Finite element simulation on posterior tibial tendinopathy: Load transfer alteration and implications to the onset of pes planus

Biomechanical role of bone grafting for calcaneal fracture fixation in the presence of bone defect: A finite element analysis

BACKGROUND

The purpose of this study was to compare the biomechanical stress and stability of calcaneal fixations with and without bone defect, before and after bone grafting, through a computational approach.

METHODS

A finite element model of foot-ankle complex was reconstructed, impoverished with a Sanders III calcaneal fracture without bone defect and with moderate and severe bone defects. Plate fixations with and without bone grafting were introduced with walking stance simulated. The stress and fragment displacement of the calcaneus were evaluated.

FINDINGS

Moderate and severe defect increased the calcaneus stress by 16.11% and 32.51%, respectively and subsequently decreased by 10.76% and 20.78% after bone grafting. The total displacement was increased by 3.99% and 24.26%, respectively by moderate and severe defect, while that of posterior joint facet displacement was 86.66% and 104.44%. The former was decreased by 25.73% and 35.96% after grafting, while that of the latter was reduced by 88.09% and 84.78% for moderate and severe defect, respectively.

INTERPRETATION

Our finite element prediction supported that bone grafting for fixation could enhance the stability and reduce the risk of secondary stress fracture in cases of bone defect in calcaneal fracture.

Differential contribution of lateral plantar foot ligaments to lateral column stability - A cadaver based sectioning analysis

Lateral column (LC) instability occurs in adult acquired flatfoot deformity (AAFD). Differential ligament contribution to LC stability is unknown. The primary aim was to quantify this by using cadaver sectioning of lateral plantar ligaments. We also determined the relative contribution of each ligament to dorsal translation of the metatarsal head in the sagittal plane. 17 below-knee cadaveric specimens, preserved by vascular embalming method, were dissected to expose plantar fascia, long/short plantar ligaments (L/SPL), calcaneocuboid (CC) capsule and inferior 4th/5th tarsometatarsal (TMT) capsule. Dorsal forces of 0 N, 20 N and 40 N were applied to the plantar 5th metatarsal head after sequential ligament sectioning in different orders. Pins provided linear axes on each bone, allowing relative angular bone displacements to be calculated. Photography and ImageJ processing software were then used for analysis. The LPL (and CC capsule) had the greatest contribution to metatarsal head motion (107 mm) after isolated sectioning. In the absence of other ligaments, sectioning these resulted in significantly increased hindfoot-forefoot angulation (p ≤ 0.0003). Isolated TMT capsule sectioning demonstrated significant angular displacement even when other ligaments remained intact (with intact L/SPL, p = 0.0005). CC joint instability required both LPL and capsular sectioning for significant angulation to occur, whilst TMT joint stability was largely dependent on its capsule. The relative contribution of static restraints to the lateral arch has not yet been quantified. This study provides useful information on relative ligament contribution to both CC and TMT joint stability, which may in turn improve understanding of surgical interventions used to restore arch stability.

Quantifying increased lateral column instability in Adult Acquired Flatfoot Deformity (AAFD)

AAFD comprises ligamentous failure and tendon overload, mainly focused on the symptomatic posterior tibial tendon and the spring ligament. Increased lateral column (LC) instability arising in AAFD is not defined or quantified. This study aims to quantify the increased LC motion in unilateral symptomatic planus feet, using the contralateral unaffected asymptomatic foot as an internal control. In this case matched analysis, 15 patients with unilateral stage 2 AAFD foot and an unaffected contralateral foot were included. Lateral foot translation was measured as a guide to spring ligament competency. Medial and LC dorsal sagittal instability were assessed by direct measurement of dorsal 1st and 4th/5th metatarsal head motion and further video analysis. The mean increase in dorsal LC sagittal motion (between affected vs unaffected foot) was 5.6 mm (95% CI [4.63-6.55], p < 0.001). The mean increase in the lateral translation score was 42.8 mm (95% CI [37.48-48.03], p < 0.001). The mean increase in medial column dorsal sagittal motion was 6.8 mm (95% CI [5.7-7.8], p < 0.001). Video analysis also showed a statistically significant increase in LC dorsal sagittal motion between affected and unaffected sides (p < 0.001). This is the first study that quantifies a statistically significant increased LC dorsal motion in feet with AAFD. Understanding its pathogenesis and its link to talonavicular/spring ligament laxity improves foot assessment and may allow the development of future preventative treatment strategies.

Disease-Specific Finite element Analysis of the Foot and Ankle

Finite-element analysis is a computational modeling technique that can be used to quantify parameters that are difficult or impossible to measure externally in a geometrically complex structure such as the foot and ankle. It has been used to improve our understanding of pathomechanics and to evaluate proposed treatments for several disorders, including progressive collapsing foot deformity, ankle arthritis, syndesmotic injury, ankle fracture, plantar fasciitis, diabetic foot ulceration, hallux valgus, and lesser toe deformities. Parameters calculated from finite-element models have been widely used to make predictions about their biomechanical correlates.

