Publications by authors named "Ilse Jonkers"

146 Publications

Subject-Specific Spino-Pelvic Models Reliably Measure Spinal Kinematics During Seated Forward Bending in Adult Spinal Deformity.

Front Bioeng Biotechnol 2021 1;9:720060. Epub 2021 Sep 1.

Department of Development and Regeneration, Faculty of Medicine, Institute for Orthopaedic Research and Training (IORT), KU Leuven, Leuven, Belgium.

Image-based subject-specific models and simulations are recently being introduced to complement current state-of-the-art mostly static insights of the adult spinal deformity (ASD) pathology and improve the often poor surgical outcomes. Although the accuracy of a recently developed subject-specific modeling and simulation framework has already been quantified, its reliability to perform marker-driven kinematic analyses has not yet been investigated. The aim of this work was to evaluate the reliability of this subject-specific framework to measure spine kinematics in ASD patients, in terms of 1) the overall test-retest repeatability; 2) the inter-operator agreement of spine kinematic estimates; and, 3) the uncertainty of those spine kinematics to operator-dependent parameters of the framework. To evaluate the overall repeatability 1], four ASD subjects and one control subject participated in a test-retest study with a 2-week interval. At both time instances, subject-specific spino-pelvic models were created by one operator to simulate a recorded forward trunk flexion motion. Next, to evaluate inter-operator agreement 2], three trained operators each created a model for three ASD subjects to simulate the same forward trunk flexion motion. Intraclass correlation coefficients (ICC's) of the range of motion (ROM) of conventional spino-pelvic parameters [lumbar lordosis (LL), sagittal vertical axis (SVA), thoracic kyphosis (TK), pelvic tilt (PT), T1-and T9-spino-pelvic inclination (T1/T9-SPI)] were used to evaluate kinematic reliability 1] and inter-operator agreement 2]. Lastly, a Monte-Carlo probabilistic simulation was used to evaluate the uncertainty of the intervertebral joint kinematics to operator variability in the framework, for three ASD subjects 3]. LL, SVA, and T1/T9-SPI had an excellent test-retest reliability for the ROM, while TK and PT did not. Inter-operator agreement was excellent, with ICC values higher than test-retest reliability. These results indicate that operator-induced uncertainty has a limited impact on kinematic simulations of spine flexion, while test-retest reliability has a much higher variability. The definition of the intervertebral joints in the framework was identified as the most sensitive operator-dependent parameter. Nevertheless, intervertebral joint estimations had small mean 90% confidence intervals (1.04°-1.75°). This work will contribute to understanding the limitations of kinematic simulations in ASD patients, thus leading to a better evaluation of future hypotheses.
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http://dx.doi.org/10.3389/fbioe.2021.720060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8440831PMC
September 2021

Guide to mechanical characterization of articular cartilage and hydrogel constructs based on a systematic in silico parameter sensitivity analysis.

J Mech Behav Biomed Mater 2021 Aug 24;124:104795. Epub 2021 Aug 24.

Soft Tissue Biomechanics Group, Biomechanics Division, Mechanical Engineering Department, KU Leuven, Leuven, Belgium.

Osteoarthritis is a whole joint disease with cartilage degeneration being an important manifestation. Tissue engineering treatment is a solution for repairing cartilage defects by implantation of chondrocyte-laden hydrogel constructs within the defect. In silico models have recently been introduced to simulate and optimize the design of these constructs. These models require accurate knowledge on the mechanical properties of the hydrogel constructs and cartilage explants, which are challenging to obtain due to their anisotropic structure and time-dependent behaviour. We performed a systematic in silico parameter sensitivity analysis to find the most efficient unconfined compression testing protocols for mechanical characterization of hydrogel constructs and cartilage explants, with a minimum number of tests but maximum identifiability of the material parameters. The construct and explant were thereby modelled as porohyperelastic and fibril-reinforced poroelastic materials, respectively. Three commonly used loading regimes were simulated in Abaqus (ramp, relaxation and dynamic loading) with varying compressive strain magnitudes and rates. From these virtual experiments, the resulting material parameters were obtained for each combination using a numerical inverse identification scheme. For hydrogels, maximum sensitivity to the different material parameters was found when using a single step ramp loading (20% compression with 10%/s rate) followed by 15 min relaxation. For cartilage explants, a two-stepped ramp loading (10% compression with 10%/s rate and 10% compression with 1%/s rate), each step followed by 15 min relaxation, yielded the maximum sensitivity to the different material parameters. With these protocols, the material parameters could be retrieved with the lowest amount of uncertainty (hydrogel: < 2% and cartilage: < 6%). These specific results and the overall methodology can be used to optimize mechanical testing protocols to yield reliable material parameters for in silico models of cartilage and hydrogel constructs.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104795DOI Listing
August 2021

An Framework of Cartilage Degeneration That Integrates Fibril Reorientation and Degradation Along With Altered Hydration and Fixed Charge Density Loss.

Front Bioeng Biotechnol 2021 22;9:680257. Epub 2021 Jun 22.

Department of Movement Sciences, KU Leuven, Leuven, Belgium.

Injurious mechanical loading of articular cartilage and associated lesions compromise the mechanical and structural integrity of joints and contribute to the onset and progression of cartilage degeneration leading to osteoarthritis (OA). Despite extensive and research, it remains unclear how the changes in cartilage composition and structure that occur during cartilage degeneration after injury, interact. Recently, techniques provide a unique integrated platform to investigate the causal mechanisms by which the local mechanical environment of injured cartilage drives cartilage degeneration. Here, we introduce a novel integrated Cartilage Adaptive REorientation Degeneration (CARED) algorithm to predict the interaction between degenerative variations in main cartilage constituents, namely collagen fibril disorganization and degradation, proteoglycan (PG) loss, and change in water content. The algorithm iteratively interacts with a finite element (FE) model of a cartilage explant, with and without variable depth to full-thickness defects. In these FE models, intact and injured explants were subjected to normal (2 MPa unconfined compression in 0.1 s) and injurious mechanical loading (4 MPa unconfined compression in 0.1 s). Depending on the mechanical response of the FE model, the collagen fibril orientation and density, PG and water content were iteratively updated. In the CARED model, fixed charge density (FCD) loss and increased water content were related to decrease in PG content. Our model predictions were consistent with earlier experimental studies. In the intact explant model, minimal degenerative changes were observed under normal loading, while the injurious loading caused a reorientation of collagen fibrils toward the direction perpendicular to the surface, intense collagen degradation at the surface, and intense PG loss in the superficial and middle zones. In the injured explant models, normal loading induced intense collagen degradation, collagen reorientation, and PG depletion both on the surface and around the lesion. Our results confirm that the cartilage lesion depth is a crucial parameter affecting tissue degeneration, even under physiological loading conditions. The results suggest that potential fibril reorientation might prevent or slow down fibril degradation under conditions in which the tissue mechanical homeostasis is perturbed like the presence of defects or injurious loading.
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http://dx.doi.org/10.3389/fbioe.2021.680257DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8258121PMC
June 2021

Similar sensorimotor transformations control balance during standing and walking.

