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Showing 1401 - 1600 of 1720 Journals sorted alphabetically
Virology Journal     Open Access   (Followers: 6)
Virulence     Full-text available via subscription   (Followers: 1)
Virus Evolution     Open Access   (Followers: 1)
Virus Genes     Hybrid Journal   (Followers: 1)
Virus Research     Hybrid Journal   (Followers: 1)
Visnyk of Dnipropetrovsk University. Biology, ecology     Open Access   (Followers: 2)
Visnyk of Dnipropetrovsk University. Biology, medicine     Open Access  
Walailak Journal of Science and Technology     Open Access  
Web Ecology     Open Access   (Followers: 5)
Weed Science     Full-text available via subscription   (Followers: 6)
Weed Technology     Full-text available via subscription   (Followers: 2)
West African Journal of Applied Ecology     Open Access  
Western Undergraduate Research Journal : Health and Natural Sciences     Open Access  
Wetlands     Hybrid Journal   (Followers: 24)
Wildlife Biology     Open Access   (Followers: 15)
Wildlife Research     Hybrid Journal   (Followers: 16)
Wiley Interdisciplinary Reviews - System Biology and Medicine     Hybrid Journal   (Followers: 5)
Wiley Interdisciplinary Reviews : Developmental Biology     Hybrid Journal   (Followers: 3)
Wiley Interdisciplinary Reviews : Membrane Transport and Signaling     Hybrid Journal  
Wiley Interdisciplinary Reviews : RNA     Hybrid Journal   (Followers: 3)
World Crop Pests     Full-text available via subscription   (Followers: 1)
World Mycotoxin Journal     Full-text available via subscription   (Followers: 6)
Xenobiotica     Hybrid Journal   (Followers: 8)
Yeast     Hybrid Journal   (Followers: 9)
Zebrafish     Hybrid Journal   (Followers: 1)
Zeitschrift für Evidenz, Fortbildung und Qualität im Gesundheitswesen     Full-text available via subscription   (Followers: 5)
Zeitschrift für Naturforschung C : A Journal of Biosciences     Open Access   (Followers: 2)

