| 1. |
- Jedenmalm, Anneli, et al.
(författare)
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Validation of a 3D CT method for measurement of linear wear of acetabular cups : A hip simulator study
- 2011
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3674 .- 1745-3682. ; 82:1, s. 35-41
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Tidskriftsartikel (refereegranskat)abstract
- Material and methods Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner. Results The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17 degrees A degrees. Interpretation This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy.
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| 2. |
- Olivecrona, Henrik, et al.
(författare)
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A new computed tomography-based radiographic method to detect early loosening of total wrist implants
- 2007
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Ingår i: Acta Radiologica. - London, UK : Informa Healthcare. - 0284-1851 .- 1600-0455. ; 48:9, s. 997-1003
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Tidskriftsartikel (refereegranskat)abstract
- Background: Diagnosis of loosening of total wrist implants is usually late using routine radiographs. Switching modality to computed tomography (CT) should aid in early diagnosis. Purpose: To propose and evaluate the accuracy of a new CT method for assessing loosening of the carpal component in total wrist arthroplasty. Material and Methods: A protocol encompassing volume registration of paired CT scans of patients with unexplained pain in a prosthetically replaced wrist (used in clinical routine) is presented. Scans are acquired as a dynamic examination under torsional load. Using volume registration, the carpal component of the prosthesis is brought into spatial alignment. After registration, prosthetic loosening is diagnosed by a shift in position of the bones relative to the prosthesis. This study is a preclinical validation of this method using a human cadaverous arm with a cemented total wrist implant and tantalum markers. Seven CT scans of the arm were acquired. The scans were combined into 21 pairs of CT volumes. The carpal component was registered in each scan pair, and the residual mismatch of the surrounding tantalum markers and bone was analyzed both visually and numerically. Results: The detection limit for prosthetic movement was less than 1 mm. Conclusion: The results of this study demonstrate that CT volume registration holds promise to improve detection of movement of the carpal component at an earlier stage than is obtainable with plain radiography.
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| 3. |
- Harnden, Ross, et al.
(författare)
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Multifunctional Carbon Fiber Composites : A Structural, Energy Harvesting, Strain-Sensing Material
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 14:29, s. 33871-33880
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Tidskriftsartikel (refereegranskat)abstract
- Multifunctional structural materials are capable of reducing system level mass and increasing efficiency in load -carrying structures. Materials that are capable of harvesting energy from the surrounding environment are advantageous for autono-mous electrically powered systems. However, most energy harvesting materials are non-structural and add parasitic mass, reducing structural efficiency. Here, we show a structural energy harvesting composite material consisting of two carbon fiber (CF) layers embedded in a structural battery electrolyte (SBE) with a longitudinal modulus of 100 GPa-almost on par with commercial CF pre-pregs. Energy is harvested through mechanical deforma-tions using the piezo-electrochemical transducer (PECT) effect in lithiated CFs. The PECT effect creates a voltage difference between the two CF layers, driving a current when deformed. A specific power output of 18 nW/g is achieved. The PECT effect in the lithiated CFs is observed in tension and compression and can be used for strain sensing, enabling structural health monitoring with low added mass. The same material has previously been shown capable of shape morphing. The two additional functionalities presented here result in a material capable of four functions, further demonstrating the diverse possibilities for CF/SBE composites in multifunctional applications in the future.
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| 4. |
- Iversen, Maura D., et al.