PLoS Comput Biol 2021 Jun 25;17(6):e1008369. Epub 2021 Jun 25.

Department of Movement Sciences, KU Leuven, Belgium.

Standing and walking balance control in humans relies on the transformation of sensory information to motor commands that drive muscles. Here, we evaluated whether sensorimotor transformations underlying walking balance control can be described by task-level center of mass kinematics feedback similar to standing balance control. We found that delayed linear feedback of center of mass position and velocity, but not delayed linear feedback from ankle angles and angular velocities, can explain reactive ankle muscle activity and joint moments in response to perturbations of walking across protocols (discrete and continuous platform translations and discrete pelvis pushes). Feedback gains were modulated during the gait cycle and decreased with walking speed. Our results thus suggest that similar task-level variables, i.e. center of mass position and velocity, are controlled across standing and walking but that feedback gains are modulated during gait to accommodate changes in body configuration during the gait cycle and in stability with walking speed. These findings have important implications for modelling the neuromechanics of human balance control and for biomimetic control of wearable robotic devices. The feedback mechanisms we identified can be used to extend the current neuromechanical models that lack balance control mechanisms for the ankle joint. When using these models in the control of wearable robotic devices, we believe that this will facilitate shared control of balance between the user and the robotic device.
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http://dx.doi.org/10.1371/journal.pcbi.1008369DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8266079PMC
June 2021

ESB Clinical Biomechanics Award 2020: Pelvis and hip movement strategies discriminate typical and pathological femoral growth - Insights gained from a multi-scale mechanobiological modelling framework.

Clin Biomech (Bristol, Avon) 2021 Jul 5;87:105405. Epub 2021 Jun 5.

Human Movement Biomechanics Research Group, KU Leuven, Belgium.

Background: Many children with cerebral palsy (CP) develop skeletal deformities during childhood. So far, it is unknown why some children with CP develop bony deformities whereas others do not. The aims of this study were to (i) investigate what loading characteristics lead to typical and pathological femoral growth, and (ii) evaluate why some children with CP develop femoral deformities whereas other do not.

Methods: A multi-scale mechanobiological modelling workflow was used to simulate femoral growth based on three-dimensional motion capture data of six typically developing children and 16 children with CP. Based on the growth results, the participants with CP were divided into two groups: typical growth group and pathological growth group. Gait kinematics and femoral loading were compared between simulations resulting in typical growth and those resulting in pathologic growth.

Findings: Hip joint contact forces were less posteriorly-oriented in the pathological growth simulations compared to the typical ones. Compared to the typically developing participants, the CP group with pathological femoral growth presented increased knee flexion and no hip extension. The CP group with simulated typical growth presented similar sagittal plane joint kinematics but differed in the frontal plane pelvic and hip movement strategy, which normalized the hip joint contact force and therefore contributed to typical femoral growth trends.

Interpretation: Our simulation results identified specific gait features, which may contribute to pathological femoral growth. Furthermore, the hip joint contact force orientation in the sagittal plane seems to be the dominant factor for determining femoral growth simulations.
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http://dx.doi.org/10.1016/j.clinbiomech.2021.105405DOI Listing
July 2021

Generic scaled versus subject-specific models for the calculation of musculoskeletal loading in cerebral palsy gait: Effect of personalized musculoskeletal geometry outweighs the effect of personalized neural control.

Clin Biomech (Bristol, Avon) 2021 Jul 1;87:105402. Epub 2021 Jun 1.

Human Movement Biomechanics Research Group, KU Leuven, Belgium.

Background: Musculoskeletal modelling is used to assess musculoskeletal loading during gait. Linear scaling methods are used to personalize generic models to each participant's anthropometry. This approach introduces simplifications, especially when used in paediatric and/or pathological populations. This study aimed to compare results from musculoskeletal simulations using various models ranging from linear scaled to highly subject-specific models, i.e., including the participant's musculoskeletal geometry and electromyography data.

Methods: Magnetic resonance images (MRI) and gait data of one typically developing child and three children with cerebral palsy were analysed. Musculoskeletal simulations were performed to calculate joint kinematics, joint kinetics, muscle forces and joint contact forces using four modelling frameworks: 1) Generic-scaled model with static optimization, 2) Generic-scaled model with an electromyography-informed approach, 3) MRI-based model with static optimization, and 4) MRI-based model with an electromyography-informed approach.

Findings: Root-mean-square-differences in joint kinematics and kinetics between generic-scaled and MRI-based models were below 5° and 0.15 Nm/kg, respectively. Root-mean-square-differences over all muscles was below 0.2 body weight for every participant. Root-mean-square-differences in joint contact forces between the different modelling frameworks were up to 2.2 body weight. Comparing the simulation results from the typically developing child with the results from the children with cerebral palsy showed similar root-mean-square-differences for all modelling frameworks.

Interpretation: In our participants, the impact of MRI-based models on joint contact forces was higher than the impact of including electromyography. Clinical reasoning based on overall root-mean-square-differences in musculoskeletal simulation results between healthy and pathological participants are unlikely to be affected by the modelling choice.
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http://dx.doi.org/10.1016/j.clinbiomech.2021.105402DOI Listing
July 2021

3D free-hand ultrasound to register anatomical landmarks at the pelvis and localize the hip joint center in lean and obese individuals.

Sci Rep 2021 May 20;11(1):10650. Epub 2021 May 20.

Laboratory of Gait and Movement Analysis, Orthopedic Hospital Vienna-Speising, Vienna, Austria.

3D free-hand ultrasound (3DFUS) is becoming increasingly popular to assist clinical gait analysis because it is cost- and time-efficient and does not expose participants to radiation. The aim of this study was to evaluate its reliability in localizing the anterior superior iliac spine (ASIS) at the pelvis and the hip joint centers (HJC). Additionally, we evaluated its accuracy to get a rough estimation of the potential to use of 3DFUS to segment bony surface. This could offer potential to register medical images to motion capture data in future. To evaluate reliability, a test-retest study was conducted in 16 lean and 19 obese individuals. The locations of the ASIS were determined by manual marker placement (MMP), an instrumented pointer technique (IPT), and with 3DFUS. The HJC location was also determined with 3DFUS. To quantify reliability, intraclass correlation coefficients (ICCs), the standard error of measurement (SEm), among other statistical parameters, were calculated for the identified locations between the test and retest. To assess accuracy, the surface of a human plastic pelvic phantom was segmented with 3DFUS in a distilled water bath in 27 trials and compared to a 3D laser scan of the pelvis. Regarding reliability, the MMP, but especially the IPT showed high reliability in lean (SEm: 2-3 mm) and reduced reliability in obese individuals (SEm: 6-15 mm). Compared to MMP and IPT, 3DFUS presented lower reliability in the lean group (SEm: 2-4 mm vs. 2-8 mm, respectively) but slightly better values in the obese group (SEm: 7-11 mm vs. 6-16 mm, respectively). Correlations between test-retest reliability and torso body fat mass (% of body mass) indicated a moderate to strong relationship for MMP and IPT but only a weak correlation for the 3DFUS approach. The water-bath experiments indicated an acceptable level of 3.5 (1.7) mm of accuracy for 3DFUS in segmenting bone surface. Despite some difficulties with single trials, our data give further rise to the idea that 3DFUS could serve as a promising tool in future to inform marker placement and hip joint center location, especially in groups with higher amount of body fat.
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http://dx.doi.org/10.1038/s41598-021-89763-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8170673PMC
May 2021

The association between gait analysis measures associated with crouch gait, functional health status and daily activity levels in cerebral palsy.

