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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  [3177 journals]
  • Impact of isotropic constitutive descriptions on the predicted peak wall
           stress in abdominal aortic aneurysms
    • Authors: V. Man; S. Polzer; T.C. Gasser; T. Novotny; J. Bursa
      Pages: 49 - 57
      Abstract: Publication date: March 2018
      Source:Medical Engineering & Physics, Volume 53
      Author(s): V. Man, S. Polzer, T.C. Gasser, T. Novotny, J. Bursa
      Biomechanics-based assessment of Abdominal Aortic Aneurysm (AAA) rupture risk has gained considerable scientific and clinical momentum. However, computation of peak wall stress (PWS) using state-of-the-art finite element models is time demanding. This study investigates which features of the constitutive description of AAA wall are decisive for achieving acceptable stress predictions in it. Influence of five different isotropic constitutive descriptions of AAA wall is tested; models reflect realistic non-linear, artificially stiff non-linear, or artificially stiff pseudo-linear constitutive descriptions of AAA wall. Influence of the AAA wall model is tested on idealized ( n = 4 ) and patient-specific ( n = 16 ) AAA geometries. Wall stress computations consider a (hypothetical) load-free configuration and include residual stresses homogenizing the stresses across the wall. Wall stress differences amongst the different descriptions were statistically analyzed. When the qualitatively similar non-linear response of the AAA wall with low initial stiffness and subsequent strain stiffening was taken into consideration, wall stress (and PWS) predictions did not change significantly. Keeping this non-linear feature when using an artificially stiff wall can save up to 30% of the computational time, without significant change in PWS. In contrast, a stiff pseudo-linear elastic model may underestimate the PWS and is not reliable for AAA wall stress computations.

      PubDate: 2018-02-26T04:34:46Z
      DOI: 10.1016/j.medengphy.2018.01.002
      Issue No: Vol. 53 (2018)
  • Editorial
    • Authors: Richard A. Black (PhD CSci CEng FIMechE FIPEM)
      First page: 1
      Abstract: Publication date: January 2018
      Source:Medical Engineering & Physics, Volume 51
      Author(s): Richard A. Black (PhD CSci CEng FIMechE FIPEM)

      PubDate: 2018-01-05T20:47:59Z
      DOI: 10.1016/j.medengphy.2017.12.001
      Issue No: Vol. 51 (2018)
  • CT image segmentation methods for bone used in medical additive
    • Authors: Maureen van Eijnatten; Roelof van Dijk; Johannes Dobbe; Geert Streekstra; Juha Koivisto; Jan Wolff
      Pages: 6 - 16
      Abstract: Publication date: January 2018
      Source:Medical Engineering & Physics, Volume 51
      Author(s): Maureen van Eijnatten, Roelof van Dijk, Johannes Dobbe, Geert Streekstra, Juha Koivisto, Jan Wolff
      Aim of the study The accuracy of additive manufactured medical constructs is limited by errors introduced during image segmentation. The aim of this study was to review the existing literature on different image segmentation methods used in medical additive manufacturing. Methods Thirty-two publications that reported on the accuracy of bone segmentation based on computed tomography images were identified using PubMed, ScienceDirect, Scopus, and Google Scholar. The advantages and disadvantages of the different segmentation methods used in these studies were evaluated and reported accuracies were compared. Results The spread between the reported accuracies was large (0.04 mm – 1.9 mm). Global thresholding was the most commonly used segmentation method with accuracies under 0.6 mm. The disadvantage of this method is the extensive manual post-processing required. Advanced thresholding methods could improve the accuracy to under 0.38 mm. However, such methods are currently not included in commercial software packages. Statistical shape model methods resulted in accuracies from 0.25 mm to 1.9 mm but are only suitable for anatomical structures with moderate anatomical variations. Conclusions Thresholding remains the most widely used segmentation method in medical additive manufacturing. To improve the accuracy and reduce the costs of patient-specific additive manufactured constructs, more advanced segmentation methods are required.

      PubDate: 2018-01-05T20:47:59Z
      DOI: 10.1016/j.medengphy.2017.10.008
      Issue No: Vol. 51 (2018)
  • The effects of cutting parameters on cutting forces and heat generation
           when drilling animal bone and biomechanical test materials
    • Authors: Akos Cseke; Robert Heinemann
      Pages: 24 - 30
      Abstract: Publication date: January 2018
      Source:Medical Engineering & Physics, Volume 51
      Author(s): Akos Cseke, Robert Heinemann
      The research presented in this paper investigated the effects of spindle speed and feed rate on the resultant cutting forces (thrust force and torque) and temperatures while drilling SawBones® biomechanical test materials and cadaveric cortical bone (bovine and porcine femur) specimens. It also investigated cortical bone anisotropy on the cutting forces, when drilling in axial and radial directions. The cutting forces are only affected by the feed rate, whereas the cutting temperature in contrast is affected by both spindle speed and feed rate. The temperature distribution indicates friction as the primary heat source, which is caused by the rubbing of the tool margins and the already cut chips over the borehole wall. Cutting forces were considerably higher when drilling animal cortical bone, in comparison to cortical test material. Drilling direction, and therewith anisotropy, appears to have a negligible effect on the cutting forces. The results suggest that this can be attributed to the osteons being cut at an angle rather than in purely axial or radial direction, as a result of a twist drill's point angle.

      PubDate: 2018-01-05T20:47:59Z
      DOI: 10.1016/j.medengphy.2017.10.009
      Issue No: Vol. 51 (2018)
  • A flow-leak correction algorithm for pneumotachographic work-of-breathing
           measurement during high-flow nasal cannula oxygen therapy
    • Authors: Francesco Montecchia; Fabio Midulla; Paola Papoff
      Abstract: Publication date: Available online 2 March 2018
      Source:Medical Engineering & Physics
      Author(s): