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Gait restoration of individuals with spinal cord injury can be partially achieved using active orthoses or exoskeletons. To improve the walking ability of each patient as much as possible, it is important to personalize the parameters that define the device actuation. This study investigates whether using an optimal control-based predictive simulation approach to personalize pre-defined knee trajectory parameters for an active knee-ankle-foot orthosis (KAFO) used by spinal cord injured (SCI) subjects could potentially be an alternative to the current trial-and-error approach. We aimed to find the knee angle trajectory that produced an improved orthosis-assisted gait pattern compared to the one with passive support (locked knee). We collected experimental data from a healthy subject assisted by crutches and KAFOs (with locked knee and with knee flexion assistance) and from an SCI subject assisted by crutches and KAFOs (with locked knee). First, we compared different cost functions and chose the one that produced results closest to experimental locked knee walking for the healthy subject (angular coordinates mean RMSE was 5.74°). For this subject, we predicted crutch-orthosis-assisted walking imposing a pre-defined knee angle trajectory for different maximum knee flexion parameter values, and results were evaluated against experimental data using that same pre-defined knee flexion trajectories in the real device. Finally, using the selected cost function, gait cycles for different knee flexion assistance were predicted for an SCI subject. We evaluated changes in four clinically relevant parameters: foot clearance, stride length, cadence, and hip flexion ROM. Simulations for different values of maximum knee flexion showed variations of these parameters that were consistent with experimental data for the healthy subject (e.g., foot clearance increased/decreased similarly in experimental and predicted motions) and were reasonable for the SCI subject (e.g., maximum parame, Peer Reviewed, Postprint (published version)

An emerging option for internal hemipelvectomy surgery is custom prosthesis reconstruction. This option typically recapitulates the resected pelvic bony anatomy with the goal of maximizing post-surgery walking function while minimizing recovery time. However, the current custom prosthesis design process does not account for the patient’s post-surgery prosthesis and bone loading patterns, nor can it predict how different surgical or rehabilitation decisions (e.g., retention or removal of the psoas muscle, strengthening the psoas) will affect prosthesis durability and post-surgery walking function. These factors may contribute to the high observed failure rate for custom pelvic prostheses, discouraging orthopedic oncologists from pursuing this valuable treatment option. One possibility for addressing this problem is to simulate the complex interaction between surgical and rehabilitation decisions, post-surgery walking function, and custom pelvic prosthesis design using patient-specific neuromusculoskeletal models. As a first step toward developing this capability, this study used a personalized neuromusculoskeletal model and direct collocation optimal control to predict the impact of ipsilateral psoas muscle strength on walking function following internal hemipelvectomy with custom prosthesis reconstruction. The influence of the psoas muscle was targeted since retention of this important muscle can be surgically demanding for certain tumors, requiring additional time in the operating room. The post-surgery walking predictions emulated the most common surgical scenario encountered at MD Anderson Cancer Center in Houston. Simulated post-surgery psoas strengths included 0% (removed), 50% (weakened), 100% (maintained), and 150% (strengthened) of the pre-surgery value. However, only the 100% and 150% cases successfully converged to a complete gait cycle. When post-surgery psoas strength was maintained, clinical gait features were predicted, including increased stance width, Peer Reviewed, Objectius de Desenvolupament Sostenible::3 - Salut i Benestar, Postprint (published version)

Most assistive devices available today are unable to improve gait asymmetries due to the lack of knowledge on how to directly enforce kinematic symmetry in the formulation of cost functions. We designed a cost function to potentially target kinematic symmetry, and observed improvements in gait asymmetries specifically at the hip and ankle., Peer Reviewed, Postprint (published version)

Background Despite favourable outcomes relatively few surgeons offer high tibial osteotomy (HTO) as a treatment option for early knee osteoarthritis, mainly due to the difficulty of achieving planned correction and reported soft tissue irritation around the plate used to stablise the osteotomy. To compare the mechanical safety of a new personalised 3D printed high tibial osteotomy (HTO) device, created to overcome these issues, with an existing generic device, a case-control in silico virtual clinical trial was conducted. Methods Twenty-eight knee osteoarthritis patients underwent computed tomography (CT) scanning to create a virtual cohort; the cohort was duplicated to form two arms, Generic and Personalised, on which virtual HTO was performed. Finite element analysis was performed to calculate the stresses in the plates arising from simulated physiological activities at three healing stages. The odds ratio indicative of the relative risk of fatigue failure of the HTO plates between the personalised and generic arms was obtained from a multi-level logistic model. Results Here we show, at 12 weeks post-surgery, the odds ratio indicative of the relative risk of fatigue failure was 0.14 (95%CI 0.01 to 2.73, p¿=¿0.20). Conclusions This novel (to the best of our knowledge) in silico trial, comparing the mechanical safety of a new personalised 3D printed high tibial osteotomy device with an existing generic device, shows that there is no increased risk of failure for the new personalised design compared to the existing generic commonly used device. Personalised high tibial osteotomy can overcome the main technical barriers for this type of surgery, our findings support the case for using this technology for treating early knee osteoarthritis., Postprint (published version)

