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Musculoskeletal simulations are used to estimate muscle-tendon and joint contact forces (JCF). Personalizing the model's femoral geometry has been shown to improve the accuracy of JCF calculations. It is, however, unknown if the personalized geometry improves the agreement between estimated muscle activations and experimentally measured electromyography (EMG) signals. Does personalizing the musculoskeletal geometry improve the agreement between estimated muscle activations and EMG signals in terms of timing? We retrospectively analysed data from Bosmans et al. [5] , which included three-dimensional motion capture data, EMG signals of eight lower limb muscles on each leg, and magnetic resonance imaging (MRI) data from seven children with cerebral palsy. For each patient we created a generic-scaled model and MRI-based model, which accounted for the subject-specific musculoskeletal geometry. We calculated muscle activations, muscle-tendon forces and JCF. Muscle activations were compared to the EMG signals using coefficient of determination and cosines similarity. MRI-based models altered the magnitude of muscle activations and had a large impact on JCF but did not change the muscle activations profiles and therefore did not improve the agreement with EMG signals. MRI-based models do not alter the shape of muscle activations. Hence, if detailed muscle activations are a desired output of the simulations, EMG-informed modeling approaches should be used for musculoskeletal simulation in children with cerebral palsy. Furthermore, our study highlighted that altered JCF does not necessarily mean accurate muscle activations. To improve patient-specific simulations, future work should focus on developing methods to estimate cost functions representative for the neural control of children with cerebral palsy. • We compared generic with medical imaging-based musculoskeletal models. • MRI-based models do not improve the estimation of muscle activation. • MRI-based models have a big impact on joint contact forces. • Altered joint contact forces do not necessarily mean accurate muscle activations. [ABSTRACT FROM AUTHOR]

Neuromusculoskeletal models are a powerful tool to investigate the internal biomechanics of an individual. However, commonly used neuromusculoskeletal models are generated via linear scaling of generic templates derived from elderly adult anatomies and poorly represent a child, let alone children with a neuromuscular disorder whose musculoskeletal structures and muscle activation patterns are profoundly altered. Model personalization can capture abnormalities and appropriately describe the underlying (altered) biomechanics of an individual. In this work, we explored the effect of six different levels of neuromusculoskeletal model personalization on estimates of muscle forces and knee joint contact forces to tease out the importance of model personalization for normal and abnormal musculoskeletal structures and muscle activation patterns. For six children, with and without cerebral palsy, generic scaled models were developed and progressively personalized by (1) tuning and calibrating musculotendon units' parameters, (2) implementing an electromyogram-assisted approach to synthesize muscle activations, and (3) replacing generic anatomies with image-based bony geometries, and physiologically and physically plausible muscle kinematics. Biomechanical simulations of gait were performed in the OpenSim and CEINMS software on ten overground walking trials per participant. A mixed-ANOVA test, with Bonferroni corrections, was conducted to compare all models' estimates. The model with the highest level of personalization produced the most physiologically plausible estimates. Model personalization is crucial to produce physiologically plausible estimates of internal biomechanical quantities. In particular, personalization of musculoskeletal anatomy and muscle activation patterns had the largest effect overall. Increased research efforts are needed to ease the creation of personalized neuromusculoskeletal models. [ABSTRACT FROM AUTHOR]

This review article provides an overview of techniques used to determine human knee joint contact forces during squatting. The main two approaches are experimental and theoretical. Thigh calf contact has a significant effect on knee forces and should not be neglected. In this study, data were searched electronically and organized by techniques to find knee joint contact force during squatting theoretically and experimentally. There was a large variation in peak tibiofemoral (CV = 0.45) and patellofemoral (CV = 0.38) contact forces predicted theoretically. However, very little variation was observed between peak tibiofemoral contact forces (CV = 0.12) measured in vivo experimentally but measured knee joint force is available up to a limited knee flexion angle. There was a reduction in knee joint contact forces due to thigh calf contact. Literature of knee joint contact force prediction theoretically during squatting incorporating thigh calf contact force is very limited. [ABSTRACT FROM AUTHOR]

Total knee replacement (TKR) is one of the most performed orthopedic surgeries to treat knee joint diseases in the elderly population. Although the survivorship of knee implants may extend beyond two decades, the poor outcome rate remains considerable. A recent computational approach used to better understand failure modes and improve TKR outcomes is based on the combination of musculoskeletal (MSK) and finite element models. This combined multiscale modeling approach is a promising strategy in the field of computational biomechanics; however, some critical aspects need to be investigated. In particular, the identification and quantification of the uncertainties related to the boundary conditions used as inputs to the finite element model due to a different definition of the MSK model are crucial. Therefore, the aim of this study is to investigate this problem, which is relevant for the model credibility assessment process. Three different generic MSK models available in the OpenSim platform were used to simulate gait, based on the experimental data from the fifth edition of the “Grand Challenge Competitions to Predict in vivo Knee Loads.” The outputs of the MSK analyses were compared in terms of relative kinematics of the knee implant components and joint reaction (JR) forces and moments acting on the tibial insert. Additionally, the estimated knee JRs were compared with those measured by the instrumented knee implant so that the “global goodness of fit” was quantified for each model. Our results indicated that the different kinematic definitions of the knee joint and the muscle model implemented in the different MSK models influenced both the motion and the load history of the artificial joint. This study demonstrates the importance of examining the influence of the model assumptions on the output results and represents the first step for future studies that will investigate how the uncertainties in the MSK models propagate on disease-specific finite element model results.

