Foot Type Biomechanics Part 2: are structure and anthropometrics related to function?

Differences in ankle and knee muscle architecture and plantar pressure distribution among women with knee osteoarthritis

BACKGROUND

The aim of this study was to compare the plantar pressure distribution and knee and ankle muscle architecture in women with and without knee osteoarthritis (OA).

METHODS

Fifty women with knee OA (mean age = 52.11 ± 4.96 years, mean Body mass index (BMI) = 30.94 ± 4.23 kg/m2) and 50 healthy women as a control group (mean age = 50.93 ± 3.78 years, mean BMI = 29.06 ± 4.82 kg/m2) were included in the study. Ultrasonography was used to evaluate knee and ankle muscles architecture and femoral cartilage thickness. The plantar pressure distribution was evaluated using the Digital Biometry Scanning System and Milleri software (DIASU, Italy). Static foot posture was evaluated using the Foot Posture Index (FPI), and pain severity was assessed using the Visual Analog Scale.

RESULTS

The OA group exhibited lower muscle thickness in Rectus Femoris (RF) (p = 0.003), Vastus Medialis (VM) (p = 0.004), Vastus Lateralis (p = 0.023), and Peroneus Longus (p = 0.002), as well as lower Medial Gastrocnemius pennation angle (p = 0.049) and higher Fat thickness (FT) in RF (p = 0.033) and VM (p = 0.037) compared to the control group. The OA group showed thinner femoral cartilage thickness (p = 0.001) and higher pain severity (p = 0.001) than the control groups. FPI scores were higher (p = 0.001) in OA group compared to the control group. The plantar pressure distribution results indicated an increase in total surface (p = 0.027), total load (p = 0.002), medial load (p = 0.005), and lateral load (p = 0.002) on dominant side in OA group compared to the control group.

CONCLUSIONS

Knee and ankle muscle architecture, knee extensor muscle FT, and plantar pressure distribution in the dominant foot differed in individuals with knee OA compared to the control group.

Relationship between the strength of the ankle and toe muscles and functional stability in young, healthy adults

This study investigates the relationship between ankle and toe strength and functional stability in young adults, with a sample comprising sixteen females and fourteen males. The research employed force platform data to determine the center of foot pressure (COP) and calculated the forward functional stability index (FFSI) through foot anthropometric measurements. Strength measurements of toe and ankle muscles, during maximal isometric flexion and extension, were conducted using force transducers. Notable positive correlations were found between toe flexor strength and FFSI (left flexor: r = 0.4, right flexor: r = 0.38, p < 0.05), not influenced by foot anthropometry. Contrarily, no significant correlation was observed between ankle muscle strength and FFSI, despite a positive correlation with the COP range. The moderate correlation coefficients suggest that while toe flexor strength is a contributing factor to functional stability, it does not solely determine functional stability. These findings highlight the critical role of muscle strength in maintaining functional stability, particularly during forward movements and emphasize the utility of FFSI alongside traditional COP measures in balance assessment. It is recommended to employ a multifaceted approach is required in balance training programs.

Influence of motor capacity of the lower extremity and mobility performance on foot plantar pressures in community-dwelling older women

Objectives

To investigate the associations of motor capacity of the lower extremity and mobility performance in daily physical activities with peak foot plantar pressures during walking among older women.

Methods

Using the data collected among 58 community-dwelling older women (68.66 ± 3.85 years), Pearson correlation and multiple linear regression analyses were performed to analyze the associations of motor capacity of the lower extremity (the 30-s chair stand test, the timed one-leg stance with eyes closed, and the Fugl-Meyer assessment of lower extremity), mobility performance in daily physical activities (the average minutes of moderate to vigorous physical activity every day and the metabolic equivalents), and foot plantar pressures (peak force and peak pressure) with the age and body fat percentage as covariates.

Results

(1) The motor capacity of the lower extremity has higher explanatory power for peak foot plantar pressures compared with the mobility performance in daily physical activities. (2) Higher body fat percentage was positively associated with peak force and pressure, while a lower score on the Fugl-Meyer assessment of lower extremity was negatively associated with both of them. (3) The metabolic equivalents were positively associated with the peak force, while the 30-s chair stand test was negatively associated with it.

Conclusions

Mobility performance in daily physical activities can be significant predictors for peak foot plantar pressures among older women. The significant predictor variables include the Fugl-Meyer assessment of lower extremity, the 30-s chair stand test, and metabolic equivalents.

Evaluation of the relationship between truss/windlass mechanisms and foot stiffness while walking

BACKGROUND

The truss/windlass coefficients ware reported as a surrogate parameter for foot stiffness while walking. However, the construct validity and reliability of whether the truss/windlass coefficients reflect foot stiffness have not been sufficiently validated. This study validated the truss/windlass coefficient reflects the construct validity and reliability of foot stiffness.

METHODS

Participants were 25 healthy young males (21.6 ± 0.7 years). Foot stiffness was assessed using Simplified Foot Stiffness. It was determined by dividing the difference in foot load between sitting and standing by the rate of change in navicular height. The truss/windlass coefficient was calculated as the behavior of the foot arch during middle to late stance. To assess the reliability of each parameter, intraclass correlation coefficients (ICC 1.1) and Bland-Altman analysis were used, and Spearman's rank correlation coefficients were used to determine construct validity.

RESULTS

The truss coefficient (ICC1.1 0.86) and Simplified Foot Stiffness (ICC1.1 0.87) demonstrated high reliability and no systematic error. However, the windlass coefficient (ICC1.1 0.73) demonstrated moderate reliability and proportional error. Furthermore, the truss coefficient had a significant positive correlation with Simplified Foot Stiffness (r = 0.504; p < 0.01), whereas the windlass coefficient did not (r = 0.06; p = 0.67).

CONCLUSION

The truss coefficient was proposed as a highly reliable parameter that reflects foot stiffness. However, the windlass coefficient has a proportional error, despite being moderately reliable.