Computational prediction of 3D crutch-assisted walking patterns is a challenging problem that could be applied to study different biomechanical aspects of crutch walking in virtual subjects, to assist physiotherapists to choose the optimal crutch walking pattern for a specific subject, and to help in the design and control of exoskeletons, when crutches are needed for balance. The aim of this work is to generate a method to predict three-dimensional crutch-assisted walking motions following different patterns without tracking any experimental data. To reach this goal, we collected gait data from a healthy subject performing a four-point non-alternating crutch walking pattern, and developed a 3D torque-driven full-body model of the subject including the crutches and foot- and crutch-ground contact models. First, we developed a predictive (i.e., no tracking of experimental data) optimal control problem formulation to predict crutch walking cycles following the same pattern as the experimental data collected, using different cost functions. To reduce errors with respect to reference data, a cost function combining minimization terms of angular momentum, mechanical power, joint jerk and torque change was chosen. Then, the problem formulation was adapted to handle different foot- and crutch-ground conditions to make it capable of predicting three new crutch walking patterns, one of them at different speeds. A key aspect of our algorithm is that having ground reactions as additional controls allows one to define phases inside the cycle without the need of formulating a multiple-phase problem, thus facilitating the definition of different crutch walking patterns., Postprint (author's final draft)

Aplicat embargament des de la data de defensa fins al dia 30 de setembre de 2021, Walking impairment after spinal cord injury leads to a decreased quality of life, other serious health conditions, and substantial health care costs. Consequently, gait restoration is a high priority among spinal cord-injured (SCI) subjects; and it can be partially achieved using active orthoses or exoskeletons, together with some type of external support for balance (e.g., crutches or a walker). Customisation of active orthoses control algorithms to maximise the walking ability of each patient is currently done through trial-and-error methods, making it difficult if not impossible to identify the best active control parameters for any particular patient. An objective simulation-based method that accounts for patient-specific needs would lead to a patient-tailored assistive device development process. Multibody system dynamics has been used for many years for the biomechanical analysis and simulation of human motion. Moreover, optimal control is being used to predict novel human motions, while methods to develop patient-specific neuromusculoskeletal models are currently being investigated. There are published studies that show the potential that subject-specific simulations have to improve rehabilitation treatments and assistive device adaptation to specific subjects. However, researchers have not yet fully demonstrated the effectiveness of these methods using a larger number of patients and a wider variety of treatments.In this thesis, we have investigated the use of optimal control formulations to predict crutch-orthosis-assisted walking using torque-driven multibody dynamic models. The main objective has been to develop a simulation tool to predict crutch-orthosis-assisted walking that could serve in the future as a basis to support the design and control of an active knee-ankle-foot orthosis. The approach used involved development of a subject-specific torque-driven model based on a current available model in OpenSim, into which orthoses and crutches were incorp, El deteriorament de la marxa després d'una lesió medul·lar disminueix la qualitat de vida, i porta com a conseqüència altres limitacions de salut i un alt cost sanitari. És per això que el restabliment de la marxa és una prioritat per totes les persones amb lesió medul·lar. Aquest restabliment pot ser assolit parcialment utilitzant exoesquelets o ortesis actives, amb l'ajuda d'algun suport extern per mantenir l'equilibri, com crosses o un caminador. La personalització del algorismes de control de les ortesis actives per tal de maximitzar el rendiment de la marxa de cada pacient actualment es fa a través de mètodes de prova i error. Això fa que sigui difícil (si no pràcticament impossible) identificar els millors paràmetres de control per cada pacient. Un mètode objectiu basat en simulació i que tingui en compte les necessitats específiques de cada pacient podria portar-nos cap a un procés de desenvolupament de dispositius d'assistència personalitzats al pacient. La dinàmica de sistemes multisòlid s'ha utilitzat durant bastants anys per a l'anàlisi biomecànica i la simulació del moviment humà. A més, s'estan utilitzant mètodes de control òptim per predir el moviment humà, i s'estan investigant altres mètodes per desenvolupar models neuro-musculo-esquelètics adaptats al pacient. Hi ha estudis publicats que mostren el potencial que tenen les simulacions que utilitzen models personalitzats al pacient de millorar els tractaments de rehabilitació i l'adaptació de dispositius d'assistència a pacients concrets. Tot i així, els investigadors no han demostrat encara l'efectivitat d'aquests mètodes usant un nombre gran de pacients i una varietat més gran de tractaments.En aquesta tesi, hem investigat l'ús de formulacions de control òptim per a predir marxa assistida amb crosses i ortesis actives mitjançant models dinàmics multisòlid a nivell esquelètic. L'objectiu principal ha estat desenvolupar una eina de simulació per tal de predir marxa assistida amb crosses i ortesis acti, Postprint (published version)