Evaluation of the heel external rotation test in soft tissue deficiencies associated with adult acquired flatfoot deformity (AAFD). A cadaver sectioning analysis

BACKGROUND

To date, evaluation of the heel external rotation test has not been taken with respect to AAFD. Traditional 'gold standard' tests do not account for the contribution of the midfoot ligaments towards instability. These tests would be flawed as any midfoot instability may produce a false positive result.

AIMS

To evaluate the differential contribution of the spring, deltoid and other local ligaments in external rotation generated at the heel.

METHODS

Serial ligament sectioning was performed on 16 cadaveric specimens, with a 40 N-external rotation force applied to the heel. These were divided into four groups with different sequences of ligament sectioning. Measurements of the total amount/range of external, tibiotalar and subtalar rotation were made.

RESULTS

The deep component of the deltoid ligament (DD) was the main ligament influencing heel external rotation (P < 0.05, in all cases), and acted primarily at the tibiotalar joint (87.9 %). The spring ligament (SL) influenced heel external rotation predominantly (91.2 %) at the subtalar joint (STJ). Greater than 20 degrees external rotation could only be achieved with DD sectioning. The interosseous (IO) and cervical (CL) ligaments did not significantly contribute to external rotation at either joint (P > 0.05).

CONCLUSION

Clinically relevant external rotation (>20 degrees) is solely attributable to DD failure in the presence of intact lateral ligaments (LL). This test may improve detection of DD instability and allow clinicians to subclassify patients with Stage 2 AAFD into those where DD may or may not be compromised.

Efficacy of Plantar Orthoses in Paediatric Flexible Flatfoot: A Five-Year Systematic Review

Paediatric flexible flatfoot (PFF) is a very common condition and a common concern among parents and various healthcare professionals. There is a multitude of conservative and surgical treatments, with foot orthoses (FO) being the first line of treatment due to their lack of contraindications and because the active participation of the child is not required, although the evidence supporting them is weak. It is not clear what the effect of FO is, nor when it is advisable to recommend them. PFF, if left untreated or uncorrected, could eventually cause problems in the foot itself or adjacent structures. It was necessary to update the existing information on the efficacy of FO as a conservative treatment for the reduction in signs and symptoms in patients with PFF, to know the best type of FO and the minimum time of use and to identify the diagnostic techniques most commonly used for PFF and the definition of PFF. A systematic review was carried out in the databases PubMed, EBSCO, Web of Science, Cochrane, SCOPUS and PEDro using the following strategy: randomised controlled trials (RCTs) and controlled clinical trials (CCTs) on child patients with PFF, compared to those treated with FO or not being treated, assessing the improvement of signs and symptoms of PFF. Studies in which subjects had neurological or systemic disease or had undergone surgery were excluded. Two of the authors independently assessed study quality. PRISMA guidelines were followed, and the systematic review was registered in PROSPERO: CRD42021240163. Of the 237 initial studies considered, 7 RCTs and CCTs published between 2017 and 2022 met the inclusion criteria, representing 679 participants with PFF aged 3-14 years. The interventions of the included studies differed in diagnostic criteria, types of FO and duration of treatment, among others. All articles conclude that FO are beneficial, although the results must be taken with caution due to the risk of bias of the included articles. There is evidence for the efficacy of FO as a treatment for PFF signs and symptoms. There is no treatment algorithm. There is no clear definition for PFF. There is no ideal type of FO, although all have in common the incorporation of a large internal longitudinal arch.

The impact of ligament tears on joint contact mechanics in progressive collapsing foot deformity: A finite element study

BACKGROUND

Patients with longstanding progressive collapsing foot deformity often develop osteoarthritis of the ankle, midfoot, or hindfoot joints, which can be symptomatic or lead to fixed deformities that complicate treatment. The development of deformity is likely caused by ligament degeneration and tears. However, the effect of individual ligament tears on changes in joint contact mechanics has not been investigated.

METHODS

A validated finite element model of the foot was used to compare joint contact areas, forces, and pressures between the intact and collapsed foot, and to evaluate the effect of individual ligament tears on joint contact mechanics.

FINDINGS

Collapsing the foot resulted in an increase in contact pressure in the subtalar, calcaneocuboid, tibiotalar, medial naviculocuneiform, and first tarsometatarsal joints but a decrease in contact pressure in the talonavicular joint. Rupture of the spring ligament was the main contributor to increased calcaneocuboid and subtalar joint contact pressures and decreased medial naviculocuneiform and first tarsometatarsal joint contact pressures, as well as talonavicular subluxation. Deltoid ligament rupture was the primary source of increased contact pressure in the medial naviculocuneiform, first tarsometatarsal, and tibiotalar joints.

INTERPRETATION

Degenerative tearing of the ligaments in flatfoot deformity leads to increased joint contact pressures, primarily in the calcaneocuboid, subtalar, and tibiotalar joints, which has been implicated in the development of osteoarthritis in these joints. An improved understanding of the relationship between ligament tears and joint contact pressures could provide support for the use of ligament reconstructions to prevent the development of arthrosis.