The assessment of knee or hip joint loading by external joint moments is mainly used to draw conclusions on clinical decision making. However, the correlation between internal and external loads has not been systematically analyzed. This systematic review aims, therefore, to clarify the relationship between external and internal joint loading measures during gait. A systematic database search was performed to identify appropriate studies for inclusion. In total, 4,554 articles were identified, while 17 articles were finally included in data extraction. External joint loading parameters were calculated using the inverse dynamics approach and internal joint loading parameters by musculoskeletal modeling or instrumented prosthesis. It was found that the medial and total knee joint contact forces as well as hip joint contact forces in the first half of stance can be well predicted using external joint moments in the frontal plane, which is further improved by including the sagittal joint moment. Worse correlations were found for the peak in the second half of stance as well as for internal lateral knee joint contact forces. The estimation of external joint moments is useful for a general statement about the peak in the first half of stance or for the maximal loading. Nevertheless, when investigating diseases as valgus malalignment, the estimation of lateral knee joint contact forces is necessary for clinical decision making because external joint moments could not predict the lateral knee joint loading sufficient enough. Dependent on the clinical question, either estimating the external joint moments by inverse dynamics or internal joint contact forces by musculoskeletal modeling should be used.

Reduced external knee adduction moments in the second half of stance after total hip replacement have been reported in hip osteoarthritis patients. This reduction is thought to shift the load from the medial to the lateral knee compartment and as such increase the risk for knee osteoarthritis. The knee adduction moment is a surrogate for the load distribution between the medial and lateral compartments of the knee and not a valid measure for the tibiofemoral contact forces which are the result of externally applied forces and muscle forces. The purpose of this study was to investigate whether the distribution of the tibiofemoral contact forces over the knee compartments in unilateral hip osteoarthritis patients 1 year after receiving a primary total hip replacement differs from healthy controls. Musculoskeletal modeling on gait was performed in OpenSim using the detailed knee model of Lerner et al. (2015) for 19 patients as well as for 15 healthy controls of similar age. Knee adduction moments were calculated by the inverse dynamics analysis, medial and lateral tibiofemoral contact forces with the joint reaction force analysis. Moments and contact forces of patients and controls were compared using Statistical Parametric Mapping two-sample t-tests. Knee adduction moments and medial tibiofemoral contact forces of both the ipsi- and contralateral leg were not significantly different compared to healthy controls. The contralateral leg showed 14% higher medial tibiofemoral contact forces compared to the ipsilateral (operated) leg during the second half of stance. During the first half of stance, the lateral tibiofemoral contact force of the contralateral leg was 39% lower and the ratio 32% lower compared to healthy controls. In contrast, during the second half of stance the forces were significantly higher (39 and 26%, respectively) compared to healthy controls. The higher ratio indicates a changed distribution whereas the increased lateral tibiofemoral contact forces indicate a higher lateral knee joint loading in the contralateral leg in OA patients after total hip replacement (THR). Musculoskeletal modeling using a detailed knee model can be useful to detect differences in the load distribution between the medial and lateral knee compartment which cannot be verified with the knee adduction moment.

Cerebral palsy is a complex neuromuscular disorder that affects the sufferers in multiple different ways. Neuromusculoskeletal models are promising tools that can be used to plan patient-specific treatments for cerebral palsy. However, current neuromusculoskeletal models are typically scaled from generic adult templates that poorly represent paediatric populations. Furthermore, muscle activations are commonly computed via optimisation methods, which may not reproduce co-contraction observed in cerebral palsy. Alternatively, calibrated EMG-informed approaches within OpenSim can capture pathology-related muscle activation abnormalities, possibly enabling more feasible estimations of muscle and joint contact forces. Two identical twin brothers, aged 13, one with unilateral cerebral palsy and the other typically developing, were enrolled in the study. Four neuromusculoskeletal models with increasing subject-specificity were built in OpenSim and CEINMS combining literature findings, experimental motion capture, EMG and MR data for both participants. The physiological and biomechanical validity of each model was assessed by quantifying its ability to track experimental joint moments and muscle excitations. All developed models accurately tracked external joint moments; however EMG-informed models better tracked muscle excitations compared to neural solutions generated by static optimisation. Calibrating muscle-tendon unit parameters with EMG data allowed for more physiologically plausible joint contact forces estimates. Further scaling the maximal isometric force of muscles with MR-derived muscle volumes did not affect model predictions. Given their ability to identify atypical joint contact forces profiles and accurately reproduce experimental data, calibrated EMG-informed models should be preferred over generic models using optimisation methods in informing the management of cerebral palsy. • Personalisation of musculoskeletal models is important in studying cerebral palsy. • Electromyography data to inform models allow to capture atypical muscle activity. • Calibration of muscle-tendon unit parameters ensures physiological force estimates. • The use of medical images to scale muscle parameters may not improve model outcomes. [ABSTRACT FROM AUTHOR]

