Material properties of the plantar aponeurosis

Direct visualization and measurement of the plantar aponeurosis behavior in foot arch deformation via the windlass mechanism

The plantar aponeurosis (PA) is an elastic longitudinal band that contributes to the generation of a propulsive force in the push-off phase during walking and running through the windlass mechanism. However, the dynamic behavior of the PA remains unclear owing to the lack of direct measurement of the strain it generates. Therefore, this study aimed to visualize and quantify the PA behavior during two distinct foot postures: (i) neutral posture and (ii) windlass posture with midtarsal joint plantarflexion and metatarsophalangeal joint dorsiflexion, using computed tomography scans. Six healthy adult males participated in the experiment, and three-dimensional reconstruction of the PA was conducted to calculate its path length, width, thickness, and cross-sectional area. This study successfully visualized and quantified the morphological changes in the PA induced by the windlass mechanism, providing a precise reference for biomechanical modeling. This study also highlighted the interindividual variability in the PA morphology and stretching patterns. Although the windlass posture was not identical to that observed in the push-off phase during walking, the observed PA behavior provides valuable insights into its mechanics and potential implications for foot disorders.

Effects of different contact angles during forefoot running on the stresses of the foot bones: a finite element simulation study

Introduction: The purpose of this study was to compare the changes in foot at different sole-ground contact angles during forefoot running. This study tried to help forefoot runners better control and improve their technical movements by comparing different sole-ground contact angles. Methods: A male participant of Chinese ethnicity was enlisted for the present study, with a recorded age of 25 years, a height of 183 cm, and a body weight of 80 kg. This study focused on forefoot strike patterns through FE analysis. Results: It can be seen that the peak von Mises stress of M1-5 (Metatarsal) of a (Contact angle: 9.54) is greater than that of b (Contact angle: 7.58) and c (Contact angle: 5.62) in the three cases. On the contrary, the peak von Mises stress of MC (Medial Cuneiform), IC (Intermediate Cuneiform), LC (Lateral Cuneiform), C (Cuboid), N (Navicular), T (Tarsal) in three different cases is opposite, and the peak von Mises stress of c is greater than that of a and b. The peak von Mises stress of b is between a and c. Conclusion: This study found that a reduced sole-ground contact angle may reduce metatarsal stress fractures. Further, a small sole-ground contact angle may not increase ankle joint injury risk during forefoot running. Hence, given the specialized nature of the running shoes designed for forefoot runners, it is plausible that this study may offer novel insights to guide their athletic pursuits.

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.

The Effect of Endoscopic Partial Plantar Fasciotomy on Morphologic and Functional Properties of the Foot

BACKGROUND

The lifetime risk of plantar fasciitis is 10%, and operative treatment in the form of endoscopic partial plantar fascia release are often performed in cases refractory for nonsurgical treatment. The effect of the operation on the biomechanical properties of the foot has only been sparsely studied.

METHODS

This is a prospective, observational study of 25 patients with plantar fasciitis, for a minimum of 3 months, verified by ultrasonographic scanning, who had endoscopic partial fasciotomy. A bony spur was resected if present. At the calcaneal insertion, the medial half of the central band of the plantar fascia was excised in full thickness. The biomechanical properties of the foot were evaluated before surgery and 12 months postoperatively.

RESULTS

Foot length increased 0.17 cm (P = .03), the width of the central zone 0.35 cm (P = .019), the modified arch index 0.05 (P = .032), and the Foot Posture Index 1.0 (P = .0014). There were no significant changes in rearfoot eversion angle, ankle dorsiflexion and jump distance, or in magnetic resonance imaging-measured 3D navicular position from pre- to postoperation, with or without loading, and no changes in ultrasonographically measured heel pad thickness. A tantalum bead (0.7-mm-diameter) was inserted during operation into the most proximal part of the released medial plantar fascia. Radiographs obtained few days postoperatively and 1 year later revealed no changes in the tantalum-calcaneus distance in supine position, but an increase from 48.3 to 50.7 mm (P = .045) in one-leg standing, suggesting a higher flexibility of the remaining fascia. Patients with a body mass index above and below 27.0 demonstrated no significant differences in any of the assessments at 12 months.

CONCLUSION

There were minimal changes in the measured foot morphologic and functional properties at 1-year follow-up, after endoscopic partial plantar fascia release.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Effects of Midsole Hardness on the Mechanical Response Characteristics of the Plantar Fascia during Running

High long-term stress on the plantar fascia (PF) is the main cause of plantar fasciitis. Changes in the midsole hardness (MH) of running shoes are an important factor leading to the alteration of the PF. This study aims to establish a finite-element (FE) model of the foot-shoe, and investigates the effects of midsole hardness on PF stress and strain. The FE foot-shoe model was built in ANSYS using computed-tomography imaging data. Static structural analysis was used to simulate the moment of running push and stretch. Plantar stress and strain under different MH levels were quantitatively analyzed. A complete and valid 3D FE model was established. With an increase in MH from 10 to 50 Shore A, the overall stress and strain of the PF were decreased by approximately 1.62%, and the metatarsophalangeal (MTP) joint flexion angle was decreased by approximately 26.2%. The height of the arch descent decreased by approximately 24.7%, but the peak pressure of the outsole increased by approximately 26.6%. The established model in this study was effective. For running shoes, increasing the MH reduces the stress and strain of PF, but also imposes a higher load on the foot.

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.

Characterizing the mechanical function of the foot's arch across steady-state gait modes

The arch of the human foot has historically been likened to either a truss, a rigid lever, or a spring. Growing evidence indicates that energy is stored, generated, and dissipated actively by structures crossing the arch, suggesting that the arch can further function in a motor- or spring-like manner. In the present study, participants walked, ran with a rearfoot strike pattern, and ran with a non-rearfoot strike pattern overground while foot segment motions and ground reaction forces were recorded. To quantify the midtarsal joint's (i.e., arch's) mechanical behavior, a brake-spring-motor index was defined as the ratio between midtarsal joint net work and the total magnitude of joint work. This index was statistically significantly different between each gait condition. Index values decreased from walking to rearfoot strike running to non-rearfoot strike running, indicating that the midtarsal joint was most motor-like when walking and most spring-like in non-rearfoot running. The mean magnitude of elastic strain energy stored in the plantar aponeurosis mirrored the increase in spring-like arch function from walking to non-rearfoot strike running. However, the behavior of the plantar aponeurosis could not account for a more motor-like arch in walking and rearfoot strike running, given the lack of main effect of gait condition on the ratio between net work and total work performed by force in the plantar aponeurosis about the midtarsal joint. Instead, the muscles of the foot are likely altering the motor-like mechanical function of the foot's arch, the operation of these muscles between gait conditions warrants further investigation.

