Effects of plantar fascia stiffness on the biomechanical responses of the ankle-foot complex

Subject-specific material properties of the heel pad: An inverse finite element analysis

Individuals with diabetes are at a higher risk of developing foot ulcers. To better understand internal soft tissue loading and potential treatment options, subject-specific finite element (FE) foot models have been used. However, existing models typically lack subject-specific soft tissue material properties and only utilize subject-specific anatomy. Therefore, this study determined subject-specific hindfoot soft tissue material properties from one non-diabetic and one diabetic subject using inverse FE analysis. Each subject underwent cyclic MRI experiments to simulate physiological gait and to obtain compressive force and three-dimensional soft tissue imaging data at 16 phases along the loading-unloading cycles. The FE models consisted of rigid bones and nearly-incompressible first-order Ogden hyperelastic skin, fat, and muscle (resulting in six independent material parameters). Then, calcaneus and loading platen kinematics were computed from imaging data and prescribed to the FE model. Two analyses were performed for each subject. First, the skin, fat, and muscle layers were lumped into a single generic soft tissue material and optimized to the platen force. Second, the skin, fat, and muscle material properties were individually determined by simultaneously optimizing for platen force, muscle vertical displacement, and skin mediolateral bulging. Our results indicated that compared to the individual without diabetes, the individual with diabetes had stiffer generic soft tissue behavior at high strain and that the only substantially stiffer multi-material layer was fat tissue. Thus, we suggest that this protocol serves as a guideline for exploring differences in non-diabetic and diabetic soft tissue material properties in a larger population.

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.

A Bio-Inspired Arched Foot with Individual Toe Joints and Plantar Fascia

This paper presents the design and testing of an arched foot with several biomimetic features, including five individual MTP (toe) joints, four individual midfoot joints, and plantar fascia. The creation of a triple-arched foot represents a step further in bio-inspired design compared to other published designs. The arched structure creates flexibility that is similar to human feet with a vertical deflection of up to 12 mm. The individual toe joints enable abduction-adduction in the forefoot and therefore a natural pronation motion. Adult female bone data was obtained and converted into a CAD model to accurately identify the location of bones, joints, and arches. An analytical model is presented that gives the relationship between the vertical stiffness and horizontal stiffness of the longitudinal arches and therefore allows the optimization of stiffness elements. Experimental tests have demonstrated a vertical arch stiffness of 76 N/mm which is similar to adult human feet. The range of movement of the foot is similar to human feet with the following values: dorsi-plantarflexion (28°/37°), inversion-eversion (30°/15°), and abduction-adduction (30°/39°). Tests have also demonstrated a three-point contact with the ground that is similar to human feet.

Understanding the form and function in Chinese bound foot from last-generation cases

Purpose: Foot adaptation in the typically developed foot is well explored. In this study, we aimed to explore the form and function of an atypical foot, the Chinese bound foot, which had a history of over a thousand years but is not practised anymore. Methods: We evaluated the foot shape and posture via a statistical shape modelling analysis, gait plantar loading distribution via gait analysis, and bone density adaptation via implementing finite element simulation and bone remodelling prediction. Results: The atypical foot with binding practice led to increased foot arch and vertically oriented calcaneus with larger size at the articulation, apart from smaller metatarsals compared with a typically developed foot. This shape change causes the tibia, which typically acts as a load transfer beam and shock absorber, to extend its function all the way through the talus to the calcaneus. This is evident in the bound foot by i) the reduced center of pressure trajectory in the medial-lateral direction, suggesting a reduced supination-pronation; ii) the increased density and stress in the talus-calcaneus articulation; and iii) the increased bone growth in the bound foot at articulation joints in the tibia, talus, and calcaneus. Conclusion: Knowledge from the last-generation bound foot cases may provide insights into the understanding of bone resorption and adaptation in response to different loading profiles.

Plantar fascia stiffness in patients with type 2 diabetes mellitus: Stiffness effect on fall risk and gait speed

AIMS

The primary objective was to compare patients with type 2 diabetes mellitus (T2DM) and healthy peers in terms of plantar fascia (PF) stiffness, fall risk, and gait speed. The second objective was to examine the relationship between stiffness of PF and fall risk, gait speed.

METHODS

Fifty patients diagnosed with T2DM (mean duration = 10.74 ± 7.07 years) were included. Myotonometer was used to evaluate the stiffness of PF. To assess the risk of falling, and gait speed, the International Fall Efficiency Scale (FES-I) and the 4-Meter Gait Speed Test (4mGST) were used, respectively.

RESULTS

Compared to healthy controls, PF stiffness (right foot mean difference = 148.99 N/m, left foot mean difference = 113.13 N/m p < .001) was higher in the T2DM group. The FES-I and 4mGST scores were worse in the group with T2DM (p < .05). 12.8 % of FES-I and 23.4 % of 4mGST variance were explained by stiffness of PF.

CONCLUSIONS

The results of the study showed that the stiffness of PF changed in patients with T2DM. There was a decrease in gait speed and an increase in the risk of falling as PF stiffness increased.

Ligament Insufficiency with Flatfoot: Spring Ligament and Deltoid Ligament

The objective of this article was to review the deltoid ligament and spring ligament specifically as they pertain to ligament insufficiency and adult-acquired flatfoot deformity. Discussion includes the normal and abnormal biomechanical forces that extend through these ligaments in normal and flatfoot deformity. Current literature related to spring ligament repair as part of the flatfoot deformity reconstruction is also reviewed.

Regional differences in the mechanical properties of the plantar aponeurosis

The plantar aponeurosis functions to support the foot arch during weight bearing. Accurate anatomy and material properties are critical in developing analytical and computational models of this tissue. We determined the cross-sectional areas and material properties of four regions of the plantar aponeurosis: the proximal middle and distal middle portions of the tissue and the medial (to the first ray) and lateral (to the fifth ray) regions. Bone-plantar aponeurosis-bone specimens were harvested from fifteen cadaveric feet. Cross-sectional areas were measured using molding, casting, and sectioning methods. Mechanical testing was performed using displacement control triangle waves (0.5, 1, 2, 5, and 10 Hz) loaded to physiologic tension by estimating from body weight and area ratio of the region. Five specimens were tested for each region. Regional deformations were recorded by a high-speed video camera. There were overall differences in cross-sectional areas and biomechanical behavior across regions. The stress-strain responses are non-linear and mainly elastic (energy loss 3.6% to 7.2%). Moduli at the proximal middle and distal middle regions (400 and 522 MPa) were significantly higher than the medial and lateral regions (225 and 242 MPa). The effect of frequency on biomechanical outcomes was small (e.g., 3.5% change in modulus), except for energy loss (107% increase as frequency increased from 0.5 to 10 Hz). These results indicate that the plantar aponeurosis tensile response is non-linear, nearly elastic, and frequency independent. The cross-sectional area and material properties differ by region, and we suggest that such differences be included to accurately model this structure.