  First | 1 2 3 4 5 6 7 8 | Last

Journal Cover Medical Engineering & Physics
  [SJR: 0.784]   [H-I: 76]   [9 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1350-4533
   Published by Elsevier Homepage  [3089 journals]
  • Hemodynamic assessment of extra-cardiac tricuspid valves using particle
           image velocimetry
    • Authors: Munirah Ismail; Foad Kabinejadian; Yen Ngoc Nguyen; Edgar Tay Lik Wui; Sangho Kim; Hwa Liang Leo
      Pages: 1 - 11
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Munirah Ismail, Foad Kabinejadian, Yen Ngoc Nguyen, Edgar Tay Lik Wui, Sangho Kim, Hwa Liang Leo
      There has not been much progress in the development of transcatheter tricuspid valves to treat tricuspid regurgitation because of the difficulty in anchoring a stented valve onto the complex tricuspid annulus. Hence, the concept of heterotopic implantation of the transcatheter tricuspid valve onto the cavo-atrial junction was proposed. However, to date there has been no detailed in vitro investigation of the hemodynamic performance of this new device. The study utilises both 2-D and 3-D particle image velocimetry (PIV) to interrogate the flow patterns in the vicinity of the extra-cardiac tricuspid valves in an in vitro physiological flow loop, specifically at four measurement locations in the cavo-atrial anatomy. Comparison of the 2-D and 3-D PIV results revealed that accuracy of 2-D PIV would be acceptable at time point and at measurement locations where the velocity was mostly planar with minimal or low out-of-plane flow such as at the outlet of the superior vena cava valve at the point of valve closure. The results also showed that the RSS in the vicinity of the valves were relatively low (∼150 dynes/cm2) with the exception of that in the leakage jet at the upstream of the valve. The leakage in the leaflets could be a result of the use of aortic valve leaflets which was more suited for the higher pressured environment of the left side of the heart. The stent design could also be customised for implantation in the vena cava. In summary, these issues could be eradicated with improvements to the leaflet and stent design which would enhance the haemodynamics of the post-implantation flow performance.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.08.003
      Issue No: Vol. 50 (2017)
  • Hemodynamic parameters that may predict false-lumen growth in type-B
           aortic dissection after endovascular repair: A preliminary study on
           long-term multiple follow-ups
    • Authors: Huanming Xu; Zhenfeng Li; Huiwu Dong; Yilun Zhang; Jianyong Wei; Paul N. Watton; Wei Guo; Duanduan Chen; Jiang Xiong
      Pages: 12 - 21
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Huanming Xu, Zhenfeng Li, Huiwu Dong, Yilun Zhang, Jianyong Wei, Paul N. Watton, Wei Guo, Duanduan Chen, Jiang Xiong
      Thoracic endovascular aortic repair (TEVAR) is commonly applied in type-B aortic dissection. For patients with dissection affects descending aorta and extends downward to involve abdominal aorta and possibly iliac arteries, false lumen (FL) expansion might occur post-TEVAR. Predictions of dissection development may assist in medical decision on re-intervention or surgery. In this study, two patients are selected with similar morphological features at initial presentation but with different long-term FL development post-TEVAR (stable and enlarged FL). Patient-specific models are established for each of the follow-ups. Flow boundaries and computational validations are obtained from Doppler ultrasound velocimetry. By analyzing the hemodynamic parameters, the false-to-true luminal pressure difference (PDiff) and particle relative residence time (RRT) are found related to FL remodeling. It is found that (i) the position of the first FL flow entry is the watershed of negative-and-positive PDiff and, in long-term follow-ups, and the position of largest PDiff is consistent with that of the greatest increase of FL width; (ii) high RRT occurs at the FL proximal tip and similar magnitude of RRT is found in both stable and enlarged cases; (iii) comparing to the RRT at 7days post-TEVAR, an increase of RRT afterwards in short-term is found in the stable case while a slight decrease of this parameter is found in the enlarged case, indicating that the variation of RRT in short-term post-TEVAR might be potential to predict long-term FL remodeling.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.08.011
      Issue No: Vol. 50 (2017)
  • Ulna-humerus contact mechanics: Finite element analysis and experimental
           measurements using a tactile pressure sensor
    • Authors: Mohsen Sharifi Renani; Munsur Rahman; Akin Cil; Antonis P. Stylianou
      Pages: 22 - 28
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Mohsen Sharifi Renani, Munsur Rahman, Akin Cil, Antonis P. Stylianou
      Elbow articular cartilage withstands high compressive and shear forces while protecting the bone from excessive loading. Better understanding of elbow cartilage contact mechanics can provide insight into cartilage degeneration. In this study a tactile pressure sensor was used to measure the contact pressure distribution within the ulno-humeral joint of two cadaver specimens at 20° flexion angle across three different axial loads of 80 N, 110 N, and 140 N. Corresponding 3D finite element (FE) models were constructed from magnetic resonance imaging (MRI) and contact analysis was performed for each specimen with boundary and loading conditions identical to the experiment. Direct comparison between FE results and experimental measurements was conducted for the validation of the FE models and a sensitivity analysis was employed for assessing the effect of cartilage parameters on the model's outputs. The results showed a good agreement between the FE models and the experiments in terms of contact characteristics. The sensitivity analysis demonstrated that outcomes of the model, particularly peak contact pressure is more sensitive to the Poisson's ratio rather than to Young's modulus under static conditions. This result suggests that selection of Poisson's ratio is very critical for accurate prediction of contact mechanics within the ulno-humeral joint.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.08.010
      Issue No: Vol. 50 (2017)
  • Intra- and inter-session reliability of traditional and entropy-based
           variables describing stance on a wobble board
    • Authors: Lucia Bizovska; Miroslav Janura; Zdenek Svoboda; Martin Cerny; Jana Krohova; Maros Smondrk
      Pages: 29 - 34
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Lucia Bizovska, Miroslav Janura, Zdenek Svoboda, Martin Cerny, Jana Krohova, Maros Smondrk
      A wobble board (WB) is a balance rehabilitation tool that is used in physiotherapy to improve strength and stability. The WB tested in this study includes a sensory module for measuring patients’ tilt and rotation during stance. The aim of this study was to assess the reliability and validity of a balance measurement using a WB. Thirty healthy young adults participated in this study. The participants stood on the WB to simultaneously record the tilt of the WB and the center of pressure data using a force plate. The data were recorded during five measurement sessions on various days, with four trials each. Sways, velocities and indexes of complexity (CI) were computed. For reliability assessment, we used intra-class correlation coefficients within and between sessions; for validity, we computed Spearman correlation coefficients. The velocities and CI showed good intra-session reliability, and the sways showed mostly poor intra-session reliability. The results of inter-session reliability showed good to excellent reliability for CI, poor reliability for sways and poor to good reliability for velocities. The Spearman correlation coefficient showed excellent agreement between the mean velocities computed from the force plate and the WB. Our results confirm that the WB tested is suitable for stability assessment in young adults.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.08.017
      Issue No: Vol. 50 (2017)
  • Shifts in the relationship between motor unit recruitment thresholds
           versus derecruitment thresholds during fatigue
    • Authors: Matt S. Stock; Jacob A. Mota
      Pages: 35 - 42
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Matt S. Stock, Jacob A. Mota
      Muscle fatigue is associated with diminished twitch force amplitude. We examined changes in the motor unit recruitment versus derecruitment threshold relationship during fatigue. Nine men (mean age = 26 years) performed repeated isometric contractions at 50% maximal voluntary contraction (MVC) knee extensor force until exhaustion. Surface electromyographic signals were detected from the vastus lateralis, and were decomposed into their constituent motor unit action potential trains. Motor unit recruitment and derecruitment thresholds and firing rates at recruitment and derecruitment were evaluated at the beginning, middle, and end of the protocol. On average, 15 motor units were studied per contraction. For the initial contraction, three subjects showed greater recruitment thresholds than derecruitment thresholds for all motor units. Five subjects showed greater recruitment thresholds than derecruitment thresholds for only low-threshold motor units at the beginning, with a mean cross-over of 31.6% MVC. As the muscle fatigued, many motor units were derecruited at progressively higher forces. In turn, decreased slopes and increased y-intercepts were observed. These shifts were complemented by increased firing rates at derecruitment relative to recruitment. As the vastus lateralis fatigued, the central nervous system's compensatory adjustments resulted in a shift of the regression line of the recruitment versus derecruitment threshold relationship.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.08.015
      Issue No: Vol. 50 (2017)
  • Trapeziometacarpal joint contact varies between men and women during three
           isometric functional tasks
    • Authors: Marco T.Y. Schneider; Ju Zhang; Joseph J. Crisco; Arnold-Peter C. Weiss; Amy L. Ladd; Kumar Mithraratne; Poul Nielsen; Thor Besier
      Pages: 43 - 49
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Marco T.Y. Schneider, Ju Zhang, Joseph J. Crisco, Arnold-Peter C. Weiss, Amy L. Ladd, Kumar Mithraratne, Poul Nielsen, Thor Besier
      Trapeziometacarpal (TMC) joint osteoarthritis (OA) affects women two to six times more than men, and is influenced by stresses and strains in the cartilage. The purpose of this study was to characterise sex and age differences in contact area and peak stress location of the healthy TMC joint during three isometric tasks including pinch, grasp and jar twist. CT images of the hand from 50 healthy adult men and women were used to create a statistical shape model that was used to create finite element models for each subject and task. Force-driven simulations were performed to evaluate cartilage contact area and peak stress location. We tested for sex and age differences using Principal Component Analysis, linear regression, and Linear Discriminant Analysis. We observed sex differences in peak stress location during pinch (p = .0206), grasp (p = .0264), and jar twist (p = .0484). The greatest sex differences were observed during jar twist, where 94% of peak stresses in men were located in the centre compared with 50% in the central–volar region in women. These findings show that peak stress locations are more variable in women during grasp and jar twist than men, and suggest that women may employ different strategies to perform these tasks.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.09.002
      Issue No: Vol. 50 (2017)
  • Motorized adaptive compression system for enhancing venous return: A
           feasibility study on healthy individuals
    • Authors: Mahan Rahimi; Andrew P. Blaber; Carlo Menon
      Pages: 65 - 74
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Mahan Rahimi, Andrew P. Blaber, Carlo Menon
      Notwithstanding the extensive use of conventional compression devices in managing venous disorders, these modalities have shortages that diminish their treatment efficacy and lessen patient adherence to therapy. The purpose of this study was to develop an improved compression system that eliminates the flaws of the existing devices. A motorized bandage was designed that takes advantage of continuous feedback from force-sensing resistors to apply reproducible, controlled pressure on the lower extremities. The performance of the device in enhancing venous return was explored in a pilot test on 11 healthy participants, wherein graded lower body negative pressure was employed as a surrogate of passive standing. Each subject underwent two experiments; with and without pressure application over the calves. A two-way repeated-measures analysis of variance revealed a significant difference in the mean hemodynamic responses when the compression bandage was in action (p < .05). Specifically, a meaningful increase was observed in mean arterial pressure by 5%, diastolic blood pressure by 8% and left ventricular ejection time by 4%; and a significant decrease of 5% and 6% was noticed in heart rate and pulse pressure, respectively. These results demonstrate the capability of the designed system in attenuating the imposed orthostatic stress on cardiovascular system.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.10.005
      Issue No: Vol. 50 (2017)
  • Iterative approach for 3D reconstruction of the femur from un-calibrated
           2D radiographic images
    • Authors: Kibeom Youn; Moon Seok Park; Jehee Lee
      Pages: 89 - 95
      Abstract: Publication date: December 2017
      Source:Medical Engineering & Physics, Volume 50
      Author(s): Kibeom Youn, Moon Seok Park, Jehee Lee
      Three-dimensional reconstruction of the femur is important for surgical planning in patients with cerebral palsy. This study aimed to reconstruct the three-dimensional femur shape from un-calibrated bi-planar radiographic images using self-calibration to allow for low-dose preoperative planning. The existing self-calibration techniques require anatomical landmarks that are clearly visible on bi-planar images, which are not available on the femur. In our newly developed method, the self-calibration is performed so that the contour of the statistical shape matches the image contour while the statistical shape is concomitantly optimized. The proposed approach uses conventional radiograph systems and can be easily incorporated into existing clinical protocols, as compared to other reconstruction methods.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.08.016
      Issue No: Vol. 50 (2017)
  • Robotic assistants in personal care: A scoping review
    • Authors: A. Bilyea; N. Seth; S. Nesathurai; H.A. Abdullah
      Pages: 1 - 6
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): A. Bilyea, N. Seth, S. Nesathurai, H.A. Abdullah
      The aim of this study is to present an overview of the technological advances in the field of robotics developed for assistance with activities of daily living (ADL), and to present areas where further research is required. Four databases were searched for articles presenting either a novel design of one of these personal care robotic system or trial results relating to these systems. Articles presenting nine different robotic personal care systems were examined, six of which had been developed after 2005. These six also all have publications relating to their trials. In the majority of trials, patient independence was improved with operation of the robotic device for a specific subset of ADL. A map of the current state of the field of personal care robotics is presented in this study. Areas requiring further research include improving feedback and awareness, as well as refining control methods and pre-programmed behaviors. Developing an affordable, easy to use system would help fill the current gap in the commercial market.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.06.038
      Issue No: Vol. 49 (2017)
  • A mechanistic force model for simulating haptics of hand-held bone burring
    • Authors: Avinash Danda; Mathew A. Kuttolamadom; Bruce L. Tai
      Pages: 7 - 13
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Avinash Danda, Mathew A. Kuttolamadom, Bruce L. Tai
      This paper presents a mechanistic model to predict the forces experienced during bone burring with application to haptic feedback for virtual reality surgical simulations. Bone burring is a hand-held operation where the force perceived by the surgeon depends on the cutting tool orientation and motion. The model of this study adapted the concept of specific cutting energy and material removal rate based on machining theory to calculate force distribution on the spherical tool surface in a three-dimensional setting. A design of experiments with three tool cutting angles and three feed motions was performed to calibrate and validate the model. Despite some variance in the results, model predictions showed similar trends to experimental force patterns. While the actual force profile also exhibits significant oscillation, the dominant frequencies of this oscillating force component were found to be independent of cutting and non-cutting instances, and hence could be imposed as a uniform background signal. Though the presented model is primarily applicable to abrasive burrs, it has far-reaching applications within other types of surgical simulations as well.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.06.041
      Issue No: Vol. 49 (2017)
  • Second generation prototype of a variable stiffness transverse plane
           adapter for a lower limb prosthesis
    • Authors: Corey Pew; Glenn K. Klute
      Pages: 22 - 27
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Corey Pew, Glenn K. Klute
      The prescription and fitting of a traditional lower limb prosthesis often focuses on straight walking, neglecting maneuvers such as turning and pivoting that require flexibility in the transverse plane. Current devices that allow transverse plane movement only offer a fixed stiffness and are incapable of adapting to varying daily activities. Pilot testing of a first-generation variable stiffness torsion adapter (VSTA I) showed a benefit for individuals with lower limb amputation by reducing peak transverse plane moments at the residual limb which could lead to increased comfort, but testing was limited due to excessive device height and mass. The VSTA II, a second-generation prototype, is capable of discrete stiffness variation from 0.31 to 1.29 Nm/° in 0.25 Nm/° increments with ±30° of motion in addition to fully locked operation. Stiffness variation is enabled by five independent spring subunits that can be combined in parallel to create different, linear, stiffness settings. The VSTA II features a reduced mass (51% reduction) and height (42% reduction) compared to its predecessor along with a tether-free controller and power system. These improvements will permit greater recruitment for amputee studies, and allow for advanced testing both in and out of the lab.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.002
      Issue No: Vol. 49 (2017)
  • Development of an acoustic measurement protocol to monitor acetabular
           implant fixation in cementless total hip Arthroplasty: A preliminary study
    • Authors: Quentin Goossens; Steven Leuridan; Petr Henyš; Jorg Roosen; Leonard Pastrav; Michiel Mulier; Wim Desmet; Kathleen Denis; Jos Vander Sloten
      Pages: 28 - 38
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Quentin Goossens, Steven Leuridan, Petr Henyš, Jorg Roosen, Leonard Pastrav, Michiel Mulier, Wim Desmet, Kathleen Denis, Jos Vander Sloten
      In cementless total hip arthroplasty (THA), the initial stability is obtained by press-fitting the implant in the bone to allow osseointegration for a long term secondary stability. However, finding the insertion endpoint that corresponds to a proper initial stability is currently based on the tactile and auditory experiences of the orthopedic surgeon, which can be challenging. This study presents a novel real-time method based on acoustic signals to monitor the acetabular implant fixation in cementless total hip arthroplasty. Twelve acoustic in vitro experiments were performed on three types of bone models; a simple bone block model, an artificial pelvic model and a cadaveric model. A custom made beam was screwed onto the implant which functioned as a sound enhancer and insertor. At each insertion step an acoustic measurement was performed. A significant acoustic resonance frequency shift was observed during the insertion process for the different bone models; 250 Hz (35%, second bending mode) to 180 Hz (13%, fourth bending mode) for the artificial bone block models and 120 Hz (11%, eighth bending mode) for the artificial pelvis model. No significant frequency shift was observed during the cadaveric experiment due to a lack of implant fixation in this model. This novel diagnostic method shows the potential of using acoustic signals to monitor the implant seating during insertion.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.006
      Issue No: Vol. 49 (2017)
  • Synergistic experimental and numerical characterization of a dry-heat,
           fluid-warming device
    • Authors: Winston Tan; Eph M. Sparrow; John M. Gorman; Jungwon Ahn
      Pages: 39 - 45
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Winston Tan, Eph M. Sparrow, John M. Gorman, Jungwon Ahn
      Fluids that are infused into the human body must be at a temperature that is compatible with the internal thermal state of the body. Since infusants are typically stored at temperatures that are too low for compatibility, a heating means is required to achieve the appropriate infusion temperature. This paper sets forth a synergistic investigation involving coupled experimentation and numerical simulation of the characteristics of one of the main categories of body-fluid heating means. The methodology developed here serves equally well as a design optimization tool. The paper encompasses two stages: (a) an experimental and numerical evaluation of a generic warming device in common use and (b) a redesign utilizing the same tools to elevate the performance of devices of this category. The numerical simulation dealt with steady and unsteady three-dimensional fluid flow and heat transfer which are endemic to devices of this kind. The two-pronged approach developed here was shown to be capable of coping with an operating feature called stopflow wherein an officiating physician orders an immediate cessation of fluid flow. The thermal events following stopflow are well described by the numerical simulations.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.007
      Issue No: Vol. 49 (2017)
  • The variation in frequency locations in Doppler ultrasound spectra for
           maximum blood flow velocities in narrowed vessels
    • Authors: Yingyun Zhang; Yufeng Zhang; Lian Gao; Li Deng; Xiao Hu; Kexin Zhang; Haiyan Li
      Pages: 46 - 55
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Yingyun Zhang, Yufeng Zhang, Lian Gao, Li Deng, Xiao Hu, Kexin Zhang, Haiyan Li
      This study assessed the variation in the frequency locations in the Doppler ultrasound spectra for the maximum blood flow velocities of in vessels with different degrees of bilaterally axisymmetric stenosis. This was done by comparing the relationship between the velocity distributions and corresponding Doppler power spectra. First, a geometric vessel model with axisymmetric stenosis was established. This made it possible to obtain the blood flow velocity distributions for different degrees of stenosis from the solutions of the Navier–Stokes equations. Then, the Doppler spectra were calculated for the entire segment of the vessel that was covered by the sound field. Finally, the maximum frequency locations for the spectra were determined based on the intersections of the maximum values chosen from the calculated blood flow velocity distributions and their corresponding spectra. The computational analysis showed that the maximum frequencies, which corresponded to the maximum blood flow velocities for different degrees of stenosis, were located at different positions along the spectral falling edges. The location for a normal (stenosis free) vessel was in the middle of the falling edge. For vessels with increasing degrees of stenosis, this location shifted approximately linearly downward along the falling edge. For 40% stenosis, the location reached a position at the falling edge of 0.32. Results obtained using the Field II simulation tool demonstrated the validity of the theoretical analysis and calculations, and may help to improve the maximum velocity estimation accuracy for Doppler blood flow spectra in stenosed vessels.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.004
      Issue No: Vol. 49 (2017)
  • In vitro performance of a shape memory polymer foam-coated coil
           embolization device
    • Authors: Anthony J. Boyle; Mark A. Wierzbicki; Scott Herting; Andrew C. Weems; Adam Nathan; Wonjun Hwang; Duncan J. Maitland
      Pages: 56 - 62
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Anthony J. Boyle, Mark A. Wierzbicki, Scott Herting, Andrew C. Weems, Adam Nathan, Wonjun Hwang, Duncan J. Maitland
      Intracranial saccular aneurysm treatment using endovascular embolization devices are limited by aneurysm recurrence that can lead to aneurysm rupture. A shape memory polymer (SMP) foam-coated coil (FCC) embolization device was designed to increase packing density and improve tissue healing compared to current commercial devices. FCC devices were fabricated and tested using in vitro models to assess feasibility for clinical treatment of intracranial saccular aneurysms. FCC devices demonstrated smooth delivery through tortuous pathways similar to control devices as well as greater than 10 min working time for clinical repositioning during deployment. Furthermore, the devices passed pilot verification tests for particulates, chemical leachables, and cytocompatibility. Finally, devices were successfully implanted in an in vitro saccular aneurysm model with large packing density. Though improvements and future studies evaluating device stiffness were identified as a necessity, the FCC device demonstrates effective delivery and packing performance that provides great promise for clinical application of the device in treatment of intracranial saccular aneurysms.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.009
      Issue No: Vol. 49 (2017)
  • Does stabilization of the degenerative lumbar spine itself produce
           multifidus atrophy'
    • Authors: Young Eun Kim; Hae Won Choi
      Pages: 63 - 70
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Young Eun Kim, Hae Won Choi
      The effect of stabilization of the degenerative segment on changes in the pattern of paraspinal muscle activity was investigated using a previously developed musculoskeletal model. Muscle activity change depending on L4-L5 segment stabilization with and without taking into account the presence of multifidus atrophy according to direct invasion of the back muscle during surgery (MADIBM) was analysed in erect standing and 20° flexed postures. For the stabilization of the degenerative segment, a fusion or non-fusion stabilization with a pedicle-based dynamic stabilization system (PBDS) was applied. During erect standing, fusion generated a 12% reduction in the total multifidus muscle force, while its reduction was 6.6% with PBDS application. The presence of MADIBM produced 23.0% and 22.5% reductions in fusion and with PBDS application, respectively. During 20° flexion, 10.5% and 9.3% reductions were produced for fusion and PBDS application, respectively, and the corresponding values were 23.4% and 23.0%, respectively, in the presence of MADIBM. Increased facet joint contact forces were produced at the non-stabilized levels after stabilization while in erect standing posture. Alterations in muscle activity, which could be regarded as adaptions to altered spinal stability, may generate unexpected secondary problems in the spine.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.008
      Issue No: Vol. 49 (2017)
  • Non-linear finite element model to assess the effect of tendon forces on
           the foot-ankle complex
    • Authors: Enrique Morales-Orcajo; Thales R. Souza; Javier Bayod; Estevam Barbosa de Las Casas
      Pages: 71 - 78
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Enrique Morales-Orcajo, Thales R. Souza, Javier Bayod, Estevam Barbosa de Las Casas
      A three-dimensional foot finite element model with actual geometry and non-linear behavior of tendons is presented. The model is intended for analysis of the lower limb tendon forces effect in the inner foot structure. The geometry of the model was obtained from computational tomographies and magnetic resonance images. Tendon tissue was characterized with the first order Ogden material model based on experimental data from human foot tendons. Kinetic data was employed to set the load conditions. After model validation, a force sensitivity study of the five major foot extrinsic tendons was conducted to evaluate the function of each tendon. A synergic work of the inversion-eversion tendons was predicted. Pulling from a peroneus or tibialis tendon stressed the antagonist tendons while reducing the stress in the agonist. Similar paired action was predicted for the Achilles tendon with the tibialis anterior. This behavior explains the complex control motion performed by the foot. Furthermore, the stress state at the plantar fascia, the talocrural joint cartilage, the plantar soft tissue and the tendons were estimated in the early and late midstance phase of walking. These estimations will help in the understanding of the functional role of the extrinsic muscle-tendon-units in foot pronation-supination.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.010
      Issue No: Vol. 49 (2017)
  • Novel curved surface preparation technique for knee resurfacing
    • Authors: Jianmo Li; Susannah Clarke; Justin P Cobb; Andrew A Amis
      Pages: 89 - 93
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Jianmo Li, Susannah Clarke, Justin P Cobb, Andrew A Amis
      Conventional tools are incapable of preparing the curved articular surface geometry required during cartilage repair procedures. A novel curved surface preparation technique was proposed and tested to provide an accurate low-cost solution. Three shapes of samples, with flat, 30 mm radius and 60 mm radius surfaces, were manufactured from foam bone substitute for testing. Registering guides and cutting guides were designed and 3-D printed to fit onto the foam samples. A rotational cutting tool with an adapter was used to prepare the surfaces following the guidance slots in the cutting guides. The accuracies of the positions and shapes of the prepared cavities were measured using a digital calliper, and the surface depth accuracy was measured using a 3-D scanner. The mean shape and position errors were both approximately ± 0.5 mm and the mean surface depth error ranged from 0 to 0.3 mm, range − 0.3 to + 0.45 mm 95% CI. This study showed that the technique was able to prepare a curved surface accurately; with some modification it can be used to prepare the knee surface for cartilage repair.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.07.011
      Issue No: Vol. 49 (2017)
  • Vibration-based fixation assessment of tibial knee implants: A combined in
           vitro and in silico feasibility study
    • Authors: Steven Leuridan; Quentin Goossens; Tom Vander Sloten; Koen De Landsheer; Hendrik Delport; Leonard Pastrav; Kathleen Denis; Wim Desmet; Jos Vander Sloten
      Pages: 109 - 120
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): Steven Leuridan, Quentin Goossens, Tom Vander Sloten, Koen De Landsheer, Hendrik Delport, Leonard Pastrav, Kathleen Denis, Wim Desmet, Jos Vander Sloten
      The preoperative diagnosis of loosening of cemented tibial knee implants is challenging. This feasibility study explored the basic potential of a vibration-based method as an alternative diagnostic technique to assess the fixation state of a cemented tibia implant and establish the method's sensitivity limits. A combined in vitro and in silico approach was pursued. Several loosening cases were simulated. The largest changes in the vibrational behavior were obtained in the frequency range above 1500 Hz. The vibrational behavior was described with two features; the frequency response function and the power spectral density band power. Using both features, all experimentally simulated loosening cases could clearly be distinguished from the fully cemented cases. By complementing the experimental work with an in silico study, it was shown that loosening of approximately 14% of the implant surface on the lateral and medial side was detectable with a vibration-based method. Proximal lateral and medial locations on the tibia or locations toward the edge of the implant surface measured in the longitudinal direction were the most sensitive measurement and excitation locations to assess implant fixation. These results contribute to the development of vibration-based methods as an alternative follow-up method to detect loosened tibia implants.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.08.007
      Issue No: Vol. 49 (2017)
  • Detection of ventricular premature beats based on the pressure signals of
           a hemodialysis machine
    • Authors: Mattias Holmer; Juan Pablo Martínez; Eduardo Gil; Frida Sandberg; Bo Olde; Leif Sörnmo
      Abstract: Publication date: Available online 8 December 2017
      Source:Medical Engineering & Physics
      Author(s): Mattias Holmer, Juan Pablo Martínez, Eduardo Gil, Frida Sandberg, Bo Olde, Leif Sörnmo
      Monitoring of ventricular premature beats (VPBs), being abundant in hemodialysis patients, can provide information on cardiovascular instability and electrolyte imbalance. In this paper, we describe a method for VPB detection which explores the signals acquired from the arterial and the venous pressure sensors, located in the extracorporeal blood circuit of a hemodialysis machine. The pressure signals are mainly composed of a pump component and a cardiac component. The cardiac component, severely overshadowed by the pump component, is estimated from the pressure signals using an earlier described iterative method. A set of simple features is extracted, and linear discriminant analysis is performed to classify beats as either normal or ventricular premature. Performance is evaluated on signals from nine hemodialysis treatments, using leave-one-out crossvalidation. The simultaneously recorded and annotated photoplethysmographic signal serves as the reference signal, with a total of 149,686 normal beats and 3574 VPBs. The results show that VPBs can be reliably detected, quantified by a Youden’s J statistic of 0.9, for average cardiac pulse pressures exceeding 1 mmHg; for lower pressures, the J statistic drops to 0.55. It is concluded that the cardiac pressure signal is suitable for VPB detection, provided that the average cardiac pulse pressure exceeds 1 mmHg.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.004
  • Full-field strain distribution in multi-vertebra spine segments: An in
           vitro application of digital image correlation
    • Authors: Marco Palanca; Miguel Marco; Maria Luisa Ruspi; Luca Cristofolini
      Abstract: Publication date: Available online 8 December 2017
      Source:Medical Engineering & Physics
      Author(s): Marco Palanca, Miguel Marco, Maria Luisa Ruspi, Luca Cristofolini
      The biomechanics of the spine is experimentally assessed in terms of range of motion and overall stiffness. Quantification of the surface strain distribution is currently limited either to the vertebrae or the discs, whereas a full-field approach to measure the strain distribution in a multi-vertebra segment is currently missing. The aim of this work was to explore the feasibility of using Digital Image Correlation (DIC) to measure the strain distribution simultaneously on the vertebral bodies and the intervertebral discs of spine segments in different loading configurations. Three porcine spine segments were tested. A white-on-black speckle pattern was prepared which covered the hard and soft tissues. Two different loading configurations (flexion and lateral bending) were reproduced, while two sides of the spine were analyzed with DIC. Measurements were successfully performed on the entire region of interest of all specimens, in both configurations. The DIC analysis highlighted the strain gradients present on the spine segments including tension and compression associated with bending, the direction of principal strains in the different regions, as well as bulging of the discs under compression. Strains of tens of thousands microstrain were measured in the discs, and below 2000 microstrain in the bone. This work showed the feasibility of applying DIC on spine segments including hard and soft tissues. It also highlights the need for a full-field investigation, because of the strain inhomogeneity in the vertebrae and discs.
      Graphical abstract image