Validation of an Automated Optical Scanner for a Comprehensive Anthropometric Analysis of the Foot and Ankle

Background: Our objective was to conduct a comprehensive analysis of the reproducibility of foot and ankle anthropometric measurements with a three-dimensional (3D) optical scanner. Methods: We evaluated thirty-nine different anthropometric parameters obtained with a 3D Laser UPOD-S Full-Foot Scanner in a healthy population of twenty subjects. We determined the variance of the measurements for each foot/ankle, and the average variance among different subjects. Results: For 40 feet and ankles (15 women and 5 men; mean age 35.62 +/- 9.54 years, range 9-75 years), the average variance was 1.4 ± 2 (range 0.1 to 8). Overall, the mean absolute measurement error was <1 mm, with a maximum variance percentage of 8.3%. Forefoot and midfoot circumferences had a low variance <2.5, with variance percentages <1%. Hindfoot circumferences, malleolar heights, and the length of the first and fifth metatarsal to the ground contact points showed the highest variance (range 1 to 7). Conclusions: The UPOD-S Full-Foot optical Scanner achieved a good reproducibility in a large set of foot and ankle anthropometric measurements. It is a valuable tool for clinical and research purposes.

Is Morton's neuroma in a pes planus or pes cavus foot lead to differences in pressure distribution and gait parameters?

Morton's neuroma (MN) is a compressive neuropathy of the common digital plantar nerve causing forefoot pain. Foot posture and altered plantar pressure distribution have been identified as predispoing factors, however no studies have compared individuls with different foot postures with MN. Thus, we aimed to compare the effect of MN on spatiotemporal gait parameters and foot-pressure distribution in individuals with pes planus and pes cavus. Thirty-eight patients with unilateral MN were evaluated between June and August 2021. Nineteen patients with bilateral pes planus and 19 age and gender-matched patients with pes cavus who had no prior surgery were recruited. A Zebris FDM-THM-S treadmill system (Zebris Medical GmbH, Germany) was used to evaluate step length, stride length, step width, step time, stride time, cadence, velocity, foot-pressure distribution, force and whole stance phase, loading response, mid stance, pre-swing and swing phase percentages. There were no significant differences between the groups in spatiotemporal gait parameters (p > 0.05). Patients with pes planus displayed the following results for step length (49.36 ± 8.38), step width (9.05 ± 2.12), stance phase percentage (65.92 ± 2.11), swing phase percentage (34.08 ± 2.12), gait speed (2.96 ± 0.55), and cadence (100.57 ± 8.84). In contrast, patients with pes cavus displayed the following results for step length (49.06 ± 8.37), step width (8.10 ± 2.46), stance phase percentage (64.96 ± 1.61), swing phase percentage (34.79 ± 1.60), gait speed (2.95 ± 0.65), and cadence (99.73 ± 13.81). Foot-pressure distribution values showed no differences were detected in force, forefoot, and rearfoot pressure distribution, except for midfoot force (p < 0.05). The forefoot, midfoot, and rearfoot pressure values for the pronated group were 32.14 ± 10.90, 13.80 ± 3.03, and 22.78 ± 5.10, and for the supinated group were 33.50 ± 11.49, 14.23 ± 3.11 and 24.93 ± 6.52. MN does not significantly affect spatiotemporal gait parameters or foot-pressure distribution in patients with pes cavus or pes planus.

Age, Gender, Body Mass Index, and Foot Loading During Gait

Background

The aim was to analyze changes in normal functional parameters of gait analysis by aging, sex, and body mass index (BMI).

Methods

A cross-sectional study with a consecutive sample of asymptomatic subjects was performed between 2014 and 2020. Primary outcomes were time and force parameters (contact time and center of force [CoF] time), in the heel, midfoot, and metatarsal areas, measured using an in-office force platform.

Results

A total of 156 subjects (312 feet) were included, including 67% of women with a mean age of 47 years. The mean of total contact time was similar in males and females (P = .695) and across BMI (P = .413). Contact time did not show differences by region (P = .648 heel, P = .286 midfoot, and P = .690 metatarsal). CoF time in the heel and metatarsal areas did not change between males and females (P = .288 and P = .879, respectively); meanwhile, it was different in midfoot (P = .002). Maximum force showed a reduction between sexes in the heel (P = .039) but did not in the midfoot and metatarsal areas. By age, differences were detected in the heel and metatarsal areas in females (P = .002 and P = .001) and the metatarsal area in males (P = .001). According to the age groups, total contact time increased in females (P = .001) but not in males (P = .018), and no differences were detected between foot areas. In females, CoF time did not change either foot areas or age groups. In males, CoF time values increased in the midfoot area in the older group (P = .001).

Conclusion

Time variables did not change by foot region, independent of age, sex, and BMI. Heel maximum force decreased in females, probably linked to adaptive phenomena by aging. The midfoot remains stable, and acts as an undamaged "bridge." These parameters could be interpreted as normal in asymptomatic subjects.

Level of Evidence

Level III, diagnostic and prognostic.

Biomechanical Implications of Congenital Conditions of the Foot/Ankle

Segmental foot and ankle models are often used as part of instrumented gait analysis when planning interventions for complex congenital foot conditions. More than 40 models have been used for clinical analysis, and it is important to understand the technical differences among models. These models have been used to improve clinical planning of pediatric foot conditions including clubfoot, planovalgus, and equinovarus. They have also been used to identify clinically relevant subgroups among pediatric populations, quantify postoperative outcomes, and explain variability in healthy populations.

Parámetros biomecánicos de la función del pie medidos en el consultorio del especialista en Ortopedia y Traumatología

Introducción: Los estudios dinámicos de la función del pie habitualmente se realizan en laboratorios de marcha de gran complejidad. El objetivo de este estudio fue analizar parámetros funcionales utilizando una plataforma de fuerza en una serie de pacientes asintomáticos evaluados en consultorios externos. Materiales y Métodos: Estudio de corte transversal que incluyó una serie consecutiva de pacientes asintomáticos voluntarios a quienes se les realizó una medición con una plataforma de fuerza (TekScan MatScan®, Boston, MA, EE.UU.) entre 2014 y 2020, en la Ciudad Autónoma de Buenos Aires, Argentina. Resultados: Se incluyeron 316 registros de 158 pacientes con mediciones bilaterales. La mayoría eran mujeres (66,5%) y el promedio de la edad era de 47 años (DE 16.1). Se evaluaron 14 variables, correspondientes a parámetros de fuerza, trayectoria y tiempo de contacto de la fuerza. El tiempo de contacto total fue de 0,79 segundos (DE 0,09), el CoF time según la región del pie fue del 20% en el talón, 26% en el mediopié y 46% en el antepié. El CPEI (center of pressure excursion index) fue del 16,55% (DE 7,14). Conclusiones: Se comunican los parámetros funcionales del pie en pacientes asintomáticos. Se midieronel tiempo de contacto del pie en el suelo, la fuerza (en talón, mediopié y antepié) y la trayectoria de la fuerza con una plataforma de fuerza. No se utilizaron radiaciones ionizantes. Estos hallazgos podrían ser utilizados como valores de referencia para detectar marchas patológicas. Nivel de Evidencia: II  

