The relative skin movement of the foot: a 2-D roentgen photogrammetry study

Quantification of soft tissue artifacts using CT registration and subject-specific multibody modeling

The potential use of gait analysis for quantitative preoperative planning in total hip arthroplasty (THA) has previously been demonstrated. However, the joint kinematic data measured through this process tend to be unreliable for surgical planning due to distortions caused by soft tissue artifacts (STAs). In this study, we developed a novel motion capture framework by combining computed tomography (CT)-based postural calibration and subject-specific multibody dynamics modeling to prevent the effect of STAs in measuring hip kinematics. Three subjects with femoroacetabular impingement syndrome were recruited, and CT data for each patient were collected by attaching marker clusters near the hip. A subject-specific multibody hip joint model was developed based on reconstructed CT data. Spring-dashpot network calculations were performed to minimize the distance between the anatomical landmark and its corresponding infrared reflective marker. The STAs of the thigh was described as six degrees of freedom viscoelastic bushing elements, and their parameter values were identified via smooth orthogonal decomposition. Least squares optimization was used to modify the pelvic rotations to compensate for the rigid components of STAs. The results showed that CT-assisted motion tracking enabled the successful identification of STA influences in gait and squat positions. Furthermore, STA effects were found to alter maximal pelvis tilt and hip rotations during a squat. Compared to other techniques, such as dual fluoroscopic imaging, the adopted framework does not require additional medical imaging for patients undergoing robot-assisted THA surgery and is thus a practical way of evaluating hip joint kinematics for preoperative surgical planning.

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

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

Present and future of gait assessment in clinical practice: Towards the application of novel trends and technologies

Background

Despite being available for more than three decades, quantitative gait analysis remains largely associated with research institutions and not well leveraged in clinical settings. This is mostly due to the high cost/cumbersome equipment and complex protocols and data management/analysis associated with traditional gait labs, as well as the diverse training/experience and preference of clinical teams. Observational gait and qualitative scales continue to be predominantly used in clinics despite evidence of less efficacy of quantifying gait.

Research objective

This study provides a scoping review of the status of clinical gait assessment, including shedding light on common gait pathologies, clinical parameters, indices, and scales. We also highlight novel state-of-the-art gait characterization and analysis approaches and the integration of commercially available wearable tools and technology and AI-driven computational platforms.

Methods

A comprehensive literature search was conducted within PubMed, Web of Science, Medline, and ScienceDirect for all articles published until December 2021 using a set of keywords, including normal and pathological gait, gait parameters, gait assessment, gait analysis, wearable systems, inertial measurement units, accelerometer, gyroscope, magnetometer, insole sensors, electromyography sensors. Original articles that met the selection criteria were included.

Results and significance

Clinical gait analysis remains highly observational and is hence subjective and largely influenced by the observer's background and experience. Quantitative Instrumented gait analysis (IGA) has the capability of providing clinicians with accurate and reliable gait data for diagnosis and monitoring but is limited in clinical applicability mainly due to logistics. Rapidly emerging smart wearable technology, multi-modality, and sensor fusion approaches, as well as AI-driven computational platforms are increasingly commanding greater attention in gait assessment. These tools promise a paradigm shift in the quantification of gait in the clinic and beyond. On the other hand, standardization of clinical protocols and ensuring their feasibility to map the complex features of human gait and represent them meaningfully remain critical challenges.

The Amsterdam Foot Model: a clinically informed multi-segment foot model developed to minimize measurement errors in foot kinematics

BACKGROUND

Foot and ankle joint kinematics are measured during clinical gait analyses with marker-based multi-segment foot models. To improve on existing models, measurement errors due to soft tissue artifacts (STAs) and marker misplacements should be reduced. Therefore, the aim of this study is to define a clinically informed, universally applicable multi-segment foot model, which is developed to minimize these measurement errors.

METHODS

The Amsterdam foot model (AFM) is a follow-up of existing multi-segment foot models. It was developed by consulting a clinical expert panel and optimizing marker locations and segment definitions to minimize measurement errors. Evaluation of the model was performed in three steps. First, kinematic errors due to STAs were evaluated and compared to two frequently used foot models, i.e. the Oxford and Rizzoli foot models (OFM, RFM). Previously collected computed tomography data was used of 15 asymptomatic feet with markers attached, to determine the joint angles with and without STAs taken into account. Second, the sensitivity to marker misplacements was determined for AFM and compared to OFM and RFM using static standing trials of 19 asymptomatic subjects in which each marker was virtually replaced in multiple directions. Third, a preliminary inter- and intra-tester repeatability analysis was performed by acquiring 3D gait analysis data of 15 healthy subjects, who were equipped by two testers for two sessions. Repeatability of all kinematic parameters was assessed through analysis of the standard deviation (σ) and standard error of measurement (SEM).

RESULTS

The AFM was defined and all calculation methods were provided. Errors in joint angles due to STAs were in general similar or smaller in AFM (≤2.9°) compared to OFM (≤4.0°) and RFM (≤6.7°). AFM was also more robust to marker misplacement than OFM and RFM, as a large sensitivity of kinematic parameters to marker misplacement (i.e. > 1.0°/mm) was found only two times for AFM as opposed to six times for OFM and five times for RFM. The average intra-tester repeatability of AFM angles was σ:2.2[0.9°], SEM:3.3 ± 0.9° and the inter-tester repeatability was σ:3.1[2.1°], SEM:5.2 ± 2.3°.

CONCLUSIONS

Measurement errors of AFM are smaller compared to two widely-used multi-segment foot models. This qualifies AFM as a follow-up to existing foot models, which should be evaluated further in a range of clinical application areas.

Comparison of the kinematics, repeatability, and reproducibility of five different multi-segment foot models

BACKGROUND

Multi-segment foot models (MFMs) for assessing three-dimensional segmental foot motions are calculated via various analytical methods. Although validation studies have already been conducted, we cannot compare their results because the experimental environments in previous studies were different from each other. This study aims to compare the kinematics, repeatability, and reproducibility of five MFMs in the same experimental conditions.

METHODS

Eleven healthy males with a mean age of 26.5 years participated in this study. We created a merged 29-marker set including five MFMs: Oxford (OFM), modified Rizzoli (mRFM), DuPont (DFM), Milwaukee (MiFM), and modified Shriners Hospital for Children Greenville (mSHCG). Two operators applied the merged model to participants twice, and then we analysed two relative angles of three segments: shank-hindfoot (HF) and hindfoot-forefoot (FF). Coefficients of multiple correlation (CMC) and mean standard errors were used to assess repeatability and reproducibility, and statistical parametric mapping (SPM) of the t-value was employed to compare kinematics.