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.003
  • Inducing targeted failure in cadaveric testing of 3-segment spinal units
           with and without simulated metastases
    • Authors: Karlijn H.J. Groenen; Dennis Janssen; Yvette M. van der Linden; Jan G.M. Kooloos; Jasper Homminga; Nico Verdonschot; Esther Tanck
      Abstract: Publication date: Available online 8 December 2017
      Source:Medical Engineering & Physics
      Author(s): Karlijn H.J. Groenen, Dennis Janssen, Yvette M. van der Linden, Jan G.M. Kooloos, Jasper Homminga, Nico Verdonschot, Esther Tanck
      We propose an experimental setup and protocol able to induce targeted failure of the middle vertebra in 3-segment spinal units and to capture the specimens’ deformation in their post-failure state. Sixteen 3-segment spinal units with and without artificial metastases were destructively tested in axial compression using one of two failure criteria; either: (A) A clear drop in force (>10–15% of peak force) (n = 4); or (B) A minimum displacement of 5 mm (n = 12). Subsequently, the specimens were fully fixated in polymethylmethacrylate (PMMA), thereby preserving their post-failure state. Pre- and post-experiment computed tomography (CT) scans were acquired to determine the occurrence of failure in one of the vertebral bodies. All specimens were successfully fixated in their post-failure state. When applying failure criterion A, two specimens showed signs of failure. When applying failure criterion B, all specimens showed signs of failure; in 9 out of 12 specimens this occurred in the middle vertebrae only. In conclusion, this research provides an experimental setup and protocol able to induce targeted failure of 3-segment spinal units and to capture the specimens’ deformation in their post-failure state. Furthermore, this study illustrates the importance of an adequate failure criterion for successful simulation of vertebral fractures in an experimental setup.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.007
  • Instrumented socket inserts for sensing interaction at the limb-socket
    • Authors: Eric C. Swanson; Jake B. McLean; Katheryn J. Allyn; Christian B. Redd; Joan E. Sanders
      Abstract: Publication date: Available online 8 December 2017
      Source:Medical Engineering & Physics
      Author(s): Eric C. Swanson, Jake B. McLean, Katheryn J. Allyn, Christian B. Redd, Joan E. Sanders
      The objective of this research was to investigate a strategy for designing and fabricating computer-manufactured socket inserts that were embedded with sensors for field monitoring of limb-socket interactions of prosthetic users. An instrumented insert was fabricated for a single trans-tibial prosthesis user that contained three sensor types (proximity sensor, force sensing resistor, and inductive sensor), and the system was evaluated through a sequence of laboratory clinical tests and two days of field use. During in-lab tests 3 proximity sensors accurately distinguish between don and doff states; 3 of 4 force sensing resistors measured gradual pressure increases as weight-bearing increased; and the inductive sensor indicated that as prosthetic socks were added the limb moved farther out of the socket and pistoning amplitude decreased. Multiple sensor types were necessary in analysis of field collected data to interpret how sock changes affected limb-socket interactions. Instrumented socket inserts, with sensors selected to match clinical questions of interest, have the potential to provide important insights to improve patient care.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.006
  • Validation of single-plane fluoroscopy and 2D/3D shape-matching for
           quantifying shoulder complex kinematics
    • Authors: Rebekah L. Lawrence; Arin M. Ellingson; Paula M. Ludewig
      Abstract: Publication date: Available online 8 December 2017
      Source:Medical Engineering & Physics
      Author(s): Rebekah L. Lawrence, Arin M. Ellingson, Paula M. Ludewig
      Fluoroscopy and 2D/3D shape-matching has emerged as the standard for non-invasively quantifying kinematics. However, its accuracy has not been well established for the shoulder complex when using single-plane fluoroscopy. The purpose of this study was to determine the accuracy of single-plane fluoroscopy and 2D/3D shape-matching for quantifying full shoulder complex kinematics. Tantalum markers were implanted into the clavicle, humerus, and scapula of four cadaveric shoulders. Biplane radiographs were obtained with the shoulder in five humerothoracic elevation positions (arm at the side, 30°, 60°, 90°, maximum). Images from both systems were used to perform marker tracking, while only those images acquired with the primary fluoroscopy system were used to perform 2D/3D shape-matching. Kinematics errors due to shape-matching were calculated as the difference between marker tracking and 2D/3D shape-matching and expressed as root mean square (RMS) error, bias, and precision. Overall RMS errors for the glenohumeral joint ranged from 0.7 to 3.3° and 1.2 to 4.2 mm, while errors for the acromioclavicular joint ranged from 1.7 to 3.4°. Errors associated with shape-matching individual bones ranged from 1.2 to 3.2° for the humerus, 0.5 to 1.6° for the scapula, and 0.4 to 3.7° for the clavicle. The results of the study demonstrate that single-plane fluoroscopy and 2D/3D shape-matching can accurately quantify full shoulder complex kinematics in static positions.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.005
  • Integrated experimental and computational approach to laser machining of
           structural bone
    • Authors: Narendra B. Dahotre; Soundarapandian Santhanakrishnan; Sameehan S. Joshi; Riaz J.K. Khan; Daniel P. Fick; William B. Robertson; Raymond K. Sheh; Charlie N. Ironside
      Abstract: Publication date: Available online 8 December 2017
      Source:Medical Engineering & Physics
      Author(s): Narendra B. Dahotre, Soundarapandian Santhanakrishnan, Sameehan S. Joshi, Riaz J.K. Khan, Daniel P. Fick, William B. Robertson, Raymond K. Sheh, Charlie N. Ironside
      This study describes the fundamentals of laser–bone interaction during bone machining through an integrated experimental-computational approach. Two groups of laser machining parameters identified the effects of process thermodynamics and kinetics on machining attributes at micro to macro. A continuous wave Yb-fiber Nd:YAG laser (wavelength 1070 nm) with fluences in the range of 3.18 J/mm2–8.48 J/mm2 in combination of laser power (300 W–700 W) and machining speed (110 mm/s–250 mm/s) were considered for machining trials. The machining attributes were evaluated through scanning electron microscopy observations and compared with finite element based multiphysics-multicomponent computational model predicted values. For both groups of laser machining parameters, experimentally evaluated and computationally predicted depths and widths increased with increased laser energy input and computationally predicted widths remained higher than experimentally measured widths whereas computationally predicted depths were slightly higher than experimentally measured depths and reversed this trend for the laser fluence >6 J/mm2. While in both groups, the machining rate increased with increased laser fluence, experimentally derived machining rate remained lower than the computationally predicted values for the laser fluences lower than ∼4.75 J/mm2 for one group and ∼5.8 J/mm2 for other group and reversed in this trend thereafter. The integrated experimental-computational approach identified the physical processes affecting machining attributes.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.010
  • Reducing the sensation of electrical stimulation with dry electrodes by
           using an array of constant current sources
    • Authors: Cassandra D Solomons; Martin Slovak; Ben Heller; Anthony T. Barker
      Abstract: Publication date: Available online 1 December 2017
      Source:Medical Engineering & Physics
      Author(s): Cassandra D Solomons, Martin Slovak, Ben Heller, Anthony T. Barker
      Hydrogel electrodes are commonly used for functional and other electrical stimulation applications since the hydrogel layer has been shown to considerably reduce the perception of stimulation compared to dry electrodes. However, these hydrogel electrodes must be changed regularly as they dry out or become contaminated with skin cells and sweat products, thus losing their adhesiveness and resistive properties. Dry electrodes are longer lasting but are more uncomfortable due to unequal current distribution (current hogging). We hypothesise that if current through a dry electrode is equally shared amongst an array of small sub-electrodes, current hogging and thus the sensitivity perceived due to stimulation will be reduced. We constructed an 8 × 8 array of millimetre sized dry electrodes that could either be activated as individual current sources, or together as one large source. A study was performed with 13 participants to investigate the differences in sensation between the two modes of operation. The results showed that 12 out of 13 participants found the new (distributed-constant-current) approach allowed higher stimulation for the same sensation. The differences in sensation between single and multiple sources became larger with higher intensity levels.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.001
  • Validation of an alignment method using motion tracking system for
           in-vitro orientation of cadaveric hip joints with reduced set of
           anatomical landmarks
    • Authors: Suzan Bsat; Ifaz Haider; Andrew Speirs; Paul Beaulé; Hanspeter Frei
      Abstract: Publication date: Available online 1 December 2017
      Source:Medical Engineering & Physics
      Author(s): Suzan Bsat, Ifaz Haider, Andrew Speirs, Paul Beaulé, Hanspeter Frei
      Accurate in-vitro orientation of cadaveric hip joints is challenging due to limited available anatomical landmarks. Published hip joint in-vitro investigations commonly lack details on methods used to achieve reported orientations and the accuracy with which the desired orientation has been achieved. The aim of this study was to develop an accurate method for orienting hip joints with limited anatomical landmarks for in-vitro investigations, and to compare this method against orientation using guiding axes and by visual approximation. The proposed orientation method resulted in orientation angles achieved to within one degree (SD ± 0.58°). For most specimens, orientation using physical tools resulted in errors of ±8° and ±12° in at least one of three orientation angles used to place the femur and pelvis in neutral orientation, respectively. Precision was also worse, with SDs ranging from ±1° to ±5° for orientation angles of femoral specimens and SDs ranging from ±1° to ±8° for pelvic specimens. The error in the orientation angles was worse for orientation by visual approximation and the range of SDs were greater for both the femur and pelvis. Finite element modeling was used to assess the effects of observed orientation errors, on prediction of fracture load. In most cases, the largest error in fracture load among all trials exceeded 30%, relative to a femur oriented without any error in the orientation angles.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.11.002
  • Functional testing on engineered cartilage to identify the role played by
    • Authors: Ling Wang; Hao Shen; Jichang Nie; Dichen Li; Hongbin Fan; Zhongmin Jin; Chaozong Liu
      Abstract: Publication date: Available online 24 November 2017
      Source:Medical Engineering & Physics
      Author(s): Ling Wang, Hao Shen, Jichang Nie, Dichen Li, Hongbin Fan, Zhongmin Jin, Chaozong Liu
      Compressive loading is crucial for tissue regeneration in cartilage; however, the role played by shearing induced from translational or rotational motion of the knee joint has yet to be identified. This study aims at investigating the effects of in vivo like dynamic load–compression integrated with shearing on tissue regeneration, particularly to identify the role played by shearing induced from rotational motion. Tissue samples fabricated from a calcium alginate hydrogel embedded with chondrocytes were subjected to a dynamic tissue culture. Three culturing regimes were included: a static culture control (CON), compression combined with shearing induced from translational motion (CS), and compression combined with shearing induced from both translational and rotational motion (CSR). The results indicate that the CS group has a significantly larger chondrocyte proliferation rate (p < .01), and that the CSR group has no advantages over the CS group. However, the CSR group was found to have a marked influence on the matrix synthesis compared to that of the CS group (p < .01). It can be concluded that shearing from individual joint motions offers a different contribution to the chondrocyte proliferation, matrix synthesis, and phenotype maintenance, and better insight into these individual roles will be necessary for determining the efficacy of in vivo/vitro cartilageous tissue functionalization.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.10.011
  • Deviations in frequency and mode of vibration in whole-body vibration
           training devices with long-term and regular use
    • Authors: Tobias S. Kaeding; Sanam Moghaddamnia; Momme Kück; Lothar Stein
      Abstract: Publication date: Available online 16 November 2017
      Source:Medical Engineering & Physics
      Author(s): Tobias S. Kaeding, Sanam Moghaddamnia, Momme Kück, Lothar Stein
      Research regarding whole body vibration training (WBVT) and its practical use may be hindered by the fact that WBVT devices generate frequencies and/or modes of vibration different from their preset adjustments. This research aimed to clarify whether prolonged regular use can generate such deviations in frequency and mode of vibration. Three WBVT devices, each used for approximately 13 months in two research projects, were tested with an accelerometer before start of the 1st study, after four months, and after 13 months (the completion of the 2nd study). Divergences between the preset and measured frequencies were calculated for all measurements. Furthermore, the total harmonic distortion (THD), an index for signal deviations from a perfect sine wave, and the sum signal-to-modulation-noise-ratio (SMNR), an indicator of fidelity, were recorded. One device had a significantly larger machine run time than the other two, and it displayed the most pronounced signs of impaired function concerning frequency, mode of vibration, and random variability (SMNR) after prolonged use. These results indicate that prolonged use will result in divergences between the preset and actual applied frequencies as well as in the mode of vibration and other accuracy measurements.