Foot shape is related to load-induced shape deformations, but neither are good predictors of plantar soft tissue stiffness

Modern human feet are considered unique among primates in their capacity to transmit propulsive forces and re-use elastic energy. Considered central to both these capabilities are their arched configuration and the plantar aponeurosis (PA). However, recent evidence has shown that their interactions are not as simple as proposed by the theoretical and mechanical models that established their significance. Using three-dimensional foot scans and statistical shape and deformation modelling, we show that the shape of the longitudinal and transverse arches varies widely among the healthy adult population, and that the former is subject to load-induced arch flattening, whereas the latter is not. However, longitudinal arch shape and flattening are only one of the various foot shape-deformation relationships. PA stiffness was also found to vary widely. Yet only a small amount of this variability (approx. 10-18%) was explained by variations in foot shape, deformation and their combination. These findings add to the mounting evidence showing that foot mechanics are complex and cannot be accurately represented by simple models. Especially the interactions between longitudinal arch and PA appear to be far less constrained than originally proposed, most likely due to the many degrees of freedom provided by the structural complexity of our feet.

Effect of Age and BMI on Sonographic Findings of Plantar Fascia

Biomechanical dysfunction of the foot is most common cause of plantar fascia disorder and obesity and increasing age are well-known risk factors. Due to being inexpensive and quick, ultrasound imaging techniques are considered the modality of choice to assess plantar fascia. The aim of this study was to investigate the effect of age and body mass index (BMI) on sonographic findings of plantar fascia in normal population. Ultrasonography was used to measure the plantar fascia thickness of 148 healthy adults (54 males, 36.5% and 94 females, 63.5%) during a period of one year. The age, BMI, and walking distance of each participant were recorded and statistically analyzed. The mean plantar fascia thicknesses at 0.5, 1.0, and 2.0 cm distal to the insertion of the plantar fascia were 1.76 ± 0.32 mm, 2.50 ± 0.50 mm and 2.11 ± 0.41 mm respectively. The mean plantar fascia thickness for individuals ≥45 years and BMI ≥25 were significantly higher (p < .001) compared to individuals <45 years and BMI <25. In a normal population, the thickness of the plantar fascia determined by ultrasound measurement was less than 3 mm. We recommend using the position 1.0 cm distal to the calcaneal insertion of the plantar fascia as the reference point for diagnosing plantar fasciitis. The thickness of plantar fascia was significantly increased with age and BMI whereas gender, walking activity, exercise and running did not seem to affect the plantar fascia thickness.

Isokinetic Analysis of Flexible Flatfoot: Is It a Weakness of Proprioception and Muscle Strength?

BACKGROUND

Although flexible flatfoot (FF) in children is a foot deformity that is frequently encountered in daily orthopedics practice, its etiology is still controversial. The aim of this study was to determine whether there is a weakness in muscle strength and proprioception in patients with FF.

METHODS

The study group consisted of 16 cases with FF, and the control group consisted of 25 volunteers with normal feet. An isokinetic dynamometer was used to assess muscle strength and proprioception of movement directions of plantarflexion, dorsiflexion, eversion (EV), and inversion (INV) in both groups.

RESULTS

There was no statistically significant difference between the groups in strength of plantarflexion and dorsiflexion muscles, whereas in the control group, proprioception of all four movement directions and strengths of the EV and INV muscles were found to be statistically significantly higher (P < .05).

CONCLUSIONS

There is weakness in EV and INV muscle strength and proprioception disorder in patients with FF. We recommend conducting further studies that validate muscle weakness and proprioception disorders with different study designs and evaluate the effectiveness of improving muscle strength and proprioception weakness in FF.

Comparison of static balance and gait between subjects with plantar fasciitis and age-matched controls

BACKGROUND

Plantar fasciitis (PF) is a common condition amongst athletes as well as in non-sporting population. It is characterised by a sharp pain under the calcaneus during walking. The impact of pain due to PF on gait and static balance is examined in this observational study.

OBJECTIVE

To compare gait and balance between individuals with PF and age-matched controls without PF.

METHOD

A cross-sectional observational study was executed in an Outpatient Rehabilitation Centre. Twenty-nine participants were included, 14 with PF, and 15 age-matched healthy asymptomatic individuals. Main outcome measures were foot pain, foot function index (FFI), static balance measured with modified Romberg test, static balance measured on the TYMO® system, and gait with the G-Walk System.

RESULTS

Foot pain and FFI were adversely related to balance and gait parameters in subjects with PF. Static balance with eyes open and eyes closed on firm and soft surface measured on the TYMO® balance platform as well as gait parameters measured with the G-Walk system, were significantly lower in subjects with PF compared to age-matched healthy controls.

CONCLUSION

PF negatively affects parameters of static balance measured with TYMO® system and gait parameters measured with the G-Walk System. However, the Romberg balance test did not detect differences between subjects with PF and age-matched healthy controls.

A Critical Biomechanical Evaluation of Foot and Ankle Soft Tissue Repair

The objective of this article is to review the biomechanical stresses that occur during normal physiologic function of lower extremity soft tissue anatomic structures and to use this as a baseline for a critical analysis of the medical literature because it relates to surgical reconstruction following injury. The Achilles tendon, anterior talofibular ligament, plantar plate, and spring ligament are specifically evaluated.

3D printed auxetic heel pads for patients with diabetic mellitus

More than 422 million people worldwide suffered from diabetes mellitus (DM) in 2021. Diabetic foot is one the most critical complications resultant of DM. Foot ulceration and infection are frequently arisen, which are associated with changes in the mechanical properties of the plantar soft tissues, peripheral arterial disease, and sensory neuropathy. Diabetic insoles are currently the mainstay in reducing the risk of foot ulcers by reducing the magnitude of the pressure on the plantar Here, we propose a novel pressure relieving heel pad based on a circular auxetic re-entrant honeycomb structure by using three-dimensional (3D) printing technology to minimize the pressure on the heel, thus reducing the occurrence of foot ulcers. Finite element models (FEMs) are developed to evaluate the structural changes of the developed circular auxetic structure upon exertion of compressive forces. Moreover, the effects of the internal angle of the re-entrant structure on the peak contact force and the mean pressure acting on the heel as well as the contact area between the heel and the pads are investigated through a finite element analysis (FEA). Based on the result from the validated FEMs, the proposed heel pad with an auxetic structure demonstrates a distinct reduction in the peak contact force (∼10%) and the mean pressure (∼14%) in comparison to a conventional diabetic insole (PU foam). The characterized result of the designed circular auxetic structure not only provides new insights into diabetic foot protection, but also the design and development of various impact resistance products.