Different Design Feature Combinations of Flatfoot Orthosis on Plantar Fascia Strain and Plantar Pressure: A Muscle-Driven Finite Element Analysis With Taguchi Method

Customized foot orthosis is commonly used to modify foot posture and relieve foot pain for adult acquired flexible flatfoot. However, systematic investigation of the influence of foot orthotic design parameter combination on the internal foot mechanics remains scarce. This study aimed to investigate the biomechanical effects of different combinations of foot orthoses design features through a muscle-driven flatfoot finite element model. A flatfoot-orthosis finite element model was constructed by considering the three-dimensional geometry of plantar fascia. The plantar fascia model accounted for the interaction with the bulk soft tissue. The Taguchi approach was adopted to analyze the significance of four design factors combination (arch support height, medial posting inclination, heel cup height, and material stiffness). Predicted plantar pressure and plantar fascia strains in different design combinations at the midstance instant were reported. The results indicated that the foot orthosis with higher arch support (45.7%) and medial inclination angle (25.5%) effectively reduced peak plantar pressure. For the proximal plantar fascia strain, arch support (41.8%) and material stiffness (37%) were strong influencing factors. Specifically, higher arch support and softer material decreased the peak plantar fascia strain. The plantar pressure and plantar fascia loading were sensitive to the arch support feature. The proposed statistics-based finite element flatfoot model could assist the insole optimization and evaluation for individuals with flatfoot.

Biomechanical Analysis of a Novel Double-Point Fixation Method for Displaced Intra-Articular Calcaneal Fractures

The development of minimally invasive procedures and implant materials has improved the fixation strength of implants and is less traumatic in surgery. The purpose of this study was to propose a novel “double-point fixation” for calcaneal fractures and compare its biomechanical stability with the traditional “three-point fixation.” A three-dimensional finite element foot model with a Sanders type IIIAB calcaneal fracture was developed based on clinical images comprising bones, plantar fascia, ligaments, and encapsulated soft tissue. Double-point and three-point fixation resembled the surgical procedure with a volar distal radius plate and calcaneal locking plate, respectively. The stress distribution, fracture displacement, and change of the Böhler angle and Gissane’s angle were estimated by a walking simulation using the model, and the predictions between the double-point and three-point fixation were compared at heel-strike, midstance, and push-off instants. Double-point fixation demonstrated lower bone stress (103.3 vs. 199.4 MPa), but higher implant stress (1,084.0 vs. 577.9 MPa). The model displacement of double-point fixation was higher than that of three-point fixation (3.68 vs. 2.53 mm). The displacement of the posterior joint facet (0.127 vs. 0.150 mm) and the changes of the Böhler angle (0.9° vs. 1.4°) and Gissane’s angle (0.7° vs. 0.9°) in double-point fixation were comparably lower. Double-point fixation by volar distal radius plates demonstrated sufficient and favorable fixation stability and a lower risk of postoperative stress fracture, which may potentially serve as a new fixation modality for the treatment of displaced intra-articular calcaneal fractures.

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.

Effect of Displacement Degree of Distal Chevron Osteotomy on Metatarsal Stress: A Finite Element Method

BACKGROUND

The stress of foot bone can effectively evaluate the functional damage caused by foot deformity and the results of operation. In this study, the finite element method was used to investigate the degree of displacement of distal chevron osteotomy on metatarsal stress and metatarsophalangeal joint load; Methods: Four finite element models of displacement were established by using the CT images of a patient with moderate hallux valgus (hallux valgus angle and intermetatarsal angle were 26.74° and 14.09°, respectively), and the validity of the model was verified. Each finite element model consisted of bones and various cartilage structures, ligaments, and plantar fascia, as well as encapsulated soft tissue. Except for soft tissue, the material properties of other parts were isotropic linear elastic material, and the encapsulated soft tissue was set as nonlinear hyperelastic material. The mesh was tetrahedral mesh. Link elements were used in ligament and plantar fascia. A ground reaction force with a half-body weight was applied at the bottom of the floor to simulate the ground reaction when standing. The upper surfaces of the encapsulated soft tissue, distal tibia, and distal fibula were fixed. The stress distribution of metatarsals and the stress of cartilage of the first metatarsophalangeal joint were compared and analyzed; Results: Compared with the hallux valgus without osteotomy, the stress of the first metatarsals and second metatarsals of 2-4 mm decreased, and the stress of the interarticular cartilage of the first metatarsophalangeal joint with 4 mm was reduced. In the case of 6 mm, the stress value between the first metatarsal and the first metatarsophalangeal joint increased, and 4 mm was the most suitable distance; Conclusions: Compared with the hallux valgus without osteotomy, the stress of the first metatarsals and second metatarsals of 2-4 mm decreased, and the stress of the interarticular cartilage of the first metatarsophalangeal joint with 4 mm was reduced. In the case of 6 mm, the stress value between the first metatarsal and the first metatarsophalangeal joint increased, and 4 mm was the most suitable distance. For the degree of displacement of the distal chevron osteotomy, the postoperative stability and the stress distribution of metatarsal bone should be considered. Factors such as hallux valgus angle, intermetatarsal angle, patient's age, body weight, and metatarsal width should be considered comprehensively. The factors affecting osteotomy need to be further explored. The degree of displacement of osteotomy can be evaluated by FE method before the operation, and the most suitable distance can be obtained.