J Pediatr Rehabil Med 2021;14(2):227-235

School of Physiotherapy, Royal College of Surgeons in Ireland, Dublin, Ireland.

Purpose: The aim of this study was to examine the relationship between gait analysis measures associated with crouch gait, functional health status and daily activity in ambulant cerebral palsy (CP).

Methods: Three-dimensional gait analysis was carried out on 35 ambulant participants with bilateral CP crouch gait (knee flexion at mid-stance (KFMS) ⩾ 190). KFMS, knee-flexion at initial contact, gait speed and step-lengths were extracted for analysis. Steps/day and sedentary time/day were assessed using an ActivPAL accelerometer. Functional health status was assessed using the five relevant domains of the Pediatric Outcomes Data Collection Instrument (PODCI) questionnaire. Associations between variables were assessed with correlation coefficients and multivariable linear regression.

Results: There were no significant correlations between KFMS and PODCI domains (ρ=-0.008-0.110) or daily activity (ρ=-0.297-0.237) variables. In contrast, multivariable analysis found that step-length was independently associated with the Sports and Physical Function (p= 0.030), Transfers and Basic Mobility (p= 0.041) and Global Function (< 0.001) domains of the PODCI assessment. Gait speed was independently associated with mean steps/day (p< 0.001).

Conclusions: Step length and gait speed are more strongly associated with functional health status and daily activity than knee flexion during stance in children and adolescents with CP crouch gait.
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http://dx.doi.org/10.3233/PRM-200676DOI Listing
January 2021

A Dynamic Optimization Approach for Solving Spine Kinematics While Calibrating Subject-Specific Mechanical Properties.

Ann Biomed Eng 2021 Sep 13;49(9):2311-2322. Epub 2021 Apr 13.

Department of Movement Sciences, KU Leuven, Leuven, Belgium.

This study aims to propose a new optimization framework for solving spine kinematics based on skin-mounted markers and estimate subject-specific mechanical properties of the intervertebral joints. The approach enforces dynamic consistency in the entire skeletal system over the entire time-trajectory while personalizing spinal stiffness. 3D reflective markers mounted on ten vertebrae during spine motions were measured in ten healthy volunteers. Biplanar X-rays were taken during neutral stance of the subjects wearing the markers. Calculated spine kinematics were compared to those calculated using inverse kinematics (IK) and IK with imposed generic kinematic constraints. Calculated spine kinematics compared well with standing X-rays, with average root mean square differences of the vertebral body center positions below 10.1 mm and below [Formula: see text] for joint orientation angles. For flexion/extension and lateral bending, the lumbar rotation distribution patterns, as well as the ranges of rotations matched in vivo literature data. The approach outperforms state-of-art IK and IK with constraints methods. Calculated ratios reflect reduced spinal stiffness in low-resistance zone and increased stiffness in high-resistance zone. The patterns of calibrated stiffness were consistent with previously reported experimentally determined patterns. This approach will further our insight into spinal mechanics by increasing the physiological representativeness of spinal motion simulations.
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http://dx.doi.org/10.1007/s10439-021-02774-3DOI Listing
September 2021

Computationally efficient optimization method to quantify the required surgical accuracy for a ligament balanced TKA.

IEEE Trans Biomed Eng 2021 Mar 29;PP. Epub 2021 Mar 29.

Objective: This study proposes a computationally efficient method to quantify the effect of surgical inaccuracies on ligament strain in total knee arthroplasty (TKA). More specifically, this study describes a framework to determine the implant position and required surgical accuracy that results in a ligament balanced post-operative outcome with a probability of 90%.

Methods: The response surface method is used to translate uncertainty in the implant position parameters to uncertainty in the ligament strain. The designed uncertainty quantification technique allows for an optimization with feasible computational cost towards the planned implant position and the tolerated surgical error for each of the twelve degrees of freedom of the implant position.

Results: It is shown that the error does not allow for a ligament balanced TKA with a probability of 90% using preoperative planning. Six critical implant position parameters can be identified, namely AP translation, PD translation, VV rotation, IE rotation for the femoral component and PD translation, VV rotation for the tibial component.

Conclusion: We introduced an optimization process that allows for the computation of the required surgical accuracy for a ligament balanced postoperative outcome using preoperative planning with feasible computational cost.

Significance: Towards the research society, the proposed method allows for a computationally efficient uncertainty quantification on a complex model. Towards surgical technique developers, six critical implant position parameters were identified, which should be the focus when refining surgical accuracy of TKA, leveraging better patient satisfaction.
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http://dx.doi.org/10.1109/TBME.2021.3069330DOI Listing
March 2021

Evaluation of functional muscle anatomy scalability in the canine hind limb.

Anat Histol Embryol 2021 May 16;50(3):637-644. Epub 2021 Mar 16.

Faculty of Veterinary Medicine, Department of Medical Imaging of Domestic Animals and Orthopaedics of Small Animals, Ghent University, Merelbeke, Belgium.

In contrast to other mammals, the large variation in dog sizes is not accompanied by any significant genetic re-organization. In order to study the relationship between body mass, limb length and the functional anatomical muscle parameters of the canine hind limb, a large dataset comprising of muscle masses, optimal muscle fibre lengths and physiological cross-sectional area's (PCSA) were acquired for twenty-five muscles in ten dogs of sizes varying between 20 kg and 52 kg. The potential of body mass and limb length for reliably scaling individual muscle masses, optimal muscle fibre lengths and PCSA's were examined. For the majority of the muscles of the canine hind limb, neither body mass nor limb length were reliable scaling parameter for either muscle masses, PCSA's and optimal fibre length. These results indicate the need of a breed-specific approach to musculoskeletal modelling in future canine musculoskeletal research.
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http://dx.doi.org/10.1111/ahe.12666DOI Listing
May 2021

Single leg hop for distance symmetry masks lower limb biomechanics: time to discuss hop distance as decision criterion for return to sport after ACL reconstruction?

Br J Sports Med 2021 Mar 9. Epub 2021 Mar 9.

Department of Movement Sciences, Human Movement Biomechanics Research Group, KU Leuven, Leuven, Belgium.