Lower extremity muscle strength training is a focus of rehabilitation following total hip arthroplasty (THA). Strength of the hip abductor muscle group is a predictor of overall function following THA. The purpose of this study was to investigate the effects of hip abductor strengthening following rehabilitation on joint contact forces (JCFs) in the lower extremity and low back during a high demand step down task. Five THA patients performed lower extremity maximum isometric strength tests and a stair descent task. Patient-specific musculoskeletal models were created in OpenSim and maximum isometric strength parameters were scaled to reproduce measured pre-operative joint torques. A pre-operative forward dynamic simulation of each patient performing the stair descent was constructed using their corresponding patient-specific model to predict JCFs at the ankle, knee, hip, and low back. The hip abductor muscles were strengthened with clinically supported increases (0–30%) above pre-operative values in a probabilistic framework to predict the effects on peak JCFs (99% confidence bounds). Simulated hip abductor strengthening resulted in lower peak JCFs relative to pre-operative for all five patients at the hip (18.9–23.8 ± 16.5%) and knee (20.5–23.8 ± 11.2%). Four of the five patients had reductions at the ankle (7.1–8.5 ± 11.3%) and low back (3.5–7.0 ± 5.3%) with one patient demonstrating no change. The reduction in JCF at the hip joint and at joints other than the hip with hip abductor strengthening demonstrates the dynamic and mechanical interdependencies of the knee, hip and spine that can be targeted in early THA rehabilitation to improve overall patient function. [ABSTRACT FROM AUTHOR]

The purpose of this study was to systematically quantify distal radioulnar joint stability with a cadaveric model, using radiographic and joint contact force measurements. Six fresh-frozen cadavers underwent sequential ulnar styloid osteotomies. Posteroanterior and lateral stress radiographs were obtained and joint contact forces and areas were measured. Posteroanterior radiographs showed a significant increase in the distal radioulnar joint gap after osteotomy of the base of the ulnar styloid. Contact force and contact area measurements were not significantly different. We conclude that fractures that involve the ulnar styloid base should be considered for operative fixation when carrying out open reduction and internal fixation of fractures of the distal radius. [ABSTRACT FROM AUTHOR]

Background: Cam-type femoroacetabular impingement (FAI) is a causative factor for hip pain and early hip osteoarthritis. Although cam FAI can alter hip joint biomechanics, it is unclear what role muscle forces play and how they affect the hip joint loading. Purpose/Hypothesis: The purpose was to examine the muscle contributions and hip contact forces in individuals with symptomatic cam FAI during level walking. Patients with symptomatic cam FAI would demonstrate different muscle and hip contact forces during gait. Study Design: Controlled laboratory study. Methods: Eighteen patients with symptomatic cam FAI were matched for age and body mass index with 18 control participants. Each participant’s walking kinematics and kinetics were recorded throughout a gait cycle (ipsilateral foot-strike to ipsilateral foot-off) by use of a motion capture system and force plates. Muscle and hip contact forces were subsequently computed by use of a musculoskeletal modeling program and static optimization methods. Results: The FAI group walked slower and with shorter steps, demonstrating reduced joint motions and moments during contralateral foot-strike, compared with the control group. The FAI group showed reduced psoas major (median, 1.1 newtons per bodyweight [N/BW]; interquartile range [IQR], 1.0-1.5 N/BW) and iliacus forces (median, 1.2 N/BW; IQR, 1.0-1.6 N/BW), during contralateral foot-strike, compared with the control group (median, 1.6 N/BW; IQR, 1.3-1.6 N/BW, P = .004; and median, 1.5 N/BW; IQR, 1.3-1.6 N/BW, P = .03, respectively), which resulted in lower hip contact forces in the anterior (P = .026), superior (P = .02), and medial directions (P = .038). The 3 vectors produced a resultant peak force at the anterosuperior aspect of the acetabulum for both groups, with the FAI group demonstrating a substantially lower magnitude. Conclusion: FAI participants altered their walking kinematics and kinetics, especially during contralateral foot-strike, as a protective mechanism, which resulted in reduced psoas major and iliacus muscle force and anterosuperior hip contact force estimations. Clinical Relevance: Limited hip mobility not only is attributed to bone-on-bone impingement, caused by cam morphology, but could be attributed to musculature as well. Not only would the psoas major and iliacus be able to protect the hip joint during flexion-extension, athletic conditioning could further strengthen core muscles for improved hip mobility and pelvic balance. [ABSTRACT FROM AUTHOR]