Biomechanical comparison among five mid/hindfoot arthrodeses procedures in treating flatfoot using a musculoskeletal multibody driven finite element model

BACKGROUND AND OBJECTIVE

Mid/hindfoot arthrodesis could modify the misalignment of adult-acquired flatfoot and attenuate pain. However, the long-term biomechanical effects of these surgical procedures remain unclear, and the quantitative evidence is scarce. Therefore, we aimed to investigate and quantify the influences of five mid/hindfoot arthrodeses on the internal foot biomechanics during walking stance.

METHODS

A young participant with flexible flatfoot was recruited for this study. We reconstructed a subject-specific musculoskeletal multibody driven-finite element (FE) foot model based on the foot magnetic resonance imaging. The severe flatfoot model was developed from the flexible flatfoot through the attenuation of ligaments and the unloading of the posterior tibial muscle. The five mid/hindfoot arthrodeses simulations (subtalar, talonavicular, calcaneocuboid, double, and triple arthrodeses) and a control condition (no arthrodesis) were performed simultaneously in the detailed foot multibody dynamics model and FE model. Muscle forces calculated by a detailed multi-segment foot model and ground reaction force were used to drive the foot FE model. The internal foot loadings were compared among control and these arthrodeses conditions at the first and second vertical ground reaction force (VGRF) peak and VGRF valley instants.

RESULTS

The results indicated that the navicular heights in double and triple arthrodeses were higher than other surgical procedures, while the subtalar arthrodesis had the smallest values. Five mid/hindfoot arthrodeses reduced the peak plantar fascia stress compared to control. However, double and triple arthrodeses increased the peak medial cuneo-navicular joint contact pressures and peak foot pressures as well as the metatarsal bones stresses.

CONCLUSION

Although mid/hindfoot arthrodesis generally reduced the collapse of medial longitudinal arch and plantar fascia loading during the stance phase, the increased loading in the adjacent unfused joint and metatarsal bones for double and triple arthrodeses should be noted. These findings could account for some symptoms experienced by flatfoot patients after surgery, which may facilitate the optimization of surgical protocols.

A Three-Dimensional Printed Foot Orthosis for Flexible Flatfoot: An Exploratory Biomechanical Study on Arch Support Reinforcement and Undercut

The advancement of 3D printing and scanning technology enables the digitalization and customization of foot orthosis with better accuracy. However, customized insoles require rectification to direct control and/or correct foot deformity, particularly flatfoot. In this exploratory study, we aimed at two design rectification features (arch stiffness and arch height) using three sets of customized 3D-printed arch support insoles (R+U+, R+U-, and R-U+). The arch support stiffness could be with or without reinforcement (R+/-) and the arch height may or may not have an additional elevation, undercutting (U+/-), which were compared to the control (no insole). Ten collegiate participants (four males and six females) with flexible flatfoot were recruited for gait analysis on foot kinematics, vertical ground reaction force, and plantar pressure parameters. A randomized crossover trial was conducted on the four conditions and analyzed using the Friedman test with pairwise Wilcoxon signed-rank test. Compared to the control, there were significant increases in peak ankle dorsiflexion and peak pressure at the medial midfoot region, accompanied by a significant reduction in peak pressure at the hindfoot region for the insole conditions. In addition, the insoles tended to control hindfoot eversion and forefoot abduction though the effects were not significant. An insole with stronger support features (R+U+) did not necessarily produce more favorable outcomes, probably due to over-cutting or impingement. The outcome of this study provides additional data to assist the design rectification process. Future studies should consider a larger sample size with stratified flatfoot features and covariating ankle flexibility while incorporating more design features, particularly medial insole postings.

Is Advanced Imaging a Must in the Assessment of Progressive Collapsing Foot Deformity?

Advanced imaging modalities have, in very recent years, enabled a considerable leap in understanding progressive collapsing foot deformity, evolving from a simple confirmation of clinical diagnostic using basic measurements to minute understanding of soft tissue and bone involvements. MRI and weight-bearing cone-beam computed tomography are enabling the development of new 3-dimensional measurement modalities. The identification of key articular and joint markers of advanced collapse will allow surgeons to better indicate treatments and assess chances of success with conservative therapies and less invasive surgical procedures, with the hope of improving patient outcomes.

