1,721,047 research outputs found
THE EFFECT of COMPUTED TOMOGRAPHY CURRENT REDUCTION on PROXIMAL FEMUR SUBJECT-SPECIFIC FINITE ELEMENT MODELS
No full textMany studies have addressed the modulation of computed tomography (CT) parameters, and particularly of tube current, to obtain a good compromise between the X-ray dose to the patient and the image quality for diagnostic applications. This study aimed at evaluating the influence of dose reduction by means of tube current reduction on the CT-based subject-specific finite element (FE) modeling. To this aim, CT scans at stepwise reduced values of tube current from 180mAs to 80mAs were performed on: (i) a densitometric phantom, to quantify the changes in the calibration equation; (ii) a fresh-frozen, water submersed, human cadaver femur, to quantify changes in geometry reconstruction and material mapping from CT, as well as strain prediction accuracy, based on the in vitro strain measurements available; (iii) a fresh-frozen human cadaver thigh with soft tissues attached, to quantify FE results changes in conditions similar to those found in vivo. The results showed that the tube current reduction does not affect the 3D modeling and the femur FE analysis. Our pilot study highlights the possibility of performing CT scans with reduced dose to generate biomechanical models, although a confirmation by performing larger studies with clinical CT data is needed
Effect of lower-limb joint models on subject-specific musculoskeletal models and simulations of daily motor activities
Full text linkUnderstanding 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
Sensitivity of the primary stability of a cementless hip stem to its position and orientation
No full textAbstract: Using computed tomography (CT)-based preoperative
planning software, we can define with good
accuracy the position of a cementless hip stem inside the
host bone, but previous studies suggest that the pose the
surgeon achieves during freehand surgery may differ from
the planned one even by some millimeters. Advances in
simulation now make it possible to predict the primary
stability of the stem in a given position during the preoperative
planning, but is the stability predicted for the
planned pose indicative of that we can expect for the
achieved pose? The aim of the present study was to verify
how this prediction is affected by the differences observed
between the planned and the achieved poses. Two finite
element models of an implanted femur were generated,
one with the stem in the planned pose, and one with the
stem in the achieved pose, as defined from postoperative
CT scans. When compared to experimental measurements,
the model with the achieved position was clearly
more accurate (0.6 vs. 12% error over measured peak
micromotion); however, the predictions of induced micromotions
were different between the two models for less
than 13%. It is thus concluded that while the implant
position does have an effect on primary stability, the
estimate of micromotion we can get from the planned
position remains a clinically relevant indicator
Medial and lateral knee contact forces during walking, stair ascent and stair descent are more affected by contact locations than tibiofemoral alignment in knee osteoarthritis patients with varus malalignment
Full text linkIntroduction: Knee OA progression is related to medial knee contact forces, which can be altered by anatomical parameters of tibiofemoral alignment and contact point locations. There is limited and controversial literature on medial-lateral force distribution and the effect of anatomical parameters, especially in motor activities different from walking. We analyzed the effect of tibiofemoral alignment and contact point locations on knee contact forces, and the medial-lateral force distribution in knee OA subjects with varus malalignment during walking, stair ascending and stair descending.Methods: Fifty-one knee OA subjects with varus malalignment underwent weight-bearing radiographs and motion capture during walking, stair ascending and stair descending. We created a set of four musculoskeletal models per subject with increasing level of personalization, and calculated medial and lateral knee contact forces. To analyze the effect of the anatomical parameters, statistically-significant differences in knee contact forces among models were evaluated. Then, to analyze the force distribution, the medial-to-total contact force ratios were calculated from the fully-informed models. In addition, a multiple regression analysis was performed to evaluate correlations between forces and anatomical parameters.Results: The anatomical parameters significantly affected the knee contact forces. However, the contact points decreased medial forces and increased lateral forces and led to more marked variations compared to tibiofemoral alignment, which produced an opposite effect. The forces were less medially-distributed during stair negotiation, with medial-to-total ratios below 50% at force peaks. The anatomical parameters explained 30%-67% of the variability in the knee forces, where the medial contact points were the best predictors of medial contact forces.Discussion: Including personalized locations of contact points is crucial when analyzing knee contact forces in subjects with varus malalignment, and especially the medial contact points have a major effect on the forces rather than tibiofemoral alignment. Remarkably, the medial-lateral force distribution depends on the motor activity, where stair ascending and descending show increased lateral forces that lead to less medially-distributed loads compared to walking
ALBA: Agile library for biomedical applications
Full text linkEfficient and unified software tools to manage the complex imaging and modelling workflows needed for computational biomechanics research are lacking. The Agile Library for Biomedical Applications (ALBA) is an open-source C++ versatile framework that handles various data types (e.g. 2D and 3D images, surfaces, finite element models, point clouds, motion analysis data), and offers an easily extensible platform for the rapid development of specialised applications that can manage, visualise, and manipulate biomedical data. The already available functionalities have been developed in the context of computational biomechanics, quantitative image analysis and pre-operative planning in orthopaedics. Software applications built with ALBA attracted the interest of the scientific community and are currently used, both inside and outside the original research group, in finite element modelling of bones and musculoskeletal modelling. The further ALBA adoption by other centres might increase the spread of a positive attitude towards open and reproducible research in the biomechanical community and increase the sharing of algorithms and data
Can CT image deblurring improve finite element predictions at the proximal femur?