The generation of subject-specific musculoskeletal models of the lower limb has become a feasible task thanks to improvements in medical imaging technology and musculoskeletal modelling software. Nevertheless, clinical use of these models in paediatric applications is still limited for what concerns the estimation of muscle and joint contact forces. Aiming to improve the current state of the art, a methodology to generate highly personalized subject-specific musculoskeletal models of the lower limb based on magnetic resonance imaging (MRI) scans was codified as a step-by-step procedure and applied to data from eight juvenile individuals. The generated musculoskeletal models were used to simulate 107 gait trials using stereophotogrammetric and force platform data as input. To ensure completeness of the modelling procedure, muscles’ architecture needs to be estimated. Four methods to estimate muscles’ maximum isometric force and two methods to estimate musculotendon parameters (optimal fiber length and tendon slack length) were assessed and compared, in order to quantify their influence on the models’ output. Reported results represent the first comprehensive subject-specific model-based characterization of juvenile gait biomechanics, including profiles of joint kinematics and kinetics, muscle forces and joint contact forces. Our findings suggest that, when musculotendon parameters were linearly scaled from a reference model and the muscle force-length-velocity relationship was accounted for in the simulations, realistic knee contact forces could be estimated and these forces were not sensitive the method used to compute muscle maximum isometric force. [ABSTRACT FROM AUTHOR]

Electromechanical delay (EMD) and maximum isometric muscle force (F o M) are important parameters for joint contact force calculation with EMG-informed neuromusculoskeletal (NMS) models. These parameters can vary between tasks (EMD) and individuals (EMD and F o M), making it challenging to establish representative values. One promising approach is to personalise candidate parameters to the participant (e.g., F o M by regression equation) and then adjust all parameters within a calibration (i.e., numerical optimisation) to minimise error between corresponding pairs of experimental measures and model-predicted values. The purpose of this study was to determine whether calibration of an NMS model resulted in consistent joint contact forces, regardless of EMD value or personalisation of F o M. Hip, knee, and ankle contact forces were predicted for 28 participants using EMG-informed NMS models. Differences in joint contact forces with EMD were examined in six models, calibrated with EMD from 15 to 110 ms. Differences in joint contact forces with personalisation of F o M were examined in two models, both calibrated with the same initial EMD (50 ms), one with generic and one with personalised values for F o M. For all models, joint contact force peaks during the first and second halves of stance were extracted and compared using a repeated-measures analysis of variance. Calibrated models with EMD set between 35 and 70 ms produced similar magnitude and timing of peak joint contact forces. Compared with generic values, personalising and then calibrating F o M resulted in comparable peak contact forces at hip, but not knee or ankle, while also producing muscle-specific tensions similar to reported literature. Overall, EMD between 35 and 70 ms and personalised initial values of F o M before calibration are advised for EMG-informed NMS modelling. [ABSTRACT FROM AUTHOR]

We explored the tibiofemoral contact forces and the relative contributions of muscles and external loads to those contact forces during various gait tasks. Second, we assessed the relationships between external gait measures and contact forces. A calibrated electromyography-driven neuromusculoskeletal model estimated the tibiofemoral contact forces during walking (1.44±0.22ms(-1)), running (4.38±0.42ms(-1)) and sidestepping (3.58±0.50ms(-1)) in healthy adults (n=60, 27.3±5.4years, 1.75±0.11m, and 69.8±14.0kg). Contact forces increased from walking (∼1-2.8 BW) to running (∼3-8 BW), sidestepping had largest maximum total (8.47±1.57 BW) and lateral contact forces (4.3±1.05 BW), while running had largest maximum medial contact forces (5.1±0.95 BW). Relative muscle contributions increased across gait tasks (up to 80-90% of medial contact forces), and peaked during running for lateral contact forces (∼90%). Knee adduction moment (KAM) had weak relationships with tibiofemoral contact forces (all R(2)<0.36) and the relationships were gait task-specific. Step-wise regression of multiple external gait measures strengthened relationships (0.20

Understanding the validity of using musculoskeletal models is critical, making important to assess how model parameters affect predictions. In particular, assumptions on joint models can affect predictions from simulations of movement, and the identification of image-based joints is unavoidably affected by uncertainty that can decrease the benefits of increasing model complexity. We evaluated the effect of different lower-limb joint models on muscle and joint contact forces during four motor tasks, and assessed the sensitivity to the uncertainties in the identification of anatomical four-bar-linkage joints. Three MRI-based musculoskeletal models having different knee and ankle joint models were created and used for the purpose. Model predictions were compared against a baseline model including simpler and widely-adopted joints. In addition, a probabilistic analysis was performed by perturbing four-bar-linkage joint parameters according to their uncertainty. The differences between models depended on the motor task analyzed, and there could be marked differences at peak loading (up to 2.40 BW at the knee and 1.54 BW at the ankle), although they were rather small over the motor task cycles (up to 0.59 BW at the knee and 0.31 BW at the ankle). The model including more degrees of freedom showed more discrepancies in predicted muscle activations compared to measured muscle activity. Further, including image-based four-bar-linkages was robust to simulate walking, chair rise and stair ascent, but not stair descent (peak standard deviation of 2.66 BW), suggesting that joint model complexity should be set according to the imaging dataset available and the intended application, performing sensitivity analyses. [ABSTRACT FROM AUTHOR]