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.

Evaluation of assumptions in foot and ankle biomechanical models

BACKGROUND

A variety of biomechanical models have been used in studies of foot and ankle disorders. Assumptions about the element types, material properties, and loading and boundary conditions are inherent in every model. It was hypothesized that the choice of these modeling assumptions could have a significant impact on the findings of the model.

METHODS

We investigated the assumptions made in a number of biomechanical models of the foot and ankle and evaluated their effects on the results of the studies. Specifically, we focused on: (1) element choice for simulation of ligaments and tendons, (2) material properties of ligaments, cortical and trabecular bones, and encapsulating soft tissue, (3) loading and boundary conditions of the tibia, fibula, tendons, and ground support.

FINDINGS

Our principal findings are: (1) the use of isotropic solid elements to model ligaments and tendons is not appropriate because it allows them to transmit unrealistic bending and twisting moments and compressive forces; (2) ignoring the difference in elastic modulus between cortical and trabecular bones creates non-physiological stress distribution in the bones; (3) over-constraining tibial motion prevents anticipated deformity within the foot when simulating foot deformities, such as progressive collapsing foot deformity; (4) neglecting the Achilles tendon force affects almost all kinetic and kinematic parameters through the foot; (5) the axial force applied to the tibia and fibula is not equal to the ground reaction force due to the presence of tendon forces.

INTERPRETATION

The predicted outcomes of a foot model are highly sensitive to the model assumptions.

Plantar Fascia Lateral Fascicle Rupture: How Severe Can It Be?

The plantar fascia is a thick and strong group of longitudinal and transverse bands of collagen-rich tissue, consisting of central, medial, and lateral fascicles. Biomechanically, the central fascicle assumes a special role in medial longitudinal foot arch preservation. However, there is scarce data on plantar fascia medial and lateral fascicles' anatomy and pathology in the literature. We report the case of a 27-year-old male professional soccer player who presented with sudden-onset, severe lateral right rearfoot pain that had started while doing linear sprinting practice. The athlete had no relevant medical history and no history of previous right foot injuries. The radiographic study of the right foot revealed no significant changes. MRI showed a high T2 signal partially interrupting the plantar fascia lateral fascicle low signal, consistent with a lateral fascicle rupture. The rehabilitation program was initiated and included pharmacological and non-pharmacological management. He experienced an extremely favorable evolution of his condition with the absence of pain and partial weight bearing in less than one week, with a full return to sports in approximately two weeks. During dynamic foot movement, the lateral fascicle seems to be less biomechanically recruited compared to the central one; however, the strain is not negligible and might be the reason for the pathology. Still, this slightly decreased strain might explain this injury's faster healing time compared to that associated with the central fascicle. Regarding the risk factors for plantar fascia ruptures, it should be kept in mind that a tear might occur even in their absence. We intend to raise awareness about the existence of plantar fascia lateral fascicle and the possibility of associated pathology, either acute or chronic. Hopefully, in the near future, plantar fascia ruptures will get significantly more attention in the literature, enabling the creation of proper management guidelines.

Quantification of the in vivo stiffness and natural length of the human plantar aponeurosis during quiet standing using ultrasound elastography

This study aimed to identify the stiffness and natural length of the human plantar aponeurosis (PA) during quiet standing using ultrasound shear wave elastography. The shear wave velocity (SWV) of the PA in young healthy males and females (10 participants each) was measured by placing a probe in a hole in the floor plate. The change in the SWV with the passive dorsiflexion of the metatarsophalangeal (MP) joint was measured. The Young's modulus of the PA was estimated to be 64.7 ± 9.4 kPa, which exponentially increased with MP joint dorsiflexion. The PA was estimated to have the natural length when the MP joint was plantarflexed by 13.8°, indicating that the PA is stretched by arch compression during standing. However, the present study demonstrated that the estimated stiffness for the natural length in quiet standing was significantly larger than that in the unloaded condition, revealing that the PA during standing is stiffened by elongation and through the possible activation of intrinsic muscles. Such quantitative information possibly contributes to the detailed biomechanical modeling of the human foot, facilitating an improved understanding of the mechanical functions and pathogenetic mechanisms of the PA during movements.

Novel Multi-Segment Foot Model Incorporating Plantar Aponeurosis for Detailed Kinematic and Kinetic Analyses of the Foot With Application to Gait Studies

Kinetic multi-segment foot models have been proposed to evaluate the forces and moments generated in the foot during walking based on inverse dynamics calculations. However, these models did not consider the plantar aponeurosis (PA) despite its potential importance in generation of the ground reaction forces and storage and release of mechanical energy. This study aimed to develop a novel multi-segment foot model incorporating the PA to better elucidate foot kinetics. The foot model comprised three segments: the phalanx, forefoot, and hindfoot. The PA was modeled using five linear springs connecting the origins and the insertions via intermediate points. To demonstrate the efficacy of the foot model, an inverse dynamic analysis of human gait was performed and how the inclusion of the PA model altered the estimated joint moments was examined. Ten healthy men walked along a walkway with two force plates placed in series close together. The attempts in which the participant placed his fore- and hindfoot on the front and rear force plates, respectively, were selected for inverse dynamic analysis. The stiffness and the natural length of each PA spring remain largely uncertain. Therefore, a sensitivity analysis was conducted to evaluate how the estimated joint moments were altered by the changes in the two parameters within a range reported by previous studies. The present model incorporating the PA predicted that 13%–45% of plantarflexion in the metatarsophalangeal (MTP) joint and 8%–29% of plantarflexion in the midtarsal joints were generated by the PA at the time of push-off during walking. The midtarsal joint generated positive work, whereas the MTP joint generated negative work in the late stance phase. The positive and negative work done by the two joints decreased, indicating that the PA contributed towards transfer of the energy absorbed at the MTP joint to generate positive work at the midtarsal joint during walking. Although validation is limited due to the difficulty associated with direct measurement of the PA force in vivo, the proposed novel foot model may serve as a useful tool to clarify the function and mechanical effects of the PA and the foot during dynamic movements.

