Lessons from dynamic cadaver and invasive bone pin studies: do we know how the foot really moves during gait?

Special Considerations in Podiatric Science: Translational Research, Cadavers, Gait Analysis, Dermatology, and Databases

The objective of this article is to provide a brief overview of the critical analysis and design of unique and perhaps less common methodologies in podiatric science. These include basic science translational designs, cadaveric investigations, gait analyses, dermatologic studies, and database analysis. The relative advantages, disadvantages, and inherent limitations are reviewed with an intention to improve the interpretation of results and advance future foot and ankle scientific endeavors.

Reliability and correlation of weight-bearing cone beam CT and Foot Posture Index (FPI) for measurements of foot posture: a test-retest study

OBJECTIVE

To assess test-retest reliability and correlation of weight-bearing (WB) and non-weight-bearing (NWB) cone beam CT (CBCT) foot measurements and Foot Posture Index (FPI) MATERIALS AND METHODS: Twenty healthy participants (age 43.11±11.36, 15 males, 5 females) were CBCT-scanned in February 2019 on two separate days on one foot in both WB and NWB positions. Three radiology observers measured the navicular bone position. Plantar (ΔNAVplantar) and medial navicular displacements (ΔNAVmedial) were calculated as a measure of foot posture changes under loading. FPI was assessed by two rheumatologists on the same two days. FPI is a clinical measurement of foot posture with 3 rearfoot and 3 midfoot/forefoot scores. Test-retest reproducibility was determined for all measurements. CBCT was correlated to FPI total and subscores.

RESULTS

Intra- and interobserver reliabilities for navicular position and FPI were excellent (intraclass correlation coefficient (ICC) .875-.997). In particular, intraobserver (ICC .0.967-1.000) and interobserver reliabilities (ICC .946-.997) were found for CBCT navicular height and medial position. Interobserver reliability of ΔNAVplantar was excellent (ICC .926 (.812; .971); MDC 2.22), whereas the ΔNAVmedial was fair-good (ICC .452 (.385; .783); MDC 2.42 mm). Using all observers' measurements, we could calculate mean ΔNAVplantar (4.25±2.08 mm) and ΔNAVmedial (1.55±0.83 mm). We demonstrated a small day-day difference in ΔNAVplantar (0.64 ±1.13mm; p<.05), but not for ΔNAVmedial (0.04 ±1.13mm; p=n.s.). Correlation of WBCT (WB navicular height - ΔNAVmedial) with total clinical FPI scores and FPI subscores, respectively, showed high correlation (ρ: -.706; ρ: -.721).

CONCLUSION

CBCT and FPI are reliable measurements of foot posture, with a high correlation between the two measurements.

Role of Robotic Gait Simulators in Elucidating Foot and Ankle Pathomechanics

Testing with cadaveric foot and ankle specimens began as mechanical techniques to study foot function and then evolved into static simulations of specific instances of gait, before technologies were eventually developed to fully replicate the gait cycle. This article summarizes the clinical applications of dynamic cadaveric gait simulation, including foot bone kinematics and joint function, muscle function, ligament function, orthopaedic foot and ankle pathologies, and total ankle replacements. The literature was reviewed and an in-depth summary was written in each section to highlight one of the more sophisticated simulators. The limitations of dynamic cadaveric simulation were also reviewed.

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.

Repeatability of the Oxford Foot Model: Comparison of a team of assessors with different backgrounds and no prior experience of the Oxford Foot Model

RESEARCH QUESTION

What is the intra- and inter-assessor error of the Oxford Foot Model (OFM) during healthy adult walking when applied by three assessors with different professional backgrounds and lower limb marker placement experience, not native to the originators of the model and with no prior clinical experience of the model?

BACKGROUND

No previous OFM studies have examined the repeatability of more than two assessors with different backgrounds, and many of the studies have been conducted by the model originators METHODS: The OFM was applied to ten healthy adults on three separate occasions by three different assessors with varied professional experience and no prior involvement with the OFM (other than local training). Participants walked at self-selected speeds and intra/inter assessor error was calculated using the SEM + 95% upper confidence limit.

RESULTS

Inter-assessor errors ranged from 2.2° to 5.5° whereas intra-assessor errors fell between 1.8° and 5.5°. The error difference between assessors over the same joint angle varied from 0.4° (hindfoot/tibia dorsiflexion) to 1.5° (hindfoot/tibia inversion). The percentage of error to total range of motion varied from 11% (hindfoot/tibia dorsiflexion) to 126% (forefoot/hindfoot adduction).

SIGNIFICANCE

Based on commonly used recommendations, the OFM is a largely repeatable tool for measuring foot kinematics during healthy adult walking when applied by assessors with no prior OFM experience, varied experience and not native to the model originators. Intra-assessor error was lower for assessors with prior anatomical knowledge and significant lower limb marker placement experience. The proportion of inter-assessor error to movement exceeded 50% of the total range of motion for four movements, notably forefoot/hindfoot adduction (126%). As such, this movement cannot be recommended as an outcome measure. Inter- and intra-assessor error, specific to each laboratory, should be considered, along with the proportion of error to range of motion when interpreting patient data.