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Introduction: The accuracy of muscle and joint contact forces (JCF) estimated from dynamic musculoskeletal simulations is dependent upon the experimental kinematic data used as inputs. Subcutaneous adipose tissue makes the measurement of representative kinematics from motion analysis particularly challenging in overweight and obese individuals. Purpose: The purpose of this study was to develop an obesity-specific kinematic marker set/methodology that accounted for subcutaneous adiposity and to determine the effect of using such a methodology to estimate muscle and JCF in moderately obese adults. Methods: Experimental kinematic data from both the obesity-specific methodology, which utilized digitized markers and marker clusters, and a modified Helen Hayes marker methodology were used to generate musculoskeletal simulations of walking in obese and nonobese adults. Results: Good agreement was found in lower-extremity kinematics, muscle forces, and hip and knee JCF between the two marker set methodologies in the nonobese participants, demonstrating the ability for the obesity-specific marker set/methodology to replicate lower-extremity kinematics. In the obese group, marker set methodology had a significant effect on lower-extremity kinematics, muscle forces, and hip and knee JCF, with the Helen Hayes marker set methodology yielding larger muscle and first peak hip and knee contact forces compared with the estimates derived when using the obesity-specific marker set/methodology. Conclusion: This study demonstrates the need for biomechanists to account for subcutaneous adiposity during kinematic data collection and proposes a feasible solution that may improve the accuracy of musculoskeletal simulations in overweight and obese people. [ABSTRACT FROM AUTHOR]

The weakness of hip abductor muscles is related to lower-limb joint osteoarthritis, and joint overloading may increase the risk for disease progression. The relationship between muscle strength, structural joint deterioration and joint loading makes the latter an important parameter in the study of onset and followup of the disease. Since the relationship between hip abductor weakness and joint loading still remains an open question, the purpose of this study was to adopt a probabilistic modeling approach to give insights into how the weakness of hip abductor muscles, in the extent to which normal gait could be unaltered, affects ipsilateral joint contact forces. A generic musculoskeletal model was scaled to each healthy subject included in the study, and the maximum force-generating capacity of each hip abductor muscle in the model was perturbed to evaluate how all physiologically possible configurations of hip abductor weakness affected the joint contact forces during walking. In general, the muscular system was able to compensate for abductor weakness. The reduced force-generating capacity of the abductor muscles affected joint contact forces to a mild extent, w i th 50th percentile mean differences up to 0.5 BW (maximum 1.7 BW). There were greater increases in the peak knee joint loads than in loads at the hip or ankle. Gluteus medius, particularly the anterior compartment, was the abductor muscle with the most influence on hip and knee loads. Further studies should assess if these increases in joint loading may affect initiation and progression of osteoarthritis. [ABSTRACT FROM AUTHOR]

Abstract: Background: The internal joint contact forces experienced at the lower limb have been frequently studied in activities of daily living and rehabilitation activities. In contrast, the forces experienced during more dynamic activities are not well understood, and those studies that do exist suggest very high degrees of joint loading. Methods: In this study a biomechanical model of the right lower limb was used to calculate the internal joint forces experienced by the lower limb during vertical jumping, landing and push jerking (an explosive exercise derived from the sport of Olympic weightlifting), with a particular emphasis on the forces experienced by the knee. Findings: The knee experienced mean peak loadings of 2.4–4.6×body weight at the patellofemoral joint, 6.9–9.0×body weight at the tibiofemoral joint, 0.3–1.4×body weight anterior tibial shear and 1.0–3.1×body weight posterior tibial shear. The hip experienced a mean peak loading of 5.5–8.4×body weight and the ankle 8.9–10.0×body weight. Interpretation: The magnitudes of the total (resultant) joint contact forces at the patellofemoral joint, tibiofemoral joint and hip are greater than those reported in activities of daily living and less dynamic rehabilitation exercises. The information in this study is of importance for medical professionals, coaches and biomedical researchers in improving the understanding of acute and chronic injuries, understanding the performance of prosthetic implants and materials, evaluating the appropriateness of jumping and weightlifting for patient populations and informing the training programmes of healthy populations. [Copyright &y& Elsevier]

This paper presents a new method to estimate both musculo-tendon forces and detailed joint reactions during gait, using an original 3D lower limb musculo-skeletal model with 5 degrees of freedom: spherical joint at the hip and parallel mechanisms at both knee and ankle. This can be realized by employing a typical set of natural coordinates into a three-steps process. First, the kinematic constraints associated with the kinematic models are applied through a global optimization method on the marker-based kinematics. Consistent time derivatives of the positions are computed by projecting the velocities and accelerations in the null space of the Jacobian matrix. Then, a Lagrangian formulation of the equations of motion is proposed, introducing Lagrange multipliers and allowing a straight access to the musculo-tendon forces. Thanks to a parameter reduction procedure, the Lagrange multipliers are cancelled and the musculo-tendon forces can be computed directly, using a static optimization algorithm with a typical cost function. Finally, the equations of motion are rewritten with the Lagrange multipliers to compute detailed joint reactions (since they represent directly joint contact and ligament forces). Results show that the estimated musculo-tendon forces are consistent with measured EMG signals. Moreover, the use of 'anatomically' consistent kinematic models allows computing total joint reaction at hip joint and detailed joint reactions at both knee and ankle joints that are temporally consistent with the forces measured on the subject (i.e., knee joint contact forces) and the forces published in the literature (i.e., hip joint contact forces). Next step will be to optimize simultaneously musculo-tendon forces and joint reactions to investigate and understand the interactions acting into the musculo-skeletal system during gait. [ABSTRACT FROM AUTHOR]