Toward improved understanding of foot shape, foot posture, and foot biomechanics during running: A narrative review

The current narrative review has explored known associations between foot shape, foot posture, and foot conditions during running. The artificial intelligence was found to be a useful metric of foot posture but was less useful in developing and obese individuals. Care should be taken when using the foot posture index to associate pronation with injury risk, and the Achilles tendon and longitudinal arch angles are required to elucidate the risk. The statistical shape modeling (SSM) may derive learnt information from population-based inference and fill in missing data from personalized information. Bone shapes and tissue morphology have been associated with pathology, gender, age, and height and may develop rapid population-specific foot classifiers. Based on this review, future studies are suggested for 1) tracking the internal multi-segmental foot motion and mapping the biplanar 2D motion to 3D shape motion using the SSM; 2) implementing multivariate machine learning or convolutional neural network to address nonlinear correlations in foot mechanics with shape or posture; 3) standardizing wearable data for rapid prediction of instant mechanics, load accumulation, injury risks and adaptation in foot tissue and bones, and correlation with shapes; 4) analyzing dynamic shape and posture via marker-less and real-time techniques under real-life scenarios for precise evaluation of clinical foot conditions and performance-fit footwear development.

Multi-segment foot kinematics during gait following ankle arthroplasty

Ankle arthritis is a debilitating disease marked by pain and limited function. Total ankle arthroplasty improves pain while preserving motion and offers an alternative to the traditional treatment of ankle fusion. Gait analysis and functional outcomes tools can provide an objective balanced analysis of ankle replacement for the treatment of ankle arthritis. Twenty-nine patients with end-stage ankle arthritis were evaluated before and after ankle arthroplasty. Multi-segment foot and ankle kinematics were assessed annually following surgery (average 3.5 years, range 1-6 years) using the Milwaukee Foot Model and a Vicon video motion analysis system. Functional outcomes (American Orthopedic Foot and Ankle Society [AOFAS] ankle/hindfoot scale, short form 36 [SF-36] questionnaire) and temporal-spatial parameters were also assessed. Kinematic results were compared to findings from a previously collected group of healthy ambulators. AOFAS and SF-36 mean scores improved postoperatively. Walking speed and stride length increased after surgery. There were significant improvements in tibial sagittal range of motion in terminal stance and hindfoot sagittal range of motion in preswing. Decreased external rotation of the tibia and increased external rotation of the hindfoot were noted throughout the gait cycle. Pain and function improved after ankle replacement as supported by better outcomes scores, increased temporal-spatial parameters, and significant improvement in tibial sagittal range of motion during terminal stance and hindfoot sagittal range of motion during preswing. While multi-segment foot kinematics were improved, they were not restored to control values. Statement of clinical significance: Total ankle arthroplasty does not fully normalize mutli-segment gait kinematics despite improved patient-reported outcomes and gait mechanics.

ESTABLISHING THE NORMAL GAIT OF CHINESE YOUTH BASED ON THE PLANTAR PRESSURE TEST: AN EXPERIMENTAL STUDY

Objective: This study will measure the geometric and pressure centerlines of the foot’s plantar region in healthy Chinese youth to construct a gait norm. Methods: In the present experiment, 203 healthy college students and postgraduates (90 males and 113 females) were recruited as subjects. Their average age was [Formula: see text] years old, average height was [Formula: see text][Formula: see text]cm, and average weight was [Formula: see text][Formula: see text]kg. A double-blind method was used in this experiment. The plantar pressure and gait parameters of time and space among subjects were tested using a gait and balance function-training evaluation system. Data were collected using five pressure-sensor plates, based on the distribution in the geometric and pressure centers of the foot’s plantar area, according to the calculation formula of biomechanics. Results: From 20 selected subjects, the experiment gathered a total of 197 data points from the plantar pressure during walking. The results defined the foot’s centerline of maximum pressure while walking and showed that the pressure and geometric centerlines tended to converge and overlap in normal youth, irrespective of gender. In addition, differences were found between the foot’s centerline of pressure and the geometric and pressure centerlines of the plantar. Conclusion: This study showed that the plantar’s pressure and geometric centerlines can be used as a reference to assess normal gait in Chinese youth.

ISB recommendations for skin-marker-based multi-segment foot kinematics

The foot is anatomically and functionally complex, and thus an accurate description of intrinsic kinematics for clinical or sports applications requires multiple segments. This has led to the development of many multi-segment foot models for both kinematic and kinetic analyses. These models differ in the number of segments analyzed, bony landmarks identified, required marker set, defined anatomical axes and frames, the convention used to calculate joint rotations and the determination of neutral positions or other offsets from neutral. Many of these models lack validation. The terminology used is inconsistent and frequently confusing. Biomechanical and clinical studies using these models should use established references and describe how results are obtained and reported. The International Society of Biomechanics has previously published proposals for standards regarding kinematic and kinetic measurements in biomechanical research, and in this paper also addresses multi-segment foot kinematics modeling. The scope of this work is not to prescribe a particular set of standard definitions to be used in all applications, but rather to recommend a set of standards for collecting, calculating and reporting relevant data. The present paper includes recommendations for the overall modeling and grouping of the foot bones, for defining landmarks and other anatomical references, for addressing the many experimental issues in motion data collection, for analysing and reporting relevant results and finally for designing clinical and biomechanical studies in large populations by selecting the most suitable protocol for the specific application. These recommendations should also be applied when writing manuscripts and abstracts.

The quarter-ellipsoid foot: A clinically applicable 3-dimensional composite measure of foot deformation during weight bearing

STUDY DESIGN

Descriptive Laboratory OBJECTIVES: To assess change in foot morphology across loading using innovative, clinically accessible 3-dimesional composite measurements of surface area (SA), volume (V), and SA:V ratio in recreationally-active young adults.