Comparative Functional Morphology of Human and Chimpanzee Feet Based on Three-Dimensional Finite Element Analysis

To comparatively investigate the morphological adaptation of the human foot for achieving robust and efficient bipedal locomotion, we develop three-dimensional finite element models of the human and chimpanzee feet. Foot bones and the outer surface of the foot are extracted from computer tomography images and meshed with tetrahedral elements. The ligaments and plantar fascia are represented by tension-only spring elements. The contacts between the bones and between the foot and ground are solved using frictionless and Coulomb friction contact algorithms, respectively. Physiologically realistic loading conditions of the feet during quiet bipedal standing are simulated. Our results indicate that the center of pressure (COP) is located more anteriorly in the human foot than in the chimpanzee foot, indicating a larger stability margin in bipedal posture in humans. Furthermore, the vertical free moment generated by the coupling motion of the calcaneus and tibia during axial loading is larger in the human foot, which can facilitate the compensation of the net yaw moment of the body around the COP during bipedal locomotion. Furthermore, the human foot can store elastic energy more effectively during axial loading for the effective generation of propulsive force in the late stance phase. This computational framework for a comparative investigation of the causal relationship among the morphology, kinematics, and kinetics of the foot may provide a better understanding regarding the functional significance of the morphological features of the human foot.

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.

Validity and reproducibility of foot motion analysis using a stretch strain sensor

BACKGROUND

Multi-segment foot analysis is traditionally challenging to perform while subjects are wearing footwear or a foot orthosis and is difficult to apply in the clinical setting. A recently developed stretch strain sensor (STR), that is thin and highly flexible, may solve this limitation because it does not require observation using a camera and is highly portable.

RESEARCH QUESTION

This study aimed to examine the reproducibility and validity of foot motion analysis using the STR during walking and running by comparing it with a conventional motion capture system.

METHODS

Twenty-one healthy participants were examined in this study. The STR was placed on the participant's foot in one of two locations in separate experiments (spring ligament; SL and navicular drop; ND methods). Foot kinematic data during walking and running were simultaneously recorded using the STR and a three-dimensional motion capture system. Intra-class correlation (ICC) was used to assess test-retest reproducibility of the STR method. Cross-correlation coefficient evaluated the similarity of the pattern of the signals between the two systems. Pearson and Spearman correlation analysis was used to evaluate the relationships between the STR measurement and angular excursion of the forefoot or hindfoot.

RESULTS

The ICCs of the SL method were 0.95 and 0.96, and those of the ND method were 0.93 and 0.71 during walking and running, respectively. In the SL method, the pattern of the signals between the STR and forefoot frontal motion was strongly correlated. The STR measurement was significantly correlated with forefoot eversion excursion (walking: r=-0.67, running: r=-0.64, p < 0.01 each). In the ND method, the STR signal was not associated with forefoot and hindfoot kinematics.

SIGNIFICANCE

Our results showed that the STR has acceptable reproducibility and validity of foot motion analysis. This system may enable measurement of foot motion while subjects are wearing shoes and outside the laboratory.

Intrinsic foot joints adapt a stabilized-resistive configuration during the stance phase

BACKGROUND

This study evaluated the 3D angle between the joint moment and the joint angular velocity vectors at the intrinsic foot joints, and investigated if these joints are predominantly driven or stabilized during gait.

METHODS

The participants were 20 asymptomatic subjects. A four-segment kinetic foot model was used to calculate and estimate intrinsic foot joint moments, powers and angular velocities during gait. 3D angles between the joint moment and the joint angular velocity vectors were calculated for the intrinsic foot joints defined as follows: ankle joint motion described between the foot and the shank for the one-segment foot model (hereafter referred as Ankle), and between the calcaneus and the shank for the multi-segment foot model (hereafter referred as Shank-Calcaneus); joint motion described between calcaneus and midfoot segments (hereafter referred as Chopart joint); joint motion described between midfoot and metatarsus segments (hereafter referred as Lisfranc joint); joint motion described between first phalanx and first metatarsal (hereafter referred as First Metatarso-Phalangeal joint). When the vectors were approximately aligned, the moment was considered to result in propulsion (3D angle <60^o) or resistance (3D angle >120^o) at the joint. When the vectors are approximately orthogonal (3D angle close to 90°), the moment was considered to stabilize the joint.

RESULTS

The results showed that the four intrinsic joints of the foot are never fully propelling, resisting or being stabilized, but are instead subject to a combination of stabilization with propulsion or resistance during the majority of the stance phase of gait. However, the results also show that during pre-swing all four the joints are subject to moments that result purely in propulsion. At heel off, the propulsive configuration appears for the Lisfranc joint first at terminal stance, then for the other foot joints at pre-swing in the following order: Ankle, Chopart joint and First Metatarso-Phalangeal joint.

CONCLUSIONS

Intrinsic foot joints adopt a stabilized-resistive configuration during the majority of the stance phase, with the exception of pre-swing during which all joints were found to adopt a propulsive configuration. The notion of stabilization, resistance and propulsion should be further investigated in subjects with foot and ankle disorders.

Detailed analysis of the transverse arch of hallux valgus feet with and without pain using weightbearing ultrasound imaging and precise force sensors

Background

Hallux valgus is the most common forefoot deformity and affects the transverse arch structure and its force loading patterns. This study aims to clarify the differences in the transverse arch structure and the force under the metatarsal heads individually, between normal feet and hallux valgus feet, and between hallux valgus feet with pain and without pain. We further test the association between the parameters of the transverse arch and hallux valgus angle and between the parameters and pain in hallux valgus.

