The Amsterdam Foot Model: Advancing the clinical assessment of multi-segment foot kinematics during gait

The human feet are essential for our unique way of bipedal locomotion. A dysfunctional foot limits our mobility and consequently our participation in daily life. Hence, it requires careful clinical assessment before any treatment is provided to restore or maintain foot function. Musculoskeletal foot and ankle disorders can be evaluated with marker-based gait analysis. Many marker models have been developed to measure foot and ankle kinematics and several of these are used in a variety of clinical populations. However, a critical evaluation on whether the outcomes of current models actually represent the movement of the bony structures of the foot is still lacking. To further advance the clinical assessment of foot and ankle kinematic measurements during gait, measurement errors that affect the anatomical validity (i.e. accuracy) and reliability (i.e. precision) need to be quantified, and improved if required. Simultaneously, these models’ definitions and output have to align with the clinical perception of foot and ankle motions for a successful clinical application. In this thesis we aim to establish the most accurate and precise skin-marker-based method to measure clinically relevant foot and ankle kinematics during gait. First we explore and compare existing foot models. We show that the ankle angle and triceps surae muscle-tendon complex length are likely overestimated in a mono-segment foot model compared to a multi-segment foot model. Additionally, in chapter 3, we show that the two most-frequently used multi-segment foot models (i.e. the Oxford and Rizzoli Foot Models) provide different angular output for the same gait trials of normal and voluntarily pathological gait. In the second part of this thesis, we evaluate potential sources of measurement error in the Oxford and Rizzoli Foot Models to gain insight in their accuracy and precision. A well-known source of error within marker-based gait analysis are soft tissue artifacts, which are the relative motions of the skin-mounted markers with respect to their underlying bones. To measure these artifacts, we developed a low-dose loaded computed tomography scanning protocol including 10 scans with a total radiation dose that is similar to 1.5 times the dose of a single clinical foot and ankle scan (chapter 4). This protocol is used in chapter 5 to quantify the soft tissue artifacts, which are shown to be substantial and causing clinically relevant errors in multi-segment foot kinematics. Another potential source of measurement error is inconsistent marker placement. In chapter 6, we quantify the marker placement sensitivity and show that for both models each segment is highly sensitive to misplacement of at least one marker. In chapter 5 and 6, markers are identified that are most affected by soft tissue artifacts or inconsistent marker placement. The role of these markers within the model definitions should be reconsidered to improve the accuracy of the measurements and the robustness of the models to inconsistent marker placement. After these evaluation studies, we concluded that the evaluated models are affected by clinically relevant measurement errors that can lead to misinformation. Therefore, in part three of this thesis (chapter 7), we define a novel clinically-informed multi-segment foot model: the Amsterdam Foot Model. A foot and ankle expert panel was consulted to assure that the model definitions and its output align with the clinical perception. The model is explicitly based on minimizing the aforementioned measurement errors. Both types of errors were shown to be smaller in the Amsterdam Foot Model compared to the Oxford and Rizzoli Foot Models. Within the limitations of marker-based motion analysis, the clinically inspired Amsterdam Foot Model accurately and precisely measures foot and ankle kinematics during gait, while striving for an optimal combination of anatomical accuracy, clinical needs and practical applicability

The Amsterdam Foot Model: Advancing the clinical assessment of multi-segment foot kinematics during gait

