Estimating three-dimensional foot bone kinematics from skin markers using a deep learning neural network model.

The human foot is a complex structure comprising 26 bones, whose coordinated movements facilitate proper deformation of the foot, ensuring stable and efficient locomotion. Despite their critical role, the kinematics of foot bones during movement remain largely unexplored, primarily due to the absence of non-invasive methods for measuring foot bone kinematics. This study addresses this gap by proposing a neural network model for estimating foot bone movements using surface markers. To establish a mapping between the positions and orientations of the foot bones and 41 skin markers attached on the human foot, computed tomography scans of the foot with the markers were obtained with eleven healthy adults and thirteen cadaver specimens in different foot postures. The neural network architecture comprises four layers, with input and output layers containing the 41 marker positions and the positions and orientations of the nine foot bones, respectively. The mean errors between estimated and true foot bone position and orientation were 0.5 mm and 0.6 degrees, respectively, indicating that the neural network can provide 3D kinematics of the foot bones with sufficient accuracy in a non-invasive manner, thereby contributing to a better understanding of foot function and the pathogenetic mechanisms underlying foot disorders.

Vibratory testing with the 64 Hz Rydel-Seiffer tuning fork and its relation to the sural nerve action potential.

Despite its widespread use, little is known regarding the ability of the semi-quantitative Rydel-Seiffer tuning fork to designate peripheral nerve function. We sought to determine in a large sample of normal and abnormal nerves the relationship between vibration sense and compound sensory nerve action potential (SNAP) parameters recorded in a corresponding innervation area. Vibratory thresholds were determined on a scale of 0 to 8 with a 64 Hz Rydel-Seiffer tuning fork placed on the lateral malleolus of 303 subjects. Sural nerve sensory neurography was employed to derive SNAP parameters, which were related to vibration sense by means of multiple linear regression. ROC curve analysis was performed to determine the classification efficacy of the tuning fork in distinguishing normal from abnormal sural nerve responses. SNAP amplitude was the most significant predictor in the whole subjects group and in the subgroup of subjects with normal SNAPs, whereas conduction velocity played a major role in subjects with abnormal SNAPs. Age was significantly associated with vibration perception, particularly in subjects with normal SNAPs. With an area under the curve of 0.730, vibration sense was a fair classifier for decreased SNAP amplitudes. The optimal vibratory cutoff was 4.2. Age is a major determinant of vibratory test results, highlighting the importance of aging of central and peripheral pathways in mediating vibration sense. Hence, neurophysiological testing cannot be omitted in the context of polyneuropathy work-up, since even at the optimal cutoff threshold, vibratory examination still displays 40% false negative test results.

Calcaneus height is a key morphological factor of sprint performance in sprinters.

This study examined the relationships between the foot bone morphologies and sprint performance in sprinters. Foot images in 56 male sprinters obtained using magnetic resonance imaging. The relative lengths of the forefoot bones of the big and second toes, which were calculated as total lengths of the forefoot bones for each toe normalized to the foot length, correlated significantly with personal best 100-m sprint time (r = - 0.293 and - 0.459, both Ps < 0.05). The relative lengths of the rearfoot talus and calcaneus normalized to the foot length also correlated significantly with the sprint performance (r = - 0.378 and - 0.496, both Ps < 0.05). Furthermore, the relative height of the calcaneus, but not the talus, normalized to body height correlated significantly with sprint performance (r = - 0.690, P < 0.001). Additionally, the relative calcaneus height correlated significantly with the foot arch height index (r = 0.420, P = 0.001), and the foot arch height index correlated significantly with sprint performance (r = - 0.517, P < 0.001). These findings suggest that the taller calcaneus may be a key morphological factor for achieving superior sprint performance, potentially via modeling the longer forefoot and rearfoot bones and functional foot morphology in sprinters.

In vitro study of foot bone kinematics via a custom-made cadaveric gait simulator.