Methods

Women’s feet (105 feet) were divided into normal group (NORM) and hallux valgus group (HVG); and further into subgroups: hallux valgus without pain (HV Pain (-)) and hallux valgus with pain (HV Pain (+)). Transverse arch height and metatarsal heads height were measured using weight-bearing ultrasound imaging. Force under the metatarsal heads was measured using force sensors attached directly on the skin surface of the metatarsal heads. The measurements were taken in three loading positions: sitting, quiet standing and 90% weight shift on the tested foot. Differences between the groups were compared using Student t-test and Wilcoxon Exact test. Multivariate logistic analysis with adjustment for physical characteristics was also conducted.

Results

Transverse arch height was significantly higher in HVG than in NORM in all positions; there were no significant differences between HV Pain (+) and HV pain (-). Lateral sesamoid was significantly higher in HVG and HV Pain (+) than in NORM and HV Pain (-) respectively when bearing 90% of the body weight unilaterally. There was a trend of higher forces under the medial forefoot without significant difference. Transverse arch height and lateral sesamoid height were associated with the hallux valgus angle, while lateral sesamoid height was associated with forefoot pain in hallux valgus deformity.

Conclusions

This study shows the differences in the transverse arch structure between normal feet and feet with hallux valgus, and between hallux valgus feet with and without pain. This finding is noteworthy when considering future treatments of painful feet, notably the height of the lateral sesamoid which seems to play a role in forefoot pain.

Kinematic and Kinetic Comparison of Fresh Frozen and Thiel-Embalmed Human Feet for Suitability for Biomechanical Educational and Research Settings

BACKGROUND

In vitro biomechanical testing of the human foot often involves the use of fresh frozen cadaveric specimens to investigate interventions that would be detrimental to human subjects. The Thiel method is an alternative embalming technique that maintains soft-tissue consistency similar to that of living tissue. However, its suitability for biomechanical testing is unknown. Thus, the aim of this study was to determine whether Thiel-embalmed foot specimens exhibit kinematic and kinetic biomechanical properties similar to those of fresh frozen specimens.

METHODS

An observational study design was conducted at a university biomechanics laboratory. Three cadavers had both limbs amputated, with one being fresh frozen and the other preserved by Thiel's embalming. Each foot was tested while undergoing plantarflexion and dorsiflexion in three states: unloaded and under loads of 10 and 20 kg. Their segment kinematics and foot pressure mapping were assessed simultaneously.

RESULTS

No statistically significant differences were detected between fresh frozen and Thiel-embalmed sample pairs regarding kinematics and kinetics.

CONCLUSIONS

These findings highlight similar kinematic and kinetic properties between fresh frozen and Thiel-embalmed foot specimens, thus possibly enabling these specimens to be interchanged due to the latter specimens' advantage of delayed decomposition. This can open innovative opportunities for the use of these specimens in applications related to the investigation of dynamic foot function in research and education.

Use of high speed stereo radiography to assess the foot orthoses effectiveness in controlling midfoot posture during walking: A pilot study

BACKGROUND

The intent of this pilot study was to determine the feasibility of using high-speed stereo radiography (HSSR) to assess the effectiveness of footwear and foot orthoses in controlling the change in the position of the midfoot during walking in individuals with a flexible pes planus foot type.

METHODS

Four individuals (1 female; 3 male) with a mean age of 25 years (range 22-29) and a bilateral flexible pes planus foot type participated in the study. The HSSR system was used to measure 3-dimensional changes in the longitudinal arch angle (LAA) with each participant walking barefoot, shoe only and shoes with orthoses.

RESULTS

The HSSR system was found to be highly effective in measuring the change in the position of the midfoot, as measured using the LAA, when wearing footwear with or without foot orthoses. Based on an assessment of mean values, three out of the four participants demonstrated a change in the LAA as a result of using either shoes only or shoes with orthoses. The methodology used in this pilot study for assessing the effect of footwear and foot orthoses on the posture of the midfoot was highly effective with no side-effects noted by any of the study participants.

CONCLUSIONS

Future studies using the HSSR will require modifications to participant inclusion criteria as well as alterations to the data collection methodology. The HSSR system used in this study is feasible for use in larger cohort studies assessing footwear and foot orthosis effectiveness with the described modifications.

Three-dimensional innate mobility of the human foot bones under axial loading using biplane X-ray fluoroscopy

The anatomical design of the human foot is considered to facilitate generation of bipedal walking. However, how the morphology and structure of the human foot actually contribute to generation of bipedal walking remains unclear. In the present study, we investigated the three-dimensional kinematics of the foot bones under a weight-bearing condition using cadaver specimens, to characterize the innate mobility of the human foot inherently prescribed in its morphology and structure. Five cadaver feet were axially loaded up to 588 N (60 kgf), and radiographic images were captured using a biplane X-ray fluoroscopy system. The present study demonstrated that the talus is medioinferiorly translated and internally rotated as the calcaneus is everted owing to axial loading, causing internal rotation of the tibia and flattening of the medial longitudinal arch in the foot. Furthermore, as the talus is internally rotated, the talar head moves medially with respect to the navicular, inducing external rotation of the navicular and metatarsals. Under axial loading, the cuboid is everted simultaneously with the calcaneus owing to the osseous locking mechanism in the calcaneocuboid joint. Such detailed descriptions about the innate mobility of the human foot will contribute to clarifying functional adaptation and pathogenic mechanisms of the human foot.