METHODS

The feet of 53 female [mean age:20.7 ± 3.8 years, BMI:23.9 ± 4.2 kg m^-2, foot posture index (FPI):3.8 ± 3.7] and 31 male participants (mean age:20.8 ± 2.4 years, BMI:23.7 ± 2.5 kg m^-2, FPI:3.8 ± 4.1) were evaluated. FPI was assessed and foot length, width, and dorsal arch height were measured in sitting and bipedal standing and used to calculate the SA and V of a quarter-ellipsoid. ΔSA characterized foot widening and lengthening and ΔV characterized arch deformation during loading. The SA:V represented changes in both foot size and shape. Linear regression was performed to assess the effects of component foot change measures during loading on the composite measurements. The composite measures were compared to the established measures of ΔArch Height Index (ΔAHI), Arch Flexibility, Foot Mobility Magnitude (FMM), and FPI.

RESULTS

Foot width and dorsal arch height change measures were significant predictors (p < 0.001) for the ΔV and SA:V composite measures, explaining 90-91% of the variance. Significant fair to good associations (p < .05) were found between the novel and established composite measures: ΔSA: Arch flexibility (r=-0.27); SA:V: ΔAHI (r=-0.57), Arch Flexibility (r=-0.75), FMM (r=-0.30), FPI (r = 0.42).

CONCLUSION

Quarter-ellipsoid measures calculated from morphologic measurements may have clinical utility in quantifying 3-dimensional foot changes during loading and may be useful when assessing need and response to clinical interventions.

A Comparative Biomechanical Analysis during Planned and Unplanned Gait Termination in Individuals with Different Arch Stiffnesses

Although values of arch stiffness index (ASI) have been used to evaluate arch structure and injury susceptibility, investigations are limited regarding the influence of ASI on biomechanical characteristics during gait termination, which involves a challenging balance transition from walking to standing. This study aimed to explore plantar pressure distribution and lower extremity joint kinematic differences between individuals with both a stiff and flexible arch (SA and FA, respectively) during planned and unplanned gait termination (PGT and UGT, respectively). Following the calculation of ASI, sixty-five asymptomatic male subjects were classified and participated in two types of gait termination tests to acquire kinematic and plantar pressure data. Parameters were compared between SA and FA using a two-way ANOVA during PGT and UGT, respectively. UGT was found to have a larger range of motion on the hip joint in the sagittal plane and the knee joint in the transverse plane when compared with PGT. The differences in the kinematic characteristics of the lower limb joints caused by the difference in arch stiffness are mainly concentrated in the ankle and metatarsophalangeal joints. Plantar pressure data, represented by the maximum pressure, showed significant differences in the forefoot and rearfoot areas. These results suggest that ASI could change freedom of motion of the lower limb joints, and UGT tends to conduct a compensatory adjustment for the lower extremity kinetic chain. An understanding of the biomechanical characteristics of arch structures may provide additional insights into foot function and injury prediction during gait termination.

Relationships between Foot Morphology and Foot Muscle Strength in Healthy Adults

The purpose of this study was to investigate if measurements of foot morphology in sitting and standing positions can predict foot muscle strength. Twenty-six healthy male adults were recruited, and their foot morphology and foot muscle strength were measured. Foot morphological variables, toe flexor strength, and metatarsophalangeal joint flexor strength were measured by using a digital caliper, Ailitech-AFG500 dynameter and metatarsophalangeal joint flexor strength tester, respectively. Partial correlation and multivariate stepwise regression were used to explore the relationships between foot morphology and toe/metatarsophalangeal joint strength. Results adjusted by age and body mass index were as follows: (1) truncated foot length in sitting and standing positions and foot width in standing position were positively correlated with the flexor strength of the first toe; (2) foot length, foot width, and truncated foot length in both positions were positively related to the flexor strength of the other toes; (3) arch height index in sitting position and differences in navicular height were negatively associated with the flexor strength of the other toes; (4) differences in foot width were negatively associated with metatarsophalangeal joint flexor strength; and (5) the multivariate stepwise regression model showed that truncated foot length in sitting position, navicular height in standing position, differences in navicular height, foot width in sitting position, and differences in foot width were significantly correlated with toe/metatarsophalangeal joint flexor strength. Simple measurements of foot morphological characteristics can effectively predict foot muscle strength. Preliminary findings provided practical implications for the improvement of the foot ability by making specific foot muscle training sessions in professional sports and by compensating the predicted muscle strength defects to prevent foot injury.

The center of pressure progression characterizes the dynamic function of high-arched feet during walking

Background

The medial longitudinal arch height has an effect on kinetic parameters during gait and might be related to the risk of injury. For the assessment of foot structures, the center of pressure (COP) trajectory is a more reliable and practical parameter than plantar pressure. This study aimed to clarify the COP trajectory and velocity characteristics in the medial-lateral and anterior-posterior direction of individuals with a high-arched foot during barefoot walking.

Methods

Sixty-two healthy young adults were asked to walk over a Footscan pressure plate to record the COP parameters during the stance phase of walking.

Results

Compared to normal arched feet, the COP during forefoot contact and foot flat phases of high-arched feet shifted anteriorly (19.9 mm and 15.1 mm, respectively), and the mean velocity of COP in anterior-posterior direction decreased by 0.26 m/s and increased by 0.044 m/s during these two phases respectively.

Conclusions

The findings of this study suggest that the displacement and velocity of COP in anterior-posterior direction was different between high-arched and normal-arched subjects during barefoot walking, which can be used for the assessment of gait characteristics for high-arched individuals. The results of this study may provide insights into modifying clinical intervention for individuals with high-arched feet to enhance rehabilitation and prevent injuries and have implications for assessing the design of footwear and foot orthotics.

Graphical abstract

Analysis of Foot Morphology in Habitually Barefoot Group

Accurate method to identify foot morphology would further contribute to understand foot mechanism. The aim of this study is to identify foot morphology feature between habitually barefoot and shod population with 3D technology of scan. Sixty subjects both 30 habitually barefoot and 30 habitually shod participated foot scanning test. A 3-dimension laser device was applied to execute foot scanning. The findings of this study showed that habitually barefoot group displayed the foot features of the large ball perimeters, large minimal distance between hallux and other toes and the smaller hallux angle than habitually shod group. To conclude, the significant differences of foot morphology between habitually barefoot and habitually shod was mainly in forefoot area, this morphological features would provide some sights for the exploration of barefoot locomotion.