BACKGROUND: Quantifying detailed kinematics of the intrinsic foot bone during gait is crucial for understanding biomechanical functions of the foot complex musculoskeletal structure and making appropriate surgery decisions. RESEARCH QUESTION: The purpose of this experiment is to measure bone kinematic of the normal foot in a gait cycle via a custom-made cadaveric gait simulator. METHODS: In this experiment, we used a custom-made 6 degrees of freedom (DOF) of robotic gait simulator simulating normal human gait to measure the 3-dimensional (3D) kinematics of tibia, calcaneus, cuboid, navicular, medial cuneiform, first metatarsal, and fifth metatarsal through six cadaveric feet. RESULTS: The results showed that the kinematic of the intrinsic foot bones in the stance phase of the gait was successfully quantified using a custom-made robotic gait simulator. During walking stance, the joints in the medial column of foot had less movement than those in the lateral column. And during the later portion of stance, no rotational cease was observed in the movement between navicular and cuboid, calcaneocuboid joint, or cuneonavicular joint. CONCLUSION: This study described foot bone motion using a biomechanically near-physiological gait simulator with 6 DOF of the tibia. The kinematic data helps to clarify previous descriptions of several joint kinematics that are difficult to study in vivo. The methodology also provides a platform for researchers to explore more invasive foot biomechanics under dynamic and near-physiologic conditions.

Hypermobility of the First Ray: the Cinderella of the measurements conventionally assessed for correction of Hallux Valgus.

BACKGROUND AND AIM OF THE WORK: hypermobility of the first ray (FRH) began to be considered as a pathological entity from Morton's studies and was associated as a primary cause of hallux valgus (HV ). Currently, this relationship is in discussion, and various authors consider FRH as a consequence of the deformity. The purpose of this narrative review is to summarise the most influential publications relating to First Ray Mobility (FRM) to increase knowledge and promote its conventional assessment during clinical practice. METHODS: papers of the last century were selected to obtain a homogeneous and up-to-date overview of I-MTCJ mobility and HV, as well as their relationship and management. RESULTS: in recent years, FRH was studied from a biomechanical and pathophysiologic point of view. There is still not enough data regarding the aetiology of FRM. The higher rate of instability found in HV lacks an explanation of which is the cause and which is the effect. However, the Lapidus arthrodesis is still a valid method in cases of FRH and HV, even if is not rigorously indicated to treat both. When approaching FRH, radiographic or clinical findings are mandatory for the right diagnosis. CONCLUSIONS: FRM is an important factor that must be considered in routine clinical practice and prior and post HV surgery, as much as the conventional parameters assessed. Surgeons should consider performing I-MTCJ arthrodesis only if strictly necessary, also paying attention to soft tissue balancing. Improving the measurement of FRH could be useful to determine if it is a cause or effect of the HV deformity.

The effect of running on foot muscles and bones: A systematic review.

Despite the widespread evidence of running as a health-preserving exercise, little is known concerning its effect on the foot musculature and bones. While running may influence anatomical foot adaptation, it remains unclear to what extent these adaptations occur. The aim of this paper is to provide a systematic review of the studies that investigated the effects of running and the adaptations that occur in foot muscles and bones. The search was performed following the PRISMA guidelines. Relevant keywords were used for the search through PubMed/MEDLINE, Scopus and SPORTDiscus. The methodological quality of intervention studies was assessed using the Downs and Black checklist. For cross-sectional studies, the Newcastle-Ottawa scale was used. Sixteen studies were found meeting the inclusion criteria. In general, the included studies were deemed to be of moderate methodological quality. Although results of relevant literature are limited and somewhat contradictory, the outcome suggests that running may increase foot muscle volume, muscle cross-sectional area and bone density, but this seems to depend on training volume and experience. Future studies conducted in this area should aim for a standard way of reporting foot muscle/bone characteristics. Also, herein, suggestions for future research are provided.

Intensive terrestrial or marine locomotor strategies are associated with inter- and intra-limb bone functional adaptation in living female athletes.