      PubDate: 2017-12-11T06:42:52Z
      DOI: 10.1016/j.medengphy.2017.10.013
  • In vivo tibiofemoral skeletal kinematics and cartilage contact
           arthrokinematics during decline walking after isolated meniscectomy
    • Authors: Liying Zheng; Robert Carey; Eric Thorhauer; Scott Tashman; Christopher Harner; Xudong Zhang
      Abstract: Publication date: Available online 6 November 2017
      Source:Medical Engineering & Physics
      Author(s): Liying Zheng, Robert Carey, Eric Thorhauer, Scott Tashman, Christopher Harner, Xudong Zhang
      We investigated the effects of isolated meniscectomy on tibiofemoral skeletal kinematics and cartilage contact arthrokinematics in vivo. We recruited nine patients who had undergone isolated medial or lateral meniscectomy, and used a dynamic stereo-radiography (DSX) system to image the patients’ knee motion during decline walking. A volumetric model-based tracking process determined 3D tibiofemoral kinematics from the recorded DSX images. Cartilage contact arthrokinematics was derived from the intersection between tibial and femoral cartilage models co-registered to the bones. The kinematics and arthrokinematics were analyzed for early stance and loading response phase (30% of a gait cycle), comparing the affected and intact knees. Results showed that four patients with medial meniscectomy had significantly greater contact centroid excursions in the meniscectomized medial compartments while five patients with lateral meniscectomy had significantly greater cartilage contact area and lateral shift of contact centroid path in the meniscectomized lateral compartments, comparing to those of the same compartments in the contralateral intact knees. No consistent difference however was identified in the skeletal kinematics. The current study demonstrated that cartilage-based intra-articular arthrokinematics is more sensitive and insightful than the skeletal kinematics in assessing the meniscectomy effects.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.10.014
  • Measurement of physical activity in the pre- and early post-operative
           period after total knee arthroplasty for Osteoarthritis using a Fitbit
           Flex device
    • Authors: Joshua Twiggs; Lucy Salmon; Elizabeth Kolos; Emily Bogue; Brad Miles; Justin Roe
      Abstract: Publication date: Available online 6 November 2017
      Source:Medical Engineering & Physics
      Author(s): Joshua Twiggs, Lucy Salmon, Elizabeth Kolos, Emily Bogue, Brad Miles, Justin Roe
      Total knee arthroplasty (TKA) is a standard treatment for patients with end stage knee Osteoarthritis (OA) to reduce pain and restore function. The aim of this study was to assess pre- and early post-operative physical activity (PA) with Fitbit Flex devices for patients with OA undergoing TKA and determine any benchmarks for expected post-operative activity. Significant correlations of pre-operative step count, post-operative step count, Body Mass Index (BMI) and Short Form 12 Physical Component Summaries (SF-12 PCS) were found. Mean step counts varied by 3,203 steps per day between obese and healthy weight patients, and 3,786 steps per day between those with higher and lower SF-12 PCS scores, suggesting the need for benchmarks for recovery that vary by patient pre-operative factors. A backwards stepwise regression model developed to provide patient specific step count predictions at 6 weeks had an R 2 of 0.754, providing a robust patient specific benchmark for post-operative recovery, while population means from BMI and SF-12 subgroups provide a clinically practical alternative.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.10.007
  • Estimated landmark calibration of biomechanical models for inverse
    • Authors: Ursula Trinler; Richard Baker
      Abstract: Publication date: Available online 6 November 2017
      Source:Medical Engineering & Physics
      Author(s): Ursula Trinler, Richard Baker
      Inverse kinematics is emerging as the optimal method in movement analysis to fit a multi-segment biomechanical model to experimental marker positions. A key part of this process is calibrating the model to the dimensions of the individual being analysed which requires scaling of the model, pose estimation and localisation of tracking markers within the relevant segment coordinate systems. The aim of this study is to propose a generic technique for this process and test a specific application to the OpenSim model Gait2392. Kinematic data from 10 healthy adult participants were captured in static position and normal walking. Results showed good average static and dynamic fitting errors between virtual and experimental markers of 0.8 cm and 0.9 cm, respectively. Highest fitting errors were found on the epicondyle (static), feet (static, dynamic) and on the thigh (dynamic). These result from inconsistencies between the model geometry and degrees of freedom and the anatomy and movement pattern of the individual participants. A particular limitation is in estimating anatomical landmarks from the bone meshes supplied with Gait2392 which do not conform with the bone morphology of the participants studied. Soft tissue artefact will also affect fitting the model to walking trials.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.10.015
  • Study of main and cross-over effects on pressure relief among body mass
           index (BMI), body position and supporting material properties
    • Authors: Chi-leung Hui; Qilong Feng; M.S. Wong; Sau-fun Ng; Yummy Y.M. LIN
      Abstract: Publication date: Available online 3 November 2017
      Source:Medical Engineering & Physics
      Author(s): Chi-leung Hui, Qilong Feng, M.S. Wong, Sau-fun Ng, Yummy Y.M. LIN
      Pressure ulcers influence people with limited mobility who must spend a long time lying or sitting because these positions create high interfacial pressure between the body and supporting materials. Supporting materials, such as mattresses and cushions, are designed to prevent pressure ulcers by increasing the contact area, reducing the interfacial pressure or reducing the contact time. Foam is the most common supporting material for relieving pressure because it is cheap and easy to change its shape to fit the contour of the body. Past studies showed that BMI, body position and supporting material properties have an impact on relieving pressure; however, there is no study of the main and cross-over effects among these parameters. This study aims to investigate the main and cross-over effects among BMI, body position and supporting material properties on pressure relieving performance using univariate ANOVA and correlation analysis. It was found that body position and foam density were the main effect and BMI and body position, and body position and foam density were the cross-over effects on pressure relief. It was also found that low density Polyurethane (PU) foam of less than 4 cm in thickness as well as the appropriate K2 and K3 moduli are best suited for pressure relief. The actual value of foam thickness and the appropriate K2 and K3 moduli are subject to BMI values and body position. The significance of the outcomes from this study is that it will aid in optimizing the design of supporting materials with varied BMI values and body positions to greatly reduce pressure ulcers for ailing patients.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.10.012
  • Arduino control of a pulsatile flow rig
    • Authors: S. Drost; B.J. de Kruif; D. Newport
      Abstract: Publication date: Available online 3 November 2017
      Source:Medical Engineering & Physics
      Author(s): S. Drost, B.J. de Kruif, D. Newport
      This note describes the design and testing of a programmable pulsatile flow pump using an Arduino micro-controller. The goal of this work is to build a compact and affordable system that can relatively easily be programmed to generate physiological waveforms. The system described here was designed to be used in an in-vitro set-up for vascular access hemodynamics research, and hence incorporates a gear pump that delivers a mean flow of 900 ml/min in a test flow loop, and a peak flow of 1106 ml/min. After a number of simple identification experiments to assess the dynamic behaviour of the system, a feed-forward control routine was implemented. The resulting system was shown to be able to produce the targeted representative waveform with less than 3.6% error. Finally, we outline how to further increase the accuracy of the system, and how to adapt it to specific user needs.