Ruptures of the Plantar Fascia: A Systematic Review of the Literature

INTRODUCTION

Rupture of the plantar fascia is a rare condition. It can also occur spontaneously and with no history of disease of the plantar fascia, above all in athletes. This review aims to systematically analyze all cases described in the literature regarding the rupture of the plantar fascia, evaluating incidence, risk factors, and treatments, considering which procedures show the best outcomes and the highest success rate.

MATERIALS AND METHODS

A systematic review of PubMed, Google Scholar, and Cochrane review computerized databases was performed, focusing on articles about cases of rupture of the plantar fascia; 18 studies fulfilled all the criteria and were analyzed. There were no randomized controlled trials.

RESULTS

A total of 155 patients (157 foot) were included in this systematic review. Considering all the studies included, 12 patients had a spontaneous rupture, 138 patients had a diagnosis of plantar fasciitis, and 130 patients were treated with local injections of corticosteroid before the rupture. Only 2 cases of bilateral rupture were reported. In all, 15 studies reported conservative treatment, with a total of 154 patients (156 feet) included. Operative treatment was reported in 3 studies, with 3 patients (3 feet) treated.

CONCLUSIONS

Ruptures of the plantar fascia are very rare in asymptomatic patients and more common in patients treated with injection of steroids in the plantar fascia. Conservative treatment, although not standardized in the literature, led to good outcomes in most cases. Chronic ruptures of the fascia should be considered for operative treatment.

LEVELS OF EVIDENCE

Level III.

Gastrocnemius Release in the Management of Chronic Plantar Fasciitis: A Systematic Review

BACKGROUND

This systematic review aims to summarize the outcomes of gastrocnemius recession in the treatment of plantar fasciitis.

METHODS

A systematic review was performed according to PRISMA guidelines using the PubMed, Embase, Emcare, Web of Science, Scopus, and CINAHL databases. A 2-stage title/abstract and full text screening process was performed independently by 2 reviewers. Randomized controlled trials, cohort, and case-control studies reporting the results of gastrocnemius recession in patients with plantar fasciitis were included. The MINORS and Joanna Briggs Institute Criteria were used to assess study quality and risk of bias.

RESULTS

A total of 285 articles were identified, with 6 of these studies comprising 118 patients being ultimately included. Significant postoperative improvement in American Orthopaedic Foot & Ankle Society, visual analog scale, 36-Item Short Form Health Survey, Foot Forum Index, and Foot and Ankle Ability Measure scores were reported. Included studies also described an increase in ankle dorsiflexion range of motion and plantarflexion power. An overall pooled complication rate of 8.5% was seen, with persistent postoperative pain accounting for the most common reported complication. Gastrocnemius recession is associated with greater postoperative improvement than plantar fasciotomy and conservative stretching exercises.

CONCLUSION

The current evidence demonstrates that gastrocnemius recession is effective in the management of plantar fasciitis, specifically in patients with gastrocnemius contracture who do not respond to conservative treatment.

LEVEL OF EVIDENCE

Level III, Systematic review of level I-III studies.

Biomechanical Effects of Graft Shape for the Evans Lateral Column Lengthening Procedure: A Patient-Specific Finite Element Investigation

BACKGROUND

The Evans calcaneal lengthening osteotomy procedure is widely used for correcting progressive collapsing foot deformity. However, it can result in overcorrection and degenerations of the calcaneocuboid joint. Different shapes of graft have been used in the Evans calcaneal osteotomy, but potential differences in their biomechanical effects is still unclear. The present study was designed to explore the biomechanical effects of graft shape and improve the Evans procedure to avoid or minimize detrimental effects.

METHODS

Twelve patient-specific finite element models were established and validated. A triangular or rectangular wedge of varying size was inserted at the lateral edge of calcaneus, and the degree of correction was quantified. The stress in spring ligaments and plantar fascia and the contact characteristics of the talonavicular and calcaneocuboid joints were calculated and compared accordingly.

RESULTS

The rectangular graft provided a much higher degree of correction than triangular grafts did. However, the contact characteristics of the calcaneocuboid joint and talonavicular joint were abnormal, with clear sensitivity to increased graft size, and the modeled strain of the spring ligament increased.

CONCLUSION

The finite element analysis predicts that the rectangular grafts provide a higher degree of correction, but risks overcorrection compared with triangular grafts. The triangular graft may have a lower degree of disturbance to the biomechanical behaviors of the midtarsal joint.

CLINICAL RELEVANCE

The model shows that both the shape and size of an Evans osteotomy bone wedge can have effects on the contiguous joints and ligamentous structures. Those effects should be considered when selecting a bone wedge for an Evans calcaneal osteotomy.

LEVEL OF EVIDENCE

Level III, case-control study.

Finite Element Modelling of Planus and Rectus Foot Types for the Study of First Metatarsophalangeal and First Metatarsocuneiform Joint Contact Mechanics

Evaluating the contact mechanics of human joints is an important element in understanding the pathomechanics of orthopaedic diseases. Although physical testing is essential in the evaluation process, reliable computational models can augment these experiments by non-invasive predictions of biomechanical or surgical variables. The objective of this study was to perform verification of a framework for developing a medial forefoot finite element. Verification was conducted by comparing computational predictions to experimental measurements of first metatarsophalangeal and first metatarsocuneiform joint contact mechanics. A custom-built force-controlled cadaveric test-rig was used to derive measurements of contact pressure, force, and area. A quasi-static finite element was developed and driven under the same boundary and loading conditions. Calibration of cartilage moduli and mesh sensitivity analyses were performed. Mean errors in contact pressures, forces, and areas were 24%, 4%, and 40% at the first metatarsophalangeal joint and 23%, 12%, and 19% at the first Metatarsocuneiform joint, respectively. Verification of a medial forefoot finite element model development framework was presented and found to be within 30% for contact pressure and contact force of both joints. This study presents a method to verify and simulate realistic physiological loading to investigate orthopaedic diseases of the medial forefoot.