Risk of proximal femoral nail antirotation (PFNA) implant failure upon different lateral femoral wall thickness in intertrochanteric fracture: a finite element analysis

Proximal Femoral Nail Antirotation (PFNA) has been commonly used to treat intertrochanteric fractures, despite the risk of implant failure. The integrity of the femur could influence the risk of implant failure. This study evaluated the influence of lateral femoral wall thickness on the potential of implant failure. A finite element model of the hip was reconstructed from the Computed Tomography of a female patient. Five intertrochanteric fracture models at different lateral femoral wall thickness (T1 = 27.6 mm, T2 = 25.4 mm, T3 = 23.4 mm, T4 = 21.4 mm, and T5 = 19.3 mm) were then created and fixed with PFNA. We simulated a critical loading condition by a high loading case during walking. Elastoplastic material models with yield stress and failure strain were applied to the bone and implant in which breakage can be simulated using the element deletion function. In addition, the stress and displacement of the implant and femur were analysed. Implant breakage occurred at the sides of the proximal nail canal in cases of T4 and T5 which was further supported by the higher maximum von Mises stress and nail displacement. The increased stress and displacement of the implant may implicate a reduction of stability and risk of implant failure. We suggested that precaution shall be taken when the wall thickness was less than 21.4 mm.

Analysis of the main soft tissue stress associated with flexible flatfoot deformity: a finite element study

A better understanding of soft tissue stress and its role in supporting the medial longitudinal arch in flexible flatfoot could help to guide the clinical treatment. In this study, a 3-Dimensional finite element (FE) foot model was reconstructed to measure the stress of the soft tissue, and its variation in different scenarios related to flexible flatfoot. All bones, cartilages, ligaments and related tendons around the ankle, and fat pad were included in the finite element model. The equivalent stress on the articular surface of the joints in the medial longitudinal arch and the maximum principal stress of the ligaments around the ankle were obtained. The results show that the plantar fascia (PF) is the main tissue in maintaining the medial longitudinal arch. The equivalent stress of all the joints in the medial longitudinal arch increases when the PF attenuation and the talonavicular joint increases, while other joints decreases when all the three tissue attenuation. Moreover, the maximum principal stress variation of calcaneofibular ligament is largest when the PF attenuation and the tibionavicular ligament and posterior tibiotalar ligament are largest when the posterior tibial tendon (PTT) attenuation. The maximum principal stress variation of tibionavicular ligament and posterior tibiotalar ligament are even larger when all the three tissue attenuation. These findings support that the PF is the main factor in maintaining the medial longitudinal arch. The medial longitudinal arch collapse mainly affects the talonavicular joint and the calcaneofibular ligament, the tibionavicular ligament and the posterior tibiotalar ligament. This approach could help to improve the understanding of adult-acquired flatfoot deformity (AAFD).

Extrinsic foot muscle forces and joint contact forces in flexible flatfoot adult with foot orthosis: A parametric study of tibialis posterior muscle weakness

BACKGROUND

The posterior tibialis tendon dysfunction (PTTD) is typically associated with progressive flatfoot deformity, which could be alleviated with foot orthosis. However, the evaluation of tibialis posterior (TP) weakness on lower limb mechanics of flatfoot adults with foot orthoses is scarce and requires further investigation.

RESEARCH QUESTION

This study aimed to examine the effects of TP weakness on lower limb mechanics in flatfoot adults with foot orthosis through gait analysis and musculoskeletal modelling.

METHODS

Fifteen young adults with flatfoot were recruited from University to perform a gait experiment with and without foot orthoses. Data collected from the motion capture system were used to drive the musculoskeletal modelling for the estimation of the joint force and extrinsic muscle forces of the lower limb. A parametric analysis was conducted by adjusting the TP muscle strength from 40 % to 100 %. Two-way repeated measures ANOVA was used to compare the peak extrinsic foot muscle forces and joint forces among different levels of TP weakness and insole conditions.

RESULTS

TP weakness significantly increased ankle joint force superoinferiorly (F = 125.9, p < 0.001) and decreased anteroposteriorly (F = 125.9, p < 0.001), in addition to a significant increase in the muscle forces of flexor hallucis longus (p < 0.001) and flexor digitorum longus (p < 0.001). Besides, the foot orthosis significantly reduced most peak muscle forces whilst significantly reduced the second peak knee force and peak ankle force compared to the control condition (F = 8.79-30.9, p < 0.05).

SIGNIFICANCE

The increased extrinsic foot muscle forces (flexor hallucis longus and flexor digitorum longus) and ankle joint forces in the TP weakness condition indicated that TP weakness may induce compensatory muscle activation and attenuated joint load. The abnormal muscle and joint mechanics in flatfoot adults with TP weakness might be restored by the orthosis.

Analysis of transient response of the human foot based on the finite element method

BACKGROUND

The foot is an important part of the human body. Its functions are mainly walking and load-bearing. It also keeps the human body stable and absorbs ground vibrations to protect important human organs.

OBJECTIVE

Many researchers use finite element methods to study the biomechanics of the foot. However, current studies on the finite element of the foot are based on the stress and displacement response analysis of the foot under static or quasi-static conditions, ignoring the movement process of the foot and the impact of vibration. Moreover, the joint application of energy method and finite element analysis in foot biomechanics is rarely reported.

METHODS

In this paper, to obtain the foot energy transfer process, the transient response of the foot under neutral position is analyzed based on the energy method.