Musculoskeletal models have the potential to evolve into sensitive clinical tools that provide relevant therapeutic guidance. A key impediment to this is the lack of understanding as to the function of such models. In order to improve this it is useful to recognise that musculoskeletal modelling is the mathematical description of musculoskeletal movement – a process that involves the construction and solution of equations of motion. These equations are derived from standard mechanical considerations and the mathematical representation of anatomy. The fidelity of musculoskeletal models is highly dependent on the assumption that such representations also describe the function of the musculoskeletal geometry. In addition, it is important to understand the sensitivity of such representations to patient-specific variations in anatomy. The exploration of these twin considerations will be fundamental to the creation of musculoskeletal modelling tools with clinical relevance and a systematic enquiry of these key parameters is recommended. [ABSTRACT FROM AUTHOR]

Contemporary musculoskeletal modelling research is based upon the assumption that such models will evolve into clinical tools that can be used to guide therapeutic interventions. However, there are a number of questions that must be addressed before this becomes a reality. At its heart, musculoskeletal modelling is a process of formulating and then solving the equations of motion that describe the movement of body segments. Both of these steps are challenging. This article argues that traditional approaches to musculoskeletal modelling have been heavily influenced by the need to simplify this process (and in particular the solution process), and that this has to some degree resulted in approaches that are contrary to the principles of classical mechanics. It is suggested that future work is required to understand how these simplifications affect the outputs of musculoskeletal modelling studies. Equally, to increase their clinical relevance, the models of the future should adhere more closely to the classical mechanics on which they are based. [ABSTRACT FROM AUTHOR]

Abstract: Chronic shoulder impingement is a common problem for manual wheelchair users. The loading associated with performing manual wheelchair activities of daily living is substantial and often at a high frequency. Musculoskeletal modeling and optimization techniques can be used to estimate the joint contact forces occurring at the shoulder to assess the soft tissue loading during an activity and to possibly identify activities and strategies that place manual wheelchair users at risk for shoulder injuries. The purpose of this study was to validate an upper extremity musculoskeletal model and apply the model to wheelchair activities for analysis of the estimated joint contact forces. Upper extremity kinematics and handrim wheelchair kinetics were measured over three conditions: level propulsion, ramp propulsion, and a weight relief lift. The experimental data were used as input to a subject-specific musculoskeletal model utilizing optimization to predict joint contact forces of the shoulder during all conditions. The model was validated using a mean absolute error calculation. Model results confirmed that ramp propulsion and weight relief lifts place the shoulder under significantly higher joint contact loading than level propulsion. In addition, they exhibit large superior contact forces that could contribute to impingement. This study highlights the potential impingement risk associated with both the ramp and weight relief lift activities. Level propulsion was shown to have a low relative risk of causing injury, but with consideration of the frequency with which propulsion is performed, this observation is not conclusive. [Copyright &y& Elsevier]

The aim of this study was to use a biomechanical model of the shoulder to examine the characteristics of two concepts of reverse anatomy implant; those that preserve the natural glenohumeral centre such as the Bayley-Walker (B-W) replacement and those medializing it such as Delta. A biomechanical model of the shoulder was used to evaluate the biomechanical characteristics of these prostheses. The moment arms of the shoulder muscles were predicted for the implanted models over a wide workspace and were compared to those of natural anatomy. The deltoid muscle moment arms through almost all of the range of motion in the Delta model were greatest. As a result the shoulder joint contact force was decreased for this implant. Furthermore, although the B-W model predicted similar moment arms to natural anatomy, the contact force decreased owing to change in the joint constraints. Finally, it was concluded that the reverse anatomy can compensate for loss of rotator cuff muscles in terms of joint stability, yet the shoulder function depends on the individual's musculature. [ABSTRACT FROM AUTHOR]