Simple model of arch support: Relevance to Charcot Neuroarthropathy

BACKGROUND

Charcot neuropathy is a common complication resulting from poorly controlled diabetes and peripheral neuropathy leading to the collapse, and ultimately the breakdown, of the midfoot. Mechanically, it is likely that a compromised arch support in this, or any other patient group that experiences foot flattening, would be associated with slippage at the distal and proximal interface regions of the plantar surface of the foot and the adjacent support surface. This slippage, although difficult to quantify with standard motion capture systems used in a gait laboratory, could potentially be assessed with systems for monitoring interface shear stresses. However, before investing in such systems, a correlation between arch flattening and interface shear stresses needs to be verified.

METHODS

For this purpose, a sagittal plane model of a foot was developed using a multi-body dynamics package (MSC Adams). This model mimicked a subject swaying back and forth, and was constructed to show the dependence of interface stresses on altered arch support.

FINDINGS

The model's predictions matched typical FootSTEPS data: lengthening of the arch of 1-2 mm, sway oscillations of 0.22-0.33 s and frictional force differences (calcaneus relative to forefoot) of 60 N. Of clinical relevance, when the stiffness of the plantar spring (representing aponeurosis and intrinsic muscles) was reduced by 10%, the frictional force difference increased by about 6.5%.

INTERPRETATION

The clinical implications of this study are that, while arch lengthening of less than 2 mm might be difficult to measure reliably in a gait lab, using shear sensors under the forefoot and hindfoot should allow arch support to be assessed in a repeatable manner.

An Experimentally Validated Finite Element Model of the Lower Limb to Investigate the Efficacy of Blast Mitigation Systems

Improvised explosive devices (IEDs) used in the battlefield cause damage to vehicles and their occupants. The injury burden to the casualties is significant. The biofidelity and practicality of current methods for assessing current protection to reduce the injury severity is limited. In this study, a finite-element (FE) model of the leg was developed and validated in relevant blast-loading conditions, and then used to quantify the level of protection offered by a combat boot. An FE model of the leg of a 35 years old male cadaver was developed. The cadaveric leg was tested physically in a seated posture using a traumatic injury simulator and the results used to calibrate the FE model. The calibrated model predicted hindfoot forces that were in good correlation (using the CORrelation and Analysis or CORA tool) with data from force sensors; the average correlation and analysis rating (according to ISO18571) was 0.842. The boundary conditions of the FE model were then changed to replicate pendulum tests conducted in previous studies which impacted the leg at velocities between 4 and 6.7 m/s. The FE model results of foot compression and peak force at the proximal tibia were within the experimental corridors reported in the studies. A combat boot was then incorporated into the validated computational model. Simulations were run across a range of blast-related loading conditions. The predicted proximal tibia forces and associated risk of injury indicated that the combat boot reduced the injury severity for low severity loading cases with higher times to peak velocity. The reduction in injury risk varied between 6 and 37% for calcaneal minor injuries, and 1 and 54% for calcaneal major injuries. No injury-risk reduction was found for high severity loading cases. The validated FE model of the leg developed here was able to quantify the protection offered by a combat boot to vehicle occupants across a range of blast-related loading conditions. It can now be used as a design and as an assessment tool to quantify the level of blast protection offered by other mitigation technologies.

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.

Biomechanical comparison of tenodesis reconstruction for subtalar instability: a finite element analysis

Background

There are several types of tenodesis reconstruction designed for subtalar instability. However, no comprehensive comparison has been conducted among these procedures in terms of their correcting power so far. The objective of this study is to evaluate the biomechanical behaviors of 5 representative procedures through finite element analysis.

Methods

Finite element models were established and validated based on one of our previous studies. The Pisani interosseous talocalcaneal ligament (ITCL) reconstruction, Schon cervical ligament (CL) reconstruction and Choisne calcaneofibular ligament (CFL) reconstruction were compared on the model with the CFL, ITCL and CL sectioned. The Schon triligamentous reconstruction and Mann triligamentous reconstruction were compared on the model with the CFL, ITCL and CL, as well as the ATFL sectioned. The inversion and external/internal rotation were quantified at different ankle positions based on the rotational moment. Then, the stress in ligaments and reconstructed grafts and the contact characteristics of the subtalar joint under inversional stress test were calculated and compared accordingly.

Results

For single ligament reconstruction, the Choisne CFL reconstruction provided the greatest degree of correction for subtalar instability, followed by the Schon CL reconstruction and then the Pisani ITCL reconstruction. For triligamentous reconstruction, the Mann procedure outperformed the Schon procedure in alleviating the subtalar instability.

Conclusion

The finite element analysis showed that the Choisne CFL reconstruction and Mann triligamentous reconstruction provided the greatest degree of immediate postoperative subtalar stability. However, both procedures could not restore the biomechanical behaviors of the subtalar joint to normal. The long-term efficacy of these procedures warrants further investigation using a substantially larger sample of clinical cases.

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.

Surgical Repair of Complete Plantar Fascia Ruptures in High-Demand Power Athletes: An Alternative Treatment Option

Surgical repair of complete plantar fascia ruptures has not yet been reported in the literature. Operative technique and outcome are described in 2 gymnasts with heavy plyometric demands who received surgical repair compared with 3 athletes treated nonoperatively. Biomechanics and clinical implications are discussed. In the last 8 years, we have seen 5 high-demand athletes with total rupture of the plantar fascia. This is a retrospective clinical evaluation 1.5 to 8 years postinjury of all 5 patients using dynamic ultrasound, Foot Function Index, sports-specific questions, Foot Posture Index, and foot length. The operated gymnasts returned to the same level of performance within 12 months. None of the conservatively treated athletes returned to preinjury plyometric sports levels but reached a foot load capacity of distance running with the injured foot as limiting factor. Ultrasound with simultaneous dorsiflexion of the toes showed a normal fascia in the operated patients, but a slack fascia that tightened up only at terminal toe dorsiflexion in the conservatively treated group. According to the Foot Function Index, the operated patients reported no complaints, whereas the nonoperative group had clinical relevant impairments in activities of daily life. The Foot Posture Index in all nonoperated patients showed a relative shift toward pronation with increased foot length compared with the noninjured foot. The operated patients showed no difference in foot length but minimal shift into supination with a slightly altered arch contour. Surgical repair of plantar fascia ruptures is technically feasible to restore normal foot load capability with return to high-demand plyometric sports within 12 months.