Investigation of the relationship between the thickness of the plantar calcaneonavicular ligament and plantar fascia in patients with plantar fasciitis

BACKGROUND

Although patients with plantar fasciitis show spring ligament laxity, the thickness of the spring ligament in patients with plantar fasciitis remains unclear. This study aimed to elucidate the morphological characteristics of the spring ligament in patients with plantar fasciitis based on an ultrasound imaging system (US).

METHODS

Thirty feet of 30 patients (painful group) diagnosed with plantar fasciitis at our hospital and thirty feet of 30 healthy volunteers (healthy group) without plantar pain were investigated. The thicknesses of both the spring ligament and plantar fascia were assessed via a US statistical comparison of the spring ligament and plantar fascia thickness between the painful and healthy groups. This was performed using Welch's t-test, and the significance level was set at p < 0.01. In addition, Pearson's correlation coefficient was calculated to assess the correlation between the spring ligament and plantar fascia thickness in the two groups, and the significance level was set at p < 0.01.

RESULTS

The spring ligament thickness in the painful group was significantly lower than that in the healthy group (p < 0.001). The thickness of the plantar fascia in the painful group was significantly greater than that in the healthy group (p = 0.03). In addition, the correlation between the spring ligament and plantar fascia thickness was moderately negative (r = -0.42, p = 0.001). The thicker the plantar fascia in the subjects, the thinner was the spring ligament.

CONCLUSIONS

The thickness of the spring ligament in patients with plantar fasciitis decreased. The thinning of the spring ligament was negatively correlated with the thickening of the plantar fascia as per the US evaluation. Based on the spring ligament thinning determined via US evaluation, interventions such as insoles from an early stage could prevent the onset of plantar fasciitis.

Arbitrary Prestrain Values for Ligaments Cause Numerical Issues in a Multibody Model of an Ankle Joint

Experimental studies report that ligaments of the ankle joint are prestrained. The prestrain is an important aspect of modern biomechanical analysis, which can be included in the models by: applying symmetrical, arbitrary prestrains to the ligaments, assuming a strain-free location for the joint or by using experimental prestrain data. The aim of the study was to comparatively analyze these approaches. In total, 4 prestraining methods were considered. In order to do so, a symmetrical model of the ankle with six nonlinear cables and two sphere–sphere contact pairs was assumed. The model was solved in statics under moment loads up to 5 Nm. The obtained results showed that the arbitrary prestrains caused an unbalanced load for the model at rest, and in turn modified its rest location in an unpredictable way. Due to the imbalance, it was impossible to enforce the assumed prestrains and thus cartilage prestrain was required to stabilize the model. The prestraining had a significant effect on the angular displacements and the load state of the model. The findings suggest that the prestrain values are patient specific and arbitrary prestrains will not be valid for most models.

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.

Design optimization procedure for an orthopedic insole having a continuously variable stiffness/shape to reduce the plantar pressure in the foot of a diabetic patient

Foot ulcers and lower-limb amputations are among the major problems in diabetic patients. Orthopedic insoles can reduce the risk of diabetic foot ulcers in patients through pressure redistribution on the bottom of the foot. The purpose of this study was to propose an optimization method to design the dedicated insoles for diabetic patients in order to decrease the maximum plantar pressure. At first, a three-dimensional finite element model of bones, ligaments and soft tissue of a diabetic patient's foot was created using CT scan images. Then, the foot plantar pressure was calculated by means of a finite element software. Next, the stiffness and shape of a simple flat insole were separately modified to reduce the maximum foot plantar pressure. The optimization method resulted in a dedicated insole design with a continuously variable stiffness/shape within its area that creates a smooth pressure distribution for the patient comfort. The results showed a 40% reduction in the maximum foot pressure, which we attribute to the modification of insole stiffness. In addition, the optimal shape of the proposed insole decreased the maximum plantar pressure by 25% compared to the flat insole.

Three-Dimensional Finite Element Analysis and Biomechanical Analysis of Midfoot von Mises Stress Levels in Flatfoot, Clubfoot, and Lisfranc Joint Injury

Background

Midfoot deformity and injury can affect the internal pressure distribution of the foot. This study aimed to use 3D finite element and biomechanical analyses of midfoot von Mises stress levels in flatfoot, clubfoot, and Lisfranc joint injury.

Material/Methods

Normal feet, flatfeet, clubfeet (30 individuals each), and Lisfranc injuries (50 individuals) were reconstructed by CT, and 3D finite element models were established by ABAQUS. Spring element was used to simulate the plantar fascia and ligaments and set hyperelastic coefficients in encapsulated bone and ligaments. The stance phase was simulated by applying 350 N on the top of the talus. The von Mises stress of the feet and ankle was visualized and analyzed.

Results

The von Mises stress on healthy feet was higher in the lateral metatarsal and ankle bones than in the medial metatarsal bone. Among the flatfoot group, the stress on the metatarsals, talus, and navicular bones was significantly increased compared with that on healthy feet. Among patients with clubfeet, stress was mainly concentrated on the talus, and stress on the lateral metatarsal and navicular bones was significantly lower. The von Mises stress on the fractured bone was decreased, and the stress on the bone adjacent to the fractured bone was higher in Lisfranc injury. During bone dislocation alone or fracture accompanied by dislocation, the von Mises stress of the dislocated bone tended to be constant or increased.

Conclusions

Prediction of von Mises stress distribution may be used clinically to evaluate the effects of deformity and injury on changes in structure and internal pressure distribution on the midfoot.

