Dynamic Flexion Stiffness of Foot Joints During Walking

Effect of different custom-made foot orthotics on foot joint stiffness in individuals with structural hallux limitus: A quasi-experimental study

BACKGROUND

Normal dorsiflexion of the first metatarsophalangeal joint during dynamic activities is critical for effective propulsion. Therapeutic foot orthotics may address the pathomechanical loading and joint kinematics issues faced by this population. This study aims to evaluate the effect of two different types of Custom-made foot orthosis compared to shod condition on the stiffness of the rearfoot, midfoot, and 1st metatarsophalangeal joint during walking in patients with Structural Hallux Limitus.

METHODS

This quasi-experimental study used a repeated-measures design with a single cohort. 24 participants with structural hallux limitus were sampled. Two custom-made Foot Orthotics - a cut-out and an anterior forefoot stabiliser element - were compared under three conditions using minimalist SAGURO neoprene shoes: shod, shod with cut-out custom-made foot orthosis, and shod with anterior forefoot stabiliser element foot orthosis. Kinematic data were captured using a modified Bruening model. We examined the variable stiffness (quantified in Nm/Kg/rad).

FINDINGS

Significant differences were found in dynamic stiffness only between Anterior forefoot stabiliser element custom-made foot orthosis, and the patient shod during the propulsion phase at the 1st Metatarsophalangeal joint (R2 = 0,07 p = 0.027) and a difference of 0,86 Nm/kg/rad. No significant differences were observed for dynamic stiffness in any other phase of the stance period across all conditions.

INTERPRETATION

The Anterior forefoot stabiliser element, in particular, significantly increases the stiffness of the 1st Metatarsophalangeal joint compared to walking shod.

Foot kinematics and kinetics data for different static foot posture collected using a multi-segment foot model

This dataset presents human foot joints kinematics and kinetics data during walking, classified by static foot posture, filling a gap in existing lower limb databases that lack data on foot joints beyond the ankle or on static posture data, despite its link to foot and lower limb pathologies. Kinematics were recorded using a three-dimensional mocap system, and kinetics through a pressure platform, employing a multi-segment foot model including the ankle, midtarsal and first metatarsophalangeal joint. The dataset contains 350 recordings of right foot joint angles and moments and contact pressures from 70 healthy subjects with varying static posture (highly pronated, highly supinated and normal). Data were collected at 100 Hz, filtered and resampled to 100 frames throughout the stance phase. Descriptive data are also provided: age, weight, height, BMI and foot anthropometric data and foot posture index. Plots, tables and ANOVAs are included for validation. Presented in .xlsx and .mat formats, this database can assist professionals in corrective footwear design, insole customization, surgical planning, and evaluating interventions on foot dynamics.

Effect of Custom-Made Foot Orthotics on Multi-Segment Foot Kinematics and Kinetics in Individuals with Structural Hallux Limitus

The first metatarsophalangeal joint (MTPJ) and the first ray are crucial in walking, particularly during propulsion. Limitation in this joint's sagittal plane motion, known as hallux limitus, can cause compensatory movements in other joints. Some studies assessed the impact of various foot orthoses designs on the foot biomechanics; however, a comprehensive understanding is lacking. This study compared the effects of two custom-made foot orthoses (CFOs) on the foot joint kinematics and kinetics in patients with structural hallux limitus (SHL). In this quasi-experimental study, 24 patients with hallux limitus were assessed in three conditions: (i) barefoot, (ii) shod with a cut-out custom foot orthosis (cut-out CFO), and (iii) shod with an anterior forefoot-stabilized element custom foot orthosis (AFSE CFO), fitted into a minimalist neoprene shoe. Multi-segment foot kinematics and kinetics were assessed during the stance phase of the gait. A decrease in ankle and midfoot inversion, as well as in ankle plantarflexion, was found in both orthotic conditions. Regarding the first MTPJ, a greater dorsiflexion was observed with the patient being barefoot compared to both of the conditions under study. From the current finding, it should be concluded that neither of the custom foot orthoses produced the predefined functional effects.

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.