The relationship between arch height and foot length: Implications for size grading

OBJECTIVE

Medial longitudinal Arch Height is synonymous with classifying foot type and conversely foot function. Detailed knowledge of foot anthropometry is essential in the development of ergonomically sound footwear. Current Footwear design incorporates a direct proportionate scaling of instep dimensions with those of foot length. The objective of this paper is to investigate if a direct proportional relationship exists between human arch height parameters and foot length in subjects with normal foot posture.

METHOD

A healthy convenience sample of 62 volunteers was recruited to participate in this observational study. All subjects were screened for normal foot health and posture. Each subject's foot dimensions were scanned and measured using a 3D Foot Scanner. From this foot length and arch height parameters were obtained. Normalised ratios of arch height with respect to foot length were also calculated. The arch height parameters and the normalised arch ratios were used interchangeably as the dependent variables with the foot length parameters used as the independent variable for Simple Linear Regression and Correlation.

RESULTS

Analysis of foot length measures demonstrated poor correlation with all arch height parameters.

CONCLUSION

No significant relationships between arch height and foot length were found. The predictive value of the relationship was found to be poor. This holds significant implications for the current method of proportionate scaling of footwear in terms of fit and function to the midfoot region for a normative population.

Effects of medially posted insoles on foot and lower limb mechanics across walking and running in overpronating men

Anti-pronation orthoses, like medially posted insoles (MPI), have traditionally been used to treat various of lower limb problems. Yet, we know surprisingly little about their effects on overall foot motion and lower limb mechanics across walking and running, which represent highly different loading conditions. To address this issue, multi-segment foot and lower limb mechanics was examined among 11 overpronating men with normal (NORM) and MPI insoles during walking (self-selected speed 1.70±0.19m/s vs 1.72±0.20m/s, respectively) and running (4.04±0.17m/s vs 4.10±0.13m/s, respectively). The kinematic results showed that MPI reduced the peak forefoot eversion movement in respect to both hindfoot and tibia across walking and running when compared to NORM (p<0.05-0.01). No differences were found in hindfoot eversion between conditions. The kinetic results showed no insole effects in walking, but during running MPI shifted center of pressure medially under the foot (p<0.01) leading to an increase in frontal plane moments at the hip (p<0.05) and knee (p<0.05) joints and a reduction at the ankle joint (p<0.05). These findings indicate that MPI primarily controlled the forefoot motion across walking and running. While kinetic response to MPI was more pronounced in running than walking, kinematic effects were essentially similar across both modes. This suggests that despite higher loads placed upon lower limb during running, there is no need to have a stiffer insoles to achieve similar reduction in the forefoot motion than in walking.

Can positional MRI predict dynamic changes in the medial plantar arch? An exploratory pilot study

BACKGROUND

Positional MRI (pMRI) allows for three-dimensional visual assessment of navicular position. In this exploratory pilot study pMRI was validated against a stretch sensor device, which measures movement of the medial plantar arch. We hypothesized that a combined pMRI measure incorporating both vertical and medial displacement of the navicular bone induced by loading would be correlated with corresponding stretch sensor measurements.

METHODS

10 voluntary participants were included in the study. Both pMRI and subsequent stretch sensor measurements were performed in a) supine, b) standing and c) standing position with addition of 10 % body weight during static loading of the foot. Stretch sensor measurements were also performed during barefoot walking.

RESULTS

The total change in navicular position measured by pMRI was 10.3 mm (CI: 7.0 to 13.5 mm). No further displacement occurred when adding 10 % bodyweight (mean difference: 0.7 mm (CI: -0.7 to 2.0 mm), P = 0.29). The total navicular displacement correlated with stretch sensor measurement under static loading conditions (Spearman's rho = 0.66, P = 0.04) but not with measurements during walking (Spearman's rho = 0.58, P = 0.08).

CONCLUSIONS

Total navicular bone displacements determined by pMRI showed concurrent validity with stretch sensor measurements but only so under static loading conditions. Although assessment of total navicular displacement by combining concomitant vertical and medial navicular bone movements would appear advantageous compared to monoplanar measurement the combined measure did not seem to predict dynamic changes of the medial foot arch during walking, which are among several possible factors depending on different walking patterns.

Forefoot ulcer risk is associated with foot type in patients with diabetes and neuropathy

AIMS

To stratify the ulceration risk according to the foot morphology in people with diabetes and a history of forefoot neuropathic ulceration.

METHODS

A cross-sectional study was performed on 139 neuropathic individuals with diabetes and previous forefoot ulcers between January 2012 and February 2014. Foot position of the participants was evaluated by using the foot-posture index. A multivariate analysis adjusted for confounding variables was performed with the ulceration risk factors that were found in the univariate analysis.