      PubDate: 2017-11-10T21:04:18Z
      DOI: 10.1016/j.medengphy.2017.10.006
  • In-vivo viscous properties of the heel pad by stress-relaxation experiment
           based on a spherical indentation
    • Authors: Ryo Suzuki; Kohta Ito; Taeyong Lee; Naomichi Ogihara
      Abstract: Publication date: Available online 2 November 2017
      Source:Medical Engineering & Physics
      Author(s): Ryo Suzuki, Kohta Ito, Taeyong Lee, Naomichi Ogihara
      Identifying the viscous properties of the plantar soft tissue is crucial not only for understanding the dynamic interaction of the foot with the ground during locomotion, but also for development of improved footwear products and therapeutic footwear interventions. In the present study, the viscous and hyperelastic material properties of the plantar soft tissue were experimentally identified using a spherical indentation test and an analytical contact model of the spherical indentation test. Force-relaxation curves of the heel pads were obtained from the indentation experiment. The curves were fit to the contact model incorporating a five-element Maxwell model to identify the viscous material parameters. The finite element method with the experimentally identified viscoelastic parameters could successfully reproduce the measured force-relaxation curves, indicating the material parameters were correctly estimated using the proposed method. Although there are some methodological limitations, the proposed framework to identify the viscous material properties may facilitate the development of subject-specific finite element modeling of the foot and other biological materials.