The relationship between foot arch flexibility and medial-lateral ground reaction force distribution

BACKGROUND

Overuse running injury susceptibility has previously been associated with the magnitude and slope of ground reaction force profiles, most often in the vertical axis. However, despite the implications of excessive pronation and supination on injury susceptibility, very little research has examined the factors that might affect distribution of force in the medial-lateral directions.

RESEARCH QUESTION

The purpose of this study was to consider how foot structure, specifically arch flexibility, affects the distribution of ground reaction force between the medial-lateral and vertical planes of motion.

METHODS

Twenty-five participants were classified as having stiff or flexible arches, and three dimensional kinetic data were gathered while the volunteers ran at 7 mph on an instrumented treadmill. A mixed-effects ANOVA was used to analyze the effect of arch flexibility type on distribution of ground reaction force impulse in the medial and lateral directions.

RESULTS

The results suggest that individuals with relatively stiff arches experience a greater proportion of ground reaction force in the medial-lateral plane of motion, as compared with those with more flexible arches (p = 0.03). Further, the results suggest that most individuals, regardless of foot structure, experience greater impulse of force in the lateral than in the medial direction (p < 0.01).

SIGNIFICANCE

Considering previously explored relationships between ground reaction force, foot pronation/supination, and chronic running injuries, the results of this study suggest that arch flexibility could be used as a criterion for assessing injury susceptibility. Further, conclusions drawn from this study add to the discussion on the pros and cons of training or using devices to increase or restrict arch flexibility while running.

Intra- and interday reliability of the dynamic navicular rise, a new measure for dynamic foot function: A descriptive, cross-sectional laboratory study

BACKGROUND

The lack of reliable parameters to evaluate dynamic foot function, emphasizes the need for a deeper insight in foot biomechanics. The aims were to investigate the reliability of a new parameter (dynamic navicular rise dNR), and its relationship with the dynamic navicular drop (dND).

METHODS

Twenty healthy participants (mean age 30.2±8.1years) had to walk on even ground and downstairs. Data of ten trials per task on two measurement days were recorded. The dNR was defined as the difference in millimetres (mm) between the minimum navicular height (NH) during stance and the NH at toe off. To test intra- and interday reliability, Intraclass Correlation Coefficients (ICC_2.1) and repeatability were calculated. To obtain the absolute repeatability (RP) in mm, the equation RP=1.96×SD_differences was used. Furthermore, the relationship between the dNR and the dND was examined by calculating Pearson (r) or Spearman (r_s) correlation coefficients.

RESULTS

Included participants showed a mean dNR of (12.2±3.7) mm for level walking and (14.8±3.4) mm for stair descent. The ICC_2.1 for the dNR were 0.98 (intraday), 0.91 (interday) for level walking and 0.97 (intraday), 0.94 (interday) for stair descent. The interday repeatability was 3.2mm (level walking), 2.7mm (stair descent) respectively. For level walking, r was 0.31 (p=0.049), and r_s=0.88 (p<0.001) for stair descent.

CONCLUSIONS

The dNR seems to be highly reliable (ICCs), however, repeatability is unacceptable. For level walking, the dNR might be an independent measure, but not for stair climbing.

The relationship between foot posture and plantar pressure during walking in adults: A systematic review

BACKGROUND

Foot posture is a risk factor for some lower limb injuries, however the underlying mechanism is not well understood. Plantar pressure analysis is one technique to investigate the interaction between foot posture and biomechanical function of the lower limb.

RESEARCH QUESTION

The aim of this review was to investigate the relationship between foot posture and plantar pressure during walking.

METHODS

A systematic database search was conducted using MEDLINE, CINAHL, SPORTDiscus and Embase to identify studies that have assessed the relationship between foot posture and plantar pressure during walking. Included studies were assessed for methodological quality. Meta-analysis was not conducted due to heterogeneity between studies. Inconsistencies included foot posture classification techniques, gait analysis protocols, selection of plantar pressure parameters and statistical analysis approaches.

RESULTS

Of the 4213 citations identified for title and abstract review, sixteen studies were included and underwent quality assessment; all were of moderate methodological quality. There was some evidence that planus feet display higher peak pressure, pressure-time integral, maximum force, force-time integral and contact area predominantly in the medial arch, central forefoot and hallux, while these variables are lower in the lateral and medial forefoot. In contrast, cavus feet display higher peak pressure and pressure-time integral in the heel and lateral forefoot, while pressure-time integral, maximum force, force-time integral and contact area are lower for the midfoot and hallux. Centre of pressure was more laterally deviated in cavus feet and more medially deviated in planus feet. Overall, effect sizes were moderate, but regression models could only explain a small amount of variance in plantar pressure variables.

SIGNIFICANCE

Despite these significant findings, future research would benefit from greater methodological rigour, particularly in relation to the use of valid foot posture measurement techniques, gait analysis protocols, and standardised approaches for analysis and reporting of plantar pressure variables.

A minimal markerset for three-dimensional foot function assessment: measuring navicular drop and drift under dynamic conditions

Background

The validity of predicting foot pronation occurring mainly at the midfoot by surrogate measures from the rearfoot, like eversion excursion, is limited. The dynamic navicular mobility in terms of vertical navicular drop (dNDrop) and medial navicular drift (dNDrift) may be regarded as meaningful clinical indicators to represent overall foot function. This study aimed to develop a minimal approach to measure the two parameters and to examine their intra- and interday reliability during walking.

Methods

The minimal markerset uses markers at the lateral and medial caput of the 1^st and 5^th metatarsals, respectively, at the dorsal calcaneus and at the tuberosity of the navicular bone. Dynamic navicular drop and drift were assessed with three-dimensional motion capture in 21 healthy individuals using a single-examiner test-retest study design.

Results

Intra- and interday repeatability were 1.1 mm (ICC₂₁ 0.97) and 2.3 mm (ICC₂₁ 0.87) for dynamic navicular drop and 1.5 mm (ICC₂₁ 0.96) and 5.3 mm (ICC₂₁ 0.46) for dynamic navicular drift. The contribution of instrumental errors was estimated to 0.25 mm for dynamic navicular drop and 0.86 mm for dynamic navicular drift.