RESULTS

HF varus/valgus of the MiFM and mSHCG models, which rotated the segment according to radiographic or goniometric measurements during the reference frame construction, were significantly more repeatable and reproducible, compared to other models. They showed significantly more dorsiflexed HF and plantarflexed FF due to their static offset angles. DFM and mSHCG showed a greater range of motion (ROM), and some models had significantly different FF points of peak angle.

CONCLUSIONS

Under the same conditions, rotating the segment according to the appropriate offset angle obtained from radiographic or goniometric measurement increased reliability, but all MFMs had clinically acceptable reliability compared to previous studies. Moreover, in some models, especially HF varus/valgus, there were differences in ROM and points of peak angle even with no statistical difference in SPM curves. Therefore, based on the results of this study, clinicians and researchers involved in the evaluation of foot and ankle dysfunction need an understanding of the specific features of each MFM to make accurate decisions.

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

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

The influence of soft tissue artifacts on multi-segment foot kinematics

Movement of skin markers with respect to their underlying bone (i.e. soft tissue artifacts (STAs)) might corrupt the accuracy of marker-based movement analyses. This study aims to quantify STAs in 3D for foot markers and their effect on multi-segment foot kinematics as calculated by the Oxford and Rizzoli Foot Models (OFM, RFM). Fifteen subjects with asymptomatic feet were seated on a custom-made loading device on a computed tomography (CT) table, with a combined OFM and RFM marker set on their right foot. One unloaded reference CT-scan with neutral foot position was performed, followed by 9 loaded CT-scans at different foot positions. The 3D-displacement (i.e. STA) of each marker in the underlying bone coordinate system between the reference scan and other scans was calculated. Subsequently, segment orientations and joint angles were calculated from the marker positions according to OFM and RFM definitions with and without STAs. The differences in degrees were defined as the errors caused by the marker displacements. Markers on the lateral malleolus and proximally on the posterior aspect of the calcaneus showed the largest STAs. The hindfoot-shank joint angle was most affected by STAs in the most extreme foot position (40° plantar flexion) in the sagittal plane for RFM (mean: 6.7°, max: 11.8°) and the transverse plane for OFM (mean: 3.9°, max: 6.8°). This study showed that STAs introduce clinically relevant errors in multi-segment foot kinematics. Moreover, it identified marker locations that are most affected by STAs, suggesting that their use within multi-segment foot models should be reconsidered.

The modified Shriners Hospitals for Children Greenville (mSHCG) multi-segment foot model provides clinically acceptable measurements of ankle and midfoot angles: A dual fluoroscopy study

BACKGROUND

Several multi-segment foot models have been developed to evaluate foot and ankle motion using skin-marker motion analysis. However, few multi-segment models have been evaluated against a reference standard to establish kinematic accuracy.

RESEARCH QUESTION

How accurately do skin-markers estimate foot and ankle motion for the modified Shriners Hospitals for Children Greenville (mSHCG) multi-segment foot model when compared against the reference standard, dual fluoroscopy (DF), during gait, in asymptomatic participants?

METHODS

Five participants walked overground as full-body skin-marker trajectory data and DF images of the foot and shank were simultaneously acquired. Using the mSHCG model, ankle and midfoot angles were calculated throughout stance for both motion analysis techniques. Statistical parametric mapping assessed differences in joint angles and marker positions between skin-marker and DF motion analysis techniques. Paired t tests, and linear regression models were used to compare joint angles and range of motion (ROM) calculated from the two techniques.

RESULTS

In the coronal plane, the skin-marker model significantly overestimated ROM (p = 0.028). Further, the DF model midfoot ROM was significantly positively related to differences between DF and skin-marker midfoot angles (p = 0.035, adjusted R² = 0.76). In the sagittal plane, skin-markers underestimated ankle angles by as much as 7.26°, while midfoot angles were overestimated by as much as 9.01°. However, DF and skin-marker joint angles were not significantly different over stance. Skin-markers on the tibia, calcaneus, and fifth metatarsal had significantly different positions than the DF markers along the direction of walking for isolated portions that were less than 10 % of stance. Euclidean distances between DF and skin-markers positions were less than 9.36 mm.

SIGNIFICANCE

As the accuracy of the mSHCG model was formerly unknown, the results of this study provide ranges of confidence for key angles calculated by this model.

Comparing the kinematic output of the Oxford and Rizzoli Foot Models during normal gait and voluntary pathological gait in healthy adults

BACKGROUND

The Oxford Foot Model (OFM) and Rizzoli Foot Model (RFM) are the two most frequently used multi-segment models to measure foot kinematics. However, a comprehensive comparison of the kinematic output of these models is lacking.

RESEARCH QUESTION

What are the differences in kinematic output between OFM and RFM during normal gait and typical pathological gait patterns in healthy adults?.

METHODS

A combined OFM and RFM marker set was placed on the right foot of ten healthy subjects. A static standing trial and six level walking trials were collected for normal gait and for four voluntarily adopted gait types: equinus, crouch, toe-in and toe-out. Joint angles were calculated for every trial for the hindfoot relative to shank (HF-SH), forefoot relative to hindfoot (FF-HF) and hallux relative to forefoot (HX-FF). Average static joint angles of both models were compared between models. After subtracting these offsets, the remaining dynamic angles were compared using statistical parametric mapping repeated measures ANOVAs and t-tests. Furthermore, range of motion was compared between models for every angle.

RESULTS

For the static posture, RFM compared to OFM measured more plantar flexion (Δ = 6°) and internal rotation (Δ = 7°) for HF-SH, more plantar flexion (Δ = 34°) and inversion (Δ = 13°) for FF-HF and more dorsal flexion (Δ = 37°) and abduction (Δ = 12°) for HX-FF. During normal walking, kinematic differences were found in various parts of the gait cycle. Moreover, range of motion was larger in the HF-SH for OFM and in FF-HF and HX-FF for RFM. The differences between models were not the same for all gait types. Equinus and toe-out gait demonstrated most pronounced differences.

SIGNIFICANCE

Differences are present in kinematic output between OFM and RFM, which also depend on gait type. Therefore, kinematic output of foot and ankle studies should be interpreted with careful consideration of the multi-segment foot model used.

Pronation or foot movement - What is important

OBJECTIVES

Despite difficulties to quantify foot pronation non-invasively and during dynamic tasks, pronation was frequently discussed with respect to injury risk and footwear development. Typically, surrogate measures were used to approximate the movement of pronation showing inconsistent results due to the high variability in the methodology and protocols. This study determines the relationships between all identified pronation variables and aims to reduce the data set to its dominant factors.

DESIGN

Cross-sectional.