(författare)
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Self-rated walking disability and dynamic ankle joint stiffness in children and adolescents with Juvenile Idiopathic Arthritis receiving intraarticular corticosteroid joint injections of the foot
- 2019
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Ingår i: Gait & Posture. - : ELSEVIER IRELAND LTD. - 0966-6362 .- 1879-2219. ; 67, s. 257-261
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Tidskriftsartikel (refereegranskat)abstract
- Background: Children and adolescents with Juvenile Idiopathic Arthritis (JIA) exhibit deviations in ankle dynamic joint stiffness (DJS, or moment-angle relationship) compared to healthy peers, but the relationship between ankle DJS and self-reported walking impairments has not been studied. This secondary analysis aimed to investigate the relationship between ankle DJS and self-reported walking disability in juveniles with JIA, and to determine whether intraarticular corticosteroid foot injections (IACI) were associated with long term changes in ankle DJS. Research questions: Is ankle DJS altered in children with JIA reporting walking difficulties compared to children with JIA reporting no walking difficulties? Are IACIs associated with persistent alterations in ankle DJS? Methods: Gait dynamics (DJS), foot pain, and foot-related disability were assessed in 33 children with JIA before intraarticular corticoid foot injection (IACI), and three months after IACI. Using self-reported walking capacity scores, children were classified as either having no walking difficulties (ND) or having walking difficulties (WD). Inferential statistics were used to compare demographics, pain, impairment scores, and ankle DJS between the groups. Results: Before treatment, in the WD group, ankle DJS was significantly decreased both in the early rising phase (ERP = 0.03 +/- 0.02 vs. 0.05 +/- 0.02 Nm(kg*deg)(-1)) and late rising phase (LRP = 0.11 +0.06 vs. 0.24+0.22 Nm (kg*deg)(-1)) compared to the ND group. At three months, the ERP was still significantly decreased in the WD group (ERP = 0.03 +/- 0.01 vs. 0.05+0.03 Nm(kg*deg)(-1)). Significance: Among children and adolescents with JIA who reported walking difficulties prior to IACIs, alterations in DJS in early stance phase (decreased ERP) remained three months after IACI suggesting persistent gait adaptations, possibly related to pain. Pre-treatment gait analysis may aid in identifying children who will not have long term benefit from IACIs in terms of improved gait, and therefore, may be informed and have the choice to be spared the risk of side effects associated with this treatment.
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| 5. |
- Sinzinger, Fabian, et al.
(författare)
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Predicting the trabecular bone apparent stiffness tensor with spherical convolutional neural networks
- 2022
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Ingår i: Bone Reports. - : Elsevier BV. - 2352-1872. ; 16, s. 101179-
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Tidskriftsartikel (refereegranskat)abstract
- The apparent stiffness tensor is relevant for characterizing trabecular bone quality. Previous studies have used morphology-stiffness relationships for estimating the apparent stiffness tensor. In this paper, we propose to train spherical convolutional neural networks (SphCNNs) to estimate this tensor. Information of the edges, trabecular thickness, and spacing are summarized in functions on the unitary sphere used as inputs for the SphCNNs. The concomitant dimensionality reduction makes it possible to train neural networks on relatively small datasets. The predicted tensors were compared to the stiffness tensors computed by using the micro-finite element method (mu FE), which was considered as the gold standard, and models based on fourth-order fabric tensors. Combining edges and trabecular thickness yields significant improvements in the accuracy compared to the methods based on fourth-order fabric tensors. From the results, SphCNNs are promising for replacing the more expensive mu FE stiffness estimations.
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| 6. |
- Robinson, Yohan, 1977-, et al.
(författare)
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Finite element analysis of long posterior transpedicular instrumentation for cervicothoracic fractures related to ankylosing spondylitis
- 2018
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Ingår i: Global Spine Journal. - : SAGE Publications. - 2192-5682 .- 2192-5690. ; 8:6, s. 570-578
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Tidskriftsartikel (refereegranskat)abstract
- Background: Spinal fractures related to AS are often treated by long posterior stabilisation. The biomechanical rationale behind is the neutralisation of long lever arms in the ankylosed spine to avoid non-union or neurological deterioration. Despite the widespread application of long posterior instrumentation it has never been investigated in a biomechanical model. The objective of this study is to develop a finite element model for spinal fractures related to AS and to establish a biomechanical foundation for long posterior stabilisation of cervicothoracic fractures related to ankylosing spondylitis (AS).Methods: An existing finite element-model (consisting of two separately developed models) including the cervical and thoracic spine were adapted to the conditions of AS (all discs fused, C0-C1 and C1-C2 mobile) and a fracture at the level C6-C7 was simulated. Besides a normal spine (no AS, no fracture) and the uninstrumented fractured spine four different posterior transpedicular instrumentations were tested: 1. Fracture uninstrumented, 2. Short instrumentation C6-C7, 3. Medium instrumentation C5-T1, 4. Long instrumentation C3-T3, 5. Skipped level long instrumentation C3-C6-C7-T3.Three loads (1.5g, 3.0g, 4.5g) were applied according to a specific load curve. Kinematic data such as the gap distance in the fracture site were obtained. Furthermore the stresses in the ossified parts of the discs were evaluated.Findings: All posterior stabilisation methods could normalise the axial stability at the fracture site as measured with gap distance. With larger accelerations than 1.5g , it was seen that the longer instrumentations resulted in lesser maximal gap distance than the Short instrumentation. The maximum stress at the cranial instrumentation end (C3-C4) was slightly greater if every level was instrumented, than in the skipped level model. The skipped level instrumentation achieved similar rotatory stability as the long multilevel instrumentation.Interpretation: The FE model developed simulated a spinal fracture at C6-C7 level. Skipping instrumentation levels without giving up instrumentation length also reduces the stresses in the ossified tissue within the range of the instrumentation and does not decrease the stability in a finite element model of a cervicothoracic fracture related to AS. Considering the risks associated with every additional screw placed, the skipped level instrumentation has advantages with regard to patient safety. The effects of the degree of osteoporosis, screw placement and pre-existing kyphosis on the construct stability were not investigated in this study and should be a matter of further research.