OBJECTIVES: To systematically characterize intra-limb patterns of skeletal plasticity to loading among living women, in order to better understand regional complexity in structural adaptation within the lower limb and more accurately infer behavior in the past. MATERIALS AND METHODS: We used peripheral quantitative computed tomography imaging of the femur, tibia, first and second metatarsals to quantify bone morphology among female controls and athletes representative of either terrestrial or marine mobility, grouped by loading category (odd-impact, repetitive low-impact, and high-magnitude). Parameters included midshaft bone density, areas, rigidity, and shape, epiphyseal bone densities and areas. We assessed between-group differences and the influence of training history on significant variation among the loading groups. RESULTS: Terrestrial mobility strategies were best distinguished by significant midshaft periosteal hypertrophy across the lower limb/foot relative to controls, and by particularly high midshaft femoral and tibial cortical bone areas relative to rowers. Enhanced midshaft bone area was typically paired with decreased bone density among athlete groups. Sport-specific variation in training duration/timing was significantly correlated with multiple midshaft parameters. DISCUSSION: Results demonstrate characteristic patterns of intra-limb adaptation to terrestrial and marine mobility strategies among active women relative to controls, and highlight components of these patterns that may be shaped in part by differences in loading duration/timing. Additionally, our findings support constraints on skeletal variation in the distal tibia and foot relative to more proximal locations about the knee among living women. For example, metatarsal variation was constrained, but where present reflected sport-specific variation in force distribution in the foot.

Trabecular bone functional adaptation and sexual dimorphism in the human foot.

OBJECTIVES: Trabecular bone adapts to the strains placed upon the skeleton during life. Anthropological research has largely focused on linking variation in primate trabecular bone to locomotor mode, to provide a context for interpreting fossil morphology. However, intraspecific variation and its underlying mechanisms are still poorly understood. Trabecular bone is influenced by a variety of factors including body mass, age, diet, temperature, genetics, sex, and behavior. Before trabecular structure can be used to infer habitual behavior in the past, the effects of these factors need to be understood. In this article, we examine variation in trabecular structure in the human foot in four archaeological groups in relation to inferred levels of terrestrial mobility and sex. MATERIALS AND METHODS: We use high-resolution µCT scanning to examine variation in trabecular structure in the human calcaneus, talus, and first metatarsal in two relatively mobile and two relatively sedentary archaeological groups. RESULTS: The four population samples show similar patterns of trabecular variation throughout the foot, influenced by mechanical loading. Greater inferred terrestrial mobility is associated with greater bone volume fraction and thicker, more widely spaced, and less interconnected trabeculae. However, contrary to diaphyseal rigidity, only limited sexual dimorphism was found in trabecular structure. DISCUSSION: This work demonstrates that trabecular bone may serve as a useful proxy of habitual behavior in the fossil and archaeological record when other factors are carefully considered. However, the mechanisms underlying sexual dimorphism are not well understood. As such, inferring sex differences in habitual behavior is currently challenging.

One small step: A review of Plio-Pleistocene hominin foot evolution.

Bipedalism is a hallmark of being human and the human foot is modified to reflect this unique form of locomotion. Leonardo da Vinci is credited with calling the human foot "a masterpiece of engineering and a work of art." However, a scientific approach to human origins has revealed that our feet are products of a long, evolutionary history in which a mobile, grasping organ has been converted into a propulsive structure adapted for the rigors of bipedal locomotion. Reconstructing the evolutionary history of foot anatomy benefits from a fossil record; yet, prior to 1960, the only hominin foot bones recovered were from Neandertals. Even into the 1990s, the human foot fossil record consisted mostly of fragmentary remains. However, in the last two decades, the human foot fossil record has quadrupled, and these new discoveries have fostered fresh new perspectives on how our feet evolved. In this review, we document anatomical differences between extant ape and human foot bones, and comprehensively examine the hominin foot fossil record. Additionally, we take a novel approach and conduct a cladistics analysis on foot fossils (n = 19 taxa; n = 80 characters), and find strong evidence for mosaic evolution of the foot, and a variety of anatomically and functionally distinct foot forms as bipedal locomotion evolved.

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

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

The mechanism of force transference in feet of children ages two to six.