OPTIMAL MESH CRITERIA IN FINITE ELEMENT MODELING OF HUMAN FOOT: THE DEPENDENCE FOR MULTIPLE MODEL OUTPUTS ON MESH DENSITY AND LOADING BOUNDARY CONDITIONS

The use of finite element models has gained popularity in the field of foot and footwear biomechanics to predict the stress–strain distribution and the treatment effectiveness of therapeutic insoles for pathological foot conditions. However, a comprehensive evaluation of mesh quality is often ignored, meanwhile no golden standard exists for the mesh density and selection of element size at an acceptable accuracy. Here, we make a convergence test and established anatomically-realistic foot models at different mesh densities. The study compared the discrepancy in output variables to the changes of element type and mesh density under barefoot and footwear conditions with compressive and shear loads, which are commonly encountered in foot and footwear biomechanics simulations. For a range of loading conditions simulated in 125 finite element models, the peak plantar pressure consistently converged with optimal mesh size determined at 2.5[Formula: see text]mm. The convergence variable of principal strains and stress tensors, however, varies significantly. The max von-Mises stress showed strong sensitive behavior to the changes of the mesh density. The pattern for contact pressure distribution became less accurate when the element sizes increase to 6.0[Formula: see text]mm; in particular, the locations of the pressure peak do not show remarkable changes, but the size of the area of contact still changes. The current study could offer a general guideline when generating a reasonable accurate finite element models for the analysis of plantar pressure distributions and stress/strain states employed for foot and footwear biomechanics evaluations.

Real-Time Analysis of the Dynamic Foot Function: A Machine Learning and Finite Element Approach

Finite element analysis (FEA) has been widely used to study foot biomechanics and pathological functions or effects of therapeutic solutions. However, development and analysis of such foot modeling is complex and time-consuming. The purpose of this study was therefore to propose a method coupling a FE foot model with a model order reduction (MOR) technique to provide real-time analysis of the dynamic foot function. A generic and parametric FE foot model was developed and dynamically validated during stance phase of gait. Based on a design of experiment of 30 FE simulations including four parameters related to foot function, the MOR method was employed to create a prediction model of the center of pressure (COP) path that was validated with four more random simulations. The four predicted COP paths were obtained with a 3% root-mean-square-error (RMSE) in less than 1 s. The time-dependent analysis demonstrated that the subtalar joint position and the midtarsal joint laxity are the most influential factors on the foot functions. These results provide additionally insight into the use of MOR technique to significantly improve speed and power of the FE analysis of the foot function and may support the development of real-time decision support tools based on this method.

Plantar fasciitis: Talonavicular instability/spring ligament failure as the driving force behind its histological pathogenesis

The aetiology of plantar fasciitis (PF) remains uncertain and to date, it is not known if there is an association with spring ligament laxity. In this study, 28 patients with unilateral plantar fasciitis were evaluated. A digital Klaumeter was used to assess first ray for instability and lateral plane translation was used as a measure of spring ligament laxity in the affected vs unaffected foot (internal control). Retromalleolar tenderness as a sign of a reactive tibialis posterior tendon was also assessed. The mean lateral translation score for symptomatic feet was 67.2 (95% CI [63.26-71.14]), compared to asymptomatic feet mean of 33.0 (95% CI [27.35-38.65] p < 0.05). The mean TMT instability score for symptomatic feet was 11.3 (95% CI [10.29-12.3]), compared to the asymptomatic feet mean of 5.9 (95% CI [4.49-7.31] p < 0.05). 100% of symptomatic feet had a retromalleolar tenderness over the tibialis posterior compared to 14% of asymptomatic feet. This is the first study to demonstrate a statistically significant increase in spring ligament strain in feet affected with PF using internal controls. The study postulates that tensile overload at the medial plantar fascia develops secondary to spring ligament failure regardless of foot shape. Furthermore, this condition can be regarded as an early warning sign of adult acquired flat foot disorder (AAFD). Future treatments for PF should not further destabilise the medial arch. This understanding may allow development of new treatment strategies in restoring spring ligament integrity to offload the plantar fascia strain.

Effect of dynamic guidance-tubing short foot gait exercise on muscle activity and navicular movement in people with flexible flatfeet

BACKGROUND

Navicular drop is a common plantar deformity which makes the plantar medial longitudinal arch (MLA) collapse and leads to other deformities in lower extremities. Active structures are from intrinsic and extrinsic foot muscle activities such as abductor hallucis (AbdH), tibialis anterior (TA), tibialis posterior, flexor hallucis brevis, flexor digitorum brevis during dynamic situations. As AbdH plays a role as a dynamic elevator of MLA, the importance of AbdH has been emphasized and the proper recruitment of both intrinsic and extrinsic muscle is crucial for stabilization of MLA during dynamic weight bearing condition. Because the short foot (SF) exercise is difficult to perform and tends to activate the intrinsic muscles concentrically rather than a natural coordination of concentric-isometric-eccentric activation, we have developed the guidance-tubing SF gait (GFG) exercise.

OBJECTIVE

We investigated the effect of GFG exercise on muscle activity, AbdH:TA activity ratio, MLA angle, and foot pressure distribution during walking compared to SF gait (SFG) exercise.

METHODS

Thirty-two subjects with flexible flat feet were divided into two groups and performed SFG exercise with (GFG) and without guidance-tubing (SFG) for seven serial days.

RESULTS

AbdH muscle activity significantly increased from foot flat to heel rise in the GFG group (p = 0.006). The AbdH:TA activity ratio significantly increased in both the SFG (p = 0.015) group and GFG group (p = 0.006). MLA angles significantly decreased in both the SFG group (p = 0.001) and GFG group (p = 0.000), and the decrement was significantly higher in the GFG group (p = 0.001). The foot pressure distribution did not show any statistically significant change.

CONCLUSIONS

The result of this study provides a clinical implication for training MLA supporter muscles in individuals with flat feet. The overactive muscle must be inhibited first, then facilitation and strengthening are followed respectively.

Application of 3D-Printed Orthopedic Cast for the Treatment of Forearm Fractures: Finite Element Analysis and Comparative Clinical Assessment

Objective

This pilot study is aimed at investigating the mechanical characteristics of a cast-wrapped fractured forearm and performing a clinical comparative study of our own developed 3D-printed orthopedic cast.

Methods

An integrated finite element (FE) model including a forearm and a 3D-printed cast wrapping the forearm was created. The distal radial ulna in this model was cut through to mimic the bone fracture. A 400 N force and 1 Nm rotation moment, which were much larger than the loading conditions encountered in daily life for a human being, were applied on the palm. We conducted a comparative clinical study by using statistical assessment. 60 patients with forearm fractures were selected and treated with manual reduction and external fixation cast. All patients were divided into three groups with equal members (20): (a) 3D-printed external cast group, (b) traditional plaster external fixation group, and (c) splint external fixation group. The clinical efficacy, wrist function, and patient satisfaction were scored and compared.