The human feet are essential for our unique way of bipedal locomotion. A dysfunctional foot limits our mobility and consequently our participation in daily life. Hence, it requires careful clinical assessment before any treatment is provided to restore or maintain foot function. Musculoskeletal foot and ankle disorders can be evaluated with marker-based gait analysis. Many marker models have been developed to measure foot and ankle kinematics and several of these are used in a variety of clinical populations. However, a critical evaluation on whether the outcomes of current models actually represent the movement of the bony structures of the foot is still lacking. To further advance the clinical assessment of foot and ankle kinematic measurements during gait, measurement errors that affect the anatomical validity (i.e. accuracy) and reliability (i.e. precision) need to be quantified, and improved if required. Simultaneously, these models’ definitions and output have to align with the clinical perception of foot and ankle motions for a successful clinical application. In this thesis we aim to establish the most accurate and precise skin-marker-based method to measure clinically relevant foot and ankle kinematics during gait. First we explore and compare existing foot models. We show that the ankle angle and triceps surae muscle-tendon complex length are likely overestimated in a mono-segment foot model compared to a multi-segment foot model. Additionally, in chapter 3, we show that the two most-frequently used multi-segment foot models (i.e. the Oxford and Rizzoli Foot Models) provide different angular output for the same gait trials of normal and voluntarily pathological gait. In the second part of this thesis, we evaluate potential sources of measurement error in the Oxford and Rizzoli Foot Models to gain insight in their accuracy and precision. A well-known source of error within marker-based gait analysis are soft tissue artifacts, which are the relative motions of the skin-mounted markers with respect to their underlying bones. To measure these artifacts, we developed a low-dose loaded computed tomography scanning protocol including 10 scans with a total radiation dose that is similar to 1.5 times the dose of a single clinical foot and ankle scan (chapter 4). This protocol is used in chapter 5 to quantify the soft tissue artifacts, which are shown to be substantial and causing clinically relevant errors in multi-segment foot kinematics. Another potential source of measurement error is inconsistent marker placement. In chapter 6, we quantify the marker placement sensitivity and show that for both models each segment is highly sensitive to misplacement of at least one marker. In chapter 5 and 6, markers are identified that are most affected by soft tissue artifacts or inconsistent marker placement. The role of these markers within the model definitions should be reconsidered to improve the accuracy of the measurements and the robustness of the models to inconsistent marker placement. After these evaluation studies, we concluded that the evaluated models are affected by clinically relevant measurement errors that can lead to misinformation. Therefore, in part three of this thesis (chapter 7), we define a novel clinically-informed multi-segment foot model: the Amsterdam Foot Model. A foot and ankle expert panel was consulted to assure that the model definitions and its output align with the clinical perception. The model is explicitly based on minimizing the aforementioned measurement errors. Both types of errors were shown to be smaller in the Amsterdam Foot Model compared to the Oxford and Rizzoli Foot Models. Within the limitations of marker-based motion analysis, the clinically inspired Amsterdam Foot Model accurately and precisely measures foot and ankle kinematics during gait, while striving for an optimal combination of anatomical accuracy, clinical needs and practical applicability

The Physiological, Neuromuscular, and Perceptual Response to Even- and Variable-Paced 10-km Cycling Time Trials

BACKGROUND: During self-paced (SP) time trials (TTs), cyclists show unconscious nonrandom variations in power output of up to 10% above and below average. It is unknown what the effects of variations in power output of this magnitude are on physiological, neuromuscular, and perceptual variables. PURPOSE: To describe physiological, neuromuscular, and perceptual responses of 10-km TTs with an imposed even-paced (EP) and variable-paced (VP) workload. METHODS: Healthy male, trained, task-habituated cyclists (N = 9) completed three 10-km TTs. First, an SP TT was completed, the mean workload from which was used as the mean workload of the EP and VP TTs. The EP was performed with an imposed even workload, while VP was performed with imposed variations in workload of ±10% of the mean. In EP and VP, cardiorespiratory, neuromuscular, and perceptual variables were measured. RESULTS: Mean rating of perceived exertion was significantly lower in VP (6.13 [1.16]) compared with EP (6.75 [1.24]), P = .014. No mean differences were found for cardiorespiratory and almost all neuromuscular variables. However, differences were found at individual kilometers corresponding to power-output differences between pacing strategies. CONCLUSION: Variations in power output during TTs of ±10%, simulating natural variations in power output that are present during SP TTs, evoke minor changes in cardiorespiratory and neuromuscular responses and mostly affect the perceptual response. Rating of perceived exertion is lower when simulating natural variations in power output, compared with EP cycling. The imposed variations in workload seem to provide a psychological rather than a physiological or neuromuscular advantage