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.

Medial Column Biomechanics: Nonsurgical and Surgical Implications

Understanding of medial column biomechanics is paramount to a successful outcome in both conservative and surgical treatment. Dysfunctions of the dynamic stabilizers as well as the static stabilizers of the medial column play a role in pathomechanics. Conservative options for addressing the medial column include custom foot orthotics and bracing. Options for addressing the medial column surgically with the goal to restore a stable tripod configuration, include first tarsometatarsal joint arthrodesis, opening plantarflexory medial cuneiform osteotomy, and naviculocuneiform arthrodesis.

Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation

The function of the human foot is described dichotomously as a compliant structure during mid-stance and a stiff lever during push-off. The arch-spring and the windlass mechanisms, respectively, describe each of these behaviours; however, their interaction has not been quantified to date. We hypothesized that by engaging the windlass mechanism with metatarsophalangeal joint (MTPJ) dorsiflexion, we would observe stiffening of the arch and reduced energy absorption and dissipation during dynamic compressions of the foot. Using a custom apparatus, the MTPJ angle was fixed at 30 degrees of plantarflexion, neutral or 30 degrees of dorsiflexion for nine participants, with the shank positioned similarly to the end of mid-stance. The arch was compressed at two speeds, with the faster speed comparable to walking around 1.5 m s^-1 Six cameras captured the compression and elongation of the arch, along with other kinematic variables, synchronously with the ground reaction force. Combining these measures, we computed the energy absorbed, returned and dissipated in the arch. Contrary to our hypothesis, when the windlass mechanism was engaged, the arch elongated more, and absorbed and dissipated more energy than when it was not engaged. This engagement of the windlass altered the rotational axis of the mid-foot, which probably oriented the arch-spanning structures closer to their resting length, increasing their compliance. This study provides novel evidence for an interplay between the windlass and arch-spring mechanisms that aids in regulation of energy storage within the foot.

Plantar Medial Avulsion Fragment Associated With Tongue-Type Calcaneus Fractures

BACKGROUND

The plantar fascia attaches to the tuberosity of the calcaneus, which produces a distinct plantar medial avulsion (PMA) fracture fragment in certain calcaneal fractures. We hypothesized that tongue-type fractures, as described by the Essex-Lopresti classification, were more likely to be associated with this PMA fracture than joint depression fractures.

METHODS

A retrospective chart review was performed at 2 distinct Level I trauma centers to identify patients sustaining calcaneal fractures. Radiographs were then reviewed to determine the Essex-Lopresti classification, OTA classification, and presence of a PMA fracture.

RESULTS

The review yielded 271 total patients with 121 (44.6%) tongue-type (TT), 110 (40.6%) joint depression (JD), and 40 (14.8%) fractures not classifiable by the Essex-Lopresti classification. In the TT group, 73.6% of the patients had the PMA fracture whereas only 8.2% of JD and 15.0% of nonclassifiable fractures demonstrated a PMA fragment ( P < .001).

CONCLUSION

Plantar medial avulsion fractures occurred in 38.4% of the calcaneal fractures reviewed with a significantly greater proportion occurring in TT (73.6%) as opposed to JD (8.2%). Given the plantar fascia attachment to the PMA fragment, there may be clinical significance to identifying this fracture and changing treatment management; however, this requires further investigation.

LEVEL OF EVIDENCE

Level III, comparative study.

Nonanatomic versus anatomic techniques in spring ligament reconstruction: biomechanical assessment via a finite element model

Background

Several approaches to spring ligament reconstruction have been reported. However, a comparative study of nonanatomic and anatomic techniques with respect to biomechanical responses, such as kinematics and contact characteristics, has not been previously performed via a finite element analysis. The purpose of this study was to evaluate the biomechanical results of such spring ligament reconstructions via a finite element analysis.

Methods

A three-dimensional finite element model of the foot was developed and validated, and four reconstruction methods were simulated. The talonavicular dorsiflexion and abduction, hindfoot valgus, and contact characteristics in the Chopart joints were quantified in each model.

Results

Nonanatomic reconstructions corrected the talonavicular and hindfoot deformities to a greater extent than the anatomic reconstructions. The anatomic techniques also corrected the abduction and dorsiflexion deformities, although they presented insufficient power to correct for hindfoot valgus. None of the procedures restored the contact characteristics of the talonavicular and calcaneocuboid joints to those of a normal condition.

Conclusion

Nonanatomic reconstruction of the spring ligament complex provided the greatest correction for midfoot and hindfoot misalignments in flatfoot. Severe deformities with large amounts of midfoot pronation and hindfoot valgus may be better treated with nonanatomic reconstruction methods. The spring ligament reconstruction method may mitigate the need for nonanatomic bony procedures associated with complications and allows for the preservation of the triple joint complex.

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.

Biomechanical and mechanical behavior of the plantar fascia in macro and micro structures

Plantar fascia (PF) is a heterogeneous thickness structure across plantar foot. It is important significance to investigate the biomechanical behavior of the medial, middle and lateral PF regions. To investigate the non-uniform macro/micro structures of the different PF regions, the uniaxial tensile test of PF strips were performed to assess the mechanical behavior of PF. A scanning electron microscope (SEM) was used to visualize and measure the micro morphology of PF associated with collagen fibers. A three-dimensional foot finite element (FE) model was developed to quantify the tensile behavior of the internal PF. The elastic modulus of the lateral PF component (1560 MPa) was observed, followed by the medial (701 MPa), the central (1100 MPa) and the lateral (714 MPa) portions in the central component. Elongation of the central portion (0.192) was lower than the medial (0.223) and the lateral (0.227) portions. The corresponding SEM images showed that the fibers of the central portion were more densely packed and thicker compared to the ambilateral portions in the central component. While the FE model prediction also suggested that the greater elastic modulus of the central PF portion had lower strain (0.192) versus the ambilateral portions. Therefore, the lower elongation and greater elastic modulus at the central portion of PF would probably have a high risk of PF injury. The findings showed a relation between the mechanical tension and fibrous morphology of PF. This information would have a better understanding of the PF pathophysiology diseases related to tear and injury of PF.