METHODS

Forty barefoot participants (14 F, 26 M) performed four standing tasks (subneutral, bipedal, single-leg with 20° and single-leg with 30° knee flexion), over ground walking (1.5m/s) and running (3.5m/s) trials. Manual assessment data, motion capture data, ground reaction forces, and plantar pressure distributions were collected. Sixty-one commonly used pronation measures were compared using Spearman Correlations and a Principal Component Analysis (PCA).

RESULTS

Two groups of correlated variables were found, 4.2% of them correlated mainly with the longitudinal arch angle (LAA), the other 10.2% correlated with the Achilles tendon angle (β). The remaining 85.6% were not significantly correlated to each other.

CONCLUSIONS

The LAA is representative for the movement of the mid foot and β quantifies rear foot eversion relative to the shank. Since these dominant variables varied independently from each other, both cannot quantify pronation simultaneously. Therefore, it is important to consider and report both, LAA-pronation and β-pronation separately to represent prevalent foot movement properties. Separately assessing the two dominant underlying mechanisms of foot movement may lead to improved guidelines for clinical screening and footwear manufacturing.

A Review of the Evolution of Vision-Based Motion Analysis and the Integration of Advanced Computer Vision Methods Towards Developing a Markerless System

BACKGROUND

The study of human movement within sports biomechanics and rehabilitation settings has made considerable progress over recent decades. However, developing a motion analysis system that collects accurate kinematic data in a timely, unobtrusive and externally valid manner remains an open challenge.

MAIN BODY

This narrative review considers the evolution of methods for extracting kinematic information from images, observing how technology has progressed from laborious manual approaches to optoelectronic marker-based systems. The motion analysis systems which are currently most widely used in sports biomechanics and rehabilitation do not allow kinematic data to be collected automatically without the attachment of markers, controlled conditions and/or extensive processing times. These limitations can obstruct the routine use of motion capture in normal training or rehabilitation environments, and there is a clear desire for the development of automatic markerless systems. Such technology is emerging, often driven by the needs of the entertainment industry, and utilising many of the latest trends in computer vision and machine learning. However, the accuracy and practicality of these systems has yet to be fully scrutinised, meaning such markerless systems are not currently in widespread use within biomechanics.

CONCLUSIONS

This review aims to introduce the key state-of-the-art in markerless motion capture research from computer vision that is likely to have a future impact in biomechanics, while considering the challenges with accuracy and robustness that are yet to be addressed.

Model-based tracking of the bones of the foot: A biplane fluoroscopy validation study

Measuring foot kinematics using optical motion capture is technically challenging due to the depth of the talus, small bone size, and soft tissue artifact. We present a validation of our biplane X-ray system, demonstrating its accuracy in tracking the foot bones directly. Using an experimental linear/rotary stage we imaged pairs of tali, calcanei, and first metatarsals, with embedded beads, through 30 poses. Model- and bead-based algorithms were employed for semi-automatic tracking. Translational and rotational poses were compared to the experimental stage (a reference standard) to determine registration performance. For each bone, 10 frames per pose were analyzed. Model-based: The resulting overall translational bias of the six bones was 0.058 mm with a precision of ± 0.049 mm. The overall rotational bias of the six bones was 0.42° with a precision of ± 0.41°. Bead-based: the overall translational bias was 0.037 mm with a precision of ± 0.032 mm and for rotation was 0.29° with a precision of ± 0.26°. We validated the accuracy of our system to determine the spatial position and orientation of isolated foot bones, including the talus, calcaneus, and first metatarsal over a range of quasi-static poses. Although the accuracy of dynamic motion was not assessed, use of an experimental stage establishes a reference standard.

A comparison of different over-the-counter foot orthotic devices on multi-segment foot biomechanics

BACKGROUND

Over-the-counter foot orthoses are a cost-effective alternative to custom-made devices. However, few studies have compared over-the-counter devices and most biomechanical research involving orthoses has focused on rearfoot biomechanics.

OBJECTIVES

To determine changes in multi-segment foot biomechanics during shod walking in three commercially available over-the-counter devices: SOLE, SuperFeet and Powerstep when compared to no orthotic.

STUDY DESIGN

Repeated measures, cross-sectional study.

METHODS

Retroreflective markers were placed on the right limb of 18 participants representing forefoot, midfoot, rearfoot and shank segments. Three-dimensional kinematics were recorded using an eight-camera motion capture system while participants walked on a treadmill and the order of condition was randomized between four conditions: SOLE, SuperFeet, Powerstep and no orthotic.

RESULTS

All over-the-counter devices exhibited significant decreases in plantar fascia strain compared to no orthotic and only Powerstep exhibited significant decreases in peak rearfoot eversion. Medial longitudinal arch deformation was not reduced for any over-the-counter device.

CONCLUSION

Different over-the-counter devices exhibited specific alterations in rearfoot kinematics and all reduced plantar fascia strain by varying amounts. These over-the-counter-specific kinematic changes should be taken into consideration when recommending these devices as a treatment option.

CLINICAL RELEVANCE

Over-the-counter orthoses are a cost-effective alternative to custom-made devices. We demonstrated that three commonly used over-the-counter devices influence foot kinematics and plantar fascia strain differently. Clinicians can use these results to provide more tailored treatment options for their patients.

The use of a static measure to predict foot posture at midstance during walking

Previous studies have successfully used the longitudinal arch angle (LAA) to assess foot posture, but the measurement consistency and ability of the LAA to predict dynamic foot posture during activity in a variety of foot types have not been evaluated. The purpose of this study was to determine the reliability of the LAA as well as if the clinical method of assessing the LAA could be used to predict the LAA at midstance during walking for supinated, normal, and pronated foot types. The Arch Height Ratio was used to select 35 participants with 12 supinated, 46 normal, and 12 pronated feet. A standard goniometer was used to measure the LAA (CLINIC_LAA) on both feet while standing. Both feet were then filmed using a high speed camera while walking on a treadmill. The LAA was determined by the angle formed by two lines drawn between the markers placed on the first metatatarsal and medial malleolus with the apex the navicular tuberosity. The LAA in midstance (WALK_LAA) was determined using the mean of five walking trials. The reliability of the CLINIC_LAA assessed on both feet by two raters over two days were excellent. There was no difference between the left and right foot for the CLINIC_LAA. The Pearson correlation between CLINIC_LAA and WALK_LAA for all 70 feet was r=0.96 (r²=0.92). The results indicate the LAA is highly predictive of foot posture at midstance in walking explaining over 90% of the variance for a wide range of foot types.