An exploration of muscle co-activation during different walking speeds and the association with lower limb joint stiffness

The aim of this study was to determine the muscle co-activations and joint stiffnesses around the hip, knee, and ankle during different walking speeds and to define the relationships between muscle co-activation and joint stiffness. Twenty-seven healthy subjects (age: 19.6 ± 2.2 years, height: 176.0 ± 6.0 cm, mass: 69.7 ± 8.9 kg) were recruited. Muscle co-activations (CoI) and lower limb joints stiffnesses were investigated during stance phase at different walking speeds using Repeated Measures ANOVA with Sidak post-hoc tests. Correlations between muscle co-activations, joints stiffnesses, and walking speeds were also investigated using Pearson Product Moment correlations. The results indicated that the hip and ankle joints stiffness increased with walking speed (p < 0.001) during the weight acceptance phase, and positive correlations were seen between walking speed and Rectus Femoris (RF) and Biceps Femoris (BF) CoI (p < 0.001), and a negative correlation was seen between walking speed and tibialis anterior (TA) and lateral gastrocnemius (LG) CoI (p < 0.001) during the weight acceptance phase, and the RF/BF CoI during pre-swing. These results provide new information on the variations in muscle co-activation around the hip, knee and ankle joints and their association with joint stiffness, and on the responses of stiffness and muscle co-activation to walking speed. The techniques presented could have further application and help our understanding of the effects of gait retraining and injury mechanisms.

Foot Sole Contact Forces vs. Ground Contact Forces to Obtain Foot Joint Moments for In-Shoe Gait-A Preliminary Study

In-shoe models are required to extend the clinical application of current multisegment kinetic models of the bare foot to study the effect of foot orthoses. Work to date has only addressed marker placement for reliable kinematic analyses. The purpose of this study is to address the difficulties of recording contact forces with available sensors. Ten participants walked 5 times wearing two different types of footwear by stepping on a pressure platform (ground contact forces) while wearing in-shoe pressure sensors (foot sole contact forces). Pressure data were segmented by considering contact cells' anteroposterior location, and were used to compute 3D moments at foot joints. The mean values and 95% confidence intervals were plotted for each device per shoe condition. The peak values and times of forces and moments were computed per participant and trial under each condition, and were compared using mixed-effect tests. Test-retest reliability was analyzed by means of intraclass correlation coefficients. The curve profiles from both devices were similar, with higher joint moments for the instrumented insoles at the metatarsophalangeal joint (~26%), which were lower at the ankle (~8%) and midtarsal (~15%) joints, although the differences were nonsignificant. Not considering frictional forces resulted in ~20% lower peaks at the ankle moments compared to previous studies, which employed force plates. The device affected both shoe conditions in the same way, which suggests the interchangeability of measuring joint moments with one or the other device. This hypothesis was reinforced by the intraclass correlation coefficients, which were higher for the peak values, although only moderate-to-good. In short, both considered alternatives have drawbacks. Only the instrumented in-soles provided direct information about foot contact forces, but it was incomplete (evidenced by the difference in ankle moments between devices). However, recording ground reaction forces offers the advantage of enabling the consideration of contact friction forces (using force plates in series, or combining a pressure platform and a force plate to estimate friction forces and torque), which are less invasive than instrumented insoles (which may affect subjects' gait).

Metatarsophalangeal Joint Dynamic Stiffness During Toe Rocker Changes With Walking Speed

Dynamic joint stiffness (or simply "stiffness") is a customization criteria used to tune mechanical properties of orthotic and prosthetic devices. This study examines metatarsophalangeal (MTP) joint stiffness during the toe-rocker phase of barefoot walking and establishes baseline characteristics of MTP joint stiffness. Ten healthy individuals walked at 4 speeds (0.4, 0.6, 0.8, and 1.0 statures·s-1) over level ground. MTP sagittal plane joint angles and moments were calculated during the toe-rocker phase of stance. Least-squares linear regressions were conducted on the MTP moment versus angle curve to determine joint stiffness during early toe rocker and late toe rocker. Multilevel linear models were used to test for statistically significant differences between conditions. Early toe rocker stiffness was positive, while late toe rocker was negative. Both early toe rocker and late toe rocker stiffness increased in magnitude significantly with speed. This study establishes baseline characteristics of MTP joint stiffness in healthy walking, which previously had not been examined through a range of controlled walking speeds. This information can be used in the future as design criteria for orthotic and prosthetic ankle and ankle-foot devices that can imitate, support, and facilitate natural human foot motion during walking better than existing devices.

Analysis of foot kinematics during toe walking in able-bodied individuals using the Oxford Foot Model

Various neurological and musculoskeletal disorders can induce pathologic toe walking and lead to changes in foot kinematics. In this study, we analyzed the differences in foot kinematics between toe walking and heel-toe walking (HW) in able-bodied individuals. Twenty young healthy adults performed three gaits: HW, comfortable-height toe walking (CTW), and maximum-height toe walking (MTW). Oxford Foot Model was used for gait analysis. Toe walking showed increase of forefoot plantarflexion and hindfoot internal rotation compared to HW. Thus, our results may help distinguish the pathologic mechanism of the equinus gait in various disorders from the kinematic change of toe walking itself.

Leg and lower limb dynamic joint stiffness during different walking speeds in healthy adults

BACKGROUND

The differences and relationship between joint stiffness and leg stiffness can be used to characterize the lower limb behavior during different walking speeds.