RESULTS

Two hundred and fifty-eight feet were analysed, 104 (40.3%) feet had a history of ulceration on the forefoot and 154 (59.7%) feet had no previous ulceration. Two positive tests of neuropathy (p<0.001; CI[1.961-6.249] OR 3.500), presence of deformities (p=0.043; CI[1.020-3.599] OR 1.916) and foot type (p=0.039) showed an association with ulceration risk in multivariate analyses. Pronated feet showed a higher risk of ulceration than supinated feet (p=0.011; CI[1.253-5.708] OR 2.675), while significant differences between neutral and supinated feet were not found (p=0.221; CI[0.719-2.753] OR 1.476).

CONCLUSIONS

A pronated foot has a higher risk of ulceration on the forefoot in neuropathic people with deformities and diabetes mellitus. Foot type should be evaluated in people at risk of ulceration.

Development of a Robotic Assembly for Analyzing the Instantaneous Axis of Rotation of the Foot Ankle Complex

Ankle instantaneous axis of rotation (IAR) measurements represent a more complete parameter for characterizing joint motion. However, few studies have implemented this measurement to study normal, injured, or pathological foot ankle biomechanics. A novel testing protocol was developed to simulate aspects of in vivo foot ankle mechanics during mid-stance gait in a human cadaveric specimen. A lower leg was mounted in a robotic testing platform with the tibia upright and foot flat on the baseplate. Axial tibia loads (ATLs) were controlled as a function of a vertical ground reaction force (vGRF) set at half body weight (356 N) and a 50% vGRF (178 N) Achilles tendon load. Two specimens were repetitively loaded over 10 degrees of dorsiflexion and 20 degrees of plantar flexion. Platform axes were controlled within 2 microns and 0.008 degrees resulting in ATL measurements within ±2 N of target conditions. Mean ATLs and IAR values were not significantly different between cycles of motion, but IAR values were significantly different between dorsiflexion and plantar flexion. A linear regression analysis showed no significant differences between slopes of plantar flexion paths. The customized robotic platform and advanced testing protocol produced repeatable and accurate measurements of the IAR, useful for assessing foot ankle biomechanics under different loading scenarios and foot conditions.

Dynamic navicular motion measured using a stretch sensor is different between walking and running, and between over-ground and treadmill conditions

Background

Non-invasive evaluation of in-shoe foot motion has traditionally been difficult. Recently a novel ‘stretch-sensor’ was proposed as an easy and reliable method to measure dynamic foot (navicular) motion. Further validation of this method is needed to determine how different gait analysis protocols affect dynamic navicular motion.

Methods

Potential differences in magnitude and peak velocity of navicular motion using the ‘stretch sensor’ between (i) barefoot and shod conditions; (ii) overground and treadmill gait; and/or (iii) running and walking were evaluated in 26 healthy participants. Comparisons were made using paired t-tests.

Results

Magnitude and velocity of navicular motion was not different between barefoot and shod walking on the treadmill. Compared to walking, velocity of navicular motion during running was 59% and 210% higher over-ground (p < 0.0001) and on a treadmill (p < 0.0001) respectively, and magnitude of navicular motion was 23% higher during over-ground running compared to over-ground walking (p = 0.02). Compared to over-ground, magnitude of navicular motion on a treadmill was 21% and 16% greater during walking (p = 0.0004) and running (p = 0003) respectively. Additionally, maximal velocity of navicular motion during treadmill walking was 48% less than walking over-ground (p < 0.0001).

Conclusion

The presence of footwear has minimal impact on navicular motion during walking. Differences in navicular motion between walking and running, and treadmill and over-ground gait highlight the importance of task specificity during gait analysis. Task specificity should be considered during design of future research trials and in clinical practice when measuring navicular motion.

Association of footprint measurements with plantar kinetics: a linear regression model

BACKGROUND

The use of foot measurements to classify morphology and interpret foot function remains one of the focal concepts of lower-extremity biomechanics. However, only 27% to 55% of midfoot variance in foot pressures has been determined in the most comprehensive models. We investigated whether dynamic walking footprint measurements are associated with inter-individual foot loading variability.

METHODS

Thirty individuals (15 men and 15 women; mean ± SD age, 27.17 ± 2.21 years) walked at a self-selected speed over an electronic pedography platform using the midgait technique. Kinetic variables (contact time, peak pressure, pressure-time integral, and force-time integral) were collected for six masked regions. Footprints were digitized for area and linear boundaries using digital photo planimetry software. Six footprint measurements were determined: contact area, footprint index, arch index, truncated arch index, Chippaux-Smirak index, and Staheli index. Linear regression analysis with a Bonferroni adjustment was performed to determine the association between the footprint measurements and each of the kinetic variables.

RESULTS

The findings demonstrate that a relationship exists between increased midfoot contact and increased kinetic values in respective locations. Many of these variables produced large effect sizes while describing 38% to 71% of the common variance of select plantar kinetic variables in the medial midfoot region. In addition, larger footprints were associated with larger kinetic values at the medial heel region and both masked forefoot regions.

CONCLUSIONS

Dynamic footprint measurements are associated with dynamic plantar loading kinetics, with emphasis on the midfoot region.