Abstract: Background: Femoral stress fractures tend to occur at the neck, medial proximal-shaft, and distal-shaft. The purpose of this study was to determine the internal femoral forces and moments during running. It was expected that larger loads would occur at these common sites of femoral stress fracture. Methods: Ten subjects ran at their preferred running speed over a force platform while motion capture data were collected. Static optimization in conjunction with a SIMM musculoskeletal model was used to determine individual muscle forces of the lower extremity. Joint contact forces were determined, and a quasi-static approach was used to calculate internal forces and moments along a centroid path through the femur. Findings: The largest mean peak loads were observed at the following regions: anterior–posterior shear, 7.47 bodyweights (BW) at the distal-shaft (posteriorly directed); axial force, 11.40BW at the distal-shaft (compression); medial–lateral shear, 3.75BW at the neck (medially directed); anterior–posterior moment, 0.42BWm at the proximal-shaft (medial surface compression); torsional moment, 0.20BWm at the distal-shaft (external rotation); medial–lateral moment, 0.44BWm at the distal-shaft (anterior surface compression). Interpretation: The mechanical loading environment of the femur during running appears to explain well the redundancy in femoral stress fracture location. We observed the largest internal loads at the three femoral sites prone to stress fracture. [Copyright &y& Elsevier]

Abstract: Axial tibiofemoral joint contact forces were non-invasively determined for two high range of motion (high flexion) squatting activities. An electromagnetic motion tracking system and a non-conductive force platform were used to collect kinematic and kinetic data. An innovative scaling method was used to model subject-specific muscle group moment arms. One subject attained a peak axial tibiofemoral joint contact force of 49.7N/kg during squatting at 149.9° knee flexion. Average joint angles and average axial joint contact forces were calculated for each of the activities in order to facilitate a comparison with stair climbing data. Compared to stair climbing, the maximum average joint contact forces during the squatting activities occurred at significantly higher flexion angles (p <0.05.) The relative simplicity of the method makes it useful for application to large subject groups from diverse regions. The results of this study can be applied to the diagnosis and treatment of pathologies, and to the development of high range of motion (ROM) knee replacements. [Copyright &y& Elsevier]

Surgical intervention of the knee joint routinely endeavors to recreate a physiologically normal joint loading environment. The loading conditions resulting from osteotomies, fracture treatment, ligament replacements, and arthroplasties of the knee are considered to have an impact on the long term clinical outcome; however, knowledge regarding in vivo loading conditions is limited. Using a previously validated musculoskeletal lower limb model, we predicted the tibio-femoral joint contact forces that occur in the human knee during the common daily activities of walking and stair climbing. The average resultant peak force during walking was 3.1 times body weight (BW) across four total hip arthroplasty patients. Inter-individual variations proved larger than the variation of forces for each patient repeating the same task. Forces through the knee were considerably larger during stair climbing than during walking: the average resultant peak force during stair climbing was 5.4 BW although peaks of up to 6.2 BW were calculated for one particular patient. Average anteroposterior peak shear components of 0.6 BW were determined during walking and 1.3 BW during stair climbing. These results confirm both the joint contact forces reported in the literature and the importance of muscular activity in creating high forces across the joint. The magnitudes of these forces, specifically in shear, have implications for all forms of surgical intervention in the knee. The data demonstrate that high contact and shear forces are generated during weight bearing combined with knee flexion angles greater than approximately 15°. Clinically, the conditions that produce these larger contact forces should be avoided during post-operative rehabilitation. [Copyright &y& Elsevier]

Background and aim. High tibial osteotomies attempt to recreate physiologically normal joint loading. Previous studies have discussed the influence of mal-alignment on the distribution of static loads to the medial and lateral compartments of the knee. The aim of this study was to determine the influence of mal-alignment on the tibio-femoral loading conditions during dynamic activities. Material and methods. Using a musculo-skeletal model of the lower limb, which had been previously validated with in vivo data, in this study we modified the alignment of the knee in four patients, from a normal position to the extremes of 8° valgus and 10° varus mal-alignment. The resulting tibio-femoral joint contact forces were examined while patients were walking and stair climbing. Results. Varying the mal-alignment resulted in a highly individual response in joint loads. Deviations from the normal alignment produced an increase in loading, with valgus generating a more rapid increase in loading than a varus deformity of the same amount. Varus deformities of 10° resulted in increases in peak contact force from an average of 3.3-times bodyweight (BW) up to a peak of 7.4 BW (+45% to +114%) while patients were walking, whilst increases of 15% up to 35% were determined for stair climbing. Increases of up to 140% were calculated at 8° valgus during walking and up to 53% for stair climbing. Conclusion. This study demonstrated a clear dependence of the individual joint loads on axial knee alignment. Based on the sensitivity of joint loading to valgus mal-alignment, more than 3° of over-correction of a varus deformity to valgus should be carefully reconsidered. [ABSTRACT FROM AUTHOR]