The aim of this study was to design an algorithm to quantify the plantar force transference of children from ages 2-6. In total, 319 healthy children without abnormal gait patterns, foot deformities or injuries, able to walk independently, and with normal BMIs were recruited, and their plantar force distributions were measured. Their plantar areas were divided into ten parts: the hallux, toes #2-5, the first to fifth metatarsal heads (1st-5th MTH), the mid-foot (MF), medial heel (MH) and lateral heel (LH), in which a relative force-time integral (FTIrel) (%) was calculated. Our results show that the FTIrel was significantly transferred along either the transverse or longitudinal arches. The middle of the forefoot and the toe areas were the two main loading regions in children aged 2-3, and posterior to anterior FTIrel shifting was typical. However, anterior to posterior and lateral to medial FTI transferences were found in children aged 5-6, and major loading was found in the heel area. Further, loading in the mid-foot varied with the child's development and was observed to tend to decrease over time. Overall, according to the algorithm designed in this study, these results demonstrated that the development of the arches, both in transverse and longitudinal directions, had already begun in early stages of toddlerhood. Meanwhile, the arches were an important attractor engaged in the windlass mechanism while walking, and they played a major role as bridges to promote posterior to anterior and medial to lateral force transference.

The Glasgow-Maastricht foot model, evaluation of a 26 segment kinematic model of the foot.

BACKGROUND: Accurately measuring of intrinsic foot kinematics using skin mounted markers is difficult, limited in part by the physical dimensions of the foot. Existing kinematic foot models solve this problem by combining multiple bones into idealized rigid segments. This study presents a novel foot model that allows the motion of the 26 bones to be individually estimated via a combination of partial joint constraints and coupling the motion of separate joints using kinematic rhythms. METHODS: Segmented CT data from one healthy subject was used to create a template Glasgow-Maastricht foot model (GM-model). Following this, the template was scaled to produce subject-specific models for five additional healthy participants using a surface scan of the foot and ankle. Forty-three skin mounted markers, mainly positioned around the foot and ankle, were used to capture the stance phase of the right foot of the six healthy participants during walking. The GM-model was then applied to calculate the intrinsic foot kinematics. RESULTS: Distinct motion patterns where found for all joints. The variability in outcome depended on the location of the joint, with reasonable results for sagittal plane motions and poor results for transverse plane motions. CONCLUSIONS: The results of the GM-model were comparable with existing literature, including bone pin studies, with respect to the range of motion, motion pattern and timing of the motion in the studied joints. This novel model is the most complete kinematic model to date. Further evaluation of the model is warranted.

The effect of posture on the osseous relations in the foot.

BACKGROUND: Discrepancies observed between clinical findings and a weightbearing foot X-ray might be caused by a patients' positioning. This study's main objective was to determine the effect of a subjects' posture on the osseous relations of the foot. METHODS: Anatomical markers were placed on the skin of the foot of 17 subjects. A plantar pressure plate assessed the percentage weight on the foot and weight distribution over the foot. Medial longitudinal foot angles were derived from the markers and compared between the 10 postures. The effect of percentage weight and weight distribution on the foot angles was determined by multiple regression analysis. RESULTS: The foot angles were significantly affected by the postures. The multiple regression analysis revealed the weight on the foot and the mediolateral weight distribution over the foot as important factors for the foot angles. CONCLUSION: A subjects posture significantly influences the osseous relations in the foot.

Skeletal plasticity in response to embryonic muscular activity underlies the development and evolution of the perching digit of birds.

Most birds have an opposable digit 1 (hallux) allowing the foot to grasp, which evolved from the non-opposable hallux of early theropod dinosaurs. An important morphological difference with early theropods is the twisting of the long axis of its metatarsal. Here, we show how embryonic musculature and the onset of its activity are required for twisting of metatarsal 1 (Mt1) and retroversion of the hallux. Pharmacologically paralyzed embryos do not fully retrovert the hallux and have a straight Mt1 shaft, phenocopying the morphology of early tetanuran dinosaurs. Molecular markers of cartilage maturation and ossification show that differentiation of Mt1 is significantly delayed compared to Mt2-4. We hypothesize on how delayed maturation may have increased plasticity, facilitating muscular twisting. Our experimental results emphasize the importance of embryonic muscular activity in the evolutionary origin of a crucial adaptation.