RESULTS

The results show that: (1) In this model, the energy analysis follows the conservation of energy, which indicates that the transient response analysis has obtained a reasonable response. (2) When the foot touches the ground, the strain energy of the calcaneus, second metatarsal and third metatarsal is relatively large, which is consistent with the main stress concentration area of the plantar. (3) The gravity of the human body is mainly transmitted through the talus to the calcaneus, while the effect of transmittal through the scaphoid to the cuneiform bone and metatarsal is weak.

CONCLUSION

This study can not only more clearly and intuitively reflect the energy transfer and source of various skeletal foreheads in the foot, but also provide a new research idea for the study of foot biomechanics.

Influence of arch support heights on the internal foot mechanics of flatfoot during walking: A muscle-driven finite element analysis

BACKGROUND

Different arch support heights of the customized foot orthosis could produce different effects on the internal biomechanics of the foot. However, quantitative evidence is scarce. Therefore, we aimed to investigate and quantify the influence of arch support heights on the internal foot biomechanics during walking stance.

METHODS

We reconstructed a foot finite element model from a volunteer with flexible flatfoot. The model enabled a three-dimensional representation of the plantar fascia and its interactions with surrounding osteotendinous structures. The volunteer walked in foot orthosis with different arch heights (low, neutral, and high). Muscle forces during gaits were calculated by a multibody model and used to drive a foot finite element model. The foot contact pressures and plantar fascia strains in different regions were compared among the insole conditions at the first and second vertical ground reaction force (VGRF) peak and VGRF valley instants.

RESULTS

The results indicated that peak foot pressures decreased in balanced standing and second VGRF as the arch support height increased. However, peak midfoot pressures increased during all simulated instants. Meanwhile, high arch support decreased the plantar fascia loading by 5%-15.4% in proximal regions but increased in the middle and distal regions.

CONCLUSION

Although arch support could generally decrease the plantar foot pressure and plantar fascia loading, the excessive arch height may induce high midfoot pressure and loadings at the central portion of the plantar fascia. The consideration of fascia-soft tissue interaction in modeling could improve the prediction of plantar fascia strains towards design optimization for orthoses.

Finite element method based parametric study of Gastrocnemius-soleus recession: implications to the treatment of midfoot-forefoot overload syndrome

Gastrocnemius-soleus recession has been used to treat midfoot-forefoot overload syndrome and plantar fasciitis induced by equinus of the ankle joint. A controlled and selective amount of recession is imperative to maintain muscle strength and stability. The objective of this study was to conduct a parametric study to quantify the relationship between the level of recession and plantar fascia stress. A finite element model of the foot-ankle-shank complex was reconstructed from magnetic resonance and computed tomography images of a 63-year-old normal female. The model was validated by comparing modeled stresses to the measured plantar pressure distribution of the model participant during balanced standing. The midstance and push-off instants of walking stance were simulated with different levels and combinations of gastrocnemius-soleus recession resembled by different amounts of muscle forces. Halving the muscle forces at midstance reduced the average plantar fascia stress by a quarter while reducing two-third of the muscle forces at push-off reduced the average fascia stress by 18.2%. While the first ray of the plantar fascia experienced the largest stress among the five fasciae, the stress was reduced by 77.8% and 16.9% when the load was halved and reduced by two-third at midstance and push-off instants, respectively. Reduction in fascia stress implicates a lower risk of plantar fasciitis and other midfoot-forefoot overload syndromes. The outcome of this study can aid physicians to determine the amount of gastrocnemius-soleus recession towards patients with vdifferent levels of plantar fascia overstress. A detailed three-dimensional modelling on the plantar fascia is warranted in future study.

Biomechanical analysis of minimally invasive crossing screw fixation for calcaneal fractures: Implications to early weight-bearing rehabilitation

BACKGROUND

Minimally invasive fixation using crossing screws was believed to produce satisfactory clinical outcome whereas its stability in early weight-bearing remained controversial. This study aimed to analyze the biomechanical stability of minimally invasive fixation during balanced standing and walking stance, and provide evidence for early rehabilitation.

METHODS

A finite element model of foot-ankle-shank complex was reconstructed based on computed tomography and magnetic resonance images, and validated by plantar pressure of the model participant. A Sanders III calcaneal fracture was created on the model, and then fixed using crossing screws. The predicted stress distribution, fracture displacement, Bohler's angle and Gissane's angle were compared between the intact calcaneus and fracture model with the fixation.

FINDINGS

Postoperatively, the concentrated stress appeared at the junction of the calcaneus and its surrounding tissues (especially Achilles tendon, plantar fascia and ligaments) during standing and walking stances, and the stress exceeded the yield strength of trabecular bone. The longitudinal screws sustained the highest stresses and concentrated at the tips and the calcaneal tuberosity junction. The displacement of posterior joint facet, Bohler's angle, and Gissane's angle were within the acceptable range either standing or walking after the fixation.

INTERPRETATION

Early weight-bearing standing and walking after minimally invasive fixation may cause high stress concentration thereby induce calcaneus stress fractures and other complications like plantar fasciitis and heel pain, so it should not be supported. The peri-calcaneus tendons, i.e., Achilles tendon and plantar fascia, play key roles in the stabilization of the calcaneal fracture after operation.

