Effects of foot posture on fifth metatarsal fracture healing: a finite element study

Extended finite element analysis for the 2nd and 3rd metatarsals stress fracture during push-off

Metatarsal stress fractures (MSF), particularly the 2nd and 3rd MSF, are common injuries among athletes. Although there are several practices to reduce foot and ankle injuries, there is no injury prevention program specifically designed to minimize MSF. This is mainly due to the lack of information about the loadings/postures that cause MSF. Therefore, this study aimed to investigate dangerous loadings/postures potentially causing MSF during push-off (PO). The analysis was conducted with Finite Element Modelling (FEM), calibrated with the three-point bending test, and validated with peak plantar pressure (PPP) and fracture force measurement. Extended Finite Element Method was used for MSF simulation such that ten different foot and ankle configurations were designed, with five for each of the 2nd and 3rd MSF under pure vertical loadings. A more complex loading, ankle eversion/inversion during PO, was also examined for the MSF. The average error percentage for the calibration of the model with the three-point bending test was 3.05%. The average error percentages for the validation of the model with PPP and fracture force measurements were 18% and 30%, respectively. The outcomes of pure vertical loadings indicated the higher potential for the 2nd and 3rd MSF at 30% PO and 70% PO, respectively. The results of ankle eversion/inversion loadings represented that the most dangerous posture for MSF was 30° ankle eversion for the 3rd metatarsal at 70% PO. These results provide a guide, including what postures to avoid for the 2nd and 3rd MSF among people who are at high risk of MSF.

Effect of forefoot transverse arch stiffness on foot biomechanical response--based on finite element method

Background

The plantar vault, comprising the transverse and longitudinal arches of the human foot, is essential for impact absorption, elastic energy storage, and propulsion. Recent research underscores the importance of the transverse arch, contributing over 40% to midfoot stiffness. This study aimed to quantify biomechanical responses in the ankle-foot complex by varying the stiffness of the deep metatarsal transverse ligament (DTML).

Methods

Using CT image reconstruction, we constructed a complex three-dimensional finite element model of the foot and ankle joint complex, accounting for geometric complexity and nonlinear characteristics. The focus of our study was to evaluate the effect of different forefoot transverse arch stiffness, that is, different Young's modulus values of DTML (from 135 MPa to 405 MPa), on different biomechanical aspects of the foot and ankle complex. Notably, we analyzed their effects on plantar pressure distribution, metatarsal stress patterns, navicular subsidence, and plantar fascial strain.

Results

Increasing the stiffness of the DTML has significant effects on foot biomechanics. Specifically, higher DTML stiffness leads to elevate von Mises stress in the 1st, 2nd, and 3rd metatarsals, while concurrently reducing plantar pressure by 14.2% when the Young's modulus is doubled. This stiffening also impedes navicular bone subsidence and foot lengthening. Notably, a 100% increase in the Young's modulus of DTML results in a 54.1% decrease in scaphoid subsidence and a 2.5% decrease in foot lengthening, which collectively contribute to a 33.1% enhancement in foot longitudinal stiffness. Additionally, doubling the Young's modulus of DTML can reduce the strain stretch of the plantar fascia by 38.5%.

Conclusion

Preserving DTML integrity sustains the transverse arch, enhancing foot longitudinal stiffness and elastic responsiveness. These findings have implications for treating arch dysfunction and provide insights for shoe developers seeking to enhance propulsion.

Effects of plantar fascia stiffness on the internal mechanics of idiopathic pes cavus by finite element analysis: implications for metatarsalgia