The foot core system: a new paradigm for understanding intrinsic foot muscle function.

The foot is a complex structure with many articulations and multiple degrees of freedom that play an important role in static posture and dynamic activities. The evolutionary development of the arch of the foot was coincident with the greater demands placed on the foot as humans began to run. The movement and stability of the arch is controlled by intrinsic and extrinsic muscles. However, the intrinsic muscles are largely ignored by clinicians and researchers. As such, these muscles are seldom addressed in rehabilitation programmes. Interventions for foot-related problems are more often directed at externally supporting the foot rather than training these muscles to function as they are designed. In this paper, we propose a novel paradigm for understanding the function of the foot. We begin with an overview of the evolution of the human foot with a focus on the development of the arch. This is followed by a description of the foot intrinsic muscles and their relationship to the extrinsic muscles. We draw the parallels between the small muscles of the trunk region that make up the lumbopelvic core and the intrinsic foot muscles, introducing the concept of the foot core. We then integrate the concept of the foot core into the assessment and treatment of the foot. Finally, we call for an increased awareness of the importance of the foot core stability to normal foot and lower extremity function.

Correlation between anatomic foot and ankle movement measured with MRI and with a motion analysis system.

Several studies have attempted to measure how well external markers track internal bone movement using pins drilled into the foot, but this is too invasive for the pediatric population. This study investigated how well a six segment foot model (6SFM) using external markers was able to measure bone movement in the foot compared to MRI measurements. The foot was moved into different positions using a plastic foot jig and measurements were taken with both systems. The aims were to: (1) Look at the correlation between movement tracked with an Electronic Motion Tracking System (EMTS) and by measurements derived from MRI images, specifically the principal intercept angles (PIAs) which are the angles of intersection between principal axes of inertia of bone volumes. (2) To see how well external motion measured by the 6SFM could predict PIAs. Four bone pairs had their movement tracked: Tibia-Calcaneus, Calcaneus-Cuboid, Navicular-1st Metatarsal, and 1st Metatarsal-Hallux. The results showed moderate correlation between measured PIAs and those predicted at the Tibia-Calcaneus, Navicular-1st Metatarsal, and 1st Metatarsal-Hallux joints. Moderate to high correlation was found between the PIA and movement in a single anatomic plane for all four joints at several positions. The 6SFM using the EMTS allows reliable tracking of 3D rotations in the pediatric foot, except at the Calcaneus-Cuboid joint.

Arch height and maximum rearfoot eversion during jogging in 2 static neutral positions.

CONTEXT: Clinically, lowering of the medial longitudinal arch is believed to be closely related to rearfoot eversion. However, the relationship between arch height and rearfoot eversion during gait is unclear. OBJECTIVES: (1) To examine the influence of 2 reference positions (weight-bearing neutral position [WBNP] and subtalar neutral position [STNP]) on maximum rearfoot eversion, tibial internal rotation, knee flexion, knee internal rotation, and dorsiflexion-plantar flexion of ankle joint measures during jogging and (2) to compare the relationships among static arch height, navicular drop, and the 2 maximum rearfoot eversion measures. DESIGN: Crossover study. SETTING: Gait laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-three volunteers between 18 and 40 years of age. INTERVENTION(S): Each participant stood on the treadmill in 2 static positions: WBNP and STNP. Kinematic data were obtained using a 10-camera motion analysis system (120 Hz) when participants jogged at 2.65 m/s on the treadmill in bare feet. MAIN OUTCOME MEASURE(S): Rearfoot and shank angular kinematics, navicular drop, and static arch height. RESULTS: Maximum rearfoot eversion was greater (WBNP: 4.03° ± 2.58°, STNP: 10.91° ± 5.34°) when STNP was the static reference (P < .001). A strong correlation was seen between maximum STNP eversion and navicular drop (r = 0.842) but not between WBNP and navicular drop (r = 0.216). Differences were noted in dorsiflexion and knee kinematics during gait between the static references; however, the effect sizes were low, and the mean differences were smaller than 2°, which was less than 5% of total excursion during gait. CONCLUSIONS: Using STNP rather than WBNP as the reference position affects estimates of frontal-plane rearfoot movement but not other ankle or knee motions in jogging.