      PubDate: 2017-11-03T19:03:45Z
      DOI: 10.1016/j.medengphy.2017.10.010
  • Characterization of an innovative intramedullary nail for diaphyseal
           fractures of long bones
    • Authors: Filardi
      Abstract: Publication date: November 2017
      Source:Medical Engineering & Physics, Volume 49
      Author(s): V. Filardi
      In this paper, an innovative design of nail for fractures occurring on long bones has been investigated. Its functioning is based essentially on sliding of conical surfaces, located in a spindle and in holding pins. Spindle and holding pins are connected together by a sleeve. The sliding transforms the rotational and translational motion of the spindle to a radial expansion of the holding pins, protruding inside the intramedullary canal. In order to evaluate mechanical behavior of the prosthesis different benchmarks and tests were numerically performed by an FE code. Results confirm good performances in terms of strength, under compression, bending and torque loading. Moreover, a complete model of the nail implanted on a tibia, has been developed and tested evaluating two loading configurations. Results confirmed a satisfactory behavior of the nail in terms of stress and strain shielding, comparable to the others traditional systems of prosthesis. In conclusion, this kind of nail appears to offer a good solution for elderly patients, which could not endure complications due to a complex surgery, as distal or medial screws are not necessary.

      PubDate: 2017-10-26T17:46:45Z
  • Prediction of ground reaction forces for Parkinson's disease patients
           using a kinect-driven musculoskeletal gait analysis model
    • Authors: Moataz Eltoukhy; Christopher Kuenze; Michael S. Andersen; Jeonghoon Oh; Joseph Signorile
      Abstract: Publication date: Available online 26 October 2017
      Source:Medical Engineering & Physics
      Author(s): Moataz Eltoukhy, Christopher Kuenze, Michael S. Andersen, Jeonghoon Oh, Joseph Signorile
      Kinetic gait abnormalities result in reduced mobility among individuals with Parkinson's disease (PD). Currently, the assessment of gait kinetics can only be achieved using costly force plates, which makes it difficult to implement in most clinical settings. The Microsoft Kinect v2 has been shown to be a feasible clinic-based alternative to more sophisticated three-dimensional motion analysis systems in producing acceptable spatiotemporal and kinematic gait parameters. In this study, we aimed to validate a Kinect-driven musculoskeletal model using the AnyBody modeling system to predict three-dimensional ground reaction forces (GRFs) during gait in patients with PD. Nine patients with PD performed over-ground walking trials as their kinematics and ground reaction forces were measured using a Kinect v2 and force plates, respectively. Kinect v2 model-based and force-plate measured peak vertical and horizontal ground reaction forces and impulses produced during the braking and propulsive phases of the gait cycle were compared. Additionally, comparison of ensemble curves and associated 90% confidence intervals (CI90) of the three-dimensional GRFs were constructed to investigate if the Kinect sensor could provide consistent and accurate GRF predictions throughout the gait cycle. Results showed that the Kinect v2 sensor has the potential to be an effective clinical assessment tool for predicting GRFs produced during gait for patients with PD. However, the observed findings should be replicated and model reliability established prior to integration into the clinical setting.