Results

In the condition of 400 N loading, the fracture displacements in anterior-posterior (AP), posterior-anterior (PA), medial to lateral (ML), and lateral to medial (LM) compression directions were 1.2648, 1.3253, 0.8503, and 0.8957 (mm), respectively, and the corresponding fracture stresses were 4.5986, 3.9129, and 5.0334, 7.9197 (MPa), respectively. In the inward (IR) and outward (OR) rotations, the fracture displacements were both 0.02628 (mm), and the corresponding fracture surface stresses were 0.1733 and 0.1723 (MPa), respectively. In the clinical efficacy, wrist function, and patient comfort evaluation, the total scores of group A were both higher than those in groups B and C (P < 0.05).

Conclusion

A 3D-printed orthopedic cast was capable of exerting appropriate mechanical correction loads on specific areas to maintain optimal alignment of a fractured forearm and thus could achieve the favorable clinical efficacy and patient comfort.

Experimental and finite element investigation of total ankle replacement: A review of literature and recommendations

This paper briefly reviews the different methodology, technology, challenges, and outcomes of various studies related to TAR prosthesis based on numerical and experimental techniques. Very less in-vitro experimental studies on TAR have been found than finite element (FE) studies. Due to the invasive nature of the experimental approach, inadequacy and less clinical information, computational modelling has been widely used by the researchers. This paper critically examines the part related to FE modelling and experimental analysis. Some recommendation related to modelling of bones, cartilages, ligaments, muscles, and implant-bone interface condition were discussed for better understanding the results and better clinical significance.

A Planar Model of an Ankle Joint with Optimized Material Parameters and Hertzian Contact Pairs

The ankle is one of the most complicated joints in the human body. Its features a plethora of elements with complex behavior. Their functions could be better understood using a planar model of the joint with low parameter count and low numerical complexity. In this study, an accurate planar model of the ankle with optimized material parameters was presented. In order to obtain the model, we proposed an optimizational approach, which fine-tuned the material parameters of two-dimensional links substituting three-dimensional ligaments of the ankle. Furthermore, the cartilage in the model was replaced with Hertzian contact pairs. The model was solved in statics under moment loads up to 5 Nm. The obtained results showed that the structure exhibited angular displacements in the range of the ankle joint and that their range was higher in dorsiflexion than plantarflexion. The structure also displayed a characteristic ramp up of the angular stiffness. The results obtained from the optimized model were in accordance with the experimental results for the ankle. Therefore, the proposed method for fine-tuning the material parameters of its links could be considered viable.

Functional gradient structural design of customized diabetic insoles

Diabetic foot is a common and serious complication of diabetes, largely due to sensory neuropathy and excessive mechanical stresses. Studies have shown that reducing the contact pressure can effectively lower the incidence of diabetic foot. A new design method is proposed in this study for optimizing the stress distribution of the contact surfaces between the foot and the insole by applying functional gradient structural properties to the insole. Finite element analysis was employed for studying the contact mechanics, which laid the foundation for modulus readjustment during the optimization process. The moduli of the materials were correlated to the properties of the structural porous units. The customized insoles were manufactured using additive manufacturing technology and put into mechanical test. Results show that the designed insole helps in increasing the foot contact area by approximately 30% and reducing the peak contact pressure by 35%. Hence, the proposed method can be used to design customized insoles, particularly diabetic insoles, by offering better contact mechanics and good potential for reducing the severity of diabetic foot. The methodology is equally applicable to other designs involving optimization of material properties.

Flatfeet: Biomechanical implications, assessment and management

Several complications due to flatfeet have been reported in previous literature such as poor postural stability, injuries, pathologies, and discomfort. Early detection and appropriate management are mandatory to minimize these effects. There are different feet assessments established in the field with distinct advantages and disadvantages. Additionally, selection of management methods from various options should be done vigilantly as the application differs according to the individual. Therefore, the objective of this article is to review previous literature on structural anatomy, pathomechanics, assessment, and proper management of flatfeet to provide a condensed summary for healthcare professionals, occupational therapists, kinesiologists, biomechanists, coaches, and ergonomists.

Analysis of the stress distribution of the subtalar joint and fusion efficacy after double-screw insertion

BACKGROUND

Screw fixation is a typical technique for the isolated subtalar joint. However, no consensus has been reached on how to select the most suitable insertion position and direction. This study aims to find the ideal screw insertion and then explore its influence on the clinical efficacy of subtalar fusion by analyzing the effects of different cannulated screw insertions on the stress distribution, anti-rotary strength, and anti-inversion/eversion strength of the subtalar joint.

METHODS

In this study, we investigated three cannulated screw insertions for subtalar fusion: screw insertion with the most uniform stress distribution (group A), lateral-medial parallel screw insertion (group B), and traditional longitudinally parallel screw insertion (group C). The effects of these three insertions on the loading stress of the subtalar joint (including stress distribution, anti-inversion/eversion strength, and anti-rotary strength) were comparatively analyzed with the three-dimensional finite element method to screen the ideal screw insertion. Moreover, a prospective study was conducted to analyze the influence of the ideal screw insertion on subtalar fusion, including the fusion rate, fusion time, and clinical efficacy (VAS score, AOFAS score, and complications).

RESULTS

Group B was worse than group A with respect to the stress distribution uniformity, but slightly better than group C, and better than both groups A and C in terms of the anti-rotary strength and anti-inversion/eversion strength. The screw insertion based on the most uniform stress distribution is not feasible in surgery. Therefore, the lateral-medial antiparallel screw insertion is the ideal insertion. From January 2012 to June 2016, 48 cases were treated by subtalar fusion with the ideal screw insertion, and then followed up for 30.6 months (12-48 months). The fusion was proved in all 48 cases with a fusion rate of 100% by X-ray or CT scan. The mean time of fusion was 12.8 weeks (12-16 weeks). The VAS score decreased from 6.00 before operation to 1.03 on the last visit (P < 0.05), and the AOFAS score increased from 57.0 to 85.6 (P < 0.05), with a good and excellent rate of 95.8%.

CONCLUSIONS

The lateral-medial parallel screw insertion not only demonstrates a good stress distribution profile of the subtalar joint but also has advantages such as easy localization and operation during surgery, as well as a high fusion rate and few complications after surgery. Therefore, it is a safe, accurate, and effective fixation mode that is worthy of being popularized clinically.

Biomechanical evaluation of the first ray in pre-/post-operative hallux valgus: A comparative study

BACKGROUND

Deformity of the first ray in hallux valgus patient has been deemed to mainly contribute to instability of the metatarsophalangeal joint. However, it is not clear whether the fixation of the distal osteotomy fragment and transposition of the sesamoid represent the best method for hallux valgus treatment. The aim of this study was to examine how postoperative hallux valgus osteotomy affects the stability of the first ray.