Finite Element Analysis of Generalized Ligament Laxity on the Deterioration of Hallux Valgus Deformity (Bunion)

Hallux valgus is a common foot problem affecting nearly one in every four adults. Generalized ligament laxity was proposed as the intrinsic cause or risk factor toward the development of the deformity which was difficult to be investigated by cohort clinical trials. Herein, we aimed to evaluate the isolated influence of generalized ligament laxity on the deterioration using computer simulation (finite element analysis). We reconstructed a computational foot model from a mild hallux valgus participant and conducted a gait analysis to drive the simulation of walking. Through parametric analysis, the stiffness of the ligaments was impoverished at different degrees to resemble different levels of generalized ligament laxity. Our simulation study reported that generalized ligament laxity deteriorated hallux valgus by impairing the load-bearing capacity of the first metatarsal, inducing higher deforming force, moment and malalignment at the first metatarsophalangeal joint. Besides, the deforming moment formed a deteriorating vicious cycle between hallux valgus and forefoot abduction and may result in secondary foot problems, such as flatfoot. However, the metatarsocuneiform joint did not show a worsening trend possibly due to the overriding forefoot abduction. Controlling the deforming load shall be prioritized over the correction of angles to mitigate deterioration or recurrence after surgery.

Immediate Effects of Medially Posted Insoles on Lower Limb Joint Contact Forces in Adult Acquired Flatfoot: A Pilot Study

Flatfoot is linked to secondary lower limb joint problems, such as patellofemoral pain. This study aimed to investigate the influence of medial posting insoles on the joint mechanics of the lower extremity in adults with flatfoot. Gait analysis was performed on fifteen young adults with flatfoot under two conditions: walking with shoes and foot orthoses (WSFO), and walking with shoes (WS) in random order. The data collected by a vicon system were used to drive the musculoskeletal model to estimate the hip, patellofemoral, ankle, medial and lateral tibiofemoral joint contact forces. The joint contact forces in WSFO and WS conditions were compared. Compared to the WS group, the second peak patellofemoral contact force (p < 0.05) and the peak ankle contact force (p < 0.05) were significantly lower in the WSFO group by 10.2% and 6.8%, respectively. The foot orthosis significantly reduced the peak ankle eversion angle (p < 0.05) and ankle eversion moment (p < 0.05); however, the peak knee adduction moment increased (p < 0.05). The reduction in the patellofemoral joint force and ankle contact force could potentially inhibit flatfoot-induced lower limb joint problems, despite a greater knee adduction moment.

Finite element analysis of subtalar joint arthroereisis on adult-acquired flexible flatfoot deformity using customised sinus tarsi implant

Background

Subtalar arthroereisis may cause sinus tarsi pain complications. In this study, we aimed to introduce a customised implant that facilitated treatment effect and less impingement. The biomechanical outcome between the intact and implant conditions was compared using finite element analysis.

Methods

A female patient with flatfoot (age: 36 years, height: 156 ​cm, body mass: 51 ​kg) was recruited as the model patient. The customised implant was designed from the extracted geometry. Boundary and loading conditions were assumed from the data of a normal participant. Four gait instants, including the ground reaction force first peak (25% stance), valley (45%), initial push-off (60%) and second peak (75%) were analyzed.

Results

The navicular height was elevated by 4.2% at 25% stance, whereas the strain of the spring, plantar cuneonavicular and plantar cuboideonavicular ligaments were reduced. The talonavicular joint force decreased and the calcaneocuboid joint increased by half and 67%, respectively, representing a lateralised load pathway. There was a stress concentration at the sulcus tali reaching 15.29 ​MPa

Conclusion

Subtalar arthroereisis using a customised implant may produce some positive treatment effects in terms of navicular height elevation, ligament strain relief and lateralised joint loading pathway. Although the concentrated stress at the sulcus tali did not exceed the threshold of bone breakdown, we could not rule out the potential of vascular disturbance owing to the remarkable elevation of stress. Future study may enlarge the contact area of the bone–implant interface by considering customisation based on the dynamic change of the sinus tarsi during walking gait.

The translational potential of this article

Geometry mismatch of prefabricated implants could be the reason for complications. With the advancement of 3D printing, customising implant becomes possible and may improve treatment outcome. This study implemented a theoretical model approach to explore its potential under a simulation of walking.

Pediatric Flatfeet-A Disease Entity That Demands Greater Attention and Treatment

Background: Pediatric flatfoot is a common deformity. Unfortunately, the common opinion has been that most children with this faulty foot structure will simply out-grow it, despite no radiographic evidence to support this claim. Every step on a deformed foot leads to excessive tissue strain and further joint damage. Many forms of conservative and surgical treatments have been offered. This study was aimed at investigating the effectiveness of non-surgical and surgical treatment options. Main Text: faulty-foot structure is the leading cause of many secondary orthopedic deformities. A wide range of treatments for pediatric flatfeet have been recommended from the "do-nothing" approach, observation, to irreversible reconstructive surgery. Most forms of conservative care lack evidence of osseous realignment and stability. A conservative surgical option of extra-osseous talotarsal joint stabilization provides patients an effective form of treatment without the complications associated with other irreversible surgical procedures. Conclusion: Pediatric flatfeet should not be ignored or downplayed. The sooner effective treatment is prescribed, the less damage will occur to other parts of the body. When possible, a more conservative corrective procedure should be performed prior to irreversible, joint destructive options.