Multisegment Kinematics of the Spinal Column: Soft Tissue Artifacts Assessment

A major challenge in the assessment of intersegmental spinal column angles during trunk motion is the inherent error in recording the movement of bony anatomical landmarks caused by soft tissue artifacts (STAs). This study aims to perform an uncertainty analysis and estimate the typical errors induced by STA into the intersegmental angles of a multisegment spinal column model during trunk bending in different directions by modeling the relative displacement between skin-mounted markers and actual bony landmarks during trunk bending. First, we modeled the maximum displacement of markers relative to the bony landmarks with a multivariate Gaussian distribution. In order to estimate the distribution parameters, we measured these relative displacements on five subjects at maximum trunk bending posture. Then, in order to model the error depending on trunk bending angle, we assumed that the error grows linearly as a function of the bending angle. Second, we applied our error model to the trunk motion measurement of 11 subjects to estimate the corrected trajectories of the bony landmarks and investigate the errors induced into the intersegmental angles of a multisegment spinal column model. For this purpose, the trunk was modeled as a seven-segment rigid-body system described using 23 reflective markers placed on various bony landmarks of the spinal column. Eleven seated subjects performed trunk bending in five directions and the three-dimensional (3D) intersegmental angles during trunk bending were calculated before and after error correction. While STA minimally affected the intersegmental angles in the sagittal plane (<16%), it considerably corrupted the intersegmental angles in the coronal (error ranged from 59% to 551%) and transverse (up to 161%) planes. Therefore, we recommend using the proposed error suppression technique for STA-induced error compensation as a tool to achieve more accurate spinal column kinematics measurements. Particularly, for intersegmental rotations in the coronal and transverse planes that have small range and are highly sensitive to measurement errors, the proposed technique makes the measurement more appropriate for use in clinical decision-making processes.

Normative rearfoot motion during barefoot and shod walking using biplane fluoroscopy

PURPOSE

The ankle rearfoot complex consists of the ankle and subtalar joints. This is an observational study on two test conditions of the rearfoot complex. Using high-speed biplane fluoroscopy, we present a method to measure rearfoot kinematics during normal gait and compare rearfoot kinematics between barefoot and shod gait.

METHODS

Six male subjects completed a walking trial while biplane fluoroscopy images were acquired during stance phase. Bone models of the calcaneus and tibia were reconstructed from computed tomography images and aligned with the biplane fluoroscopy images. An optimization algorithm was used to determine the three-dimensional position of the bones and calculate rearfoot kinematics.

RESULTS

Peak plantarflexion was higher (barefoot: 9.1°; 95% CI 5.2:13.0; shod: 5.7°; 95% CI 3.6:7.8; p = 0.015) and neutral plantar/dorsiflexion occurred later in the stance phase (barefoot: 31.1%; 95% CI 23.6:38.6; shod: 17.7%; 95% CI 14.4:21.0; p = 0.019) during barefoot walking compared to shod walking. An eversion peak of 8.7° (95% CI 1.9:15.5) occurred at 27.8% (95% CI 18.4:37.2) of stance during barefoot walking, while during shod walking a brief inversion to 1.2° (95% CI -2.1:4.5; p = 0.021) occurred earlier (11.5% of stance; 95% CI 0.2:22.8; p = 0.008) during stance phase. The tibia was internally rotated relative to the calcaneus throughout stance phase in both conditions (barefoot: 5.1° (95% CI -1.4:11.6); shod: 3.6° (95% CI -0.4:7.6); ns.).

CONCLUSIONS

Biplane fluoroscopy can allow for detailed quantification of dynamic in vivo ankle kinematics during barefoot and shod walking conditions. This methodology could be used in the future to study hindfoot pathology after trauma, for congenital disease and after sports injuries such as instability.

LEVEL OF EVIDENCE

II.

Direct assessment of 3D foot bone kinematics using biplanar X-ray fluoroscopy and an automatic model registration method

BACKGROUND

Quantifying detailed 3-dimensional (3D) kinematics of the foot in contact with the ground during locomotion is crucial for understanding the biomechanical functions of the complex musculoskeletal structure of the foot. Biplanar X-ray fluoroscopic systems and model-based registration techniques have recently been employed to capture and visualise 3D foot bone movements in vivo, but such techniques have generally been performed manually. In the present study, we developed an automatic model-registration method with biplanar fluoroscopy for accurate measurement of 3D movements of the skeletal foot.

METHODS

Three-dimensional surface models of foot bones were generated prior to motion measurement based on computed tomography. The bone models generated were then registered to biplanar fluoroscopic images in a frame-by-frame manner using an optimisation technique, to maximise similarity measures between occluding contours of the bone surface models with edge-enhanced fluoroscopic images, while avoiding mutual penetration of bones. A template-matching method was also introduced to estimate the amount of bone translation and rotation prior to automatic registration.

RESULTS

We analysed 3D skeletal movements of a cadaver foot mobilized by a robotic gait simulator. The 3D kinematics of the calcaneus, talus, navicular and cuboid in the stance phase of the gait were successfully reconstructed and quantified using the proposed model-registration method. The accuracy of bone registration was evaluated as 0.27 ± 0.19 mm and 0.24 ± 0.19° (mean ± standard deviation) in translation and rotation, respectively, under static conditions, and 0.36 ± 0.19 mm and 0.42 ± 0.30° in translation and rotation, respectively, under dynamic conditions.

CONCLUSIONS

The measurement was confirmed to be sufficiently accurate for actual analysis of foot kinematics. The proposed method may serve as an effective tool for understanding the biomechanical function of the human foot during locomotion.

Medial longitudinal arch mechanics before and after a 45-minute run

BACKGROUND

Medial longitudinal arch integrity after prolonged running has yet to be well documented. We sought to quantify changes in medial longitudinal arch kinematics before and after a 45-min run in healthy recreational runners.

METHODS

Thirty runners performed barefoot seated, standing, and running trials before and after a 45-min shod treadmill run. Navicular displacement, arch lengthening, and the arch height index were used to quantify arch deformation, and the arch rigidity index was used to quantify arch stiffness.

RESULTS

There were no statistically significant differences in mean (95% confidence interval) values for navicular displacement (5.6 mm [4.7-6.4 mm]), arch lengthening (3.2 mm [2.6-3.9 mm]), change in arch height index (0.015 [0.012-0.018]), or arch rigidity index (0.95 [0.94-0.96]) after the 45-min run (all multivariate analyses of variance P ≥ .065).

CONCLUSIONS

Because there were no statistically significant changes in arch deformation or rigidity, the structures of a healthy, intact medial longitudinal arch are capable of either adapting to cyclical loading or withstanding a 45-min run without compromise.

Soft tissue artefacts of the human back: comparison of the sagittal curvature of the spine measured using skin markers and an open upright MRI

Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R², of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes.

Forefoot deformation during stance: does the forefoot collapse during loading?

