Wenxin Niu

Kinematics, kinetics, and electromyogram of ankle during drop landing: a comparison between dominant and non-dominant limb.

The biomechanical difference between the dominant and non-dominant limb has seldom been studied during double-leg landing. The objective of this study was to evaluate the effectiveness of limb laterality on the ankle kinematics, kinetics and electromyogram (EMG) during drop landing. Sixteen healthy adults were recruited and dropped individually from platforms with three different heights (0.32 m, 0.52 m, and 0.72 m). The ground reaction force, ankle joint kinematics, and surface EMG of tibialis anterior (TA) and lateral gastrocnemius (LG) were measured in both lower extremities. Two-way analysis of variance was used to analyze the effects of laterality and dropping height. The peak angular velocities in dorsiflexion and abduction were significantly higher in the dominant ankle, whereas the pre- and post-landing EMG amplitudes of the TA were significantly higher in the non-dominant limb. Compared with the dominant side, the non-dominant ankle has a more effective protective mechanism in that excessive joint motion is restrained by greater ankle flexor activity. Compared with the non-dominant side, the dominant ankle joint is in greater injury risk during drop landing, and data measured in the dominant limb may produce more conservative conclusions for injury protection or prediction.

Deformation and stress distribution of the human foot after plantar ligaments release: a cadaveric study and finite element analysis.

The majority of foot deformities are related to arch collapse or instability, especially the longitudinal arch. Although the relationship between the plantar fascia and arch height has been previously investigated, the stress distribution remains unclear. The aim of this study was to explore the role of the plantar ligaments in foot arch biomechanics. We constructed a geometrical detailed three-dimensional (3-D) finite element (FE) model of the human foot and ankle from computer tomography images. The model comprised the majority of joints in the foot as well as bone segments, major ligaments, and plantar soft tissue. Release of the plantar fascia and other ligaments was simulated to evaluate the corresponding biomechanical effects on load distribution of the bony and ligamentous structures. These intrinsic ligaments of the foot arch were sectioned to simulate different pathologic situations of injury to the plantar ligaments, and to explore bone segment displacement and stress distribution. The validity of the 3-D FE model was verified by comparing results with experimentally measured data via the displacement and von Mise stress of each bone segment. Plantar fascia release decreased arch height, but did not cause total collapse of the foot arch. The longitudinal foot arch was lost when all the four major plantar ligaments were sectioned simultaneously. Plantar fascia release was compromised by increased strain applied to the plantar ligaments and intensified stress in the midfoot and metatarsal bones. Load redistribution among the centralized metatarsal bones and focal stress relief at the calcaneal insertion were predicted. The 3-D FE model indicated that plantar fascia release may provide relief of focal stress and associated heel pain. However, these operative procedures may pose a risk to arch stability and clinically may produce dorsolateral midfoot pain. The initial strategy for treating plantar fasciitis should be non-operative.

Finite element analysis of foot and ankle impact injury: risk evaluation of calcaneus and talus fracture

Introduction Foot and ankle impact injury is common in geriatric trauma and often leads to fracture of rearfoot, including calcaneus and talus. The objective of this study was to assess the influence of foot impact on the risk of calcaneus and talus fracture via finite element analysis. Methods A three-dimensional finite element model of foot and ankle was constructed based on magnetic resonance images of a female aged 28. The foot sustained a 7-kg passive impact through a foot plate. The simulated impact velocities were from 2.0 to 7.0 m/s with 1.0 m/s interval. Results At 5.0 m/s impact velocity, the maximum von Mises stress of the trabecular calcaneus and talus were 3.21MPa and 2.41MPa respectively, while that of the Tresca stress were 3.46MPa and 2.55MPa. About 94% and 84% of the trabecular calcaneus and talus exceeded the shear yielding stress, while 21.7% and 18.3% yielded the compressive stress. The peak stresses were distributed around the talocalcaneal articulation and the calcaneal tuberosity inferiorly, which corresponded to the common fracture sites. Conclusions The prediction in this study showed that axial compressive impact at 5.0 m/s could produce considerable yielding of trabecular bone in both calcaneus and talus, dominantly by shear and compounded with compression that predispose the rearfoot in the risk of fracture. This study suggested the injury pattern and fracture mode of high energy trauma that provides insights in injury prevention and fracture management.