Most assistive devices available today are unable to improve gait asymmetries due to the lack of knowledge on how to directly enforce kinematic symmetry in the formulation of cost functions. We designed a cost function to potentially target kinematic symmetry, and observed improvements in gait asymmetries specifically at the hip and ankle., Postprint (published version)

Treatment design for musculoskeletal disorders using in silico patient-specific dynamic simulations is becoming a clinical possibility. However, these simulations are sensitive to model parameter values that are difficult to measure experimentally, and the influence of uncertainties in these parameter values on the accuracy of estimated knee contact forces remains unknown. This study evaluates which musculoskeletal model parameters have the greatest influence on estimating accurate knee contact forces during walking. We performed the evaluation using a two-level optimization algorithm where musculoskeletal model parameter values were adjusted in the outer level and muscle activations were estimated in the inner level. We tested the algorithm with different sets of design variables (combinations of optimal muscle fiber lengths, tendon slack lengths, and muscle moment arm offsets) resulting in nine different optimization problems. The most accurate lateral knee contact force predictions were obtained when tendon slack lengths and moment arm offsets were adjusted simultaneously, and the most accurate medial knee contact force estimations were obtained when all three types of parameters were adjusted together. Inclusion of moment arm offsets as design variables was more important than including either tendon slack lengths or optimal muscle fiber lengths alone to obtain accurate medial and lateral knee contact force predictions. These results provide guidance on which musculoskeletal model parameter values should be calibrated when seeking to predict in vivo knee contact forces accurately., Postprint (updated version)

Walking impairment due to spinal cord injury can be improved using active orthoses, together with some type of external support such as crutches for balance. This study explores how optimal control problem formulation affects the ability to generate dynamically consistent crutch walking simulations with active orthosis assistance that closely reproduce experimental data. The investigation compares eight optimal tracking problem formulations using a torque-driven full-body skeletal model of a healthy subject walking with active knee-ankle-foot orthoses and forearm crutches. We have found that small adjustments to ground reactions are required to achieve convergence, tracking of joint instead of marker coordinates significantly improves convergence, and minimising joint jerks instead of joint accelerations has only a minor effect on the problem convergence. These results provide guidance for future work that seeks to develop predictive optimal control simulations that can identify orthosis control parameters that maximise improvement in walking function on an individual patient basis., Postprint (author's final draft)

Objectives Opening wedge high tibial osteotomy (HTO) is an established surgical procedure for the treatment of early-stage knee arthritis. Other than infection, the majority of complications are related to mechanical factors – in particular, stimulation of healing at the osteotomy site. This study used finite element (FE) analysis to investigate the effect of plate design and bridging span on interfragmentary movement (IFM) and the influence of fracture healing on plate stress and potential failure. Materials and Methods A 10° opening wedge HTO was created in a composite tibia. Imaging and strain gauge data were used to create and validate FE models. Models of an intact tibia and a tibia implanted with a custom HTO plate using two different bridging spans were validated against experimental data. Physiological muscle forces and different stages of osteotomy gap healing simulating up to six weeks postoperatively were then incorporated. Predictions of plate stress and IFM for the custom plate were compared against predictions for an industry standard plate (TomoFix). Results For both plate types, long spans increased IFM but did not substantially alter peak plate stress. The custom plate increased axial and shear IFM values by up to 24% and 47%, respectively, compared with the TomoFix. In all cases, a callus stiffness of 528 MPa was required to reduce plate stress below the fatigue strength of titanium alloy. Conclusion We demonstrate that larger bridging spans in opening wedge HTO increase IFM without substantially increasing plate stress. The results indicate, however, that callus healing is required to prevent fatigue failure., Peer Reviewed, Postprint (published version)

The authors are working on the personalisation of an innovative low-cost, lightweight, and easy-to-use active orthosis to facilitate over-ground walking with crutches by individuals with spinal cord injury (SCI) who possess remaining hip function. Personalisation will involve selection of the best knee motor control strategy for each subject, using predictive walking simulations that combine OpenSim patient-specific models with GPOPS-II optimal control predictions. In the present work, we describe a direct collocation optimal control framework to obtain a dynamically consistent walking motion that reproduces experimental measurements., Postprint (published version)

n recent years, interest has grown in predicting human motion, for example, to study cause-effect relations for a specific task [1]. To predict human motion, researchers typically use optimization-based methods that minimize a certain cost function. The objective of this study is to analyze two different optimal control formulations that track experimental data from a healthy gait cycle to obtain a dynamically consistent walking motion, i.e., with minimal residual wrench applied to the pelvis., Postprint (published version)