Background: We evaluated the lower limb status of athletes after anterior cruciate ligament reconstruction (ACLR) during the propulsion and landing phases of a single leg hop for distance (SLHD) task after they had been cleared to return to sport. We wanted to evaluate the biomechanical components of the involved (operated) and uninvolved legs of athletes with ACLR and compare these legs with those of uninjured athletes (controls).

Methods: We captured standard video-based three-dimensional motion and electromyography (EMG) in 26 athletes after ACLR and 23 healthy controls during SLHD and calculated lower limb and trunk kinematics. We calculated lower limb joint moments and work using inverse dynamics and computed lower limb muscle forces using an EMG-constrained musculoskeletal modelling approach. Between-limb (within ACLR athletes) and between-group differences (between ACLR athletes and controls) were evaluated using paired and independent sample t-tests, respectively.

Results: Significant differences in kinematics (effect sizes ranging from 0.42 to 1.56), moments (0.39 to 1.08), and joint work contribution (0.55 to 1.04) were seen between the involved and uninvolved legs, as well as between groups. Athletes after ACLR achieved a 97%±4% limb symmetry index in hop distance but the symmetry in work done by the knee during propulsion was only 69%. During landing, the involved knee absorbed less work than the uninvolved, while the uninvolved knee absorbed more work than the control group. Athletes after ACLR compensated for lower knee work with greater hip work contribution and by landing with more hip flexion, anterior pelvis tilt, and trunk flexion.

Conclusion: Symmetry in performance on a SLHD test does not ensure symmetry in lower limb biomechanics. The distance hopped is a poor measure of knee function, and largely reflects hip and ankle function. Male athletes after ACLR selectively unload the involved limb but outperform controls on the uninvolved knee.
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http://dx.doi.org/10.1136/bjsports-2020-103677DOI Listing
March 2021

Towards the Monitoring of Functional Status in a Free-Living Environment for People with Hip or Knee Osteoarthritis: Design and Evaluation of the JOLO Blended Care App.

Sensors (Basel) 2020 Dec 5;20(23). Epub 2020 Dec 5.

REVAL Rehabilitation Research, Hasselt University, 3590 Diepenbeek, Belgium.

(1) Background: Joint loading is an important parameter in patients with osteoarthritis (OA). However, calculating joint loading relies on the performance of an extensive biomechanical analysis, which is not possible to do in a free-living situation. We propose the concept and design of a novel blended-care app called JOLO (Joint Load) that combines free-living information on activity with lab-based measures of joint loading in order to estimate a subject's functional status. (2) Method: We used an iterative design process to evaluate the usability of the JOLO app through questionnaires. The user interfaces that resulted from the iterations are described and provide a concept for feedback on functional status. (3) Results: In total, 44 people (20 people with OA and 24 health-care providers) participated in the testing of the JOLO app. OA patients rated the latest version of the JOLO app as moderately useful. Therapists were predominantly positive; however, their intention to use JOLO was low due to technological issues. (4) Conclusion: We can conclude that JOLO is promising, but further technological improvements concerning activity recognition, the development of personalized joint loading predictions and a more comfortable means to carry the device are needed to facilitate its integration as a blended-care program.
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http://dx.doi.org/10.3390/s20236967DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7730884PMC
December 2020

The effect of hip muscle weakness and femoral bony deformities on gait performance.

Gait Posture 2021 01 25;83:280-286. Epub 2020 Oct 25.

Department of Movement Sciences, KU Leuven, Leuven, Belgium.

Background: Children with cerebral palsy (CP) present with a pathological gait pattern due to musculoskeletal impairments, such as muscle weakness and altered bony geometry. However, the effect of these impairments on gait performance is still unknown. Research aim:This study aimed to explore the effect of hip muscle weakness and femoral deformities on the gait performance of CP and typical developing (TD) subjects.

Methods: 6400 musculoskeletal models were created by weakening the hip extensors, abductors, adductors and flexors from 0% to 75 % and increasing the femoral anteversion angle (FAA) and neck shaft angle (NSA) from 20° to 60° and 120° to 160°, respectively. One TD and five CP gait patterns were imposed to each model and muscle forces were calculated. The effect of weakness and bony deformities on the capability gap (CG) at the hip, i.e. the lack in hip moment generating capacity to perform the gait pattern, was investigated using regression analysis.

Results: The CG of apparent equinus, stiff knee gait, TD gait, jump gait and true equinus increased with 0.080, 0.038, 0.015, 0.023 and 0.005 Nm/kg per 10 percent hip abductor weakness increase, with 0.211, 0.130, 0.056, 0.045 and 0.011 Nm/kg per 10 degrees FAA increase and with 0.163, 0.080, 0.036, 0.043 and 0.011 Nm/kg per 10 degrees NSA increase, respectively. Combined weakness and bony deformities explained 96 %, 85 %, 82 %, 65 %, 40 % and 35 % of the variance in the CG of apparent equinus, TD gait, stiff knee gait, jump gait, true equinus and crouch gait, respectively.

Significance: The results suggest that surgical correction of femoral deformities is more likely to be effective than strength training of hip muscles in enhancing CP gait performance. Jump gait, true equinus and especially crouch were more robust, while apparent equinus and stiff knee gait were limited by hip weakness and femoral deformities.
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http://dx.doi.org/10.1016/j.gaitpost.2020.10.022DOI Listing
January 2021

Hip Muscle Forces and Contact Loading During Squatting After Cam-Type FAI Surgery.

J Bone Joint Surg Am 2020 Nov;102(Suppl 2):34-42

School of Human Kinetics (D.S.C., E.K., and M.L.), Division of Orthopaedic Surgery (P.E.B.), and Department of Mechanical Engineering (M.L.), University of Ottawa, Ottawa, Ontario, Canada.

Background: The purpose of this study was to compare muscle forces and hip contact forces (HCFs) during squatting in patients with cam-type femoroacetabular impingement (cam-FAI) before and after hip corrective surgery and with healthy control participants.

Methods: Ten symptomatic male patients with cam-FAI performed deep squatting preoperatively and at 2 years postoperatively. Patients were matched by age and body mass index to 10 male control participants. Full-body kinematics and kinetics were computed, and muscle forces and HCFs were estimated using a musculoskeletal model and static optimization. Normalized squat cycle (%SC) trials were compared using statistical nonparametric mapping (SnPM).

Results: Postoperatively, patients with cam-FAI squatted down with higher anterior pelvic tilt, higher hip flexion, and greater hip extension moments than preoperatively. Preoperative patients demonstrated lower anterior pelvic tilt and lower hip flexion compared with the participants in the control group. Postoperative patients showed increased semimembranosus force compared with their preoperative values. Preoperative forces were lower than the control group for the adductor magnus, the psoas major, and the semimembranosus; however, the preoperative patients showed greater inferior gluteus maximus forces than the patients in the control group, whereas the postoperative patients did not differ from the control patients. Higher posterior, superior, and resultant HCF magnitudes were identified postoperatively in comparison with the preoperative values. Preoperative posterior HCF was lower than in the control group, whereas the postoperative posterior HCF did not differ from those in the control group.