An ultrasound based non-invasive method for the measurement of intrinsic foot kinematics during gait

Soft tissue artefact (STA) and marker placement variability are sources of error when measuring the intrinsic kinematics of the foot. This study aims to demonstrate a non-invasive, combined ultrasound and motion capture (US/MC) technique to directly measure foot skeletal motion. The novel approach is compared to a standard motion capture protocol. Fourteen participants underwent instrumented barefoot analysis of foot motion during gait. Markers were attached to foot allowing medial longitudinal arch angle and navicular height to be determined. For the US/MC technique, the navicular marker was replaced by an ultrasound transducer which was secured to the foot allowing the skeletal landmark to be imaged. Ultrasound cineloops showing the location of the navicular tuberosity during the walking trials were synchronised with motion capture measurements and markers mounted on the probe allowed the true position of the bony landmark to be determined throughout stance phase. Two discrete variables, minimum navicular height and maximum MLA angle, were compared between the standard and US/MC protocols. Significant differences between minimum navicular height (P=0.004, 95% CI (1.57, 6.54)) and maximum medial longitudinal arch angle (P=0.0034, 95% CI (13.8, 3.4)) were found between the measurement methods. The individual effects of STA and marker placement error were also assessed. US/MC is a non-invasive technique which may help to provide more accurate measurements of intrinsic foot kinematics.

Reliability of clinically relevant 3D foot bone angles from quantitative computed tomography

BACKGROUND

Surgical treatment and clinical management of foot pathology requires accurate, reliable assessment of foot deformities. Foot and ankle deformities are multi-planar and therefore difficult to quantify by standard radiographs. Three-dimensional (3D) imaging modalities have been used to define bone orientations using inertial axes based on bone shape, but these inertial axes can fail to mimic established bone angles used in orthopaedics and clinical biomechanics. To provide improved clinical relevance of 3D bone angles, we developed techniques to define bone axes using landmarks on quantitative computed tomography (QCT) bone surface meshes. We aimed to assess measurement precision of landmark-based, 3D bone-to-bone orientations of hind foot and lesser tarsal bones for expert raters and a template-based automated method.

METHODS

Two raters completed two repetitions each for twenty feet (10 right, 10 left), placing anatomic landmarks on the surfaces of calcaneus, talus, cuboid, and navicular. Landmarks were also recorded using the automated, template-based method. For each method, 3D bone axes were computed from landmark positions, and Cardan sequences produced sagittal, frontal, and transverse plane angles of bone-to-bone orientations. Angular reliability was assessed using intraclass correlation coefficients (ICCs) and the root mean square standard deviation (RMS-SD) for intra-rater and inter-rater precision, and rater versus automated agreement.

RESULTS

Intra- and inter-rater ICCs were generally high (≥ 0.80), and the ICCs for each rater compared to the automated method were similarly high. RMS-SD intra-rater precision ranged from 1.4 to 3.6° and 2.4 to 6.1°, respectively, for the two raters, which compares favorably to uni-planar radiographic precision. Greatest variability was in Navicular: Talus sagittal plane angle and Cuboid: Calcaneus frontal plane angle. Precision of the automated, atlas-based template method versus the raters was comparable to each rater's internal precision.

CONCLUSIONS

Intra- and inter-rater precision suggest that the landmark-based methods have adequate test-retest reliability for 3D assessment of foot deformities. Agreement of the automated, atlas-based method with the expert raters suggests that the automated method is a valid, time-saving technique for foot deformity assessment. These methods have the potential to improve diagnosis of foot and ankle pathologies by allowing multi-planar quantification of deformities.

Biomechanics of asymmetric ankle osteoarthritis and its joint-preserving surgery

More than half of the patients with ankle osteoarthritis have a malalignment of the hindfoot. These patients might benefit from joint-preserving realignment surgery. This article provides an overview of the effects of asymmetric ankle osteoarthritis on the patients' biomechanical and neuromuscular gait patterns in comparison to data from healthy subjects. Furthermore, data from gait analyses after joint-preserving realignment surgery are presented that give an indication of the biomechanical and neuromuscular adaptations to supramalleolar osteotomies.

An in vitro approach to the evaluation of foot-ankle kinematics: Performance evaluation of a custom-built gait simulator

Despite their well-known limitations, in vitro experiments have several benefits over in vivo techniques when exploring foot biomechanics under conditions characteristic of gait. In this study, we present a new setup for dynamic in vitro gait simulation that integrates a numerical model for generating the tibial kinematics control input, and we present an innovative methodology to measure full three-dimensional joint kinematics during gait simulations. The gait simulator applies forces to the tendons. Tibial kinematics in the sagittal plane is controlled using a numerical model that takes into account foot morphology. The methodology is validated by comparing joint rotations measured during gait simulation with those measured in vivo. In addition, reliability and accuracy of the control system as well as simulation input and output repeatability are quantified. The results reflect good control performance and repeatability of the control inputs, vertical ground reaction force, center of pressure displacement, and joint rotations and translations. In addition, there is a good correspondence to in vivo kinematics for most patterns of motion at the ankle, subtalar, and Chopart’s joints. Therefore, these results show the relevance and validity of including specimen-specific information for defining the control inputs.

The effects of prolonged running on foot posture: a repeated measures study of half marathon runners using the foot posture index and navicular height

Background

Different foot postures are associated with alterations in foot function, kinetics and the subsequent occurrence of injury. Little is known about changes in foot posture following prolonged weightbearing exercise. This study aimed to identify changes in foot posture after running a half marathon.

Methods

Foot posture was measured using the Foot Posture Index (FPI-6) and navicular height in thirty volunteer participants before and after running a half marathon. FPI-6 scores were converted to Rasch logit values and means compared for these and navicular height using an ANOVA.