RESEARCH QUESTION

This study aimed to investigate the differences in whole leg and lower limb joint stiffness at different walking speeds and the interactions between leg and lower limb joint stiffness.

METHODS

Twenty-seven healthy adults, seventeen males (age: 19.6 ± 2.2 years, height: 176.0 ± 6.0 cm, mass: 69.7 ± 8.9 kg), and ten females (age: 19.1 ± 1.9 years, height: 164.0 ± 3.0 cm, mass: 59.6 ± 3.8 kg), were recruited. Dynamic leg and joint stiffness were calculated during eccentric loading from data recorded using 3D infrared motion analysis and force plates at slow, normal, and fast walking speeds. Differences in dynamic stiffness, joint angles and moments were explored between the walking speeds using Repeated Measures ANOVA with Sidak post-hoc tests. Correlations between leg, joint stiffness, and walking speed were also explored.

RESULTS

The results indicated that the leg dynamic stiffness is decreased by walking speed, however, hip and ankle joint stiffness were increased (p < 0.001) and knee stiffness was unaffected. Leg stiffness showed no correlation with hip, knee, or ankle stiffness. A positive significant correlation was seen between hip and ankle stiffness (p < 0.01) and between knee and ankle stiffness (p < 0.001), however, no correlation was seen between hip and knee stiffness.

SIGNIFICANCE

These results suggest leg stiffness is not associated with lower limb joint stiffness during eccentric loading. This provides new information on the responses of ankle, knee and hip joint stiffness to walking speed.

Ankle and midtarsal joint quasi-stiffness during walking with added mass

Examination of how the ankle and midtarsal joints modulate stiffness in response to increased force demand will aid understanding of overall limb function and inform the development of bio-inspired assistive and robotic devices. The purpose of this study is to identify how ankle and midtarsal joint quasi-stiffness are affected by added body mass during over-ground walking. Healthy participants walked barefoot over-ground at 1.25 m/s wearing a weighted vest with 0%, 15% and 30% additional body mass. The effect of added mass was investigated on ankle and midtarsal joint range of motion (ROM), peak moment and quasi-stiffness. Joint quasi-stiffness was broken into two phases, dorsiflexion (DF) and plantarflexion (PF), representing approximately linear regions of their moment-angle curve. Added mass significantly increased ankle joint quasi-stiffness in DF (p < 0.001) and PF (p < 0.001), as well as midtarsal joint quasi-stiffness in DF (p < 0.006) and PF (p < 0.001). Notably, the midtarsal joint quasi-stiffness during DF was ~2.5 times higher than that of the ankle joint. The increase in midtarsal quasi-stiffness when walking with added mass could not be explained by the windlass mechanism, as the ROM of the metatarsophalangeal joints was not correlated with midtarsal joint quasi-stiffness (r = -0.142, p = 0.540). The likely source for the quasi-stiffness modulation may be from active foot muscles, however, future research is needed to confirm which anatomical structures (passive or active) contribute to the overall joint quasi-stiffness across locomotor tasks.

Variability of the Dynamic Stiffness of Foot Joints: Effect of Gait Speed

BACKGROUND

Comparison of dynamic stiffness of foot joints was previously proposed to investigate pathologic situations with changes in the properties of muscle and passive structures. Samples must be controlled to reduce the variability within groups being compared, which may arise from different sources, such as gait speed or Foot Posture Index (FPI).

METHODS

Variability in the measurement of the dynamic stiffness of ankle, midtarsal, and metatarsophalangeal joints was studied in a controlled sample of healthy men with normal FPI, and the effect of gait speed was analyzed. In experiment 1, dynamic stiffnesses were obtained in three sessions, five trials per session, for each participant, taking the mean value across trials as representative of each session. In experiment 2, five trials were considered at slow, comfortable, and fast velocities.

RESULTS

Similar intersession and intrasession errors and intraparticipant errors within sessions were found, indicating the goodness of using five trials per session for averaging. The intraparticipant and interparticipant variability data provided can be used to select the sample size in future comparative analyses. Significant differences with gait speed were observed in most dynamic stiffnesses considered, with a general rise when gait speed increased, especially at the midtarsal joint, this being attributed to an active modulation produced by the central nervous system.

CONCLUSIONS

Differences with gait speed were higher than intrasession and intersession repeatability errors for the propulsion phases at the ankle and midtarsal joints; comparative analyses at these phases need more exhaustive control of gait speed to reduce the required sample size.

Kinematics reduction applied to the comparison of highly-pronated, normal and highly-supinated feet during walking

BACKGROUND

Kinematic analysis could help to study how variations in the static foot posture affect lower limb biomechanical function. The analysis of foot kinematics is complex because it involves managing the time-dependent joint angles in different joints and in all three planes of motion. But it could be simplified if joint angles are coordinated.