Conclusions: Higher postoperative anterior pelvic tilt was associated with an indication of return to closer to normal pelvic motion, which resembled data from the control group. Lower preoperative anterior pelvic tilt was associated with muscle force imbalance, indicated by decreased semimembranosus and increased gluteus maximus forces. The overall increased postoperative muscle forces were associated with improved pelvic mobility and increased HCFs that were comparable with the control-group standards.

Clinical Relevance: Muscle forces and HCFs may be indicative of postoperative joint health restoration and alleviated symptoms.
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http://dx.doi.org/10.2106/JBJS.20.00078DOI Listing
November 2020

Development and validation of a modeling workflow for the generation of image-based, subject-specific thoracolumbar models of spinal deformity.

J Biomech 2020 09 17;110:109946. Epub 2020 Jul 17.

Institute for Orthopaedic Research and Training (IORT), Department of Development and Regeneration, Research Orthopedie, Herestraat 49, 3000 Leuven, Belgium; Division of Orthopaedics, University Hospitals Leuven, Leuven, Belgium. Electronic address:

Quantitative dynamic evaluation of spino-pelvic motion in subjects with spinal deformity using optical motion analysis is currently lacking. The aim of this study was to develop and validate subject-specific, thoracolumbar spine multi-body skeletal models for evaluating spino-pelvic kinematics in a spinal deformity population. A new workflow for creating subject-specific spino-pelvic models in a weight-bearing position through computed tomography (CT) and biplanar radiography is described. As part of a two-step validation process the creation of such a model was first validated against a ground truth CT reconstruction of a plastinated cadaver. Secondly, biplanar radiographic images of one healthy and 12 adult spinal deformity subjects were obtained in two standing positions: upright and bent. Two subject-specific models for each of these subjects were then created to represent both standing positions. The result of inverse kinematics solutions, simulating the specific bending motion using the upright models, are compared with the models created in bent position, quantifying the marker-based spino-pelvic tracking accuracy. The workflow created spinal deformity models with mean accuracies between 0.71-1.95 mm and 1.25-2.27° for vertebral positions and orientations, respectively. In addition, the mean marker-based spino-pelvic tracking accuracies were between 0.9-1.8 mm and 2.9-5.6° for vertebral positions and rotations, respectively. This study presented the first validated biplanar radiography-based method to generate subject-specific spino-pelvic, rigid body models that allows the inclusion of subject-specific bone geometries, the personalization of the 3D weight-bearing spinal alignment with accuracy comparable to clinically used software for 3D reconstruction, and the localization of external markers in spinal deformity subjects. This work will allow new concepts of dynamic functionality evaluation of patients with spinal deformity.
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http://dx.doi.org/10.1016/j.jbiomech.2020.109946DOI Listing
September 2020

Automated muscle elongation measurement during reverse shoulder arthroplasty planning.

J Shoulder Elbow Surg 2021 Mar 21;30(3):561-571. Epub 2020 Jul 21.

Biomechanics Section, KU Leuven, Leuven, Belgium.

Background: Adequate deltoid and rotator cuff elongation in reverse shoulder arthroplasty is crucial to maximize postoperative functional outcomes and to avoid complications. Measurements of deltoid and rotator cuff elongation during preoperative planning can support surgeons in selecting a suitable implant design and position. Therefore, this study presented and evaluated a fully automated method for measuring deltoid and rotator cuff elongation.

Methods: Complete scapular and humeral models were extracted from computed tomography scans of 40 subjects. First, a statistical shape model of the complete humerus was created and evaluated to identify the muscle attachment points. Next, a muscle wrapping algorithm was developed to identify the muscle paths and to compute muscle lengths and elongations after reverse shoulder arthroplasty implantation. The accuracy of the muscle attachment points and the muscle elongation measurements was evaluated for the 40 subjects by use of both complete and artificially created partial humeral models. Additionally, the muscle elongation measurements were evaluated for a set of 50 arthritic shoulder joints. Finally, a sensitivity analysis was performed to evaluate the impact of implant positioning on deltoid and rotator cuff elongation.

Results: For the complete humeral models, all muscle attachment points were identified with a median error < 3.5 mm. For the partial humeral models, the errors on the deltoid attachment point largely increased. Furthermore, all muscle elongation measurements showed an error < 1 mm for 75% of the subjects for both the complete and partial humeral models. For the arthritic shoulder joints, the errors on the muscle elongation measurements were <2 mm for 75% of the subjects. Finally, the sensitivity analysis showed that muscle elongations were affected by implant positioning.

Discussion: This study presents an automated method for accurately measuring muscle elongations during preoperative planning of shoulder arthroplasty. The results show that the accuracy in measuring muscle elongations is higher than the accuracy in indicating the muscle attachment points. Hence, muscle elongation measurements are insensitive to the observed errors on the muscle attachment points. Related to this finding, muscle elongations can be accurately measured for both a complete humeral model and a partial humeral model. Because the presented method also showed accurate results for arthritic shoulder joints, it can be used during preoperative shoulder arthroplasty planning, in which typically only the proximal humerus is present in the scan and in which bone arthropathy can be present. As the muscle elongations are sensitive to implant positioning, surgeons can use the muscle elongation measurements to refine their surgical plan.
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http://dx.doi.org/10.1016/j.jse.2020.07.007DOI Listing
March 2021

A multi-scale modelling framework combining musculoskeletal rigid-body simulations with adaptive finite element analyses, to evaluate the impact of femoral geometry on hip joint contact forces and femoral bone growth.

PLoS One 2020 23;15(7):e0235966. Epub 2020 Jul 23.

Human Movement Biomechanics Research Group, KU Leuven, Leuven, Belgium.

Multi-scale simulations, combining muscle and joint contact force (JCF) from musculoskeletal simulations with adaptive mechanobiological finite element analysis, allow to estimate musculoskeletal loading and predict femoral growth in children. Generic linearly scaled musculoskeletal models are commonly used. This approach, however, neglects subject- and age-specific musculoskeletal geometry, e.g. femoral neck-shaft angle (NSA) and anteversion angle (AVA). This study aimed to evaluate the impact of proximal femoral geometry, i.e. altered NSA and AVA, on hip JCF and femoral growth simulations. Musculoskeletal models with NSA ranging from 120° to 150° and AVA ranging from 20° to 50° were created and used to calculate muscle and hip JCF based on the gait analysis data of a typically developing child. A finite element model of a paediatric femur was created from magnetic resonance images. The finite element model was morphed to the geometries of the different musculoskeletal models and used for mechanobiological finite element analysis to predict femoral growth trends. Our findings showed that hip JCF increase with increasing NSA and AVA. Furthermore, the orientation of the hip JCF followed the orientation of the femoral neck axis. Consequently, the osteogenic index, which is a function of cartilage stresses and defines the growth rate, barely changed with altered NSA and AVA. Nevertheless, growth predictions were sensitive to the femoral geometry due to changes in the predicted growth directions. Altered NSA had a bigger impact on the growth results than altered AVA. Growth simulations based on mechanobiological principles were in agreement with reported changes in paediatric populations.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0235966PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7377390PMC
September 2020

Virtual Reality Balance Games Provide Little Muscular Challenge to Prevent Muscle Weakness in Healthy Older Adults.