Association Between Plantar Fasciitis and Isolated Gastrocnemius Tightness

BACKGROUND

An association between plantar fasciitis and isolated gastrocnemius tightness (IGT) has been postulated in the literature; however, there have been few studies to prove this relationship. This prospective cross-sectional cohort study was aimed at determining the association between plantar fasciitis and IGT.

METHODS

Three groups comprising 45 patients with plantar fasciitis (group 1), 117 patients with foot and ankle pathology other than plantar fasciitis (group 2), and 61 patients without foot and ankle pathology (group 3) were examined for the presence of IGT using the Silfverskiöld test. Statistical tests included chi-square test, Student t test, and analysis of variance.

RESULTS

Of the patients, 101 (45.3%) had IGT: 36 (80%) in group 1, 53 (45.3%) in group 2, and 12 (19.7%) in group 3. The difference in IGT prevalence between the groups was statistically significant at P < .001. The prevalence of IGT was similar between acute and chronic plantar fasciitis at 78.9% and 80.6%, respectively.

CONCLUSION

There was a very strong association between plantar fasciitis and IGT using group 3 as a reference. This study suggests that IGT should be actively sought out and managed in patients with plantar fasciitis.

LEVEL OF EVIDENCE

Level II, cross-sectional cohort prospective study.

Differences Between Men and Women in Balance and Tremor in Relation to Plantar Fascia Laxity During the Menstrual Cycle

CONTEXT

  Although much attention has been paid to the effect of estrogen on the knee ligaments, little has been done to examine the ligaments in the foot, such as the plantar fascia, and how they may be altered during the menstrual cycle.

OBJECTIVE

  To (1) examine sex differences in plantar fascia thickness and laxity and postural sway and (2) identify any menstrual cycle effects on plantar fascia laxity, postural sway, and neuromuscular tremor between menstruation and the ovulation phase.

DESIGN

  Case-control study.

SETTING

  Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Fifteen healthy women (age = 25.9 ± 1.8 years) and 15 healthy men (age = 27.3 ± 2.0 years) volunteered to participate in this study.

INTERVENTION(S)

  We asked participants to perform 8 balance tasks on a force platform while we assessed postural sway and tremor.

MAIN OUTCOME MEASURE(S)

  Plantar fascia length and thickness unloaded and loaded with body weight were measured via ultrasound. Postural sway and tremor were measured using a force platform.

RESULTS

  Plantar fascia length and thickness with pressure were greater in ovulating women compared with men ( P < .001), but no differences were found between women during menstruation and men. Postural sway and tremor were greater at ovulation than during menstruation ( P < .05), and men had less sway than ovulating women on the 3 most difficult balance tasks ( P < .01).

CONCLUSIONS

  Plantar fascia laxity was increased and postural sway and tremor were decreased at ovulation compared with menstruation in women. Postural sway and tremor in men were the same as in women during menstruation. These findings support the need to be aware of the effect of sex hormones on balance to prevent lower extremity injuries during sport activities.

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

BACKGROUND

Posterior tibial tendinopathy is a challenging foot condition resulting in pes planus, which is difficult to diagnose in the early stage. Prior to the deformity, abnormal internal load transfer and soft tissue attenuation are anticipated. The objective of this study was to investigate the internal load transfer and strain of the ligaments with posterior tibial tendinopathy, and the implications to pes planus and other deformities.

METHODS

A three-dimensional finite element model of the foot and ankle was reconstructed from magnetic resonance images of a 28-year-old normal female. Thirty bones, plantar fascia, ligaments and tendons were reconstructed. With the gait analysis data of the model subject, walking stance was simulated. The onset of posterior tibial tendinopathy was resembled by unloading the tibialis posterior and compared to the normal condition.

FINDINGS

The load transfer of the joints at the proximal medial column was weaken by posterior tibial tendinopathy, which was compromised by the increase along the lateral column and the intercuneiforms during late stance. Besides, the plantar tarsometatarsal and cuboideonavicular ligaments were consistently over-stretched during stance. Particularly, the maximum tensile strain of the plantar tarsometatarsal ligament was about 3-fold higher than normal at initial push-off.

INTERPRETATION

Posterior tibial tendinopathy altered load transfer of the medial column and unbalanced the load between the proximal and distal side of the medial longitudinal arch. Posterior tibial tendinopathy also stretched the midfoot plantar ligaments that jeopardized midfoot stability, and attenuated the transverse arch. All these factors potentially contributed to the progress of pes planus and other foot deformities.

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.

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

The foot/ankle complex is frequently injured in many types of debilitating events, such as car crashes. Numerical models used to assess injury risk are typically minimally validated and do not account for ankle posture variations that frequently occur during these events. The purpose of this study was to evaluate a finite element model of the foot and ankle accounting for these positional changes. A model was constructed from computed tomography scans of a male cadaveric lower leg and was evaluated by comparing simulated bone positions and strain responses to experimental results at five postures in which fractures are commonly reported. The bone positions showed agreement typically within 6° or less in all anatomical directions, and strain matching was consistent with the range of errors observed in similar studies (typically within 50% of the average strains). Fracture thresholds and locations in each posture were also estimated to be similar to those reported in the literature (ranging from 6.3 kN in the neutral posture to 3.9 kN in combined eversion and external rotation). The least vulnerable posture was neutral, and all other postures had lower fracture thresholds, indicating that examination of the fracture threshold of the lower limb in the neutral posture alone may be an underestimation. This work presents an important step forward in the modeling of lower limb injury risk in altered ankle postures. Potential clinical applications of the model include the development of postural guidelines to minimize injury, as well as the evaluation of new protective systems.