An in vitro and finite element study of load redistribution in the midfoot

A good knowledge of midfoot biomechanics is important in understanding the biomechanics of the entire foot, but it has never been investigated thoroughly in the literature. This study carried out in vitro experiments and finite element analysis to investigate the midfoot biomechanics. A foot-ankle finite element model simulating the mid-stance phase of the normal gait was developed and the model validated in in vitro experimental tests. Experiments used seven in vitro samples of fresh human cadavers. The simulation found that the first principal stress peaks of all midfoot bones occurred at the navicular bone and that the tensile force of the spring ligament was greater than that of any other ligament. The experiments showed that the longitudinal strain acting on the medial cuneiform bone was −26.2±10.8 μ-strain, and the navicular strain was −240.0±169.1 μ-strain along the longitudinal direction and 65.1±25.8 μ-strain along the transverse direction. The anatomical position and the spring ligament both result in higher shear stress in the navicular bone. The load from the ankle joint to five branches of the forefoot is redistributed among the cuneiforms and cuboid bones. Further studies on the mechanism of loading redistribution will be helpful in understanding the biomechanics of the entire foot.

EFFECTS OF LATERALITY, ANKLE INVERSION AND STABILIZERS ON THE PLANTAR PRESSURE DISTRIBUTION DURING UNIPEDAL STANDING

The purpose of this research was to evaluate the standing stability with plantar pressure distribution (PPD), and to assess the effects of limb laterality, ankle inversion and stabilizer on PPD during unipedal standing. Nineteen young healthy adults were requested to stand on different inclined surfaces (level 0° and inclined 10° and 20°) with each foot. Three ankle stabilizer conditions were designed as barefoot control, elastic ankle tape and semi-rigid brace. Statistically analyzed with multivariate analysis of variance, the anterior/posterior (A/P) and medial/lateral (M/L) force ratios and total contact area (TPCA) were the main parameters to evaluate the stability. Compared with non-dominant side, the dominant foot was safer during unipedal standing with significantly greater TPCA, and especially when standing with ankle inversion due to additional significantly greater A/P force ratio. Ankle inversion harmed the stability while standing with the non-dominant foot due to significantly decreased A/P force ratio and local contact areas. Ankle brace improved the standing stability with significantly increased TPCA.

Biomechanical gender differences of the ankle joint during simulated half-squat parachute landing

INTRODUCTION A search of the literature did not reveal known gender differences in biomechanics during parachute landing. METHODS Eight male and eight female healthy adults participated in this experiment. Each individual jumped from platforms with three different heights (low: 0.32 m; medium: 0.52 m; and high: 0.72 m) and landed on flat ground in a standard half-squat parachute landing technique. The ground reaction force (GRF) normalized to bodyweight (BW), ankle joint kinematics, and the surface electromyogram (EMG) signals of the tibialis anterior (TA) and lateral gastrocnemius (LG) were measured. Two-way ANOVA was used to analyze the effects of the dropping height and gender factors. RESULTS The anterior-posterior GRF (men 1.01 BW; women 0.79 BW), rate of loading (men 260 BW x s(-1); women 127 BW x s(-1)), and absolute EMG amplitude of TA (pre-landing: men 219 microv; women 129 microv; post-landing: men 573 microv; women 288 microv) in the mens group were significantly higher than in the womens group, whereas peak angular velocity of dorsiflexion in the womens group (1627 degrees x s(-1)) was significantly higher than in the mens (1188 degrees x s(-1)). DISCUSSION Women are prone to transform the kinetic energy to the ankle motion, whereas men are more likely to transform it to friction. The co-contraction of the ankle flexor and extensor differs between genders. These factors may be associated with the higher incidence of parachute injuries among women reported by some authors.

Dynamic postural stability for double-leg drop landing

Abstract Dynamic postural stability has been widely studied for single-leg landing, but seldom considered for double-leg landing. This study aimed to evaluate the dynamic postural stability and the influence mechanism of muscle activities during double-leg drop landing. Eight recreationally active males and eight recreationally active females participated in this study and dropped individually from three heights (0.32 m, 0.52 m, and 0.72 m). Ground reaction force was recorded to calculate the time to stabilisation. Electromyographic activities were recorded for selected lower-extremity muscles. A multivariate analysis of variance was carried out and no significant influence was found in time to stabilisation between genders or limb laterals (P > 0.05). With increasing drop height, time to stabilisation decreased significantly in two horizontal directions and the lower-extremity muscle activities were enhanced. Vertical time to stabilisation was not significantly influenced by drop height. Dynamic postural stability improved by neuromuscular change more than that required due to the increase of drop height. Double-leg landing on level ground is a stable movement, and the body would often be injured before dynamic postural stability is impaired. It is understandable to protect tissues from mechanical injuries by the sacrifice of certain dynamic postural stability in the design of protective devices or athlete training.