Games Health J 2020 Jun;9(3):227-236

Musculoskeletal Research Unit, Department of Rehabilitation Sciences, Faculty of Kinesiology and Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium.

Muscle weakness is an important risk factor for falls in older adults. Intensity and duration of muscle activity are important determinants of exercise effectiveness in combating muscle weakness. The aim of this article was to assess the intensity and duration of muscle activity in virtual reality (VR) balance games. Thirty young and 30 healthy older adults played seven different VR balance games. Muscle activity of the vastus lateralis, vastus medialis, soleus, and gluteus medius was obtained using surface electromyography (EMG). The processed EMG signals were divided into 200-ms blocks, after which each block was categorized by its average normalized EMG activity, that is, >80%, 60%-80%, 40%-60%, or <40% of maximum voluntary contraction (MVC). We calculated the total number of blocks in each category to score intensity, as well as the maximal number of consecutive 200-ms blocks (MCBs) >40% MVC, to identify prolonged muscle activity. Muscle activity during game play was mostly <40% MVC and prolonged activation was lacking. Only the games that included more dynamic movements showed activation blocks of higher intensity and resulted in more MCBs. Our method allowed us to analyze the overall muscle activity and the distribution of activity over a trial. Although the activation levels during these VR games were low in general, we identified game elements that could potentially provide a strength training stimulus. Future research should aim to implement these elements, such that the intensity, prolonged activity, and rest are optimized to sufficiently challenge lower limb muscles in VR training.
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http://dx.doi.org/10.1089/g4h.2019.0036DOI Listing
June 2020

Functional movement assessment by means of inertial sensor technology to discriminate between movement behaviour of healthy controls and persons with knee osteoarthritis.

J Neuroeng Rehabil 2020 05 19;17(1):65. Epub 2020 May 19.

REVAL Rehabilitation Research Center, Hasselt University, Diepenbeek, Belgium.

Background: Apart from biomechanical alterations in movement patterns, it is known that movement limitations in persons with knee osteoarthritis (PwKOA) are related to an individual's perception and belief regarding pain and disability. To gain more insights into the functional movement behaviour of PwKOA in a clinical setting, inertial sensor technology can be applied. This study first aims to evaluate the ability of inertial sensors to discriminate between healthy controls (HC) and PwKOA. Secondly, this study aims to determine the relationship between movement behaviour, pain-related factors and disability scores.

Methods: Twelve HC and 19 PwKOA were included. Five repetitions of six functional movement tasks (walking, forward lunge, sideward lunge, ascent and descent stairs, single leg squat and sit-to-stand) were simultaneously recorded by the inertial sensor system and a camera-based motion analysis system. Statistically significant differences in angular waveforms of the trunk, pelvis and lower limb joints between HC and PwKOA were determined using one-dimensional statistical parametric mapping (SPM1D). The Knee injury and Osteoarthritis Outcome Score and TAMPA scale for Kinesiophobia were used to evaluate the relationship between discriminating joint motion, pain-related factors and disability using spearman's correlation coefficients.

Results: PwKOA had significantly less trunk rotation, internal pelvis rotation and knee flexion ROM during walking. Additionally, the reduced knee flexion (i.e. at the end of the stance phase and swing phase) was related to increased level of perceived pain. During the sideward lunge, PwKOA had significantly less knee flexion, ankle plantarflexion and hip abduction. This decreased hip abduction (i.e. during stance) was related to higher fear of movement. Finally, PwKOA had significantly less knee flexion during the forward lunge, single leg squat and during ascent and descent stairs. No significant correlations were observed with disability.

Conclusions: Inertial sensors were able to discriminate between movement characteristics of PwKOA and HC. Additionally, significant relationships were found between joint motion, perceived pain and fear of movement. Since inertial sensors can be used outside the laboratory setting, these results are promising as they indicate the ability to evaluate movement deviations. Further research is required to enable measurements of small movement deviations in clinically relevant tasks.
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http://dx.doi.org/10.1186/s12984-020-00694-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236325PMC
May 2020

A Machine Learning Approach to Estimate Hip and Knee Joint Loading Using a Mobile Phone-Embedded IMU.

Front Bioeng Biotechnol 2020 15;8:320. Epub 2020 Apr 15.

Department of Computer Science, KU Leuven, Leuven, Belgium.

Hip osteoarthritis patients exhibit changes in kinematics and kinetics that affect joint loading. Monitoring this load can provide valuable information to clinicians. For example, a patient's joint loading measured across different activities can be used to determine the amount of exercise that the patient needs to complete each day. Unfortunately, current methods for measuring joint loading require a lab environment which most clinicians do not have access to. This study explores employing machine learning to construct a model that can estimate joint loading based on sensor data obtained solely from a mobile phone. In order to learn such a model, we collected a dataset from 10 patients with hip osteoarthritis who performed multiple repetitions of nine different exercises. During each repetition, we simultaneously recorded 3D motion capture data, ground reaction force data, and the inertial measurement unit data from a mobile phone attached to the patient's hip. The 3D motion and ground reaction force data were used to compute the ground truth joint loading using musculoskeletal modeling. Our goal is to estimate the ground truth loading value using only the data captured by the sensors of the mobile phone. We propose a machine learning pipeline for learning such a model based on the recordings of a phone's accelerometer and gyroscope. When evaluated for an unseen patient, the proposed pipeline achieves a mean absolute error of 29% for the left hip and 36% for the right hip. While our approach is a step in the direction of using a minimal number of sensors to estimate joint loading outside the lab, developing a tool that is accurate enough to be applicable in a clinical context still remains an open challenge. It may be necessary to use sensors at more than one location in order to obtain better estimates.
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http://dx.doi.org/10.3389/fbioe.2020.00320DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7174587PMC
April 2020

Use of Computational Modeling to Study Joint Degeneration: A Review.

Front Bioeng Biotechnol 2020 28;8:93. Epub 2020 Feb 28.

Prometheus, Division of Skeletal Tissue Engineering, KU Leuven, Leuven, Belgium.

