could be in favor of a higher jogging speed. However, FFS jogging produced larger metatarsal stress in the 5th metatarsal and much larger tensile force of plantar fascia, which might cause metatarsal fracture and heel pain. While RFS jogging produced larger plantar pressure in the hindfoot area, larger calcaneus stress, and much larger tarsal navicular stress, which might cause heel tissue injury, calcaneus damage, and stress fracture of naviculocuneiform joint. In addition, talocrural and talocalcaneal joint cartilage could bear jogging loads, as the peak contact pressure were both small in RFS jogging and FFS jogging. Therefore, jogging with rearfoot or FFS pattern should be chosen according to the health condition of foot–ankle parts.

Establishment of a finite element model of supination-external rotation ankle joint injury and its mechanical analysis

By establishing a three-dimensional finite element model of ankle injury arising from supination and external rotation, the stress characteristics of the posterior malleolar surface can be obtained, and analysis of the corresponding stress on the lateral ankle can be conducted. Thin-layer computed tomography images of normal ankle joint in the supination and external rotation nonweight-bearing states was selected, to construct a three-dimensional data model of each ankle joint. A load was applied to examine different ankle joint stress values and pressure distributions on the surface of the posterior ankle joint. A 600 N vertical compressive and 10 Nm internal rotation load was applied in Stage III (removing the anterior tibiofibular ligament and the posterior tibiofibular ligament) of SER (supination-external rotation). When the lateral malleolar was intact, the maximum stress (132.7 MPa) was located at the point of attachment of the posterior tibiofibular ligament to the fibula, and the maximum pressure of the posterior malleolar surface was lower than 4.505 MPa. When a lateral malleolar fracture was present, the maximum stress (82.72 MPa) was located on the fibular fracture surface, and the maximum pressure of the posterior malleolar surface was 8.022 MPa. This study shows that reconstruction of the lateral malleolus in supination-external rotation ankle injuries significantly affects the stress distribution at the posterior malleolar joint surface. Through this reconstruction, the pressure distribution of the posterior malleolar joint surface can be significantly reduced.

In-Situ Fracture Tolerance of the Metatarsals During Quasi-Static Compressive Loading of the Human Foot

Accidental foot injuries including metatarsal fractures commonly result from compressive loading. The ability of personal protective equipment to prevent these traumatic injuries depends on the understanding of metatarsal fracture tolerance. However, the in situ fracture tolerance of the metatarsals under direct compressive loading to the foot's dorsal surface remains unexplored, even though the metatarsals are the most commonly fractured bones in the foot. The goal of this study was to quantify the in situ fracture tolerance of the metatarsals under simulated quasi-static compressive loading. Fresh-frozen cadaveric feet (n = 10) were mounted into a testing apparatus to replicate a natural stance and loaded at the midmetatarsals with a cylindrical bar to simulate a crushing-type injury. A 900 N compressive force was initially applied, followed by 225 N successive load increments. Specimens were examined using X-ray imaging between load increments to assess for the presence of metatarsal fractures. Descriptive statistics were conducted for metatarsal fracture force and deformation. Pearson correlation tests were used to quantify the correlation between fracture force with age and body mass index (BMI). The force and deformation at fracture were 1861 ± 642 N (mean ± standard deviation) and 22.6 ± 3.4 mm, respectively. Fracture force was correlated with donor BMI (r = 0.90). Every fractured specimen experienced a transverse fracture in the second metatarsal. New biomechanical data from this study further quantify the metatarsal fracture risk under compressive loading and will help to improve the development and testing of improved personal protective equipment for the foot to avoid catastrophic injury.

A Review of Finite Element Models of Ligaments in the Foot and Considerations for Practical Application

PURPOSE

Finite element (FE) modeling has been used as a research tool for investigating underlying ligaments biomechanics and orthopedic applications. However, FE models of the ligament in the foot have been developed with various configurations, mainly due to their complex 3D geometry, material properties, and boundary conditions. Therefore, the purpose of this review was to summarize the current state of finite element modeling approaches that have been used in the ?eld of ligament biomechanics, to discuss their applicability to foot ligament modeling in a practical setting, and also to acknowledge current limitations and challenges.

METHODS

A comprehensive literature search was performed. Each article was analyzed in terms of the methods used for: (a) ligament geometry, (b) material property, (c) boundary and loading condition related to its application, and (d) model verification and validation.

RESULTS

Of the reviewed studies, 80% of the studies used simplified representations of ligament geometry, the non-linear mechanical behavior of ligaments was taken into account in only 19.2% of the studies, 33% of included studies did not include any kind of validation of the FE model.