Musculoskeletal modelling is a common means by which to non-invasively analyse movement. Such models have largely been used to observe function in both healthy and patient populations. However, utility in a clinical environment is largely unknown. The aim of this review was to explore existing uses of musculoskeletal models as a clinical intervention, or decision-making, tool. A literature search was performed using PubMed and Scopus to find articles published since 2010 and relating to musculoskeletal modelling and joint and muscle forces. 4662 abstracts were found, of which 39 relevant articles were reviewed. Journal articles were categorised into 5 distinct groups: non-surgical treatment, orthoses assessment, surgical decision making, surgical intervention assessment and rehabilitation regime assessment. All reviewed articles were authored by collaborations between clinicians and engineers/modellers. Current uses included insight into the development of osteoarthritis, identifying candidates for hamstring lengthening surgery, and the assessment of exercise programmes to reduce joint damage. There is little evidence showing the use of musculoskeletal modelling as a tool for patient care, despite the ability to assess long-term joint loading and muscle overuse during functional activities, as well as clinical decision making to avoid unfavourable treatment outcomes. Continued collaboration between model developers should aim to create clinically-friendly models which can be used with minimal input and experience by healthcare professionals to determine surgical necessity and suitability for rehabilitation regimes, and in the assessment of orthotic devices. • Little evidence of musculoskeletal models being used in clinical practice; • Only used in assessment, rarely used directly in treatment; • Papers only authored by collaboration between clinicians and modellers; • Bespoke models should be developed for patient-specific treatment; • Biomechanists should work with clinicians to develop user-friendly tools. [ABSTRACT FROM AUTHOR]

Total knee replacement (TKR) is one of the most performed orthopedic surgeries to treat knee joint diseases in the elderly population. Although the survivorship of knee implants may extend beyond two decades, the poor outcome rate remains considerable. A recent computational approach used to better understand failure modes and improve TKR outcomes is based on the combination of musculoskeletal (MSK) and finite element models. This combined multiscale modeling approach is a promising strategy in the field of computational biomechanics; however, some critical aspects need to be investigated. In particular, the identification and quantification of the uncertainties related to the boundary conditions used as inputs to the finite element model due to a different definition of the MSK model are crucial. Therefore, the aim of this study is to investigate this problem, which is relevant for the model credibility assessment process. Three different generic MSK models available in the OpenSim platform were used to simulate gait, based on the experimental data from the fifth edition of the "Grand Challenge Competitions to Predict in vivo Knee Loads." The outputs of the MSK analyses were compared in terms of relative kinematics of the knee implant components and joint reaction (JR) forces and moments acting on the tibial insert. Additionally, the estimated knee JRs were compared with those measured by the instrumented knee implant so that the "global goodness of fit" was quantified for each model. Our results indicated that the different kinematic definitions of the knee joint and the muscle model implemented in the different MSK models influenced both the motion and the load history of the artificial joint. This study demonstrates the importance of examining the influence of the model assumptions on the output results and represents the first step for future studies that will investigate how the uncertainties in the MSK models propagate on disease-specific finite element model results., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Curreli, Di Puccio, Davico, Modenese and Viceconti.)

Reduced external knee adduction moments in the second half of stance after total hip replacement have been reported in hip osteoarthritis patients. This reduction is thought to shift the load from the medial to the lateral knee compartment and as such increase the risk for knee osteoarthritis. The knee adduction moment is a surrogate for the load distribution between the medial and lateral compartments of the knee and not a valid measure for the tibiofemoral contact forces which are the result of externally applied forces and muscle forces. The purpose of this study was to investigate whether the distribution of the tibiofemoral contact forces over the knee compartments in unilateral hip osteoarthritis patients 1 year after receiving a primary total hip replacement differs from healthy controls. Musculoskeletal modeling on gait was performed in OpenSim using the detailed knee model of Lerner et al. (2015) for 19 patients as well as for 15 healthy controls of similar age. Knee adduction moments were calculated by the inverse dynamics analysis, medial and lateral tibiofemoral contact forces with the joint reaction force analysis. Moments and contact forces of patients and controls were compared using Statistical Parametric Mapping two-sample t -tests. Knee adduction moments and medial tibiofemoral contact forces of both the ipsi- and contralateral leg were not significantly different compared to healthy controls. The contralateral leg showed 14% higher medial tibiofemoral contact forces compared to the ipsilateral (operated) leg during the second half of stance. During the first half of stance, the lateral tibiofemoral contact force of the contralateral leg was 39% lower and the ratio 32% lower compared to healthy controls. In contrast, during the second half of stance the forces were significantly higher (39 and 26%, respectively) compared to healthy controls. The higher ratio indicates a changed distribution whereas the increased lateral tibiofemoral contact forces indicate a higher lateral knee joint loading in the contralateral leg in OA patients after total hip replacement (THR). Musculoskeletal modeling using a detailed knee model can be useful to detect differences in the load distribution between the medial and lateral knee compartment which cannot be verified with the knee adduction moment., (Copyright © 2020 van Drongelen, Wesseling, Holder, Meurer and Stief.)

The purpose of this study was to systematically quantify distal radioulnar joint stability with a cadaveric model, using radiographic and joint contact force measurements. Six fresh-frozen cadavers underwent sequential ulnar styloid osteotomies. Posteroanterior and lateral stress radiographs were obtained and joint contact forces and areas were measured. Posteroanterior radiographs showed a significant increase in the distal radioulnar joint gap after osteotomy of the base of the ulnar styloid. Contact force and contact area measurements were not significantly different. We conclude that fractures that involve the ulnar styloid base should be considered for operative fixation when carrying out open reduction and internal fixation of fractures of the distal radius.