METHODS

The kinematics of the ankle, midtarsal and metatarsophalangeal joints were registered in 20 highly-pronated, 30 normal and 20 highly-supinated subjects (assessed by the Foot Posture Index - FPI) as they walked barefoot. Coordination for each sample was analysed through principal component analysis applied to the dorsiflexion, abduction and inversion angles measured. Finally, a systematic comparison among the samples was performed through a set of ANOVAs applied to the reduced variables corresponding to the factors found.

RESULTS

Three principal components (coordination patterns) accounted for about 70% of the variance of the joint angles, and were affected by the FPI. The main coordination in normal feet was the supination movement, while in highly-supinated and highly-pronated feet it was the flexion coordination of all foot joints, which could work against adaptation in cases of varying terrain. The original joint angles were reduced to three factors, and the ANOVAs applied to them showed that highly-pronated feet presented a delayed propulsion peak and smaller ranges of motion during propulsion regarding all factors, and that highly-supinated feet require more pronation time to fully support the foot during walking.

SIGNIFICANCE

The coordination patterns of normal feet might be considered the normal patterns used for an efficient gait, and may help in planning surgical procedures and designing foot prostheses or orthotics. Dimensional reduction makes it possible to perform more systematic kinematic analyses, which have revealed that highly-pronated feet are in poorer propulsive condition, and this in turn may make them more prone to injury.

Effects of foot pronation on the lower limb sagittal plane biomechanics during gait

BACKGROUND

Increased foot pronation may compromise ankle plantarflexion moment during the stance phase of gait, which may overload knee and hip.

RESEARCH QUESTION

This study investigated the influence of increased foot pronation on lower limbs angular displacement, internal moments and power in the sagittal plane and ground reaction force and center of pressure displacement during the stance phase of gait.

METHODS

Kinematic and kinetic data of 22 participants (10 women and 12 men) were collected while they walked wearing flat (control condition) and laterally wedged sandals to induce foot pronation (inclined condition). We used principal component analysis for data reduction and dependent t-test to compare differences between conditions with α = 0.05.

RESULTS

The inclined condition increased forefoot range of motion (p < 0.001; effect size = 0.73); increased ankle plantarflexion angle (p < 0.001; effect size = 0.96); reduced ankle plantarflexion moment in mid and terminal stance phases and delayed and increased ankle plantarflexion moment in late stance (p < 0.001; effect size = 0.72); increased range of ankle power during late stance (p = 0.006; effect size = 0.56); reduced knee range of moment (p < 0.001; effect size = 0.76); increased range of knee power in early stance and reduced knee power generation in late stance (p = 0.005; effect size = 0.56); reduced the anterior displacement of the center of pressure (p < 0.001; effect size = 0.82) and increased the ground reaction force in the anterior direction (p = 0.003; effect size = 0.60).

SIGNIFICANCE

Increased foot pronation compromises lower limb mechanics in the sagittal plane during the stance phase of gait. These findings are explained by the fact that foot pronation increases foot segments flexibility and compromises foot lever arm function during the stance of gait.

Effect of static foot posture on the dynamic stiffness of foot joints during walking

BACKGROUND

The static foot posture has been related to the development of lower limb injuries.

RESEARCH QUESTION

This study aimed to investigate the dynamic stiffness of foot joints during gait in the sagittal plane to understand the role of the static foot posture in the development of injuries.

METHODS

Seventy healthy adult male subjects with different static postures, assessed by the Foot Posture Index (FPI) (30 normal, 20 highly pronated and 20 highly supinated), were recruited. Kinematic and kinetic data were recorded using an optical motion capture system and a pressure platform, and dynamic stiffness at the different stages of the stance was calculated from the slopes of the linear regression on the flexion moment-angle curves. The effect of foot type on dynamic stiffness and on ranges of motion and moments was analysed using ANOVAs and post-hoc tests, and linear correlation between dynamic stiffness and FPI was also tested.

RESULTS

Highly pronated feet showed a significantly smaller range of motion at the ankle and metatarsophalangeal joints and also a larger range of moments at the metatarsophalangeal joint than highly supinated feet. Dynamic stiffness during propulsion was significantly greater at all foot joints for highly pronated feet, with positive significant correlations with the squared FPI. Highly supinated feet showed greater dynamic stiffness than normal feet, although to a lesser extent. Highly pronated feet during normal gait experienced the greatest decrease in the dorsiflexor moments during propulsion, normal feet being the most balanced regarding work generated and absorbed.

SIGNIFICANCE

Extreme static foot postures show greater dynamic stiffness during propulsion and greater absorbed work, which increases the risk of developing injuries. The data presented may be used when designing orthotics or prostheses, and also when planning surgery that modifies joint stiffness.