Metatarsalgia occurring in individuals with pes cavus is typically associated with abnormal loading patterns in the forefoot resulting from structural alterations. Simultaneously, the frequent overstress of the plantar fascia (PF) caused by the persistence of this foot deformity may further exacerbate the chronic pain induced by metatarsal overload. We aimed to investigate and quantify the effects of PF stiffness on the internal biomechanics of pes cavus using a computational modelling approach. A patient-specific finite element model of the foot-ankle complex using the actual three-dimensional geometry of idiopathic pes cavus bones and soft tissues was reconstructed. A sensitivity study was conducted to evaluate the effects of varying elastic modulus (0-700 MPa) of the PF on the metatarsal stress distribution, and force transmission through the metatarsophalangeal (MTP) and tarsometatarsal (TMT) joints in the pes cavus. The results indicated that variations in PF stiffness led to stress redistribution in the metatarsal region. Peak stress gradually reduced with decreasing stiffness until the PF was released, eventually resulting in a reduction of 22.39% compared to the reference value of 350 MPa. Furthermore, adjusting the PF stiffness to twice the reference value (700 MPa) increased the contact forces through the TMT and MTP joints by up to 23% and 116%, respectively. The reduction of PF stiffness alleviated focal metatarsal loading, and therefore, surgical fascia release can be considered to alleviate metatarsalgia in patients with pes cavus.

An investigation of the ankle contact forces in a foot with hammer toe deformity. A comparison of patient-specific approaches using finite element modeling and musculoskeletal simulation

The internal forces and stresses in the tissue are important as they are linked to the risk of mechanical trauma and injuries. Despite their value, the internal stresses and forces cannot be directly measured in-vivo. A previously validated 3D finite element model (FEM) was constructed using Magnetic Resonance Imaging (MRI) of a person with diabetes and hammer toe deformity. The foot model simulated at five different instances during the stance phase of gait. The internal stress distribution on the talus that was obtained using the FEM simulation, was used to calculate the joint reaction force at the ankle joint. In addition, the musculoskeletal model (MSM) of the participant with hammer toe foot was developed based on the gait analysis and was used to determine the muscle forces and joint reactions. The result showed that the vertical reaction forces obtained from the FEM and MSM follow a similar trend through the stance phase of gait cycle and are significantly correlated ( R=0.99). The joint reaction forces obtained through the two methods do not differ for the first 25% of the gait cycle, while the maximum difference was ∼0.7 Body weight that was observed at 50% of the stance phase. Clinical Relevance: Finite element modeling and musculoskeletal simulation can shed light on the internal forces at the ankle in pathological conditions such as hammer toe. The similarities and differences observed in the joint reaction forces calculated from the two methods can have implications in assessing the effect of clinical interventions.

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.

Associations between changes in loading pattern, deformity, and internal stresses at the foot with hammer toe during walking; a finite element approach

Over the past decade, Finite Element (FE) modelling has been used as a method to understand the internal stresses within the diabetic foot. Foot deformities such as hammer toe have been associated with increased risk of foot ulcers in diabetic patients. Hence the aim of this study is to investigate the influence of hammer toe deformity on internal stresses during walking. A 3D finite element model of the human foot was constructed based on capturing Magnetic Resonance Imaging (MRI) of a diabetic neuropathic volunteer exhibiting hammer toe. 3D gait measurements and a multi-body musculoskeletal model for the same participant were used to define muscle forces. FE simulations were run at five different instances during the stance phase of gait. Peak plantar pressure and pressure distribution results calculated from the model showed a good agreement with the experimental measurement having less than 11% errors. Maximum von Mises internal stresses in the forefoot hard tissue were observed at the 3^rd and 5^th metatarsals and 4^th proximal phalanx. Moreover, presence of hammer toe deformity was found to shift the location of maximum internal stresses on the soft tissue to the forefoot by changing the location of centre of pressure with internal stress 1.64 times greater than plantar pressure. Hammer toe deformity also showed to reduce the involvement of the first phalanx in internal/external load-bearing during walking. The findings of this study support the association between changes in loading pattern, deformity, and internal stresses in the soft tissue that lead to foot ulceration.

Early Results of a Novel Intramedullary Fixation Device for Proximal Fifth Metatarsal Fractures

BACKGROUND

Proximal fifth metatarsal fractures are commonly treated surgically due to their poor healing capacity. While intramedullary screws may be the most popular operative treatment choice, newer fixation methods continue to develop. We present a case series utilizing a novel intramedullary fixation device for proximal fifth metatarsal fractures. To our knowledge, no other study in the literature has assessed the safety and efficacy of this fixation method.

METHODS

A retrospective analysis was performed for 16 patients with proximal fifth metatarsal fractures who underwent fixation with the same novel intramedullary device. Patient charts were reviewed for fracture union, plantar fracture gapping, time to weight-bearing, refracture, perioperative complications, and secondary surgeries.