Osteoarthritis (OA), a degenerative joint disease, is the most common chronic condition of the joints, which cannot be prevented effectively. Computational modeling of joint degradation allows to estimate the patient-specific progression of OA, which can aid clinicians to estimate the most suitable time window for surgical intervention in osteoarthritic patients. This paper gives an overview of the different approaches used to model different aspects of joint degeneration, thereby focusing mostly on the knee joint. The paper starts by discussing how OA affects the different components of the joint and how these are accounted for in the models. Subsequently, it discusses the different modeling approaches that can be used to answer questions related to OA etiology, progression and treatment. These models are ordered based on their underlying assumptions and technologies: musculoskeletal models, Finite Element models, (gene) regulatory models, multiscale models and data-driven models (artificial intelligence/machine learning). Finally, it is concluded that in the future, efforts should be made to integrate the different modeling techniques into a more robust computational framework that should not only be efficient to predict OA progression but also easily allow a patient's individualized risk assessment as screening tool for use in clinical practice.
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http://dx.doi.org/10.3389/fbioe.2020.00093DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7058554PMC
February 2020

Physics-Based Simulations to Predict the Differential Effects of Motor Control and Musculoskeletal Deficits on Gait Dysfunction in Cerebral Palsy: A Retrospective Case Study.

Front Hum Neurosci 2020 18;14:40. Epub 2020 Feb 18.

Department of Movement Sciences, KU Leuven, Leuven, Belgium.

Physics-based simulations of walking have the theoretical potential to support clinical decision-making by predicting the functional outcome of treatments in terms of walking performance. Yet before using such simulations in clinical practice, their ability to identify the main treatment targets in specific patients needs to be demonstrated. In this study, we generated predictive simulations of walking with a medical imaging based neuro-musculoskeletal model of a child with cerebral palsy presenting crouch gait. We explored the influence of altered muscle-tendon properties, reduced neuromuscular control complexity, and spasticity on gait dysfunction in terms of joint kinematics, kinetics, muscle activity, and metabolic cost of transport. We modeled altered muscle-tendon properties by personalizing Hill-type muscle-tendon parameters based on data collected during functional movements, simpler neuromuscular control by reducing the number of independent muscle synergies, and spasticity through delayed muscle activity feedback from muscle force and force rate. Our simulations revealed that, in the presence of aberrant musculoskeletal geometries, altered muscle-tendon properties rather than reduced neuromuscular control complexity and spasticity were the primary cause of the crouch gait pattern observed for this child, which is in agreement with the clinical examination. These results suggest that muscle-tendon properties should be the primary target of interventions aiming to restore an upright gait pattern for this child. This suggestion is in line with the gait analysis following muscle-tendon property and bone deformity corrections. Future work should extend this single case analysis to more patients in order to validate the ability of our physics-based simulations to capture the gait patterns of individual patients pre- and post-treatment. Such validation would open the door for identifying targeted treatment strategies with the aim of designing optimized interventions for neuro-musculoskeletal disorders.
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http://dx.doi.org/10.3389/fnhum.2020.00040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7040166PMC
February 2020

Pre-treatment EMG can be used to model post-treatment muscle coordination during walking in children with cerebral palsy.

PLoS One 2020 12;15(2):e0228851. Epub 2020 Feb 12.

Department of Movement Sciences, KU Leuven, Leuven, Belgium.

When treating children with Cerebral Palsy (CP), computational simulations based on musculoskeletal models have a great potential in assisting the clinical decision-making process towards the most promising treatments. In particular, predictive simulations could be used to predict and compare the functional outcome of a series of candidate interventions. In order to be able to benefit from these predictive simulations however, it is important to know how much information about the post-treatment patient's motor control could be gathered from data available before the intervention. Within this paper, we quantified how much of the muscle activity measured after a treatment could be explained by subject-specific muscle synergies computed from EMG data collected before the intervention. We also investigated whether generic synergies could be used, in case no EMG data is available when running predictive simulations, to reproduce both pre- and post-treatment muscle activity in children with CP. Subject-specific synergies proved to be a good indicator of the patient's post-treatment motor control, explaining on average more than 85% of the post-treatment muscle activity, compared to an average of 94% when applied to the original pre-treatment data. Generic synergies explained 84% of the pre-treatment and 83% of the post-treatment muscle activity on average, but performed relatively well for patients with low selective motor control and poorly in patients with more selectivity. Our results suggest that subject-specific muscle synergies computed from pre-treatment EMG data could be used with confidence to represent the post-treatment motor control of children with CP during walking. In addition, when performing simulations involving patients with a low selective motor control, generic synergies could be a valid alternative.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0228851PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7015404PMC
May 2020

Automated quantification of glenoid bone defects using 3-dimensional measurements.

J Shoulder Elbow Surg 2020 May 23;29(5):1050-1058. Epub 2020 Jan 23.

Biomechanics Section, KU Leuven, Leuven, Belgium.

Background: Assessment of glenoid bone defects is important to select the optimal glenoid component design during shoulder arthroplasty planning and implantation. This study presents a fully automated method to describe glenoid bone loss using 3-dimensional measurements without the need for a healthy contralateral reference scapula.

Methods: The native shape of the glenoid is reconstructed by fitting a statistical shape model (SSM) of the scapula. The total vault loss percentage, local vault loss percentages, defect depth, defect area percentage, and subluxation distance and region are computed based on a comparison of the reconstructed and eroded glenoids. The method is evaluated by comparing its results with a contralateral bone-based reconstruction approach in a data set of 34 scapula and humerus pairs with unilateral glenoid bone defects.

Results: The SSM-based defect measurements deviated from the contralateral bone-based measurements with mean absolute differences of 5.5% in the total vault loss percentage, 4.5% to 8.0% in the local vault loss percentages, 1.9 mm in the defect depth, 14.8% in the defect area percentage, and 1.6 mm in the subluxation distance. The SSM-based method was statistically equivalent to the contralateral bone-based method for all parameters except the defect area percentage.

Conclusion: The presented method is able to automatically analyze glenoid bone defects using 3-dimensional measurements without the need for a healthy contralateral bone.
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http://dx.doi.org/10.1016/j.jse.2019.10.007DOI Listing
May 2020

Does a novel exergame challenge balance and activate muscles more than existing off-the-shelf exergames?

J Neuroeng Rehabil 2020 01 15;17(1). Epub 2020 Jan 15.

KU Leuven (Faculteit bewegings- en revalidatiewetenschappen), Leuven, Belgium.

Background: Novel balance-targeting exergames controlled with off-the-shelf hardware, were developed based on current recommendations for balance training in healthy older adults and documented shortcomings of existing games. The aim of this study was to explore the feasibility of these novel exergames as training tool for elderly and, more specifically whether these games can elicit more challenging weight shifts and higher levels of muscle activity compared to existing off-the-shelf exergames. Furthermore, the motivational pull in these new games was studied.

Methods: Sixteen healthy older adults were recruited to play the novel games and two reference games that were found to be the most challenging ones in terms of weight shifts or muscle activity in previous studies. Weight shifts were expressed relative to participants' Functional Limits of Stability (FLOS). Muscular challenge of the games was quantified by dividing the signal into 200 ms blocks and determining the average muscle activity within these blocks. The muscle activity was normalized to maximal voluntary contractions (MVC) to categorize the blocks in zones of < 40, 40-60, 60-80 and > 80% MVC. Subsequently, the number of blocks per intensity level and the number of consecutive blocks above 40% were determined. Motivation to play the games was assessed using the Intrinsic Motivation Inventory (IMI) and scores between the games were analyzed using Generalized Estimated Equations (GEE).