METHODS

To accurately investigate the biomechanical behavior of the first ray in pre-/postoperative hallux valgus patients, we described the relative displacement and stress distribution of the first metatarsal bone and sesamoid by imageology, test measurement and foot finite element model.

FINDINGS

Compared with the preoperative hallux valgus, the plantar pressure decreased by 47.8% and was redistributed on second metatarsal region. The peak stress and relative displacement of the distal osteotomy fragment increased by +55.7% and -59.9%, respectively. The movement of this component shifted toward the positive sagittal axis direction. In addition, the relative displacement of sesamoid decreased by 87.4% (0.18 mm) in vertical axis direction and the stress was also redistributed on medial and lateral region. Moreover, the strain of the medial main ligament was more favorable to reconstruct function of the first ray.

INTERPRETATION

The findings showed that the osteotomy method was helpful for stability of the first ray. This would provide the stability suggestions for postoperative hallux valgus fixation and guide further rehabilitation.

Finite element analysis of knee and ankle joint during gait based on motion analysis

Contact pressures in the articular cartilage during gait affect injuries and the degenerative arthritis of knee and ankle joints. However, only contact forces at the knee and ankle joints during gait can be estimated by using a rigid body dynamic model. The contact pressure distribution can be obtained quantitatively for a static posture by using finite element (FE) analysis in most cases. The purpose of this study is to develop a new method to obtain the contact pressure distribution at the knee and ankle joints during gait by integrating FE analysis with rigid body dynamic analysis. In this method, a reference FE model of the lower extremity is constructed first and is then transformed to each stance phase of the gait obtained from dynamic analysis by using homogeneous transformation. The muscle forces and ground reaction force (GRF) during gait obtained from the dynamic analysis were used as loading conditions for FE analysis. Finally, the contact pressure distribution at the tibia plateau cartilage and talus cartilage were estimated at the 1st peak, mid-stance, and the 2nd peak at the same time. The present method can provide the contact pressure distribution at the knee and ankle joints over the entire gait.

Initial stability and stress distribution of ankle arthroscopic arthrodesis with three kinds of 2-screw configuration fixation: a finite element analysis

Background

Arthroscopic ankle arthrodesis (AAA) is recognized as the standard treatment for the end-stage ankle arthritis. Two-screw configuration fixation is a typical technique for AAA; however, no consensus has been reached on how to select most suitable inserted position and direction. For better joint reduction, we developed a new configuration (2 home run-screw configuration: 2 screws are inserted from the lateral-posterior and medial-posterior malleolus into the talar neck) and investigated whether it turned out to be better than the other commonly used 2-screw configurations.

Methods

In this study, we investigated three kinds of 2-screw configurations: 2 “home run”-screw configuration (group A), crossed transverse configuration (the screw is inserted from the medial malleolus into the anterior talus and the other from the lateral tibia maintains posterior talus, group B), and 2 parallel screw configuration (2 parallel screws are inserted from the posteromedial side of the tibia into talus, group C). The effects of the above three insertions on the loading stress of the tibio-talar joint were comparatively analyzed with a three-dimensional finite element model.

Results

Group A was better than groups B and C in respect of stress distribution uniformity and superior to both groups B and C in anti-flexion strength and anti-internal rotation strength. Group A was slightly worse than group C but better than group B in anti-dorsiflexion and anti-valgus and varus strength.

Conclusions

Two “home run”-screw configuration facilitates the reduction of anterior talus dislocation of end-stage ankle arthritis. Our finite element analysis demonstrates the configuration is superior to crossed transverse and parallel configuration for arthroscopic ankle arthrodesis in terms of stress distribution and initial stability.

Bearded capuchin monkeys use joint synergies to stabilize the hammer trajectory while cracking nuts in bipedal stance

The transition from occasional to obligate bipedalism is a milestone in human evolution. However, because the fossil record is fragmentary and reconstructing behaviour from fossils is difficult, changes in the motor control strategies that accompanied this transition remain unknown. Quadrupedal primates that adopt a bipedal stance while using percussive tools provide a unique reference point to clarify one aspect of this transition, which is maintaining bipedal stance while handling massive objects. We found that while cracking nuts using massive stone hammers, wild bearded capuchin monkeys (Sapajus libidinosus) produce hammer trajectories with highly repeatable spatial profiles. Using an uncontrolled manifold analysis, we show that the monkeys used strong joint synergies to stabilize the hammer trajectory while lifting and lowering heavy hammers. The monkeys stringently controlled the motion of the foot. They controlled the motion of the lower arm and hand rather loosely, showing a greater variability across strikes. Overall, our findings indicate that while standing bipedally to lift and lower massive hammers, an arboreal quadrupedal primate must control motion in the joints of the lower body more stringently than motion in the joints of the upper body. Similar changes in the structure of motor variability required to accomplish this goal could have accompanied the evolutionary transition from occasional to obligate bipedalism in ancestral hominins.

Effect of Gender on Mechanical Properties of the Plantar Fascia and Heel Fat Pad

BACKGROUND

The purpose of the study was to investigate the plantar fascia and heel fat pad stiffness and thickness parameters in females and compare these values with those of males.

METHODS

This study was carried out in 60 healthy sedentary participants (30 female, 30 male) between the ages of 19 and 50 years. Shear wave velocity (SWV) and thickness of the plantar fascia and heel fat pad were measured with an ultrasonography device.

RESULTS

Males had a higher plantar fascia ( P = .037) and heel fat pad ( P = .001) thickness compared with females, but SWV of the plantar fascia ( P = .673), heel fat pad microchamber layer ( P = .240), and heel fat pad macrochamber layer ( P = .636) were similar in both groups. Body mass had a strong correlation with the plantar fascia ( r = 0.64, P < .001) and heel fat pad thickness ( r = 0.68, P < .001). Height had a moderate correlation with the plantar fascia ( r = 0.44, P < .001) and heel fat pad thickness ( r = 0.42, P = .001).

CONCLUSION

Plantar fascia and heel fat pad stiffness were similar in both genders; however, females had a lower plantar fascia and heel fat pad thickness compared with males. Correlation analysis results suggest that higher plantar fascia and heel fat pad thickness in males may be related to higher body mass and height.

LEVELS OF EVIDENCE

Level III: Retrospective comparative study.