Biomechanical comparison of locking plate and crossing metallic and absorbable screws fixations for intra-articular calcaneal fractures

The locking plate and percutaneous crossing metallic screws and crossing absorbable screws have been used clinically to treat intra-articular calcaneal fractures, but little is known about the biomechanical differences between them. This study compared the biomechanical stability of calcaneal fractures fixed using a locking plate and crossing screws. Three-dimensional finite-element models of intact and fractured calcanei were developed based on the CT images of a cadaveric sample. Surgeries were simulated on models of Sanders type III calcaneal fractures to produce accurate postoperative models fixed by the three implants. A vertical force was applied to the superior surface of the subtalar joint to simulate the stance phase of a walking gait. This model was validated by an in vitro experiment using the same calcaneal sample. The intact calcaneus showed greater stiffness than the fixation models. Of the three fixations, the locking plate produced the greatest stiffness and the highest von Mises stress peak. The micromotion of the fracture fixated with the locking plate was similar to that of the fracture fixated with the metallic screws but smaller than that fixated with the absorbable screws. Fixation with both plate and crossing screws can be used to treat intra-articular calcaneal fractures. In general, fixation with crossing metallic screws is preferable because it provides sufficient stability with less stress shielding.

Peak vertical ground reaction force during two-leg landing: a systematic review and mathematical modeling.

Objectives. (1) To systematically review peak vertical ground reaction force (PvGRF) during two-leg drop landing from specific drop height (DH), (2) to construct a mathematical model describing correlations between PvGRF and DH, and (3) to analyze the effects of some factors on the pooled PvGRF regardless of DH. Methods. A computerized bibliographical search was conducted to extract PvGRF data on a single foot when participants landed with both feet from various DHs. An innovative mathematical model was constructed to analyze effects of gender, landing type, shoes, ankle stabilizers, surface stiffness and sample frequency on PvGRF based on the pooled data. Results. Pooled PvGRF and DH data of 26 articles showed that the square root function fits their relationship well. An experimental validation was also done on the regression equation for the medicum frequency. The PvGRF was not significantly affected by surface stiffness, but was significantly higher in men than women, the platform than suspended landing, the barefoot than shod condition, and ankle stabilizer than control condition, and higher than lower frequencies. Conclusions. The PvGRF and root DH showed a linear relationship. The mathematical modeling method with systematic review is helpful to analyze the influence factors during landing movement without considering DH.

Effects of bone Young's modulus on finite element analysis in the lateral ankle biomechanics

Finite element analysis FEA is a powerful tool in biomechanics. The mechanical properties of biological tissue used in FEA modeling are mainly from experimental data, which vary greatly and are sometimes uncertain. The purpose of this study was to research how Youngs modulus affects the computations of a foot-ankle FEA model. A computer simulation and an in-vitro experiment were carried out to investigate the effects of incremental Youngs modulus of bone on the stress and strain outcomes in the computational simulation. A precise 3-dimensional finite element model was constructed based on an in-vitro specimen of human foot and ankle. Youngs moduli were assigned as four levels of 7.3, 14.6, 21.9 and 29.2 GPa respectively. The proximal tibia and fibula were completely limited to six degrees of freedom, and the ankle was loaded to inversion 10° and 20° through the calcaneus. Six cadaveric foot-ankle specimens were loaded as same as the finite element model, and strain was measured at two positions of the distal fibula. The bone stress was less affected by assignment of Youngs modulus. With increasing of Youngs modulus, the bone strain decreased linearly. Youngs modulus of 29.2 GPa was advisable to get the satisfactory surface strain results. In the future study, more ideal model should be constructed to represent the nonlinearity, anisotropy and inhomogeneity, as the same time to provide reasonable outputs of the interested parameters.