This study presents a specific description of forefoot deformation during the stance phase of normal human walking based on the combined analysis of pressure and three-dimensional optoelectronic measurements. Forefoot deformation is measured in forty healthy subjects using (1) a six-camera motion capture system (sampled at 250 Hz) tracking five reflective skin markers attached to the forefoot, (2) a pressure platform (sampled at 500 Hz) and (3) a forceplate (sampled at 1250 Hz). Forefoot deformation is characterized by the forefoot width, the mediolateral metatarsal arch height and the plantar pressure under the metatarsal heads. Using this setup, a typical pattern of forefoot motion is described during stance phase: From a flexible, compliant configuration at the beginning of stance phase, characterized by a decrease in mediolateral metatarsal arch height and a controlled increase in forefoot width, the forefoot turns into a stable configuration during midstance. Subsequently, the increase in mediolateral arch height and the decrease in forefoot width describe the transformation into a tight configuration during final stance. This transfer from a compliant into a rigid configuration through stance phase rejects the idea of the forefoot as a collapsing structure under increased loading.

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.

A multi-segment foot model based on anatomically registered technical coordinate systems: method repeatability in pediatric feet

Several multi-segment foot models to measure the motion of intrinsic joints of the foot have been reported. Use of these models in clinical decision making is limited due to lack of rigorous validation including inter-clinician, and inter-lab variability measures. A model with thoroughly quantified variability may significantly improve the confidence in the results of such foot models. This study proposes a new clinical foot model with the underlying strategy of using separate anatomic and technical marker configurations and coordinate systems. Anatomical landmark and coordinate system identification is determined during a static subject calibration. Technical markers are located at optimal sites for dynamic motion tracking. The model is comprised of the tibia and three foot segments (hindfoot, forefoot and hallux) and inter-segmental joint angles are computed in three planes. Data collection was carried out on pediatric subjects at two sites (Site 1: n=10 subjects by two clinicians and Site 2: five subjects by one clinician). A plaster mold method was used to quantify static intra-clinician and inter-clinician marker placement variability by allowing direct comparisons of marker data between sessions for each subject. Intra-clinician and inter-clinician joint angle variability were less than 4°. For dynamic walking kinematics, intra-clinician, inter-clinician and inter-laboratory variability were less than 6° for the ankle and forefoot, but slightly higher for the hallux. Inter-trial variability accounted for 2-4° of the total dynamic variability. Results indicate the proposed foot model reduces the effects of marker placement variability on computed foot kinematics during walking compared to similar measures in previous models.

Changes in multi-segment foot biomechanics with a heat-mouldable semi-custom foot orthotic device

Background

Semi-custom foot orthoses (SCO) are thought to be a cost-effective alternative to custom-made devices. However, previous biomechanical research involving either custom or SCO has only focused on rearfoot biomechanics. The purpose of this study was therefore to determine changes in multi-segment foot biomechanics during shod walking with and without an SCO. We chose to investigate an SCO device that incorporates a heat-moulding process, to further understand if the moulding process would significantly alter rearfoot, midfoot, or shank kinematics as compared to a no-orthotic condition. We hypothesized the SCO, whether moulded or non-moulded, would reduce peak rearfoot eversion, tibial internal rotation, arch deformation, and plantar fascia strain as compared to the no-orthoses condition.

Methods

Twenty participants had retroreflective markers placed on the right limb to represent forefoot, midfoot, rearfoot and shank segments. 3D kinematics were recorded using an 8-camera motion capture system while participants walked on a treadmill.

Results

Plantar fascia strain was reduced by 34% when participants walked in either the moulded or non-moulded SCO condition compared to no-orthoses. However, there were no significant differences in peak rearfoot eversion, tibial internal rotation, or medial longitudinal arch angles between any conditions.

Conclusions

A semi-custom moulded orthotic does not control rearfoot, shank, or arch deformation but does, however, reduce plantar fascia strain compared to walking without an orthoses. Heat-moulding the orthotic device does not have a measurable effect on any biomechanical variables compared to the non-moulded condition. These data may, in part, help explain the clinical efficacy of orthotic devices.

Medial longitudinal arch deformation during walking and stair navigation while carrying loads

BACKGROUND

Understanding the biomechanics of the medial longitudinal arch (MLA) may provide insights into injury risk and prevention, as well as function of the arch-supporting structures. Our understanding of MLA deformation is currently limited to sit-to-stand, walking, and running.

MATERIAL AND METHODS

Three-dimensional deformation of the MLA of the right foot was characterized in 17 healthy participants during several simulated activities of daily living. MLA deformation was quantified by both changes in arch length and navicular displacement during the stance phase of three motions: walking, stair ascent, and stair descent. Three levels of load were also evaluated: no load, a front load (13.6 kg), and a backpack load (13.6 kg). Force platforms and an eight-camera motion capture system were used to collect relevant lower extremity kinetic and kinematic data.

RESULTS

Motion type had a significant (p < 0.05) effect on navicular displacement and arch length elongation with navicular displacement being greatest during stair descent, while the walking and stair descent conditions showed the greatest increase in arch length. External load did not significantly affect either of these two measures (p > 0.05).

CONCLUSION

Differences in the MLA deformation variables resulting from varied dynamic activities of daily living can be greater than those during walking and should be considered.

CLINICAL RELEVANCE

Detailing the mechanics of the MLA may aid in further understanding injuries associated with the MLA, and the results of the current study indicate that these mechanics change based on activity.

Quantifying skin motion artifact error of the hindfoot and forefoot marker clusters with the optical tracking of a multi-segment foot model using single-plane fluoroscopy

The trajectories of skin-mounted markers tracked with optical motion capture are assumed to be an adequate representation of the underlying bone motions. However, it is well known that soft tissue artifact (STA) exists between marker and bone. This study quantifies the STA associated with the hindfoot and midfoot marker clusters of a multi-segment foot model. To quantify STA of the hindfoot and midfoot marker clusters with respect to the calcaneus and navicular respectively, fluoroscopic images were collected on 27 subjects during four quasi-static positions, (1) quiet standing (non-weight bearing), (2) at heel strike (weight-bearing), (3) at midstance (weight-bearing) and (4) at toe-off (weight-bearing). The translation and rotation components of STA were calculated in the sagittal plane. Translational STA at the calcaneus varied from 5.9±7.3mm at heel-strike to 12.1±0.3mm at toe-off. For the navicular the translational STA ranged from 7.6±7.6mm at heel strike to 16.4±16.7mm at toe-off. Rotational STA was relatively smaller for both bones at all foot positions. For the calcaneus they varied between 0.1±2.2° at heel-strike to 0.2±0.6° at toe-off. For the navicular, the rotational STA ranged from 0.6±0.9° at heel-strike to 0.7±0.7° at toe-off. The largest translational STA found in this study (16mm for the navicular) was smaller than those reported in the literature for the thigh and the lower leg, but was larger than the STA of individual spherical markers affixed to the foot. The largest errors occurred at toe-off position for all subjects for both the hindfoot and midfoot clusters. Future studies are recommended to quantify true three-dimensional STA of the entire foot during gait.