The Role of Arch Compression and Metatarsophalangeal Joint Dynamics in Modulating Plantar Fascia Strain in Running

Elastic energy returned from passive-elastic structures of the lower limb is fundamental in lowering the mechanical demand on muscles during running. The purpose of this study was to investigate the two length-modulating mechanisms of the plantar fascia, namely medial longitudinal arch compression and metatarsophalangeal joint (MPJ) excursion, and to determine how these mechanisms modulate strain, and thus elastic energy storage/return of the plantar fascia during running. Eighteen runners (9 forefoot and 9 rearfoot strike) performed three treadmill running trials; unrestricted shod, shod with restricted arch compression (via an orthotic-style insert), and barefoot. Three-dimensional motion capture and ground reaction force data were used to calculate lower limb kinematics and kinetics including MPJ angles, moments, powers and work. Estimates of plantar fascia strain due to arch compression and MPJ excursion were derived using a geometric model of the arch and a subject-specific musculoskeletal model of the plantar fascia, respectively. The plantar fascia exhibited a typical elastic stretch-shortening cycle with the majority of strain generated via arch compression. This strategy was similar in fore- and rear-foot strike runners. Restricting arch compression, and hence the elastic-spring function of the arch, was not compensated for by an increase in MPJ-derived strain. In the second half of stance the plantar fascia was found to transfer energy between the MPJ (energy absorption) and the arch (energy production during recoil). This previously unreported energy transfer mechanism reduces the strain required by the plantar fascia in generating useful positive mechanical work at the arch during running.

Metatarsal Loading During Gait—A Musculoskeletal Analysis

Detailed knowledge of the loading conditions within the human body is essential for the development and optimization of treatments for disorders and injuries of the musculoskeletal system. While loads in the major joints of the lower limb have been the subject of extensive study, relatively little is known about the forces applied to the individual bones of the foot. The objective of this study was to use a detailed musculoskeletal model to compute the loads applied to the metatarsal bones during gait across several healthy subjects. Motion-captured gait trials and computed tomography (CT) foot scans from four healthy subjects were used as the inputs to inverse dynamic simulations that allowed the computation of loads at the metatarsal joints. Low loads in the metatarsophalangeal (MTP) joint were predicted before terminal stance, however, increased to an average peak of 1.9 times body weight (BW) before toe-off in the first metatarsal. At the first tarsometatarsal (TMT) joint, loads of up to 1.0 times BW were seen during the early part of stance, reflecting tension in the ligaments and muscles. These loads subsequently increased to an average peak of 3.0 times BW. Loads in the first ray were higher compared to rays 2–5. The joints were primarily loaded in the longitudinal direction of the bone.

Functional restoration and risk of non-union of the first metatarsocuneiform arthrodesis for hallux valgus: A finite element approach

First metatarsocuneiform arthrodesis is one of the surgical interventions to correct hallux valgus, especially those with hypermobile first ray. There is lacking of biomechanical investigations to assess this operation. The objective of this study was to explore the functional restoration and the risk of non-union after the surgery via finite element analysis. A three-dimensional foot model was constructed from a female aged 28 via magnetic resonance imaging. Thirty bones and encapsulated bulk tissue were modeled. Walking stance was simulated by the gait analysis data of the same participant. Parts of the first metatarsal and cuneiform were resected and the bone graft was assigned with the same stiffness as adjacent bones to resemble the surgery of first metatarsocuneiform arthrodesis. The third principal stress of the first metatarsal at midstance (25% stance) and push off (60% stance) was increased by 76% and 139% respectively after the operation, while that of the second metatarsal was decreased by 14% and 66%. The operation reduced the medial deviation of the first metatarsal head by about 3.5mm during initial push off (60% stance). Besides, the bone graft could experience tensile stress inferiorly (26.51MPa). In conclusion, the increase of stress on the first metatarsal and the reduced medial excursion of the first metatarsal head after the simulated operation reflected that metatarsocuneiform arthrodesis could restore the load-bearing function of the first ray. However, inter-fragmentary compression could not be guaranteed. The appropriate course of hardware and non-weight-bearing protocol should be noted and further investigated.

The effect of the gastrocnemius on the plantar fascia

Although anatomic and functional relationship has been established between the gastrocnemius muscle, via the Achilles tendon, and the plantar fascia, the exact role of gastrocnemius tightness in foot and plantar fascia problems is not completely understood. This article summarizes past and current literature linking these 2 structures and gives a mechanical explanation based on functional models of the relationship between gastrocnemius tightness and plantar fascia. The effect of gastrocnemius tightness on the sagittal behavior of the foot is also discussed.

Constitutive modeling of time-dependent response of human plantar aponeurosis

The attention is focused on the viscoelastic behavior of human plantar aponeurosis tissue. At this purpose, stress relaxation tests were developed on samples taken from the plantar aponeurosis of frozen adult donors with age ranging from 67 to 78 years, imposing three levels of strain in the physiological range (4%, 6%, and 8%) and observing stress decay for 240 s. A viscohyperelastic fiber-reinforced constitutive model with transverse isotropy was assumed to describe the time-dependent behavior of the aponeurotic tissue. This model is consistent with the structural conformation of the tissue where collagen fibers are mainly aligned with the proximal-distal direction. Constitutive model fitting to experimental data was made by implementing a stochastic-deterministic procedure. The stress relaxation was found close to 40%, independently of the level of strain applied. The agreement between experimental data and numerical results confirms the suitability of the constitutive model to describe the viscoelastic behaviour of the plantar aponeurosis.

Anatomy and biomechanical properties of the plantar aponeurosis: a cadaveric study

Objectives

To explore the anatomy of the plantar aponeurosis (PA) and its biomechanical effects on the first metatarsophalangeal (MTP) joint and foot arch.