      PubDate: 2017-10-26T17:46:45Z
      DOI: 10.1016/j.medengphy.2017.10.004
  • Force estimation in fatigue condition using a muscle-twitch model during
           isometric finger contraction
    • Authors: Youngjin Na; Sangjoon J. Kim; Jung Kim
      Abstract: Publication date: Available online 18 October 2017
      Source:Medical Engineering & Physics
      Author(s): Youngjin Na, Sangjoon J. Kim, Jung Kim
      We propose a force estimation method in fatigue condition using a muscle-twitch model and surface electromyography (sEMG). The twitch model, which is an estimate of force by a single spike, was obtained from sEMG features and measured forces. Nine healthy subjects performed isometric index finger abduction until exhaustion for a series of dynamic contractions (0–20% MVC) to characterize the twitch model and static contractions (50% MVC) to induce muscle fatigue. Muscle fatigue was identified based on the changes of twitch model; the twitch peak decreased and the contraction time increased as muscle fatigue developed. Force estimation performance in non-fatigue and fatigue conditions was evaluated and its results were compared with that of a conventional method using the mean absolute value (MAV). In non-fatigue conditions, the performance of the proposed method (0.90 ± 0.05) and the MAV method (0.88 ± 0.06) were comparable. In fatigue conditions, the performance was significantly improved for the proposed method (0.87 ± 0.05) compared with the MAV (0.78 ± 0.09).

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.10.002
  • Non-contact and through-clothing measurement of the heart rate using
           ultrasound vibrocardiography
    • Authors: Nathan Jeger-Madiot; Jérôme Gateau; Mathias Fink; Ros-Kiri Ing
      Abstract: Publication date: Available online 17 October 2017
      Source:Medical Engineering & Physics
      Author(s): Nathan Jeger-Madiot, Jérôme Gateau, Mathias Fink, Ros-Kiri Ing
      We present a novel non-contact system for monitoring the heart rate on human subjects with clothes. Our approach is based on vibrocardiography, and measures locally skin displacements. Vibrocardiography with a laser Doppler vibrometer already allows monitoring of this vital sign, but can only be used on bare skin and requires an expensive piece of equipment. We propose here to use an airborne pulse-Doppler ultrasound system operating in the 20–60 kHz range, and comprised of an emitter focusing the ultrasound pulses on skin and a microphone recording the reflected waves. Our implementation was validated in vitro and on two healthy human subjects, using simultaneously laser vibrocardiography and electrocardiography as references. Accurate measurements of the heart rate on clothed skin suggest that our non-contact ultrasonic method could be implemented both inside and outside the clinical environment, and therefore benefit both medical and safety applications.

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.09.003
  • Modelling of thrombin generation under flow in realistic left anterior
           descending geometries
    • Authors: Konstantinos P. Papadopoulos; Grigoris T. Gerotziafas; Manolis Gavaises
      Abstract: Publication date: Available online 16 October 2017
      Source:Medical Engineering & Physics
      Author(s): Konstantinos P. Papadopoulos, Grigoris T. Gerotziafas, Manolis Gavaises
      Currently there are no available methods for prediction of thrombotic complications in Coronary Artery disease. Additionally, blood coagulation tests are mainly performed in a steady system while coagulation in vivo occurs under flow conditions. In this work, a phenomenological model for coagulation up-to thrombin generation is proposed; the model is mainly based on the results of thrombin generation assays and therefore it can account for the variation of the coagulability that is observed in different individuals. The model is applied on 3 cases of left anterior descending arteries (LAD) with 50% maximum stenosis placed at a different location and have been statistically assessed as of different complication risk. The simulations showed that parameters of thrombin generation assays obtain different values when they refer to thrombin generation under realistic coronary flow conditions. The flow conditions prevailing locally because of the geometric differences among the arterial trees can lead to different initiation times and thrombin production rates and it also alters the spatial distribution of the coagulation products. Similarly, small changes of the coagulation characteristics of blood under identical flow conditions can allow or prevent the initiation of coagulation. The results indicate that combined consideration of geometry and coagulation characteristics of blood can lead to entirely different conclusions compared to independent assessment of each factor.

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.10.001
  • A comparative surface topographical analysis of explanted total knee
           replacement prostheses: Oxidised zirconium vs cobalt chromium femoral
    • Authors: Emma Kennard; Susan C. Scholes; Raghavendra Sidaginamale; Rajkumar Gangadharan; David J. Weir; James Holland; David Deehan; Thomas J. Joyce
      Abstract: Publication date: Available online 15 October 2017
      Source:Medical Engineering & Physics
      Author(s): Emma Kennard, Susan C. Scholes, Raghavendra Sidaginamale, Rajkumar Gangadharan, David J. Weir, James Holland, David Deehan, Thomas J. Joyce
      It has been proposed that an increased surface roughness of the femoral components of Total Knee Replacements (TKRs) may be a contributing factor to the accelerated wear of the polyethylene (PE) bearing and ultimately prosthesis failure. Oxidised Zirconium was introduced to the orthopaedic market in an attempt to reduce PE wear associated failures and increase the longevity of the prosthesis. In this study, non-contacting profilometry was used to measure the surface roughness of the femoral components of 6 retrieved TKRs (3 Oxidised Zirconium (OxZr) and 3 Cobalt Chromium alloy (CoCr) femoral components) and 2 as-manufactured femoral components (1 OxZr and 1 CoCr). A semi-quantitative method was used to analyse the damage on the retrieved PE components. The S a values for the retrieved OxZr femoral components (Sa = 0.093 µm ± 0.014) and for the retrieved CoCr femoral components (Sa = 0.065 µm ± 0.005) were significantly greater (p < .05) than the roughness values for the as-manufactured femoral components (OxZr Sa = 0.061 µm ± 0.004 and CoCr Sa = 0.042 µm ± 0.003). No significant difference was seen between the surface roughness parameters of the retrieved OxZr and retrieved CoCr femoral components. There was no difference between the PE component damage scores for the retrieved OxZr TKRs compared to the retrieved CoCr TKRs. These results agree with other studies that both OxZr and CoCr femoral components roughen during time in vivo but the lack of difference between the surface roughness measurements of the two materials is in contrast to previous topographical reports. Further analysis of retrieved OxZr TKRs is recommended so that a fuller appreciation of their benefits and limitations be obtained.

      PubDate: 2017-10-19T16:18:08Z
      DOI: 10.1016/j.medengphy.2017.10.003
  • Identification of the period of stability in a balance test after stepping
           up using a simplified cumulative sum
    • Authors: Doha Safieddine; Aly Chkeir; Cyrille Herlem; Delphine Bera; Michèle Collart; Jean-Luc Novella; Moustapha Dramé; David J. Hewson; Jacques Duchêne
      Abstract: Publication date: Available online 19 September 2017
      Source:Medical Engineering & Physics
      Author(s): Doha Safieddine, Aly Chkeir, Cyrille Herlem, Delphine Bera, Michèle Collart, Jean-Luc Novella, Moustapha Dramé, David J. Hewson, Jacques Duchêne
      Falls are a major cause of death in older people. One method used to predict falls is analysis of Centre of Pressure (CoP) displacement, which provides a measure of balance quality. The Balance Quality Tester (BQT) is a device based on a commercial bathroom scale that calculates instantaneous values of vertical ground reaction force (Fz) as well as the CoP in both anteroposterior (AP) and mediolateral (ML) directions. The entire testing process needs to take no longer than 12 s to ensure subject compliance, making it vital that calculations related to balance are only calculated for the period when the subject is static. In the present study, a method is presented to detect the stabilization period after a subject has stepped onto the BQT. Four different phases of the test are identified (stepping-on, stabilization, balancing, stepping-off), ensuring that subjects are static when parameters from the balancing phase are calculated. The method, based on a simplified cumulative sum (CUSUM) algorithm, could detect the change between unstable and stable stance. The time taken to stabilize significantly affected the static balance variables of surface area and trajectory velocity, and was also related to Timed-up-and-Go performance. Such a finding suggests that the time to stabilize could be a worthwhile parameter to explore as a potential indicator of balance problems and fall risk in older people.