RESULTS

Sixteen patients with an average age of 43.3 years underwent fixation with this novel device from 2015 to 2020. Mean follow-up was 32.4 weeks. Fifteen of the 16 patients achieved radiographic union at a mean of 8.9 weeks. One patient suffered a nonunion. Mean time to full weight-bearing in, and out of, a walking boot was 6.4 and 9.8 weeks, respectively, for healed fractures. Mean plantar fracture gap improved from 1.22 mm to 0.88 mm following surgery. There were zero infections, refractures, or hardware complications. Three patients suffered iatrogenic fracture during implant insertion.

CONCLUSION

To our knowledge, this is the first report of early results for this novel intramedullary device. Excellent union rates, acceptable time to weight-bearing, and a low complication profile can be achieved. Based on our findings, we propose a safe and effective treatment option for proximal fifth metatarsal fractures.

LEVELS OF EVIDENCE

Level IV: Clinical case series.

Effects of Custom-Made Insole Materials on Frictional Stress and Contact Pressure in Diabetic Foot with Neuropathy: Results from a Finite Element Analysis

Offloading plantar pressure in a diabetic foot with neuropathy is challenging in conventional clinical practice. Custom-made insole (CMI) materials play an important role in plantar pressure reduction, but the assessment is costly and time-consuming. Finite element analysis (FEA) can provide an efficient evaluation of different insoles on the plantar pressure distribution. This study investigated the effect of CMI materials and their combinations on plantar pressure reduction for the diabetic foot with neuropathy using FEA. The study was conducted by constructing a three-dimensional foot model along with CMI to study the peak contact pressure between the foot and CMI. The softer material (E = 5 MPa) resulted in a better reduction of peak contact pressure compared with the stiffer material (E = 11 MPa). The plantar pressure was well redistributed with softer material compared with the stiffer material and its combination. In addition, the single softer material resulted in reduced frictional stress under the first metatarsal head compared with the stiffer material and the combination of materials. The softer material and its combination have a beneficial effect on plantar pressure reduction and redistribution for a diabetic foot with neuropathy. This study provided an effective approach for CMI material selection using FEA.

Proximal Fifth Metatarsal Fractures in Athletes: Management of Acute and Chronic Conditions

Proximal fifth metatarsal fractures are common in the athlete and can be a source of significant, temporary disability and missed playing time. The pattern of fracture can vary, and the type of fracture leads to a significantly different prognosis and treatment. Jones fractures of the fifth metatarsal are particularly common and difficult to treat in the athlete, can have recurrence and refracture, and require expertise to heal. Intramedullary screw fixation is currently the preferred method of fixation. Most other (non-Jones fractures and os vesalianum) proximal fifth metatarsal fractures can be treated successfully without surgery.

Ankle Structures of Professional Soccer (Football) Players With Proximal Diaphyseal Stress Fractures of the Fifth Metatarsal

Despite a high incidence of proximal diaphyseal stress fractures of the fifth metatarsal (zone 3) in soccer (football) players, studies that examine risk factors of the fractures in professional soccer players are scarce; in particular, ankle structures have not yet been investigated. This study was designed to investigate ankle structures of professional soccer players with proximal diaphyseal stress fractures of the fifth metatarsal. We reviewed the ankle radiographs of 100 professional soccer players (stress fractures n = 15; controls n = 85) and measured the medial malleolar slip angle (MMSA), the ratio of the medial malleolar length to the width of the talar dome (MML:TD ratio), the ratio of the lateral malleolar length to the width of the TD (LML:TD ratio), and the ratio of the MML to the LML (MML:LML ratio). The MMSA (p < .01: 28.7° ± 5.8° versus 23.0° ± 4.9°) in the stress fractures was significantly wider and the MML:TD ratio (p = .08: 0.49 ± 0.08 versus 0.52 ± 0.07) had a trend to be smaller compared with the values of the controls. Logistic regression analysis revealed that a wider malleolar slip angle became a factor associated with stress fractures in professional soccer players (p < .01: odds ratio 1.27, 95% confidence interval 1.110 to 1.463). Receiver operating characteristic curve with MMSA for the stress fractures was depicted with an area under the curve of 0.778, and the suitable cut-off point was set at MMSA >27° with a positive likelihood ratio of 3.67 (95% confidence interval 2.173 to 6.188). Our study results show that a wide MMSA was associated with proximal diaphyseal stress fractures of the fifth metatarsal in professional soccer players.