Prediction on the plantar fascia strain offload upon Fascia taping and Low-Dye taping during running

Background

Taping is commonly prescribed to treat plantar fasciitis for runners by virtue of its alleged ability to offload the plantar fascia and facilitate positive injury prognosis. Our study aimed to investigate how different taping methods could change the loading on the plantar fascia during running using computational simulations.

Methods

A finite element foot model was modified from a previous version to fit the study's purpose. The model featured twenty bones, bulk soft tissue, foot muscles, ligaments/tendons, and a solid part representing the plantar fascia. A runner performed several running trials under one untaped condition and two taped conditions—Low-Dye taping and Fascia taping, which were implemented by a physiotherapist using the Kinesio tapes. The captured motion data were processed to drive a scaled musculoskeletal model and calculate segmental kinematics, foot muscle force, and joint reaction force. These variables were then input as the boundary/loading conditions for finite element analyses of running. The principal tensile strain on the plantar fascia, subtalar eversion, and navicular height during the stance phase were averaged across five trials of each condition and compared using Friedman's test.

Results

Maximal subtalar eversion did not differ among conditions (p = 0.449). Fascia taping significantly reduced maximal strains on the fascia band (p = 0.034, Kendall's W = 0.64–0.76) and increased the navicular height (p = 0.013, Kendall's W = 0.84) compared with nontaping. There were no significant differences in all outcome variables between Low-Dye taping and nontaping (p = 0.173–0.618).

Conclusion

From a mechanical point of view, our study provided quantitative evidence to support the application of taping treatments for overstrained plantar fascia. The untensed fascia band by Fascia taping could be a potential indicator of pain relief for the runners. However, a prospective study targeting the patient population would be needed to address the point.

The Translational Potential of this Article

The study quantified the loading status of the plantar fascia during running and provided mechanical evidence to support the usage of taping as a mean to reduce fascial strain, thus possibly controlling injury risks for the runners. The results of the study also highlighted the importance of selecting specific taping methods based on individuals' needs.

Are there benefits of a 2D gait analysis in the evaluation of the subtalar extra-articular screw arthroereisis? Short-term investigation in children

BACKGROUND

A juvenile flexible flatfoot is a common abnormality during growth. For children with a pathological manifestation, subtalar extra-articular screw arthroereisis is a popular operative technique. Although this minimally invasive operation technique has been performed for >45 years, complications still occasionally occur. For this reason, we created this pilot study to investigate whether a two-dimensional (2D) gait analysis is able to identify functional movement deficits after surgery.

METHODS

Fourteen children (27 ft) with a mean age of 12.38 years (SD, 1.40 years) were analyzed. Biomechanics were examined before and 4 weeks after surgery using a 2D gait analysis. For this purpose, the patients were filmed on a treadmill. In focus were static and dynamic recordings of the heel angle, rearfoot angle, and the leg axis angle. In addition, the step length and self-selected speed were measured.

FINDINGS

After surgery rearfoot angle showed significant reduction (p < 0.001) from 12.49° to 3.63° under static conditions and from 12.65° to 4.58° under dynamic conditions. Heel angle responded similar (p < 0.001). There were no significant differences in self-selected speed or step length. Undoubtedly, gait analysis was able to identify intraindividual deficits, leading to a closer monitoring of five patients and an adjustment of the screw in one foot.

INTERPRETATION

By means of the 2D gait analysis, we were able to show functional improvement after subtalar extra-articular screw arthroereisis. Nonetheless, we identified a few children who still had functional abnormalities. Certainly, it is unclear whether this additional examination is able to reveal all complications that would have occurred later.

Sleeping mattress determinants and evaluation: a biomechanical review and critique

Background

Sleeping mattress parameters significantly influence sleeping comfort and health, as reflected by the extensive investigations of sleeping support biomechanics to prevent sleep-related musculoskeletal problems.

Methodology

Herein, we review the current trends, research methodologies, and determinants of mattress biomechanics research, summarizing evidence published since 2008. In particular, we scrutinize 18 articles dealing with the development of new designs, recommendation criteria, instruments/methods of spine alignment evaluation, and comparative evaluation of different designs.

Results

The review demonstrated that mattress designs have strived for customization, regional features, and real-time active control to adapt to the biomechanical features of different body builds and postures. However, the suggested threshold or target values for desirable spine alignment and body pressure distribution during sleep cannot yet be justified in view of the lack of sufficient evidence.

Conclusions

It is necessary to formulate standard objectives and protocols for carrying out mattress evaluation.