Methods

Anatomic parameters (length, width and thickness of each central PA bundle and the main body of the central part) were measured in 8 cadaveric specimens. The ratios of the length and width of each bundle to the length and width of the central part were used to describe these bundles. Six cadaveric specimens were used to measure the range of motion of the first MTP joint before and after releasing the first bundle of the PA. Another 6 specimens were used to evaluate simulated static weight-bearing. Changes in foot arch height and plantar pressure were measured before and after dividing the first bundle.

Results

The average width and thickness of the origin of the central part at the calcaneal tubercle were 15.45 mm and 2.79 mm respectively. The ratio of the length of each bundle to the length of the central part was (from medial to lateral) 0.29, 0.30, 0.28, 0.25, and 0.27, respectively. Similarly, the ratio of the widths was 0.26, 0.25, 0.23, 0.19 and 0.17. The thickness of each bundle at the bifurcation of the PA into bundles was (from medial to lateral) 1.26 mm, 1.04 mm, 0.91 mm, 0.84 mm and 0.72 mm. The average dorsiflexion of the first MTP joint increased 10.16° after the first bundle was divided. Marked acute changes in the foot arch height and the plantar pressure were not observed after division.

Conclusions

The first PA bundle was not the longest, widest, or the thickest bundle. Releasing the first bundle increased the range of motion of the first MTP joint, but did not acutely change foot arch height or plantar pressure during static load testing.

An investigation of the dynamic relationship between navicular drop and first metatarsophalangeal joint dorsal excursion

The modern human foot is a complex biomechanical structure that must act both as a shock absorber and as a propulsive strut during the stance phase of gait. Understanding the ways in which foot segments interact can illuminate the mechanics of foot function in healthy and pathological humans. It has been proposed that increased values of medial longitudinal arch deformation can limit metatarsophalangeal joint excursion via tension in the plantar aponeurosis. However, this model has not been tested directly in a dynamic setting. In this study, we tested the hypothesis that during the stance phase, subtalar pronation (stretching of the plantar aponeurosis and subsequent lowering of the medial longitudinal arch) will negatively affect the amount of first metatarsophalangeal joint excursion occurring at push-off. Vertical descent of the navicular (a proxy for subtalar pronation) and first metatarsophalangeal joint dorsal excursion were measured during steady locomotion over a flat substrate on a novel sample consisting of asymptomatic adult males and females, many of whom are habitually unshod. Least-squares regression analyses indicated that, contrary to the hypothesis, navicular drop did not explain a significant amount of variation in first metatarsophalangeal joint dorsal excursion. These results suggest that, in an asymptomatic subject, the plantar aponeurosis and the associated foot bones can function effectively within the normal range of subtalar pronation that takes place during walking gait. From a clinical standpoint, this study highlights the need for investigating the in vivo kinematic relationship between subtalar pronation and metatarsophalangeal joint dorsiflexion in symptomatic populations, and also the need to explore other factors that may affect the kinematics of asymptomatic feet.

Changes in windlass effect in response to different shoe and insole designs during walking

Windlass effect occurs during the pre-swing phase of gait cycle in which the peak tensile strain and force of the plantar aponeurosis (PA) is reached. The increased dorsiflexion angle of the 1st metatarsophalangeal (MTP) joint is the main causing factor. The aim of this study was to investigate thoroughly in finding the appropriate shoe and insole combination that can effectively decrease the windlass effect. Foot kinematic analyses of 10 normal volunteers (aged 25.2±2.1 years, height of 167.4±9.1 cm, and weight of 66.2±18.1 kg) were performed during gait under the conditions of barefoot, standard shoe (SS) with flat insole (FI) or carbon fiber insole (CFI), and rocker sole shoe (RSS) with FI or CFI. The shoe cover consisting of transparent polymer was used for accurate measurement of kinematic data as specific areas on the cover can be cut away for direct placement of reflective markers onto the skin. Under barefoot condition, the mean of maximum dorsiflexion angle of the 1st MTP joint was measured to be 48.0±7.3°, and decreased significantly to 28.2±5.7° when wearing SS with FI, and 24.1±5.7° when wearing SS with CFI. This angle was further decreased to around 13° when wearing RSS with FI or CFI. Subjects wearing footwear alone can increase the minimum medial longitudinal angle and decrease the maximum plantarflexion angle of metatarsus related to the calcaneus as compared with barefoot condition, resulting in flatter medial foot arch. Results suggested that RSS is the effective footwear in reducing the windlass effect regardless the type of insole inserted. The findings in this study provided us with the evidences in finding the appropriate footwear for treating foot disorders such as plantar fasciitis by effectively reducing the windlass effect.

Finite element analysis of the foot: model validation and comparison between two common treatments of the clawed hallux deformity

BACKGROUND

Clawed hallux is defined by first metatarsophalangeal joint extension and first interphalangeal joint flexion; it can increase plantar pressures and ulceration risk. We investigated two corrective surgical techniques, the modified Jones and flexor hallucis longus tendon transfer.

METHODS

A finite element foot model was modified to generate muscle overpulls, including extensor hallucis longus, flexor hallucis longus and peroneus longus. Both corrective procedures were simulated, predicting joint angle and plantar pressure changes.

FINDINGS

The clawed hallux deformity was generated by overpulling: 1) extensor hallucis longus, 2) peroneus longus + extensor hallucis longus, 3) extensor hallucis longus + flexor hallucis longus and 4) all three together. The modified Jones reduced metatarsophalangeal joint angles, but acceptable hallux pressure was found only when there was no flexor hallucis longus overpull. The flexor hallucis longus tendon transfer reduced deformity at the metatarsophalangeal and interphalangeal joints but may extended the hallux due to the unopposed extensor hallucis longus. Additionally, metatarsal head pressure increased with overpulling of the extensor hallucis longus + flexor hallucis longus, and all three muscles together.

INTERPRETATION

The modified Jones was effective in correcting clawed hallux deformity involving extensor hallucis longus overpull without flexor hallucis longus overpull. The flexor hallucis longus tendon transfer was effective in correcting clawed hallux deformity resulting from the combined overpull of both extensor and flexor hallucis longus, but not with isolated extensor hallucis longus overpull. An additional procedure to reduce the metatarsal head pressure may be required concomitant to the flexor hallucis longus tendon transfer. However this procedure avoids interphalangeal joint fusion.