Conclusions

Interday reliability was generally worse than intraday reliability primary due to day-to-day variations in movement patterns and the contribution of instrumental errors was below 23% for dynamic navicular drop but reached 57% for dynamic navicular drift. The minimal markerset allows to simply transfer the known concepts of navicular drop and drift from quasi-static clinical test conditions to functional tasks, which is recommended to more closely relate assessments to the functional behavior of the foot.

Electronic supplementary material

The online version of this article (10.1186/s13047-018-0257-2) contains supplementary material, which is available to authorized users.

Medial Longitudinal Arch Angle Presents Significant Differences Between Foot Types: A Biplane Fluoroscopy Study

The structure of the medial longitudinal arch (MLA) affects the foot's overall function and its ability to dissipate plantar pressure forces. Previous research on the MLA includes measuring the calcaneal-first metatarsal angle using a static sagittal plane radiograph, a dynamic height-to-length ratio using marker clusters with a multisegment foot model, and a contained angle using single point markers with a multisegment foot model. The objective of this study was to use biplane fluoroscopy to measure a contained MLA angle between foot types: pes planus (low arch), pes cavus (high arch), and normal arch. Fifteen participants completed the study, five from each foot type. Markerless fluoroscopic radiostereometric analysis (fRSA) was used with a three-dimensional model of the foot bones and manually matching those bones to a pair of two-dimensional radiographic images during midstance of gait. Statistically significant differences were found between barefoot arch angles of the normal and pes cavus foot types (p = 0.036), as well as between the pes cavus and pes planus foot types (p = 0.004). Dynamic walking also resulted in a statistically significant finding compared to the static standing trials (p = 0.014). These results support the classification of individuals following a physical assessment by a foot specialist for those with pes cavus and planus foot types. The differences between static and dynamic kinematic measurements were also supported using this novel method.

An Investigation of Structure, Flexibility, and Function Variables that Discriminate Asymptomatic Foot Types

It has been suggested that foot type considers not only foot structure (high, normal, low arch), but also function (overpronation, normal, oversupination) and flexibility (reduced, normal, excessive). Therefore, this study used canonical regression analyses to assess which variables of foot structure, function, and flexibility can accurately discriminate between clinical foot type classifications. The feet of 61 asymptomatic, healthy adults (18–77 years) were classified as cavus (N = 24), rectus (N = 54), or planus (N = 44) using standard clinical measures. Custom jigs assessed foot structure and flexibility. Foot function was assessed using an emed-x plantar pressure measuring device. Canonical regression analyses were applied separately to extract essential structure, flexibility, and function variables. A third canonical regression analysis was performed on the extracted variables to identify a combined model. The initial combined model included 30 extracted variables; however 5 terminal variables (malleolar valgus index, arch height index while sitting, first metatarsophalangeal joint laxity while standing, pressure-time integral and maximum contact area of medial arch) were able to correctly predict 80.7% of foot types. These remaining variables focused on specific foot characteristics (hindfoot alignment, arch height, midfoot mechanics, Windlass mechanism) that could be essential to discriminating foot type.

The Relationship Between Arch Height and Arch FlexibilityA Proposed Arch Flexibility Classification System for the Description of Multidimensional Foot Structure

BACKGROUND

The correlation between arch structure and injury may be related to the fact that foot structure influences foot function. Foot structure is often defined by arch height, although arch flexibility may be just as important to form a more complete description. We propose an arch flexibility classification system, analogous to arch height classification, and then use the classification system to examine the relationship between arch flexibility and arch height.

METHODS

Arch height index was calculated in 1,124 incoming military cadets, of whom 1,056 had usable data. By measuring arch height during both sitting and standing, a measurement of arch flexibility could also be calculated. These values were used to create five arch flexibility categories: very stiff, stiff, neutral, flexible, and very flexible. The distribution of arch flexibility types among arch height categories was statistically compared.

RESULTS

The goodness of fit test showed a disproportionate number of each arch flexibility type in each of the arch height categories (P < .01). The largest proportion of cavus feet was very stiff and the smallest proportion was very flexible. Conversely, the largest proportion of planus feet was very flexible and the smallest proportion was very stiff.

CONCLUSIONS

The results of this research support the common belief that cavus feet tend to be very stiff and planus feet tend to be very flexible.

Reliability of the Arch Height Index as a Measure of Foot Structure in Children

PURPOSE

To determine the intrarater and interrater reliability of the arch height index (AHI) in children developing typically. The AHI is tested with a device that measures foot structure.

METHODS

Thirty children, ages 6 to 12 years, participated for a total of n = 60 feet. The AHI measurements were taken by 2 investigators in sitting and standing and repeated twice by each investigator in a single visit. Intrarater and interrater reliabilities were determined using intraclass correlation coefficient (ICC) (2,1) statistical analysis.

RESULTS

The mean age was 9.61 ± 1.96 years. The intrarater and interrater reliability had an ICC 0.76 or more in both sitting and standing. The average AHI value was 0.36 ± 0.02 in sitting and 0.32 ± 0.02 in standing.

CONCLUSIONS

Pediatric therapists, physicians, and orthotists should consider using the AHI as an objective measure to be used for research, to assess foot structure, monitor change over time, and assist with treatment planning in children.

Multiple linear regression approach for the analysis of the relationships between joints mobility and regional pressure-based parameters in the normal-arched foot

Plantar load can be considered as a measure of the foot ability to transmit forces at the foot/ground, or foot/footwear interface during ambulatory activities via the lower limb kinematic chain. While morphological and functional measures have been shown to be correlated with plantar load, no exhaustive data are currently available on the possible relationships between range of motion of foot joints and plantar load regional parameters. Joints' kinematics from a validated multi-segmental foot model were recorded together with plantar pressure parameters in 21 normal-arched healthy subjects during three barefoot walking trials. Plantar pressure maps were divided into six anatomically-based regions of interest associated to corresponding foot segments. A stepwise multiple regression analysis was performed to determine the relationships between pressure-based parameters, joints range of motion and normalized walking speed (speed/subject height). Sagittal- and frontal-plane joint motion were those most correlated to plantar load. Foot joints' range of motion and normalized walking speed explained between 6% and 43% of the model variance (adjusted R²) for pressure-based parameters. In general, those joints' presenting lower mobility during stance were associated to lower vertical force at forefoot and to larger mean and peak pressure at hindfoot and forefoot. Normalized walking speed was always positively correlated to mean and peak pressure at hindfoot and forefoot. While a large variance in plantar pressure data is still not accounted for by the present models, this study provides statistical corroboration of the close relationship between joint mobility and plantar pressure during stance in the normal healthy foot.