Results

There was a 5 mm drop in navicular height in both feet when measured after the half marathon (P < 0.05). The FPI-6 showed a side x time interaction with an increase in score indicating a more ‘pronated’ position in the left foot of + 2 [Rasch value + 1.7] but no change in the right foot (+ 0.4 [+ 0.76]) following the half marathon.

Conclusion

The apparent differences between the FPI-6 and navicular height on the right foot may be because the FPI-6 takes soft tissue contour changes into consideration whilst the navicular height focuses on skeletal changes. The changes in foot posture towards a more pronated position may have implications for foot function, and therefore risk of injury; shoe fit and comfort and also the effect of therapeutic orthoses worn during prolonged running.

Reliability of a new supination resistance measurement device and validation of the manual supination resistance test

BACKGROUND

Kinematic observations are inconsistent in predicting lower-extremity injury risk, and research suggests that kinetic variables may be more important in this regard. Before kinetics can be prospectively investigated, we need reliable ways of measuring them clinically. A measurement instrument was manufactured that closely mirrors a manual test used to clinically estimate supination resistance force. The reliability of the instrument and the validity of the clinical test were investigated.

METHODS

The left feet of 26 healthy individuals (17 men and 9 women; mean ± SD age, 25.9 ± 9.2 years; mean ± SD weight, 77.7 ± 13.3 kg) were assessed. Foot Posture Index (FPI-6), manual supination resistance, and machine supination resistance were measured. Intrarater and interrater reliability of all of the measurements were calculated. Correlations of the supination resistance measured by the device with FPI-6, the manual supination resistance test, and body weight were investigated.

RESULTS

Interrater reliability of all of the measurements was generally poor. The supination resistance machine correlated highly with the manual supination test for the rater experienced with its use. Supination resistance measurements correlated poorly with the FPI-6 and weakly with body weight.

CONCLUSIONS

The supination resistance machine was shown to have sufficient limits of agreement for the study, but improvements need to be made for more meaningful research going forward. In this study, the force required to supinate a foot was independent of its posture, and approximately 12% of it was explained by body weight. Further work is required with a much larger sample size to build regression models that sufficiently predict supination resistance force and that will be of clinical use. The manual supination test is a valid clinical test for clinicians experienced in its use.

An apparatus to quantify anteroposterior and mediolateral shear reduction in shoe insoles

BACKGROUND

Many of the physiological changes that lead to diabetic foot ulceration, such as muscle atrophy and skin hardening, are manifested at the foot-ground interface via pressure and shear points. Novel shear-reducing insoles have been developed, but their magnitude of shear stiffness has not yet been compared with regular insoles. The aim of this study was to develop an apparatus that would apply shear force and displacement to an insole's forefoot region, reliably measure deformation, and calculate insole shear stiffness.

METHODS

An apparatus consisting of suspended weights was designed to test the forefoot region of insoles. Three separate regions representing the hallux; the first and second metatarsals; and the third, fourth, and fifth metatarsals were sheared at 20 mm/min for displacements from 0.1 to 1.0 mm in both the anteroposterior and mediolateral directions for two types of insoles (regular and shear reducing).

RESULTS

Shear reduction was found to be significant for the intervention insoles under all testing conditions. The ratio of a regular insole's effective stiffness and the experimental insole's effective stiffness across forefoot position versus shear direction, gait instance versus shear direction, and forefoot position versus gait instance was 270% ± 79%, 270% ± 96%, and 270% ± 86%, respectively. The apparatus was reliable with an average measured coefficient of variation of 0.034 and 0.069 for the regular and shear-reducing insole, respectively.

CONCLUSION

An apparatus consisting of suspended weights resting atop three locations of interest sheared across an insole was demonstrated to be capable of measuring the insole shear stiffness accurately, thus quantifying shear-reducing effects of a new type of insole.

The relationship between foot motion and lumbopelvic-hip function: a review of the literature

Excessive pronation has been implicated in the development of numerous overuse injuries of the lower limb and is suggested to cause more proximal biomechanical dysfunction. Functional foot orthoses (FFO) are frequently prescribed for lower limb injury associated with excessive foot pronation and have been demonstrated to have efficacy with specific conditions. However, the mechanism of action of FFO is largely unknown. Research investigating the kinematic and kinetic changes associated with FFO use is inconclusive. Furthermore there is a growing body of evidence suggesting that changes to muscle activity patterns in response to FFO may be responsible for their therapeutic effect. Additionally, current research suggests dysfunction of musculature of the lumbopelvic-hip complex is involved in lower extremity functional changes and is related to the development some pathologies traditionally attributed to excessive foot pronation. Evidence of temporal coupling between the hip and the foot and changes in hip muscle activity associated with FFO use further suggest a relationship between proximal and distal lower limb function. The aim of this review is to discuss the association between foot and lumbopelvic-hip complex dysfunction and injury, assess the evidence for functional changes to lower limb and lumbopelvic-hip function with FFO use and finally to discuss the potential for changes to hip musculature activation with FFO use to influence distal mechanics and produce a therapeutic benefit.