Effects of morphological and mechanical properties of plantar fascia and heel pad on balance performance in asymptomatic females

INTRODUCTION

Personal differences in morphological and mechanical properties of plantar fascia and heel fat pad may be an important parameter regarding an individual's balance performance. The purpose of this study was to investigate the effect of thickness and stiffness of heel fat pad and plantar fascia on balance performance in asymptomatic sedentary females.

MATERIALS AND METHODS

This study was carried out on 37 asymptomatic sedentary females between the ages of 19 and 35 years. Balance assessments during single-leg standing were carried out using Biodex Balance Systems (Biodex Medical Systems, Shirley, NY, USA). In this study, the individuals' balance performance was assessed using the center of balance (COB) parameters, which were the standard deviation of the COB amplitude in the anterior-posterior (AP_SD) and medial-lateral (ML_SD) directions. Stiffness and thickness measurements of heel fat pad and plantar fascia were performed using an ACUSON S3000 Ultrasound System and a 9L4 probe (4-9MHz) (Siemens Medical Solution, Mountain View, CA, USA).

RESULTS

AP_SD during single-leg standing tests had a moderate correlation with heel pad thickness (r=0.46, p=0.004) and heel pad stiffness (r=0.41, p=0.011), and a fair correlation with plantar fascia thickness (r=0.34, p=0.038) and plantar fascia stiffness (r=0.38, p=0.021). ML_SD during single-leg standing tests had a moderate correlation with heel pad thickness (r=0.41, p=0.013) and heel pad stiffness (r=0.53, p=0.001), and a fair correlation with plantar fascia thickness (r=0.40, p=0.015).

CONCLUSION

It was found that higher plantar fascia and heel fat pad stiffness and thickness are related to higher postural sway in anterior-posterior and medial-lateral directions based on the single-leg balance tests. These results suggest that the morphological and mechanical properties of plantar fascia and heel fat pad play an important role in balance performance.

MRI evaluation of ligaments and tendons of foot arch in talar dome osteochondral lesions

Background There are no publications in literature describing an association between disorders of the ligaments and tendons supporting the foot arch and osteochondral lesions of the talus (OCLT). We believe there may be a correlation between the damage of these structures. Purpose To investigate the pathologies of main ligaments and tendons that support the foot arch in sprained ankles, by reviewing magnetic resonance imaging (MRI) studies and comparing the results in two groups of patients, with and without OCLT. Material and Methods MR images from 316 patients examined in the orthopedic clinic for ankle sprain were evaluated for pathologic findings of the plantar fascia, short and long plantar ligaments, spring ligament, sinus tarsi, and ankle tendons supporting the foot arch. Findings were compared between two groups of patients: 158 patients with OCLT and 158 patients without OCLT. Results Plantar fascia, short plantar ligament, and spring ligament abnormalities were seen in 50 (31.6%), 28 (17.7%), and 60 (38%) patients with OCLT, and in nine (5.6%), three (1.9%), and 18 (11.4%) patients without OCLT, respectively ( P < 0.05). Sinus tarsi and tendon abnormalities were seen in 11 (6.7%) and nine (5.7%) patients with OCLT, and in eight (5%) and eight (5%) patients without OCLT, respectively ( P > 0.05). Two or more associated abnormalities were present in 50 (31.6%) patients with OCLT and in 11 (6.7%) without OCLT ( P < 0.05). Conclusion Plantar fascia, short plantar ligament, and spring ligament abnormalities were commonly seen in patients with OCLT on MRI, while sinus tarsi and tendon abnormalities were not. Concomitant pathologies have an increased incidence in patients with OCLT.

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.

Effects of Body Mass Index on Mechanical Properties of the Plantar Fascia and Heel Pad in Asymptomatic Participants

BACKGROUND

Musculoskeletal foot disorders have a high incidence among overweight and obese individuals. One of the important factors causing this high incidence may be plantar fascia and heel pad (HP)-related mechanical changes occurring in these individuals. The aim of the present study was to investigate the plantar fascia and HP stiffness and thickness parameters in overweight and obese individuals and compare these values with those of normal-weight individuals.

METHODS

This study was carried out in 87 (52 female, 35 male) healthy sedentary individuals between the ages of 19 and 58 years (34 ± 11 years). Participants were subsequently categorized according to body mass index (BMI) as normal weight (18.5 kg/m² < BMI < 25 kg/m²) or overweight and obese (BMI ≥25 kg/m²). Plantar fascia and HP thickness and stiffness were measured with an ultrasonography device using a linear ultrasonography probe.

RESULTS

Overweight and obese individuals had higher HP thickness ( P < .001), plantar fascia thickness ( P = .001), heel pad microchamber layer (MIC) stiffness ( P < .001), and heel pad macrochamber layer (MAC) stiffness ( P < .001), whereas they had lower plantar fascia stiffness ( P < .001) compared with the individuals with normal weight. BMI had a moderate correlation with HP thickness ( P < .001, r = 0.500), plantar fascia thickness ( P = .001, r = 0.536), MIC stiffness ( P < .001, r = 0.496), and MAC stiffness ( P < .001, r = 0.425). A negative and moderate correlation was found between BMI and plantar fascia stiffness ( P < .001, r = -0.439).

CONCLUSION

Increased BMI causes a decrease in the stiffness of plantar fascia and an increase in the thickness of the plantar fascia as well as the thickness and stiffness of HP. Increased body mass could cause changes in the mechanical properties of HP and plantar fascia.

LEVEL OF EVIDENCE

Level 3, comparative study.

Biomechanical study on surgical fixation methods for minimally invasive treatment of hallux valgus

Hallux valgus (HV) was one of the most frequent female foot deformities. The aim of this study was to evaluate mechanical responses and stabilities of the Kirschner, bandage and fiberglass fixations after the distal metatarsal osteotomy in HV treatment. Surface traction of different forefoot regions in bandage fixation and the biomechanical behavior of fiberglass bandage material were measured by a pressure sensor device and a mechanical testing, respectively. A three-dimensional foot finite element (FE) model was developed to simulate the three fixation methods (Kirschner, bandage and fiberglass fixations) in weight bearing. The model included 28 bones, sesamoids, ligaments, plantar fascia, cartilages and soft tissue. The peak Von Mises stress (MS) and compression stress (CS) of the distal fragment were predicted from the three fixation methods: Kirschner fixation (MS=6.71MPa, CS=1.232MPa); Bandage fixation (MS=14.90MPa, CS=9.642MPa); Fiberglass fixation (MS=15.83MPa, CS=19.70MPa). Compared with the Kirschner and bandage fixation, the fiberglass fixation reduced the relative movement of osteotomy fragments and obtained the maximum CS. We concluded that fiberglass fixation in HV treatment was helpful to the bone healing of distal fragment. The findings were expected to guide further therapeutic planning of HV patient.