Fifth Metatarsal Jones Fractures in the Athlete

Fifth metatarsal fractures, otherwise known as "Jones" fractures, occur commonly in athletes and nonathletes alike. While recent occurrence in the popular elite athlete has increased public knowledge and interest in the fracture, this injury is common at all levels of sport. This review will focus on all three types of Jones fractures. The current standard for treatment is operative intervention with intramedullary screw fixation. Athletes typically report an acute episode of lateral foot pain, described as an ache. Radiographic imaging with multiple views of the weightbearing injured foot are needed to confirm diagnosis. If these images are inconclusive, further magnetic resonance imaging (MRI) or computed tomography (CT) is used. Nonoperative treatment is not commonly used as the sole treatment, except when following reinjury of a stable screw fixation. While screw selection is still controversial, operative treatment with intramedullary screw fixation is the standard approach. Technical tips on screw displacement are provided for Torg (types I, II, III) fractures, cavovarus foot fractures, recurrent fractures, revision surgery, occult fractures/high-grade stress reactions, and Jones' variants. Excellent clinical outcomes can be expected in 80% to 100% of patients when using the intramedullary screw fixation to "fit and fill" the medullary canal with threads across the fracture site. Most studies show the timing for return to sports with optimal healing to be seven to twelve weeks after fixation.

LEVEL OF EVIDENCE

Level V, expert opinion.

Subject-specific finite element modelling of the human foot complex during walking: sensitivity analysis of material properties, boundary and loading conditions

The objective of this study was to develop and validate a subject-specific framework for modelling the human foot. This was achieved by integrating medical image-based finite element modelling, individualised multi-body musculoskeletal modelling and 3D gait measurements. A 3D ankle-foot finite element model comprising all major foot structures was constructed based on MRI of one individual. A multi-body musculoskeletal model and 3D gait measurements for the same subject were used to define loading and boundary conditions. Sensitivity analyses were used to investigate the effects of key modelling parameters on model predictions. Prediction errors of average and peak plantar pressures were below 10% in all ten plantar regions at five key gait events with only one exception (lateral heel, in early stance, error of 14.44%). The sensitivity analyses results suggest that predictions of peak plantar pressures are moderately sensitive to material properties, ground reaction forces and muscle forces, and significantly sensitive to foot orientation. The maximum region-specific percentage change ratios (peak stress percentage change over parameter percentage change) were 1.935-2.258 for ground reaction forces, 1.528-2.727 for plantar flexor muscles and 4.84-11.37 for foot orientations. This strongly suggests that loading and boundary conditions need to be very carefully defined based on personalised measurement data.

Biomechanical study of tarsometatarsal joint fusion using finite element analysis

Complications of surgeries in foot and ankle bring patients with severe sufferings. Sufficient understanding of the internal biomechanical information such as stress distribution, contact pressure, and deformation is critical to estimate the effectiveness of surgical treatments and avoid complications. Foot and ankle is an intricate and synergetic system, and localized intervention may alter the functions to the adjacent components. The aim of this study was to estimate biomechanical effects of the TMT joint fusion using comprehensive finite element (FE) analysis. A foot and ankle model consists of 28 bones, 72 ligaments, and plantar fascia with soft tissues embracing all the segments. Kinematic information and ground reaction force during gait were obtained from motion analysis. Three gait instants namely the first peak, second peak and mid-stance were simulated in a normal foot and a foot with TMT joint fusion. It was found that contact pressure on plantar foot increased by 0.42%, 19% and 37%, respectively after TMT fusion compared with normal foot walking. Navico-cuneiform and fifth meta-cuboid joints sustained 27% and 40% increase in contact pressure at second peak, implying potential risk of joint problems such as arthritis. Von Mises stress in the second metatarsal bone increased by 22% at midstance, making it susceptible to stress fracture. This study provides biomechanical information for understanding the possible consequences of TMT joint fusion.