The in vitro reliability of the CODA MPX30 as the basis for a method of assessing the in vivo motion of the subtalar joint

BACKGROUND

The considerable variation in subtalar joint structure and function shown by studies indicates the importance of developing a noninvasive in vivo technique for assessing subtalar joint movement. This article reports the in vitro testing of the CODA MPX30, an active infrared marker motion analysis system. This work represents the first stage in the development of a noninvasive in vivo method for measuring subtalar joint motion during walking.

METHODS

The in vitro repeatability of the CODA MPX30 system's measurements of marker position, simple and intermarker set angles, was tested. Angular orientations of markers representing the position of the talus and the calcaneus were measured using a purpose-designed marker placement model.

RESULTS

Marker location measurements were shown to vary by less than 1.0 mm in all of the planes. The measurement of a 90° angle was also found to be repeatable in all of the planes, although measurements made in the yz plane were shown to be consistently inaccurate (mean, 92.47°). Estimation of segmental orientation was found to be repeatable. Estimations of marker set orientations were shown to increase in variability after a coordinate transform was performed (maximum SD, 1.14°).

CONCLUSIONS

The CODA MPX30 was shown to produce repeatable estimations of marker position. Levels of variation in segmental orientation estimates were shown to increase subsequent to coordinate transforms. The combination of the CODA MPX30 and an appropriate marker placement model offers the basis of an in vivo measurement strategy of subtalar joint movement, an important development in the understanding of the function of the joint during gait.

'Foot' and 'surgeon': a tale of two definitions

Recent events in the USA and UK have raised questions about the appropriate definition and application of the terms 'foot' and 'surgeon'. In this editorial, we explore these issues and clarify our use of these terms in the journal.

A case-series study to explore the efficacy of foot orthoses in treating first metatarsophalangeal joint pain

Background

First metatarsophalangeal (MTP) joint pain is a common foot complaint which is often considered to be a consequence of altered mechanics. Foot orthoses are often prescribed to reduce 1^st MTP joint pain with the aim of altering dorsiflexion at propulsion. This study explores changes in 1^st MTP joint pain and kinematics following the use of foot orthoses.

Methods

The effect of modified, pre-fabricated foot orthoses (X-line^®) were evaluated in thirty-two patients with 1^st MTP joint pain of mechanical origin. The primary outcome was pain measured at baseline and 24 weeks using the pain subscale of the foot function index (FFI). In a small sub-group of patients (n = 9), the relationship between pain and kinematic variables was explored with and without their orthoses, using an electromagnetic motion tracking (EMT) system.

Results

A significant reduction in pain was observed between baseline (median = 48 mm) and the 24 week endpoint (median = 14.50 mm, z = -4.88, p < 0.001). In the sub-group analysis, we found no relationship between pain reduction and 1^st MTP joint motion, and no significant differences were found between the 1^st MTP joint maximum dorsiflexion or ankle/subtalar complex maximum eversion, with and without the orthoses.

Conclusions

This observational study demonstrated a significant decrease in 1^st MTP joint pain associated with the use of foot orthoses. Change in pain was not shown to be associated with 1^st MTP joint dorsiflexion nor with altered ankle/subtalar complex eversion. Further research into the effect of foot orthoses on foot function is indicated.

Foot structure and function in older people with radiographic osteoarthritis of the medial midfoot

OBJECTIVE

To investigate whether foot structure and dynamic foot function differ between older people with and without radiographically confirmed osteoarthritis (OA) of the talo-navicular joint (TNJ) and navicular-first cuneiform joint (N1(st)CJ).

METHOD

Dorso-plantar and lateral weighbearing foot radiographs (right feet) were obtained from 205 older people aged 61-94 years, and the presence of OA in the TNJ and N1(st)CJ was determined using a standardized atlas. Foot structure was assessed using a clinical measure (the arch index [AI]) and two radiographic measures (calcaneal inclination angle [CIA] and calcaneal-first metatarsal angle [C1MA]). Dynamic plantar pressure assessment during walking was undertaken using the Tekscan MatScan system.

RESULTS

Thirty-five participants exhibited radiographic OA in the TNJ and N1(st)CJ. There were no significant differences between the groups in relation to age, sex, weight or walking velocity. Compared to those without OA in these joints, those with OA had significantly flatter feet, as evidenced by larger AI (0.26+/-0.05 vs 0.25+/-0.05, P=0.02), smaller CIA (18.5+/-6.3 vs 21.3+/-5.4 degrees, P<0.01) and larger C1MA (137.0+/-9.3 vs 132.4+/-8.0 degrees, P<0.01), and exhibited significantly higher maximum forces in the midfoot (15.2+/-7.3 vs 11.2+/-7.0 kg, P<0.01; 36% increase).

CONCLUSION

Older people with radiographic OA of the TNJ and N1(st)CJ exhibit flatter feet and increased loading of the plantar midfoot when walking. Excessive loading of the midfoot may predispose to OA by increasing dorsal compressive forces, although prospective studies are required to confirm whether this relationship is causal.

Foot orthoses: how much customisation is necessary?

The relative merit of customised versus prefabricated foot orthoses continues to be the subject of passionate debate among foot health professionals. Although there is currently insufficient evidence to reach definitive conclusions, a growing body of research literature suggests that prefabricated foot orthoses may produce equivalent clinical outcomes to customised foot orthoses for some conditions. Consensus guidelines for the prescription of customised foot orthoses need to be developed so that the hypothesised benefits of these devices can be thoroughly evaluated.