      PubDate: 2017-09-21T13:32:43Z
      DOI: 10.1016/j.medengphy.2017.07.005
  • A combined kinematic and kinetic analysis at the residuum/socket interface
           of a knee-disarticulation amputee
    • Authors: Jinghua Tang; Michael McGrath; Nick Hale; Liudi Jiang; Dan Bader; Piotr Laszczak; David Moser; Saeed Zahedi
      Abstract: Publication date: Available online 15 September 2017
      Source:Medical Engineering & Physics
      Author(s): Jinghua Tang, Michael McGrath, Nick Hale, Liudi Jiang, Dan Bader, Piotr Laszczak, David Moser, Saeed Zahedi
      The bespoke interface between a lower limb residuum and a prosthetic socket is critical for an amputee's comfort and overall rehabilitation outcomes. Analysis of interface kinematics and kinetics is important to gain full understanding of the interface biomechanics, which could aid clinical socket fit, rehabilitation and amputee care. This pilot study aims to investigate the dynamic correlation between kinematic movement and kinetic stresses at the interface during walking tests on different terrains. One male, knee disarticulation amputee participated in the study. He was asked to walk on both a level surface and a 5° ramped surface. The movement between the residuum and the socket was evaluated by the angular and axial couplings, based on the outputs from a 3D motion capture system. The corresponding kinetic stresses at anterior-proximal (AP), posterior-proximal (PP) and anterior-distal (AD) locations of the residuum were measured, using individual stress sensors. Approximately 8° of angular coupling and up to 32 mm of axial coupling were measured when walking on different terrains. The direction of the angular coupling shows strong correlation with the pressure difference between the PP and AP sensors. Higher pressure was obtained at the PP location than the AP location during stance phase, associated with the direction of the angular coupling. A strong correlation between axial coupling length, L, and longitudinal shear was also evident at the PP and AD locations i.e. the shortening of L corresponds to the increase of shear in the proximal direction. Although different terrains did not affect these correlations in principle, interface kinematic and kinetic values suggested that gait changes can induce modifications to the interface biomechanics. It is envisaged that the reported techniques could be potentially used to provide combined kinematics and kinetics for the understanding of biomechanics at the residuum/socket interface, which may play an important role in the clinical assessment of prosthetic component settings, including socket fit quality.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.014
  • A model of blood supply to the brain via the carotid arteries: Effects of
           obstructive vs. sclerotic changes
    • Authors: O. Onaizah; T.L. Poepping; M. Zamir
      Abstract: Publication date: Available online 13 September 2017
      Source:Medical Engineering & Physics
      Author(s): O. Onaizah, T.L. Poepping, M. Zamir
      The carotid artery is one of the major supply routes of blood to the brain and a common site of vascular disease. Obstructive and sclerotic disorders within the carotid artery impact local blood flow patterns as well as overall impedance and blood supply to the brain. A lumped parameter model and an experimental in-vitro flow loop were used to study the effects of local stenosis and stiffness in the carotid artery based on a family of phantoms with different degrees of stenosis and compliance. The model also allows independent examination of the effects of downstream resistance and compliance. Mild to moderate stenosis was found to lead to minimal (∼1%) reduction in blood supply to the brain. Reduction in mean internal carotid artery (ICA) flow was statistically significant (p< 0.01) only above 70% stenosis. On the other hand, a three-fold increase in stiffness of the carotid artery, as might occur in aging, was found to lead to a modest yet statistically significant reduction (p< 0.01) in mean ICA flow. Effects of changing downstream resistance and compliance were examined. For a given pressure waveform, reduction in downstream compliance led to altered waveform shape and reduction in peak systolic flow rates where the mean flow rates were not altered. Increased downstream resistance resulted in drastic reduction in mean flow rates.

      PubDate: 2017-09-16T13:05:59Z
      DOI: 10.1016/j.medengphy.2017.08.009
  • A simulation framework for humeral head translations
    • Authors: Ehsan Sarshari; Alain Farron; Alexandre Terrier; Dominique Pioletti; Philippe Mullhaupt
      Abstract: Publication date: Available online 8 September 2017
      Source:Medical Engineering & Physics
      Author(s): Ehsan Sarshari, Alain Farron, Alexandre Terrier, Dominique Pioletti, Philippe Mullhaupt
      Humeral head translations (HHT) play a crucial role in the glenohumeral (GH) joint function. The available shoulder musculoskeletal models developed based on inverse dynamics however fall short of predicting the HHT. This study aims at developing a simulation framework that allows forward-dynamics simulation of a shoulder musculoskeletal model with a 6 degrees of freedom (DOF) GH joint. It provides a straightforward solution to the HHT prediction problem. We show that even within a forward-dynamics simulation addressing the HHT requires further information about the contact. To that end, a deformable articular contact is included in the framework defining the GH joint contact force in terms of the joint kinematics. An abduction motion in the scapula plane is simulated. The results are given in terms of HHT, GH joint contact force, contact areas, contact pressure, and cartilage strain. It predicts a superior-posterior translation of the humeral head followed by an inferior migration.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.013
  • Modal analysis for the assessment of cementless hip stem primary stability
           in preoperative THA planning
    • Authors: Andres Rondon; Elhadi Sariali; Quentin Vallet; Quentin Grimal
      Abstract: Publication date: Available online 7 September 2017
      Source:Medical Engineering & Physics
      Author(s): Andres Rondon, Elhadi Sariali, Quentin Vallet, Quentin Grimal
      This numerical vibration finite element (FE) study introduces resonance three-dimensional planning (RP3D) to assess preoperatively the primary stability of a cementless stem for total hip arthroplasty. Based on a patient’s CT-scan and a numerical model of a stem, RP3D aims at providing mechanical criteria indicative of the achievable primary stability. We investigate variations of the modal response of the stem to changes of area and apparent stiffness of the bone-implant interface. The model is computationally cheap as it does not include a mesh of the bone. The apparent stiffness of the bone is modeled by springs attached to the nodes of the stem’s mesh. We investigate an extended range of stiffness values while, in future works, patient’s specific Hounsfield values could be used to define stiffness. We report modal frequencies, shapes, and a ratio of elastic potential energies (rEPE) that quantifies the proximal motion that should be minimum for a stable stem. The modal response exhibits a clear transition between loose and tight contact as area and stiffness of the interface increase. rEPE thresholds that could potentially discriminate preoperatively between stable and unstable stems are given for a Symbios SPS® size C stem.
      Graphical abstract image

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.07.013
  • Experimental and modelling characterisation of adjustable hollow
           Micro-needle delivery systems
    • Authors: Ting-Ting Liu; Kai Chen; Min Pan
      Abstract: Publication date: Available online 7 September 2017
      Source:Medical Engineering & Physics
      Author(s): Ting-Ting Liu, Kai Chen, Min Pan
      Background Hollow micro-needles have been used increasingly less in practice because the infusion into the skin is limited by the tissue resistance to flow. The relationship between the infusion flow rate and tissue resistance pressure is not clear. Methods A custom-made, hollow micro-needle system was used in this study. The driving force and infusion flow rate were measured using a force transducer attached to an infusion pump. Evans blue dye was injected into the air, polyacrylamide gel and in-vivo mouse skin at different flow rates. Two different micro-needle lengths were used for in-vivo infusion into the mouse. A model was derived to calculate the driving force of the micro-needle infusion into the air, and the results were compared to experimental data. Results The calculated driving forces match the experimental results with different infusion flow rates. The pressure loss throughout the micro-needle delivery system was found to be two orders smaller than the resistance pressure inside the gel and mouse skin, and the resistance pressure increased with increasing flow rate. A portion of liquid backflow was observed when the flow rate was relatively larger, and the backflow was associated with a sudden larger increase in resistance pressure at a higher flow rate. Conclusions The current micro-needle delivery system is capable of administering liquid into the mouse skin at a flow rate of up to 0.15 ml/min, without causing significant backflow on the surface. The resistance pressure increases with increasing flow rate, causing infusion restriction at higher flow rates.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.012
  • Radiographic cup anteversion measurement corrected from pelvic tilt
    • Authors: Liao Wang; Andrew R. Thoreson; Robert T. Trousdale; Bernard F. Morrey; Kerong Dai; Kai-Nan An
      Abstract: Publication date: Available online 6 September 2017
      Source:Medical Engineering & Physics
      Author(s): Liao Wang, Andrew R. Thoreson, Robert T. Trousdale, Bernard F. Morrey, Kerong Dai, Kai-Nan An
      The purpose of this study was to develop a novel technique to improve the accuracy of radiographic cup anteversion measurement by correcting the influence of pelvic tilt. Ninety virtual total hip arthroplasties were simulated from computed tomography data of 6 patients with 15 predetermined cup orientations. For each simulated implantation, anteroposterior (AP) virtual pelvic radiographs were generated for 11 predetermined pelvic tilts. A linear regression model was created to capture the relationship between radiographic cup anteversion angle error measured on AP pelvic radiographs and pelvic tilt. Overall, nine hundred and ninety virtual AP pelvic radiographs were measured, and 90 linear regression models were created. Pearson's correlation analyses confirmed a strong correlation between the errors of conventional radiographic cup anteversion angle measured on AP pelvic radiographs and the magnitude of pelvic tilt (P < 0.001). The mean of 90 slopes and y-intercepts of the regression lines were −0.8 and −2.5°, which were applied as the general correction parameters for the proposed tool to correct conventional cup anteversion angle from the influence of pelvic tilt. The current method proposes to measure the pelvic tilt on a lateral radiograph, and to use it as a correction for the radiographic cup anteversion measurement on an AP pelvic radiograph. Thus, both AP and lateral pelvic radiographs are required for the measurement of pelvic posture-integrated cup anteversion. Compared with conventional radiographic cup anteversion, the errors of pelvic posture-integrated radiographic cup anteversion were reduced from 10.03 (SD = 5.13) degrees to 2.53 (SD = 1.33) degrees. Pelvic posture-integrated cup anteversion measurement improves the accuracy of radiographic cup anteversion measurement, which shows the potential of further clarifying the etiology of postoperative instability based on planar radiographs.

      PubDate: 2017-09-09T12:46:04Z
      DOI: 10.1016/j.medengphy.2017.08.008
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