Effects of soft tissue artifacts on the calculated kinematics and kinetics of the knee during stair-ascent

Biomechanics of the knee during stair-ascent has mostly been studied using skin-marker-based motion analysis techniques, but no study has reported a complete assessment of the soft tissue artifacts (STA) and their effects on the calculated joint center translation, angles and moments at the knee in normal subjects during this activity. This study aimed to bridge the gap. Twelve young adults walked up a three-step stair while data were acquired simultaneously from a three-dimensional motion capture system, a force plate and a dynamic fluoroscopy system. The "gold standards" of poses of the knee were obtained using a 3D fluoroscopy method. The STA of the markers on the thigh and shank were then calculated, together with their effects on the calculated joint center translations, angles and moments at the knee. The STA of the thigh markers were greater than those on the shank, leading to significantly underestimated flexion and extensor moments, but overestimated joint center translations during the first half of the stance phase. The results will be useful for a better understanding of the normal biomechanics of the knee during stair-ascent, as a baseline for future clinical applications and for developing a compensation method to correct for the effects of STA.

Influence of soft tissue artifacts on the calculated kinematics and kinetics of total knee replacements during sit-to-stand

The current study aimed to quantify the soft tissue artifacts of selected markers on the thigh and shank, and their effects on the calculated joint center translations, angles and moments of the knee during sit-to-stand. Ten patients with total knee replacements rose from a chair under simultaneous surveillance of a motion capture system, a force-plate and a fluoroscopy system. The "true" poses of the thigh and shank were defined by those of the femoral and tibial components obtained using a three-dimensional fluoroscopy method. The soft tissue artifacts of the skin markers were calculated as their movement relative to the underlying prosthesis components. The joint center translations, angles and moments at the knee were also calculated separately using skin markers and the registered prosthesis poses. Considerable soft tissue artifacts were found, leading to significantly underestimated flexion and internal rotation angles, and extensor moments, but overestimated joint center translations and adduction. The current study provides accurate data of the kinematics and kinetics of total knee replacements during sit-to-stand. The effects of soft tissue artifacts on the calculated joint center translations, angles and moments were also quantified for the first time in the literature. The results may help in developing guidelines for using skin markers and in establishing databases in the biomechanical assessment of sit-to-stand in patients with total knee replacements.

Motion-analysis studies of transtibial prosthesis users: a systematic review

BACKGROUND

Three-dimensional motion analysis has been used since the beginning of the 1980s to evaluate many aspects of physical function of transtibial amputees. Despite its common use for clinical research, there is large variability in methods of capturing three-dimensional data, description of these methods, reporting of joint kinematics and interpretation of research findings.

OBJECTIVES

The aim of the following review is to critically examine the specific methodologies used by researchers when collecting three-dimensional kinematic data on transtibial amputees and to provide an overview of the methods used.

STUDY DESIGN

Systematic review.

METHODS

A systematic review of the literature between January 1984 and June 2009 was conducted. A total of 68 papers were identified for review based on the following criteria: experimental research design, collection of three-dimensional kinematic data of lower-extremity joints, and inclusion of transtibial amputees as experimental subjects.

RESULTS

A number of methodological shortcomings were identified in the papers reviewed.

CONCLUSIONS

The authors recommend that future studies more appropriately address the product name and number of prosthetic components used; how the position of reflective markers on the prosthesis is defined; presentation of data from both sound and affected sides; and definition of the neutral position of the ankle when reporting kinematic data. Where possible, the authors recommend use of a control group.

CLINICAL RELEVANCE

This paper has identified numerous sources of discrepancy and potential error in kinematic data collected on trans-tibial amputees. Clinicians and researchers should make themselves aware of these issues when collecting and interpreting gait data.

Dynamics of longitudinal arch support in relation to walking speed: contribution of the plantar aponeurosis

The plantar aponeurosis (PA), in spanning the whole length of the plantar aspect of the foot, is clearly identified as one of the key structures that is likely to affect compliance and stability of the longitudinal arch. A recent study performed in our laboratory showed that tension/elongation in the PA can be predicted from the kinematics of the segments to which the PA is attached. In the present investigation, stereophotogrammetry and inverse kinematics were employed to shed light on the mechanics of the longitudinal arch and its main passive stabilizer, the PA, in relation to walking speed. When compared with a neutral unloaded position, the medial longitudinal arch underwent greater collapse during the weight-acceptance phase of stance at higher walking speed (0.1 degrees +/-1.9 degrees in slow walking; 0.9 degrees +/-2.6 degrees in fast walking; P = 0.0368). During late stance the arch was higher (3.4 degrees +/-3.1 degrees in slow walking; 2.8 degrees +/-2.7 degrees in fast walking; P = 0.0227) and the metatarsophalangeal joints more dorsiflexed (e.g. at the first metatarsophalangeal joint, 52 degrees +/-5 degrees in slow walking; 64 degrees +/-4 degrees in fast walking; P < 0.001) during fast walking. Early-stance tension in the PA increased with speed, whereas maximum tension during late stance did not seem to be significantly affected by walking speed. Although, on the one hand, these results give evidence for the existence of a pre-heel-strike, speed-dependent, arch-stiffening mechanism, on the other hand they suggest that augmentation of arch height in late stance is enhanced by higher forces exerted by the intrinsic muscles on the plantar aspect of the foot when walking at faster speeds.

The impact of hallux valgus on foot kinematics: a cross-sectional, comparative study

BACKGROUND

Hallux valgus is a very common foot deformity in modern societies. The impact of this condition on foot function has been described qualitatively and quantitatively. Published patho-mechanical models are mainly underpinned by findings originating from plantar pressure measurements. However, the kinematical patterns of the many foot segments during gait have not been quantified. This study aims to evaluate the kinematics of the various foot segments in the presence of this deformity.

METHODS

Using the Oxford Foot Model and a 12-camera Motion Analysis System, gait analysis was conducted on a convenience sample of 20 participants with hallux valgus and compared to that of 22 randomly selected symptom-free volunteers. Differences between temporal and kinematical data between groups were analyzed using the unpaired parametric Student t-test (significance level p<0.01).

RESULTS

During specific gait events, a different range of motion was found at several inter-segment angles. Particularly, the range of motion of the hallux (sagittal plane) and hindfoot (frontal-transverse planes) during stance were significantly different (p<0.01).