The effects of being habitually barefoot on foot mechanics and motor performance in children and adolescents aged 6-18 years: study protocol for a multicenter cross-sectional study (Barefoot LIFE project)

Background

Barefoot locomotion has evoked an increasing scientific interest with a controversial debate about benefits and limitations of barefoot and simulated barefoot walking and running. While most current knowledge comes from cross sectional laboratory studies, the evolutionary perspective suggests the importance of investigating the long-term effects. Observing habitually barefoot populations could fill the current gap of missing high quality longitudinal studies. Therefore, the study described in this design paper aims to investigate the effects of being habitually barefoot on foot mechanics and motor performance of children and adolescents.

Methods

This study has a cross-sectional, binational design and is part of the “Barefoot Locomotion for Individual Foot- and health Enhancement (Barefoot LIFE)” project. Two large cohorts (n_(total) = 520) of healthy children and adolescents between 6 and 18 years of age will be included respectively in Germany and South Africa. A barefoot questionnaire will be used to determine habitually barefoot individuals. The testing will be school-based and include foot mechanical (static arch height index, dynamic arch index, foot pliability) and motor performance (coordination, speed, leg power) outcomes. Gender, BMI and level of physical activity will be considered for confounding.

Discussion

The strength of this study is the comparison of two large cohorts with different footwear habits to determine long-term effects of being habitually barefoot on foot mechanics and motor performance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13047-016-0166-1) contains supplementary material, which is available to authorized users.

Adding Stiffness to the Foot Modulates Soleus Force-Velocity Behaviour during Human Walking

Previous studies of human locomotion indicate that foot and ankle structures can interact in complex ways. The structure of the foot defines the input and output lever arms that influences the force-generating capacity of the ankle plantar flexors during push-off. At the same time, deformation of the foot may dissipate some of the mechanical energy generated by the plantar flexors during push-off. We investigated this foot-ankle interplay during walking by adding stiffness to the foot through shoes and insoles, and characterized the resulting changes in in vivo soleus muscle-tendon mechanics using ultrasonography. Added stiffness decreased energy dissipation at the foot (p < 0.001) and increased the gear ratio (i.e., ratio of ground reaction force and plantar flexor muscle lever arms) (p < 0.001). Added foot stiffness also altered soleus muscle behaviour, leading to greater peak force (p < 0.001) and reduced fascicle shortening speed (p < 0.001). Despite this shift in force-velocity behaviour, the whole-body metabolic cost during walking increased with added foot stiffness (p < 0.001). This increased metabolic cost is likely due to the added force demand on the plantar flexors, as walking on a more rigid foot/shoe surface compromises the plantar flexors' mechanical advantage.

The relationship between foot arch measurements and walking parameters in children

BACKGROUND

Walking mechanics are influenced by body morphology. Foot arch height is one aspect of body morphology central to walking. However, generalizations about the relationship between arch height and walking are limited due to previous methodologies used for measuring the arch and the populations that have been studied. To gain the knowledge needed to support healthy gait in children and adults, we need to understand this relationship in unimpaired, typically developing children and adults using dynamic measures. The purpose of the current study was to examine the relationship between arch height and gait in a sample of healthy children and adults using dynamic measures.

METHODS

Data were collected from 638 participants (n = 254 children and n = 384 adults) at the Museum of Science, Boston (MOS) and from 18 4- to 8-year-olds at the Motor Development and Motor Control Laboratories. Digital footprints were used to calculate two arch indices: the Chippaux-Smirak (CSI) and the Keimig Indices (KI). The height of the navicular bone was measured. Gait parameters were captured with a mechanized gait carpet at the MOS and three-dimensional motion analyses and in-ground force plates in the Motor Development and Motor Control Laboratories.

RESULTS

Linear regression analyses on data from the MOS confirmed that as age increases, step length increases. With a linear mixed effect regression model, we found that individuals who took longer steps had higher arches as measured by the KI. However, this relationship was no longer significant when only adults were included in the model. A model restricted to children found that amongst this sample, those with higher CSI and higher KI values take longer relative step lengths. Data from the Motor Development and Motor Control Laboratories showed that both CSI and KI added to the prediction; children with lower anterior ground reaction forces had higher CSI and higher KI values. Arch height indices were correlated with navicular height.

CONCLUSIONS

These results suggest that more than one measure of the arch may be needed elucidate the relationship between arch height and gait.

Foot Morphological Difference between Habitually Shod and Unshod Runners

Foot morphology and function has received increasing attention from both biomechanics researchers and footwear manufacturers. In this study, 168 habitually unshod runners (90 males whose age, weight & height were 23±2.4 years, 66±7.1 kg & 1.68±0.13 m and 78 females whose age, weight & height were 22±1.8 years, 55±4.7 kg & 1.6±0.11 m) (Indians) and 196 shod runners (130 males whose age, weight & height were 24±2.6 years, 66±8.2 kg & 1.72±0.18 m and 66 females whose age, weight & height were 23±1.5 years, 54±5.6 kg & 1.62±0.15 m) (Chinese) participated in a foot scanning test using the easy-foot-scan (a three-dimensional foot scanning system) to obtain 3D foot surface data and 2D footprint imaging. Foot length, foot width, hallux angle and minimal distance from hallux to second toe were calculated to analyze foot morphological differences. This study found that significant differences exist between groups (shod Chinese and unshod Indians) for foot length (female p = 0.001), width (female p = 0.001), hallux angle (male and female p = 0.001) and the minimal distance (male and female p = 0.001) from hallux to second toe. This study suggests that significant differences in morphology between different ethnicities could be considered for future investigation of locomotion biomechanics characteristics between ethnicities and inform last shape and design so as to reduce injury risks and poor performance from mal-fit shoes.

Kinematic foot types in youth with equinovarus secondary to hemiplegia

BACKGROUND

Elevated kinematic variability of the foot and ankle segments exists during gait among individuals with equinovarus secondary to hemiplegic cerebral palsy (CP). Clinicians have previously addressed such variability by developing classification schemes to identify subgroups of individuals based on their kinematics.