Analysis of a kinetic multi-segment foot model. Part I: Model repeatability and kinematic validity.

Kinematic multi-segment foot models are still evolving, but have seen increased use in clinical and research settings. The addition of kinetics may increase knowledge of foot and ankle function as well as influence multi-segment foot model evolution; however, previous kinetic models are too complex for clinical use. In this study we present a three-segment kinetic foot model and thorough evaluation of model performance during normal gait. In this first of two companion papers, model reference frames and joint centers are analyzed for repeatability, joint translations are measured, segment rigidity characterized, and sample joint angles presented. Within-tester and between-tester repeatability were first assessed using 10 healthy pediatric participants, while kinematic parameters were subsequently measured on 17 additional healthy pediatric participants. Repeatability errors were generally low for all sagittal plane measures as well as transverse plane Hindfoot and Forefoot segments (median<3°), while the least repeatable orientations were the Hindfoot coronal plane and Hallux transverse plane. Joint translations were generally less than 2mm in any one direction, while segment rigidity analysis suggested rigid body behavior for the Shank and Hindfoot, with the Forefoot violating the rigid body assumptions in terminal stance/pre-swing. Joint excursions were consistent with previously published studies.

A new hominin foot from Ethiopia shows multiple Pliocene bipedal adaptations.

A newly discovered partial hominin foot skeleton from eastern Africa indicates the presence of more than one hominin locomotor adaptation at the beginning of the Late Pliocene epoch. Here we show that new pedal elements, dated to about 3.4 million years ago, belong to a species that does not match the contemporaneous Australopithecus afarensis in its morphology and inferred locomotor adaptations, but instead are more similar to the earlier Ardipithecus ramidus in possessing an opposable great toe. This not only indicates the presence of more than one hominin species at the beginning of the Late Pliocene of eastern Africa, but also indicates the persistence of a species with Ar. ramidus-like locomotor adaptation into the Late Pliocene.

Assessment of technical and biological parameters of volumetric quantitative computed tomography of the foot: a phantom study.

SUMMARY: Few studies exist for bone densitometry of the whole foot. A phantom study demonstrated the sources of error and necessary controls for accurate quantitative computed tomography of the foot. A loss in bone mineral density (BMD) in the small foot bones may be an early indicator of diabetic foot complications. INTRODUCTION: Volumetric quantitative computed tomography (vQCT) facilitates the assessment of pedal bone osteopenia, which, in the presence of peripheral neuropathy, may well be an early sign of diabetic foot deformity. To date, sources and magnitudes of error in foot vQCT measurements have not been reported. METHODS: Foot phantoms were scanned using a 64-slice CT scanner. Energy (in kilovoltage peak), table height, phantom size and orientation, location of "bone" inserts, insert material, location of calibration phantom, and reconstruction kernel were systematically varied during scan acquisition. RESULTS: Energy (in kilovoltage peak) and distance from the isocenter (table height) resulted in relative attenuation changes from -5% to 22% and -5% to 0%, respectively, and average BMD changes from -0.9% to 0.0% and -1.1% to 0.3%, respectively, compared to a baseline 120-kVp scan performed at the isocenter. BMD compared to manufacturer-specified values ranged, on average, from -2.2% to 0.9%. Phantom size and location of bone-equivalent material inserts resulted in relative attenuation changes of -1.2% to 1.4% compared to the medium-sized phantom. CONCLUSION: This study demonstrated that variations in kilovoltage peak and table height can be controlled using a calibration phantom scanned at the same energy and height as a foot phantom; however, error due to soft tissue thickness and location of bones within a foot cannot be controlled using a calibration phantom alone.