Musculoskeletal modelling of human ankle complex: Estimation of ankle joint moments

BACKGROUND

A musculoskeletal model for the ankle complex is vital in order to enhance the understanding of neuro-mechanical control of ankle motions, diagnose ankle disorders and assess subsequent treatments. Motions at the human ankle and foot, however, are complex due to simultaneous movements at the two joints namely, the ankle joint and the subtalar joint. The musculoskeletal elements at the ankle complex, such as ligaments, muscles and tendons, have intricate arrangements and exhibit transient and nonlinear behaviour.

METHODS

This paper develops a musculoskeletal model of the ankle complex considering the biaxial ankle structure. The model provides estimates of overall mechanical characteristics (motion and moments) of ankle complex through consideration of forces applied along ligaments and muscle-tendon units. The dynamics of the ankle complex and its surrounding ligaments and muscle-tendon units is modelled and formulated into a state space model to facilitate simulations. A graphical user interface is also developed during this research in order to include the visual anatomical information by converting it to quantitative information on coordinates.

FINDINGS

Validation of the ankle model was carried out by comparing its outputs with those published in literature as well as with experimental data obtained from an existing parallel ankle rehabilitation robot.

INTERPRETATION

Qualitative agreement was observed between the model and measured data for both, the passive and active ankle motions during trials in terms of displacements and moments.

Biomechanical consequences of adding plantar fascia release to metatarsal osteotomies: Changes in forefoot plantar pressures

Destruction of the normal metatarsal arch by a long metatarsal is often a cause for metatarsalgia. When surgery is warranted, distal oblique, or proximal dorsiflexion osteotomies of the long metatarsal bones are commonly used. The plantar fascia has anatomical connection to all metatarsal heads. There is controversial scientific evidence on the effect of plantar fascia release on forefoot biomechanics. In this cadaveric biomechanical study, we hypothesized that plantar fascia release would augment the plantar metatarsal pressure decreasing effects of two common second metatarsal osteotomy techniques. Six matched pairs of foot and ankle specimens were mounted on a pressure mat loading platform. Two randomly assigned surgery groups, which had received either distal oblique, or proximal dorsiflexion osteotomy of the second metatarsal, were evaluated before and after plantar fasciectomy. Specimens were loaded up to a ground reaction force of 400 N at varying Achilles tendon forces. Average pressures, peak pressures, and contact areas were analyzed. Supporting our hypothesis, average pressures under the second metatarsal during 600 N Achilles load were decreased by plantar fascia release following proximal osteotomy (p < 0.05). However contrary to our hypothesis, peak pressures under the second metatarsal were significantly increased by plantar fascia release following modified distal osteotomy, under multiple Achilles loading conditions (p < 0.05). Plantar fasciotomy should not be added to distal metatarsal osteotomy in the treatment of metatarsalgia. If proximal dorsiflexion osteotomy would be preferred, plantar fasciotomy should be approached cautiously not to disturb the forefoot biomechanics. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:800-804, 2017.

A comparison of different over-the-counter foot orthotic devices on multi-segment foot biomechanics

BACKGROUND

Over-the-counter foot orthoses are a cost-effective alternative to custom-made devices. However, few studies have compared over-the-counter devices and most biomechanical research involving orthoses has focused on rearfoot biomechanics.

OBJECTIVES

To determine changes in multi-segment foot biomechanics during shod walking in three commercially available over-the-counter devices: SOLE, SuperFeet and Powerstep when compared to no orthotic.

STUDY DESIGN

Repeated measures, cross-sectional study.

METHODS

Retroreflective markers were placed on the right limb of 18 participants representing forefoot, midfoot, rearfoot and shank segments. Three-dimensional kinematics were recorded using an eight-camera motion capture system while participants walked on a treadmill and the order of condition was randomized between four conditions: SOLE, SuperFeet, Powerstep and no orthotic.

RESULTS

All over-the-counter devices exhibited significant decreases in plantar fascia strain compared to no orthotic and only Powerstep exhibited significant decreases in peak rearfoot eversion. Medial longitudinal arch deformation was not reduced for any over-the-counter device.

CONCLUSION

Different over-the-counter devices exhibited specific alterations in rearfoot kinematics and all reduced plantar fascia strain by varying amounts. These over-the-counter-specific kinematic changes should be taken into consideration when recommending these devices as a treatment option.

CLINICAL RELEVANCE

Over-the-counter orthoses are a cost-effective alternative to custom-made devices. We demonstrated that three commonly used over-the-counter devices influence foot kinematics and plantar fascia strain differently. Clinicians can use these results to provide more tailored treatment options for their patients.

Moberg Osteotomy Shifts Contact Pressure Plantarly in the First Metatarsophalangeal Joint in a Biomechanical Model

BACKGROUND

A proximal phalangeal dorsiflexion osteotomy (Moberg osteotomy) is commonly used to treat hallux rigidus, but the mechanical explanation for its effectiveness is unclear. The purpose of our study was to test the effect of a Moberg osteotomy on first metatarsophalangeal joint contact mechanics.

METHODS

Ten cadaveric first ray specimens were dissected, with the medial band of the plantar aponeurosis preserved at its origin, and placed in a custom testing apparatus. Forefoot loads during mid-stance with the first metatarsal positioned at 10 degrees were simulated using a custom-made loading jig while contact mechanics were acquired with a thin pressure-sensitive sensor. A Moberg osteotomy was performed starting 9 mm distal to the proximal phalanx with excision of a 3-mm wedge of bone and fixated with a 2-mm Kirschner wire. The effect of the Moberg osteotomy was tested by reapplying the forefoot loads and acquiring the joint pressures. The center of pressure, peak pressure, and contact area were calculated. Paired t tests were performed to determine if the Moberg osteotomy affected joint contact mechanics.

RESULTS

The Moberg osteotomy shifted the center of contact pressure on the proximal phalanx surface more plantarly (P < .01). However, the Moberg osteotomy did not affect the peak pressure (P = .62) or the joint contact area (P = .96).

CONCLUSIONS

There were no differences in peak pressure or first MTPJ contact area, but a plantar shift in the center of pressure occurred after the Moberg osteotomy.

CLINICAL RELEVANCE

The plantar cartilage, which is often spared from arthritic changes, may be preferentially loaded and the potential edge loading following cheilectomy may be avoided with the Moberg osteotomy secondary to the plantar shift of center of pressure.