OBJECTIVE

To identify kinematic subgroups among youth with equinovarus secondary to CP using 3-dimensional multi-segment foot and ankle kinematics during locomotion as inputs for principal component analysis (PCA), and K-means cluster analysis.

METHODS

In a single assessment session, multi-segment foot and ankle kinematics using the Milwaukee Foot Model (MFM) were collected in 24 children/adolescents with equinovarus and 20 typically developing children/adolescents.

RESULTS

PCA was used as a data reduction technique on 40 variables. K-means cluster analysis was performed on the first six principal components (PCs) which accounted for 92% of the variance of the dataset. The PCs described the location and plane of involvement in the foot and ankle. Five distinct kinematic subgroups were identified using K-means clustering. Participants with equinovarus presented with variable involvement ranging from primary hindfoot or forefoot deviations to deformtiy that included both segments in multiple planes.

CONCLUSION

This study provides further evidence of the variability in foot characteristics associated with equinovarus secondary to hemiplegic CP. These findings would not have been detected using a single segment foot model. The identification of multiple kinematic subgroups with unique foot and ankle characteristics has the potential to improve treatment since similar patients within a subgroup are likely to benefit from the same intervention(s).

Dynamic plantar loading index detects altered foot function in individuals with rheumatoid arthritis but not changes due to orthotic use

BACKGROUND

Altered foot function is common in individuals with rheumatoid arthritis. Plantar pressure distributions during gait are regularly assessed in this patient group; however, the association between frequently reported magnitude-based pressure variables and clinical outcomes has not been clearly established. Recently, a novel approach to the analysis of plantar pressure distributions throughout stance phase, the dynamic plantar loading index, has been proposed. This study aimed to assess the utility of this index for measuring foot function in individuals with rheumatoid arthritis.

METHODS

Barefoot plantar pressures during gait were measured in 63 patients with rheumatoid arthritis and 51 matched controls. Additionally, 15 individuals with rheumatoid arthritis had in-shoe plantar pressures measured whilst walking in standardized footwear for two conditions: shoes-only; and shoes with prescribed custom foot orthoses. The dynamic plantar loading index was determined for all participants and conditions. Patient and control groups were compared for significant differences as were the shod and orthosis conditions.

FINDINGS

The patient group was found to have a mean index of 0.19, significantly lower than the control group's index of 0.32 (p>0.001, 95% CI [0.054, 0.197]). No significant differences were found between the shoe-only and shoe plus orthosis conditions. The loading index was found to correlate with clinical measures of structural deformity.

INTERPRETATION

The dynamic plantar loading index may be a useful tool for researchers and clinicians looking to objectively assess dynamic foot function in patients with rheumatoid arthritis; however, it may be unresponsive to changes caused by orthotic interventions in this patient group.

Biomechanical considerations of foot-ground contact in T'ai Chi Chuan

Although numerous studies have linked t'ai chi chuan (TCC) practice with benefits for balance, reduction in the number of falls, and in the fear of falling, most of them did not address the causes of these benefits in depth. Some studies, however, sought to determine the causes from the biomechanical point of view. This article aims to thoroughly describe and critically review recent papers on foot-ground contact in TCC practice, one of the parameters involved in balance biomechanics in TCC performance. No previous review on this subject has been found. Nine electronic databases were searched for publications between 1996 and 2013. Studies were excluded if they were not published in English or were abstracts, posters, or summaries from conferences. From a total of 195 articles identified, 4 randomized controlled trials and 3 non-randomized controlled trials were eligible for the analysis. The number of studies that assessed foot-ground contact in TCC and effects on normal gait, postural control improvement, and fall prevention is still quite small. These studies were based on intervention protocols and used populations that were too heterogeneous to allow reliable comparisons. According to the studies analyzed, TCC practice clearly improved parameters associated with foot-ground contact. Nevertheless, the manner in which these benefits are transferred to daily displacement habits still remains unclear.

Flexor digitorum longus transfer and medial displacement calcaneal osteotomy for the treatment of stage II posterior tibial tendon dysfunction: kinematic and functional results of fifty one feet

PURPOSE

Stage II posterior tibial tendon dysfunction (PTTD) can be treated by flexor digitorum longus (FDL) tendon transfer and medial displacement calcaneal osteotomy (MDCO). Numerous authors have studied the clinical and radiographic results of this procedure. However, little is known about the kinematic changes. Therefore, the purpose of this study was to assess plantar-pressure distribution in these patients.

METHODS

Seventy-three patients with PTTD stage II underwent FDL tendon transfer and MDCO. Plantar pressure distribution and American Orthopaedic Foot and Ankle Society (AOFAS) score were assessed 48 months after surgery. Pedobarographic parameters included lateral and medial force index of the gait line, peak pressure (PP), maximum force (MF), contact area (CA), contact time (CT) and force-time integral (FTI).

RESULTS

In the lesser-toe region, PP, MF, CT, FTI and CA were reduced and MF in the forefoot region was increased. These changes were statistically significant. We found statistically significant correlations between AOFAS score and loading parameters of the medial midfoot.

CONCLUSIONS

Study results reveal that FDL tendon transfer and MDCO leads to impaired function of the lesser toes during the stance phase. However, there seems to be a compensating increased load in the forefoot region.

Factors affecting center of pressure in older adults: the Framingham Foot Study

BACKGROUND

Although aberrant foot movement during gait has been associated with adverse outcomes in the lower extremities in clinical patients, few studies have analyzed population differences in foot function. The purpose of this study was to assess demographic differences in foot function in a large population-based study of community-dwelling adults.

METHODS

Participants in this study were from the Framingham Foot Study. Walking data were collected from both feet using a Tekscan Matscan pressure mat. Foot function was characterized using the center of pressure excursion index (CPEI). T-tests were used to assess differences between population subsets based on sex, and in men and women separately, age, body mass index (BMI), physical activity and in women, past high heel use.

RESULTS

There were 2111 participants included in this analysis. Significant differences in CPEI were noted by sex (p< 0.0001), by age in women (p = 0.04), and by past high heel use in women (p = 0.04).

CONCLUSIONS

Foot function during gait was affected by sex, as well as by age and shoe-wear in women, but not by BMI or physical activity. Future work will evaluate possible relations between CPEI and outcomes such as falls, sarcopenia, and lower extremity function.