Reliability testing of the heel marker in three-dimensional gait analysis

Introduction: In three-dimensional gait analysis, anatomical axes are defined by and therefore sensitive to marker placement. Previous analysis of the Oxford Foot Model (OFM) has suggested that the axes of the hindfoot are most sensitive to marker placement on the posterior aspect of the heel. Since other multi-segment foot models also use a similar marker, it is important to find methods to place this as accurately as possible. The aim of this pilot study was to test two different ‘jigs’ (anatomical alignment devices) against eyeball marker placement to improve reliability of heel marker placement and calculation of hindfoot angles using the OFM. Methods: Two jigs were designed using three-dimensional printing: a ratio caliper and heel mould. OFM kinematics were collected for ten healthy adults; intra-tester and inter-tester repeatability of hindfoot marker placement were assessed using both an experienced and inexperienced gait analyst for 5 clinically relevant variables. Results: For 3 out of 5 variables the intra-tester and inter-tester variability was below 2 degrees for all methods of marker placement. The ratio caliper had the lowest intra-tester variability for the experienced gait analyst in all 5 variables and for the inexperienced gait analyst in 4 out of 5 variables. However for inter-tester variability, the ratio caliper was only lower than the eyeball method in 2 out of the 5 variables. The mould produced the worst results for 3 of the 5 variables, and was particularly prone to variability when assessing average hindfoot rotation, making it the least reliable method overall. Conclusions: The use of the ratio caliper may improve intra-tester variability, but does not seem superior to the eyeball method of marker placement for inter-tester variability. The use of a heel mould is discouraged.</p

What is the added value of pedobarography for assessing functional outcome of displaced intra-articular calcaneal fractures? A systematic review of existing literature

Background: Displaced intra-articular calcaneal fractures often result in permanent disability, reduced quality of life and high socio-economic costs. Since they often result in a change in geometry of the foot, pedobarography may be useful in predicting outcome at an early stage. The aim of this study was to examine whether a correlation exists between pedobarography and functional outcomes in patients with a displaced intra-articular fracture. Methods: In this systematic review, studies were included when they investigated the correlation between pedobarography and functional outcome in displaced intra-articular calcaneal fractures. Excluded were studies on <10 patients or on animals/cadavers. Collected were baseline patient/treatment characteristics, pedobarographic data (peak pressures, maximum force and centre of pressure) and functional outcome scores. Findings: Out of 153 abstracts, 40 remained for full text screening and 9 were included. Pedobarographic measurements (pressure plate or insoles) showed a lateralization of centre of pressure, decreased pressures underneath the hindfoot, first and second toe and increased pressure underneath the midfoot and forefoot. Correlations with functional outcome were found in some combined pedobarographic results (entire foot/multiple measurements), but hardly in pressures underneath specific foot areas. Interpretation: Even though increased or decreased pressures in specific areas of the foot may not be directly related to functional outcome, combined scores often did. For pedobarography to serve as a prediction tool, it should be more standardised. However, assessing centre of pressure and altered peak pressures underneath the foot, may be useful in developing customized aids such as insoles, aiming for a more individualized improvement

Knee Angle and Stride Length in Association with Ball Speed in Youth Baseball Pitchers

The purpose of this study was to determine whether stride length and knee angle of the leading leg at foot contact, at the instant of maximal external rotation of the shoulder, and at ball release are associated with ball speed in elite youth baseball pitchers. In this study, fifty-two elite youth baseball pitchers (mean age 15.2 SD (standard deviation) 1.7 years) pitched ten fastballs. Data were collected with three high-speed video cameras at a frequency of 240 Hz. Stride length and knee angle of the leading leg were calculated at foot contact, maximal external rotation, and ball release. The associations between these kinematic variables and ball speed were separately determined using generalized estimating equations. Stride length as percentage of body height and knee angle at foot contact were not significantly associated with ball speed. However, knee angles at maximal external rotation and ball release were significantly associated with ball speed. Ball speed increased by 0.45 m/s (1 mph) with an increase in knee extension of 18 degrees at maximal external rotation and 19.5 degrees at ball release. In conclusion, more knee extension of the leading leg at maximal external rotation and ball release is associated with higher ball speeds in elite youth baseball pitchers

The effect of mono- versus multi-segment musculoskeletal models of the foot on simulated triceps surae lengths in pathological and healthy gait