Results: The novel exergames successfully elicited center of mass (COM) displacements with medians of around 80% of FLOS or higher for all directions. Furthermore, the COM displacements in the novel games were larger for each direction than in the reference games, although for one game the sideward left direction reached significance only at the third trial. Compared to the existing games, longer blocks of muscle activation above 40% MVC were found, but overall intensity remained low. IMI scores were high on all subscales, indicating that older adults experienced the games as motivating.

Conclusion: We conclude that affordable hardware can be used to create challenging and enjoyable balance training programs using exergames. The exergames that were successful in eliciting challenging weight shifts and muscle activity should now be further studied in longitudinal randomized controlled interventions, to assess effects on balance, muscle strength and eventually fall risk in healthy older adults.
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http://dx.doi.org/10.1186/s12984-019-0628-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6961365PMC
January 2020

The Transverse Gravitational Deviation Index, a Novel Gravity Line-Related Spinal Parameter, Relates to Balance Control and Health-Related Quality of Life in Adults With Spinal Deformity.

Spine (Phila Pa 1976) 2020 Jan;45(1):E25-E36

Department of Development and Regeneration, Institute for Orthopaedic Research and Training (IORT), KU Leuven, Belgium.

Study Design: Prospective cross-sectional case-control study design.

Objective: This study aims to analyze the relation between balance control as well as health-related quality of life (HRQOL) in patients with adult spinal deformity (ASD), with a novel gravity line (GL)-related 3D spinal alignment parameter, the transverse gravitational deviation index (TGDI), defined to quantify the transverse plane position of any vertebra with respect to the GL.

Summary Of Background Data: Demographic data and balance control have both been identified as important determinants of HRQOL in ASD patients during a preoperative setting. Therefore, a better understanding of the relation between spinal alignment and balance is required.

Methods: After informed consent, 15 asymptomatic healthy volunteers (mean age 60.1 ± 11.6 years old) and 55 ASD patients (mean age 63.5 ± 10.1 years old) were included. Relation between performance on BESTest as well as core outcome measures index (COMI) with spinopelvic alignment was explored using General Linear Modeling (GLM). A P-value ≤0.05 was considered statistically significant.

Results: The L3 TGDI was identified to relate to balance control in the total ASD population after correction for confounding demographic factors (P = 0.001; adjusted R = 0.500) and explained 19% of the observed variance in balance performance. In addition, COMI is related to L3 TGDI in a subgroup of ASD patients with combined coronal and sagittal malalignment of L3 (P = 0.027; slope B = 0.047), despite significant influence of age (P = 0.020).

Conclusion: In ASD patients with a combined coronal and sagittal malalignment of the L3 vertebra, both the level of balance impairment as well as HRQOL are related to the distance component of the L3 TGDI, that is, the offset between the center of the L3 vertebral body and the GL in the transverse plane.

Level Of Evidence: 2.
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http://dx.doi.org/10.1097/BRS.0000000000003301DOI Listing
January 2020

Implementation of physiological functional spinal units in a rigid-body model of the thoracolumbar spine.

J Biomech 2020 01 22;98:109437. Epub 2019 Oct 22.

Department of Movement Sciences, KU Leuven, Leuven, Belgium.

Most of the current rigid-body models of the complete thoracolumbar spine do not properly model the intervertebral joint as the highly nonlinear stiffness is not incorporated comprehensively and the effects of compressive load on stiffness is commonly being neglected. Based on published in vitro data of individual intervertebral joint flexibility, multi-level six degree-of-freedom nonlinear stiffness of functional spinal units was modelled and incorporated in a rigid-body model of the thoracolumbar spine. To estimate physiological in vivo conditions of the entire spine, stiffening effects caused by directly applied compressive loads, and contributions to mono-segmental stiffness from the rib cage as well as multi-segmental interactions in the thoracic spine were analysed and implemented. Forward dynamic simulations were performed to simulate in vitro tests that measured the load-displacement response of the spine under various loading conditions. The predicted kinematic responses of the model were in agreement with in vitro measurements, with correlations between simulated and measured segmental displacements varying between 0.66 and 0.97 (p < 0.05) and average deviations below 1.6°. Coupling relationships were found between lateral bending and axial rotation. Under compressive loads, the model behaved stiffer and showed a decreased range of motion: The flexion/extension response of the full thoracolumbar spine under compressive loads up to 800 N was found to strongly correlate with the literature (r = 0.99, p < 0.0001). The implementation of physiological functional spinal units with nonlinear stiffness properties into rigid-body models can enhance accuracy of biomechanical simulations, and enable detailed analysis of spinal kinematics under complex loading conditions seen in vivo.
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http://dx.doi.org/10.1016/j.jbiomech.2019.109437DOI Listing
January 2020

Inverse dynamic estimates of muscle recruitment and joint contact forces are more realistic when minimizing muscle activity rather than metabolic energy or contact forces.

Gait Posture 2019 10 9;74:223-230. Epub 2019 Sep 9.

Department of Movement Sciences, KU Leuven, Leuven, Belgium. Electronic address:

Background: Assessment of contact forces is essential for a better understanding of mechanical factors affecting progression of osteoarthritis. Since contact forces cannot be measured non-invasively, computer simulations are often used to assess joint loading. Contact forces are to a large extent determined by muscle forces. These muscle forces are computed using optimization techniques that solve the muscle redundancy problem by assuming that muscles are coordinated in a way that optimizes performance (e.g., minimizes muscle activity or metabolic energy). However, it is unclear which of the many proposed performance criteria best describes muscle coordination.

Research Question: Which performance criterion best describes muscle recruitment patterns and knee contact forces recorded using electromyography (EMG) and load cell instrumented prostheses?.

Methods: We solved the muscle redundancy problem based on six different groups of performance criteria: muscle activations, volume-scaled activations, forces, stresses, metabolic energy, and joint contact forces. Computed muscle excitations and knee contact forces during over-ground walking were validated against recorded EMG signals and measured contact forces for four subjects with instrumented knee prostheses in the "Grand Challenge Competition to Predict in Vivo Knee Loads" dataset.

Results: Performance criteria based on either stress or muscle activation (either unscaled or scaled by muscle volume), both to a power of 3 or 4, resulted in the best agreement between measured and simulated values. These performance criteria outperformed all other criteria in terms of agreement between simulated muscle excitations and EMG, whereas good agreement between measured and predicted contact forces was also observed for minimization of contact forces and metabolic energy.

Significance: Given the large differences in accuracy obtained with different performance criteria (e.g., root mean square errors of contact forces differed up to 0.45 body weight), the results of our study are important to improve the validity of in silico assessment of joint loading.
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http://dx.doi.org/10.1016/j.gaitpost.2019.08.019DOI Listing
October 2019
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