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| 7. |
- Rolander, Bo, et al.
(författare)
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Measurements and observations of movements at work for warehouse forklift truck operators
- 2021
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Ingår i: International Journal of Occupational Safety and Ergonomics. - : Taylor and Francis Ltd.. - 1080-3548 .- 2376-9130.
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Tidskriftsartikel (refereegranskat)abstract
- Inclinometry and video analyses can provide objective measures of physical workloads. The study aim was to measure and observe arm, back and head postures and movements among forklift truck operators (FLTOs) during a working day, analyzing differences between types of forklift trucks and to assess reported workload and health. Twenty-five male FLTOs in a high-level warehouse were randomly included. The data collected comprised technical measurements, video analyses of postures and movements, and a questionnaire measuring health, pain and workload. On average, the FLTOs rotated their head more than 45°, in total, 232 times/h. Video analysis revealed that FLTOs periodically drive the forklift truck sideways with the head rotated in the direction of travel, and in periods look upwards, in which the head is highly rotated and extended. Inclinometry and observations during the working day has the potential to be a valuable part of risk assessment promoting occupational safety and health.
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| 8. |
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| 9. |
- Zhang, Longbin, et al.
(författare)
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Estimation of Ankle Dynamic Joint Torque by a Neuromusculoskeletal Solver-informed NN Model
- 2021
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Ingår i: 2021 6th IEEE international conference on advanced robotics and mechatronics (ICARM 2021). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 75-80
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Konferensbidrag (refereegranskat)abstract
- In this paper, a neuromusculoskeletal (NMS) solver-informed artificial neural network (ANN) is proposed to estimate ankle joint torques in seven movements, including walking at fast, slow and self-selected speeds, ankle isokinetic dorsi- and plantarflexion at 60 and 90 degrees/s. The NMS solver-informed ANN model is an extension of a standard ANN model with additional features from an NMS solver, namely ankle joint torque and muscle forces. The standard ANN, the NMS solver-informed ANN and a muscle-driven NMS model, were used to predict ankle torque. Prediction accuracy were compared, based on data capture in 10 subjects. In all methods, we trained the models with measured ankle joint angle and electromyography signals as inputs. Seven different cases were investigated, using trials at different speeds across three movement types (walking, isokinetic plantarflexion and dorsiflexion) to calibrate/train models in the same movement types. The NMS solver-informed ANN model predicted ankle joint torque better than both the NMS and standard ANN models, which indicates benefit gained from integrating NMS features into standard ANN models. The proposed NMS solver informed-ANN model thus shows promise in assistance-as-needed rehabilitation exoskeleton controller design.
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| 10. |
- Liu, Hanxiao, et al.
(författare)
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Rollout approach to sensor scheduling for remote state estimation under integrity attack
- 2022
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 144
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Tidskriftsartikel (refereegranskat)abstract
- We consider the sensor scheduling problem for remote state estimation under integrity attacks. We seek to optimize a trade-off between the energy consumption of communications and the state estimation error covariance when the acknowledgment (ACK) information, sent by the remote estimator to the local sensor, is compromised. The sensor scheduling problem is formulated as an infinite horizon discounted optimal control problem with infinite states. We first analyze the underlying Markov decision process (MDP) and show that the optimal scheduling without ACK attack is of the threshold type. Thus, we can simplify the problem by replacing the original state space with a finite state space. For the simplified MDP, when the ACK is under attack, the problem is modeled as a partially observable Markov decision process (POMDP). We analyze the induced MDP that uses a belief vector as its state for the POMDP. We investigate the properties of the exact optimal solution via contractive models and show that the threshold type of solution for the POMDP cannot be readily obtained. A suboptimal solution is then obtained via a rollout approach, which is a prominent class of reinforcement learning (RL) methods based on approximation in value space. We present two variants of rollout and provide performance bounds of those variants. Finally, numerical examples are used to demonstrate the effectiveness of the proposed rollout methods by comparing them with a finite history window approach that is widely used in RL for POMDP.
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