Background: Estimating muscle-tendon complex (MTC) lengths is important for planning of soft tissue surgery and evaluating outcomes, e.g. in children with cerebral palsy (CP). Conventional musculoskeletal models often represent the foot as one rigid segment, called a mono-segment foot model (mono-SFM). However, a multi-segment foot model (multi-SFM) might provide better estimates of triceps surae MTC lengths, especially in patients with foot deformities. Research question: What is the effect of a mono- versus a multi-SFM on simulated ankle angles and triceps surae MTC lengths during gait in typically developing subjects and in children with CP with equinus, cavovarus or planovalgus foot deformities? Methods: 50 subjects were included, 10 non-affected adults, 10 typically developing children, and 30 children with spastic CP and foot deformities. During walking trials, marker trajectories were collected for two marker models, including a mono- and multi-segment foot; respectively Newington gait model and Oxford foot model. Two musculoskeletal lower body models were constructed in OpenSim with either a mono- or multi-SFM based on the corresponding marker models. Normalized triceps surae MTC lengths (soleus, gastrocnemius medialis and lateralis) and ankle angles were calculated and compared between models using statistical parametric mapping RM-ANOVAs. Root mean square error values between simulated MTC lengths were compared using Wilcoxon signed-rank and rank-sum tests. Results: Mono-SFM simulated significantly more ankle dorsiflexion (7.5 ± 1.2°) and longer triceps surae lengths (difference; soleus:2.6 ± 0.29 %, gastrocnemius medialis:1.7 ± 0.2 %, gastrocnemius lateralis:1.8 ± 0.2%) than a multi-SFM. Differences between models were larger in children with CP compared to typically developing children and larger in the stance compared to the swing phase of gait. Largest differences were found in children with CP presenting with planovalgus (4.8 %) or cavovarus (3.8 %) foot deformities. Significance: It is advisable to use a multi-SFM in musculoskeletal models when simulating triceps surae MTC lengths, especially in individuals with planovalgus or cavovarus foot deformities.</p

The effects of electromyography-assisted modelling in estimating musculotendon forces during gait in children with cerebral palsy

Neuro-musculoskeletal modelling can provide insight into the aberrant muscle function during walking in those suffering cerebral palsy (CP). However, such modelling employs optimization to estimate muscle activation that may not account for disturbed motor control and muscle weakness in CP. This study evaluated different forms of neuro-musculoskeletal model personalization and optimization to estimate musculotendon forces during gait of nine children with CP (GMFCS I-II)and nine typically developing (TD)children. Data collection included 3D-kinematics, ground reaction forces, and electromyography (EMG)of eight lower limb muscles. Four different optimization methods estimated muscle activation and musculotendon forces of a scaled-generic musculoskeletal model for each child walking, i.e. (i)static optimization that minimized summed-excitation squared; (ii)static optimization with maximum isometric muscle forces scaled to body mass; (iii)an EMG-assisted approach using optimization to minimize summed-excitation squared while reducing tracking errors of experimental EMG-linear envelopes and joint moments; and (iv)EMG-assisted with musculotendon model parameters first personalized by calibration. Both static optimization approaches showed a relatively low model performance compared to EMG envelopes. EMG-assisted approaches performed much better, especially in CP, with only a minor mismatch in joint moments. Calibration did not affect model performance significantly, however it did affect musculotendon forces, especially in CP. A model more consistent with experimental measures is more likely to yield more physiologically representative results. Therefore, this study highlights the importance of calibrated EMG-assisted modelling when estimating musculotendon forces in TD children and even more so in children with CP

The effects of electromyography-assisted modelling in estimating musculotendon forces during gait in children with cerebral palsy

Neuro-musculoskeletal modelling can provide insight into the aberrant muscle function during walking in those suffering cerebral palsy (CP). However, such modelling employs optimization to estimate muscle activation that may not account for disturbed motor control and muscle weakness in CP. This study evaluated different forms of neuro-musculoskeletal model personalization and optimization to estimate musculotendon forces during gait of nine children with CP (GMFCS I-II) and nine typically developing (TD) children. Data collection included 3D-kinematics, ground reaction forces, and electromyography (EMG) of eight lower limb muscles. Four different optimization methods estimated muscle activation and musculotendon forces of a scaled-generic musculoskeletal model for each child walking, i.e. (i) static optimization that minimized summed-excitation squared; (ii) static optimization with maximum isometric muscle forces scaled to body mass; (iii) an EMG-assisted approach using optimization to minimize summed-excitation squared while reducing tracking errors of experimental EMG-linear envelopes and joint moments; and (iv) EMG-assisted with musculotendon model parameters first personalized by calibration. Both static optimization approaches showed a relatively low model performance compared to EMG envelopes. EMG-assisted approaches performed much better, especially in CP, with only a minor mismatch in joint moments. Calibration did not affect model performance significantly, however it did affect musculotendon forces, especially in CP. A model more consistent with experimental measures is more likely to yield more physiologically representative results. Therefore, this study highlights the importance of calibrated EMG-assisted modelling when estimating musculotendon forces in TD children and even more so in children with CP