CONCLUSION

Sagittal plane kinematics of the hallux is affected by the first ray deformity in this condition. However, the impact on other segments was found to be limited. This suggests that the patho-mechanical consequences remain limited to the weight bearing function of the first ray.

Perspectives for clinical measures of dynamic foot function-reference data and methodological considerations

Several studies have investigated if static posture assessments qualify to predict dynamic function of the foot showing diverse outcomes. However, it was suggested that dynamic measures may be better suited to predict foot-related overuse problems. The purpose of this study was to establish the reliability for dynamic measures of longitudinal arch angle (LAA) and navicular height (NH) and to examine to what extent static and dynamic measures thereof are related. Intra-rater reliability of LAA and NH measures was tested on a sample of 17 control subjects. Subsequently, 79 subjects were tested while walking on a treadmill. The ranges and minimum values for LAA and NH during ground contact were identified over 20 consecutive steps. A geometric error model was used to simulate effects of marker placement uncertainty and skin movement artifacts. Results demonstrated the highest reliability for the minimum NH (MinNH), followed by the minimum LAA (MinLAA), the dynamic range of navicular height (DeltaNH) and the range of LAA (DeltaLAA) while all measures were highly reliable. Marker location uncertainty and skin movement artifacts had the smallest effects on measures of NH. The use of an alignment device for marker placement was shown to reduce error ranges for NH measures. Therefore, DeltaNH and MinNH were recommended for functional dynamic foot characterization in the sagittal plane. There is potential for such measures to be a suitable predictor for overuse injuries while being obtainable in clinical settings. Future research needs to include such dynamic but simple foot assessments in large-scale clinical studies.

An objective evaluation of a segmented foot model

Segmented foot and ankle models divide the foot into multiple segments in order to obtain more meaningful information about its functional behavior in health and disease. The goal of this research was to objectively evaluate the fidelity of a generalized three-segment foot and ankle model defined using externally mounted markers. An established apparatus that reproduces the kinematics and kinetics of gait in cadaver lower extremities was used to independently examine the validity of the rigid body assumption and the magnitude of soft tissue artifact induced by skin-mounted markers. Stance phase simulations were conducted on ten donated limbs while recording the three-dimensional kinematic trajectories of skin-mounted and then bone-mounted marker constructs. Segment kinematics were compared to underlying bone kinematics to examine the rigid body assumption. Virtual markers were calculated from the bone mounted marker set and then compared to the skin-mounted markers to examine soft tissue artifact. The shank and hindfoot segments behaved as rigid bodies. The forefoot segment violated the rigid body assumption, as evidenced by significant differences between motions of the first metatarsal and the forefoot segment, and relative motion between the first and fifth metatarsals. Motion vectors of the external skin markers relative to their virtual counterparts were no more than 3mm in each direction, and 3-7 mm overall. Artifactual marker motion had mild affects on inter-segmental kinematics. Despite errors, the segmented model appeared to perform reasonably well overall. The data presented here enable more informed interpretations of clinical findings using the segmented model approach.

Determination of the optimal locations of surface-mounted markers on the tibial segment

This study aims to determine optimal locations on the lower limbs for skin-mounted markers representing the tibial segment in three-dimensional (3D) gait analysis. It was predicted that markers located on the anterior tibial crest and malleoli would be least susceptible to soft tissue movement. Ten retro-reflective markers were attached to each tibial segment for 20 participants. Participants performed 10 walking trials and two different range-of-movement tasks (knee flexion/extension and ankle plantarflexion/dorsiflexion). The results showed a subset of four markers with inter-marker pair distances on the tibia have less than 1.6 mm variation (standard deviation (S.D.)) during walking. Minimal variation was also found in isolated ROM tasks, where marker pairs showed variability of less than 2.2 mm. Other marker locations, the femoral epicondyles and the tibial tuberosity varied up to 4 mm during walking and up to 11 mm during the isolated ROM tasks. The four marker locations that are optimal for defining the tibia are the proximal anterior tibial crest, the distal anterior tibial crest, the lateral malleolus and the medial malleolus.

Double calibration vs. global optimisation: performance and effectiveness for clinical application

For clinical application the quantification of the actual subject-specific kinematics is necessary. Soft tissue artefact (STA) propagation to joint kinematics can nullify the clinical interpretability of stereophotogrammetric analysis. STA was assessed to be strongly subject- and task-specific. The global optimisation, whose performance was assessed only on simulated data, is at the basis of several of the STA compensation methods proposed in the literature. On the other hand, the double calibration was recently proposed and resulted very effective on experimental data. In the present work, the performance of double calibration and global optimisation in reducing soft tissue artefact propagation to relevant knee joint kinematics was compared by using 3D fluoroscopy as gold standard. The mean RMSE over the repetitions for the double calibration is in the order of 1-2 degrees for joint rotations and 1-3 mm for translation, while for the global optimisation is in the order of 10 degrees and 10-15 mm, respectively. The double calibration should then be preferred for the quantification of the subject specific kinematics.

Subtalar neutral position as an offset for a kinematic model of the foot during walking

The lack of a common reference position when defining foot postures may underestimate the ability to differentiate foot function in subjects with pathology. The effect of using the subtalar neutral (STN) position as an offset for both rearfoot and forefoot through comparison of the kinematic walking patterns of subjects classified as normal (n=7) and abnormally pronated (n=14) foot postures was completed. An Optotrak Motion Analysis System (Northern Digital, Inc.) integrated with Motion Monitor Software (Innovative Sports, Inc.) was used to track three-dimensional movement of the leg, rearfoot and first metatarsal segments. Intrarater reliability of positioning the foot into STN using clinical guidelines was determined for a single rater for 21 subjects. Walking data were subsequently compared before and after an offset was applied to the rearfoot and first metatarsal segments. Repeated measures of foot positioning found the STN position to be highly repeatable (intraclass correlation coefficients>0.9), with peak errors ranging from 1.9 degrees to 4.3 degrees . Utilizing STN as the offset resulted in a significant increase in rearfoot eversion (p=0.019) during early stance, and greater first metatarsal dorsiflexion (p<0.007) across stance in the pronated foot groups that was not observed prior to applying the offset. When applied to subjects with differing foot postures, the selection of a common reference position that is both clinically appropriate and reliable may distinguish kinematic patterns during walking that are consistent with theories of abnormal pronation.