No full textObjective: Clinical application of computed tomography (CT) based finite element (FE) estimates of bone strength recently showed encouraging results [1]. However, model performance may be improved. In fact, in-vitro valida- tion studies showed systematic errors in strain prediction, especially where bone cortex is thin (i.e. the femoral neck) [2].
This work seeks to verify if, and to what extent, a CT deblurring algorithm restoring both geometry and intensity data in thin bone structures [3], can improve strain and failure load prediction accuracy of CT-based FE models of the prox- imal femur.
Material and Methods: CT scans were acquired of 14 fresh-frozen human cadaveric femora. An estimate of the 3D Point Spread Function for each CT scan was used within a deconvolution solver to perform deblurring. Using the restored images, FE models of the proximal femur were generated [4]. Each femur was tested non- destructively in both stance and fall loading configurations to measure surface strains, and then loaded to failure in stance or fall.
Deblurred FE predictions of strains and failure load were com- pared to experimental measurements, and FE predictions ob- tained from the original CT data (no deblurring).
Results: An enhancement in strain prediction accuracy was obtained using deblurred FE models, with the Standard Error of Estimate reduced by 11 % with respect to reference FE models. Marked improvements at the femoral neck were achieved (e.g. peak error reduced by 38 %). Using deblurred models, the regression equation between FE-predicted and measured failure loads was characterized by a slope not sig- nificantly different from one, with R2 = 0.89, unchanged with respect to reference models. Absolute differences between estimated and measured failure loads were consistently re- duced by deblurring in stance (mean error 10 vs. 15 %) but not in fall (32 vs. 17 %).
Conclusions: The proposed CT deblurring technique yielded moderate but significant improvements in femo- ral FE predictions, and can thus be seen as a first and worthwhile step in the improvement of CT-based FE models of the human femur
Open trabecular bone microFE models from microCT images: Ciclope new release with higher performances and verified tetra mesh option.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High tibial osteotomy effectively restores motor function during daily activities in patients with knee osteoarthritis and varus deformity
Full text linkPurpose: This study evaluated the effects of high tibial osteotomy (HTO) on spatio-temporal parameters, kinematics and kinetics during walking, stair ascent and descent, in patients with medial knee osteoarthritis and varus malalignment, by using a prospective randomized case-control design, which compares the effects of HTO with a non-surgical conservative treatment. Methods: A total of 49 patients with medial knee osteoarthritis and varus malalignment were enroled in a prospective randomized case-control study. Patients were randomly assigned to the Surgical Group (n = 25), which underwent open-wedge HTO, or the Conservative Group (n = 24), which followed non-surgical conservative treatment. An additional 20 healthy subjects were included as controls. Radiographs in double-leg stance and gait analysis during the motor activities were conducted at baseline and follow-up. Statistical comparisons of spatio-temporal parameters, joint rotations and joint moments were performed to assess the effects of surgery on motor function. Results: In the Surgical Group, HTO significantly corrected the tibiofemoral angle (from 8.3 ± 3.3° to 0.9 ± 2.4°, p < 0.001), restoring values comparable to healthy controls. Knee and ankle adduction were fully restored in all motor tasks, with significant improvements in at least 60% of the movement cycle (p < 0.05). Knee adduction and rotation moments were significantly reduced, with some patients even showing lower-than-normal knee adduction moments during walking, suggesting possible overcorrection. However, pelvic obliquity and ankle flexion remained altered, and no significant changes were observed in walking speed or stride length. The Conservative Group showed no improvements at follow-up. Conclusions: HTO effectively restores knee alignment and major motor function parameters during walking and stair tasks, whereas non-surgical conservative treatments do not lead to any improvement. However, some residual motor function deviations persist after surgery, suggesting that certain biomechanical adaptations may remain after surgical correction. Level of Evidence: Level I, randomized controlled trial
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