CONCLUSION

Further refinement in the functional modeling of ligaments, the micro-structure level characteristics, nonlinearity, and time-dependent response, may be warranted to ensure the predictive ability of the models.

In Silico Finite Element Analysis of the Foot Ankle Complex Biomechanics: A Literature Review

Computational approaches, especially finite element analysis (FEA), have been rapidly growing in both academia and industry during the last few decades. FEA serves as a powerful and efficient approach for simulating real-life experiments, including industrial product development, machine design, and biomedical research, particularly in biomechanics and biomaterials. Accordingly, FEA has been a "go-to" high biofidelic software tool to simulate and quantify the biomechanics of the foot-ankle complex, as well as to predict the risk of foot and ankle injuries, which are one of the most common musculoskeletal injuries among physically active individuals. This paper provides a review of the in silico FEA of the foot-ankle complex. First, a brief history of computational modeling methods and finite element (FE) simulations for foot-ankle models is introduced. Second, a general approach to build an FE foot and ankle model is presented, including a detailed procedure to accurately construct, calibrate, verify, and validate an FE model in its appropriate simulation environment. Third, current applications, as well as future improvements of the foot and ankle FE models, especially in the biomedical field, are discussed. Finally, a conclusion is made on the efficiency and development of FEA as a computational approach in investigating the biomechanics of the foot-ankle complex. Overall, this review integrates insightful information for biomedical engineers, medical professionals, and researchers to conduct more accurate research on the foot-ankle FE models in the future.

Analysis of Foot-Ankle-Leg Injuries in Various Under-Foot Impact Loading Environments with a Human Active Lower Limb (HALL) Model

Lower limb injuries caused by under-foot impacts often appear in sport landing, automobile collision, and anti-vehicular landmine blasts. The purpose of the present study was to evaluate a foot-ankle-leg model of the Human Active Lower Limb (HALL) model, and used it to investigate lower leg injury responses in different under-foot loading environments to provide a theoretical basis for the design of physical dummies adapted to multiple loading conditions. The model was first validated in allowable rotation loading conditions, like dorsiflexion, inversion/eversion, and external rotation. Then, its sensitivity to loading rates and initial postures was further verified through experimental data concerning both biomechanical stiffness and injury locations. Finally, the model was used to investigate the biomechanical responses of the foot-ankle-leg region in different under-foot loading conditions covering the loading rate from sport landing to blast impact. The results showed that from -15° plantarflexion to 30° dorsiflexion, the neutral posture always showed the largest tolerance, and more than 1.5 times tolerance gap was achieved between neutral posture and dorsiflexion 30°. Under-foot impacts from 2 m/s to 14 m/s, the peak tibia force increased at least 1.9 times in all postures. Thus, we consider that it is necessary to include initial posture and loading rate factors in the definition of the foot-ankle-leg injury tolerance for under-foot impact loading.

Preliminary study on the mechanisms of ankle injuries under falling and impact conditions based on the THUMS model

Ankle injuries are common in forensic practice, which are mainly caused by falling and traffic accidents. Determining the mechanisms and manners of ankle injuries is a critical and challenging problem for forensic experts. The identification of the injury mechanism is still experience-based and strongly subjective. There also lacks systematic research in current practice. In our study, based on the widely used Total Human Model of Safety 4.0 (THUMS 4.0), we utilized the finite element (FE) method to simulate ankle injuries caused by falls from different heights (5 m, 10 m and 20 m) with different landing postures (natural posture, inversion, eversion, plantar-flexion and dorsi-flexion) and injuries caused by impacts from different directions (anterior-posterior, lateral-medial and posterior-anterior) with different speeds (10 m/s, 15 m/s and 20 m/s) at different sites (ankle and lower, middle and upper sections of leg). We compared the injury morphology and analyzed the mechanisms of ankle injuries. The results showed that falling causes a specific compression fracture of the distal tibia, while fractures of the tibia and fibula diaphysis and ligament injuries caused by falling from a lower height or inversion, planter flexion or dorsiflexion at a large angle are not distinguishable from the similar injury patterns caused by impact on the middle and upper segments of the leg. No obvious compression fracture of the tibia distal was caused by the impacts, whereas ligament injuries and avulsion fractures of the medial or lateral condyle and fractures of the diaphysis of the tibia and fibula were observed. Systematic studies will be helpful in reconstructing the ankle injury processes and analyzing the mechanisms in forensic practice, providing a deeper understanding of ankle injury mechanisms for forensic experts.