Asymmetry of the active nonweightbearing foot and ankle range of motion for dorsiflexion-plantar flexion and its coupled movements in adults

Asymmetries in ankle range of motion (ROM) have been reported, but often the uninvolved limb is used as a reference in clinical practice. The study wanted to quantify the intraindividual asymmetries in dorsi-plantar flexion foot and ankle ROM and its coupled foot movements. Active triplanar nonweightbearing ROM of the foot and ankle was recorded in young healthy adults (30 male volunteers, mean age 22.8 years; 35 female volunteers, mean age 23.8 years) using an optoelectronic set-up. The sagittal plane movement (mean ROM female subjects right side 71.3 degrees, left side 71.4 degrees, P > 0.05; mean ROM male subjects right side 69 degrees , left side 68.9 degrees, P > 0.05; sex difference, P < 0.001) was coupled with frontal (mean ROM female subjects right side 16.6 degrees, left side 14.8 degrees, P > 0.05; male subjects right side 17 degrees, left side 15.3 degrees; P > 0.05; no sex difference) and horizontal (mean ROM female subjects right side 19.6 degrees, left side 18.8 degrees, P < 0.001; male subjects right side 17.6 degrees, left side 16.2 degrees, P < 0.001; sex < 0.001) plane motions. Individual fluctuating asymmetries up to 15 degrees (principal movement), and up to 29 degrees (associated movements) were measured. Overall, 20% of female and 34% of male subjects had principal plane asymmetries >5 degrees, and 50% of the subjects had asymmetries >5 degrees in the associated movements. In young adults, individual asymmetries in ankle joint complex dorsi-plantar flexion should be taken into account when using the uninvolved, contralateral limb as a reference for clinical examination.

Does a specific MR imaging protocol with a supine-lying subject replicate tarsal kinematics seen during upright standing? / Bildet ein spezifisches MR-Verfahren mit rücklings liegendem Probanden die tarsale Kinematik unter stehenden Bedingungen nach?

Magnetic resonance (MR) imaging is becoming increasingly important in the study of foot biomechanics. Specific devices have been constructed to load and position the foot while the subject is lying supine in the scanner. The present study examines the efficacy of such a newly developed device in replicating tarsal kinematics seen during the more commonly studied standing loading conditions. The results showed that although knee flexion and the externally applied load were carefully controlled, subtalar and talo-navicular joint rotations while lying during MR imaging and when standing (measured opto-electrically with markers attached to intracortical pins) did not match, nor were they systematically shifted. Thus, the proposed MR protocol cannot replicate tarsal kinematics seen during upright standing. It is concluded that specific foot loading conditions have to be considered when tarsal kinematics are evaluated. Improved replication of tarsal kinematics in different postures should comprehensively consider muscle activity, a fixed hip position, and a well-defined point of load application.

A MR Imaging Procedure to Measure Tarsal Bone Rotations

Magnetic resonance imaging offers unique insights into three-dimensional foot bone motion. Thereby, adequate devices enabling defined loading and positioning of the foot are needed to profit from this noninvasive procedure. Tarsal bone positions of three healthy subjects were repeatedly measured in a pronated and a supinated foot excursion under bodyweight with a newly developed MR imaging procedure. The quantification of the transferred motion from the loading and positioning device to the calcaneus and an estimation of the required degrees to distinguish between tarsal joint rotations were used to evaluate the applicability of the procedure to investigate tarsal joint motion. It was found that 45–70% (75–95%) of the externally applied 15deg foot pronation (supination) were transferred to the calcaneus. Furthermore, the talonavicular joint showed the largest amount of rotation up to 20deg eversion-inversion and abadduction, followed by the subtalar joint showing nearly half of that motion. Considerably less motion was found between the cuboid and calcaneus (about 2–6deg) and the cuboid nearly did not rotate relative to the navicular (on average 1deg). The estimated necessary differences between tarsal joint movements to identify individual kinematic behavior were in the order of 2deg (4deg related to the talonavicular joint). Since the results were in agreement with the literature, it is concluded that the applicability of the presented procedure to investigate tarsal bone mechanics is warranted. The possibility to evaluate 3D tarsal joint motion in combination with bone morphology (e.g., joint curvature) may provide new insights in the still uncertain relationship between foot function and foot morphology.

An investigation into the deformable characteristics of the human foot using fluoroscopic imaging

BACKGROUND

To determine the behaviour of the human foot during in vivo loading and unloading.

METHODS

Fluoroscopic imaging was used to investigate the movement of the bones and 13 skin markers during loading and unloading for the medial aspect of the left foot. A foot-pressure measuring system was compared with a force plate used to gather kinetic information, simultaneously. Four male and two female subjects performed three tasks that mimicked jumping, walking, and sprinting. Two-dimensional vector displacements were calculated between bone landmarks over time. Foot rigidity was assessed by a 5 mm length variability threshold determined as the difference between the third and first quartiles of the data set.

FINDINGS

The displacement between the first metatarso-phalangeal joint and distal aspect of the calcaneous varied more than the 5 mm threshold. A new foot model was developed which included three rigid segments joined together by hinge joints located at the first metatarso-phalangeal joint and between the anterior talus and navicular. The comparison between skin mounted markers and bone landmarks yielded a range of correlation slopes close to 1.00 for both the x- and y-directions. Foot pressure and force plate comparisons were promising (%RMS(error) approximately 10%) for the vertical ground reaction forces but not so for the centres of pressure (%RMS(error) up to 50%).

INTERPRETATION

A multi-segment foot model is required to better represent the behaviour of a human foot. No consistent skin marker movement was determined. Better pressure distribution devices need to be developed to determine more accurate foot kinetics. Precise foot kinematics are required in order that accurate ankle moments and reaction forces be determined for the purpose of assessing foot and ankle function.

A multi-segment kinematic model of the foot with a novel definition of forefoot motion for use in clinical gait analysis during walking

A multi-segment kinematic model of the foot was developed for use in a gait analysis laboratory. The foot was divided into hindfoot, talus, midfoot and medial and lateral forefoot segments. Six functional joints were defined: ankle and subtalar joints, frontal and transverse plane motions of the hindfoot relative to midfoot, supination/pronation twist of the forefoot relative to midfoot and medial longitudinal arch height-to-length ratio. Twelve asymptomatic subjects were tested during barefoot walking with a six-camera optical stereometric system and auto-reflective markers organized in triads. Repeatability of the joint motions was tested using coefficients of multiple correlation. Ankle and subtalar joint motions and twisting of the forefoot were most repeatable. Hindfoot motions were least repeatable both within-subjects and between-subjects. Hindfoot and forefoot pronation in the frontal plane was found to coincide with dropping of the medial longitudinal arch between early to mid-stance, followed by supination and rising of the arch in late stance and swing phase. This multi-segment foot model addresses an unfortunate shortcoming in current gait analysis practice-the inability to measure motion within the foot. Such measurements are crucial if gait analysis is to remain relevant in the orthopaedic and rehabilitative treatment of the foot and ankle.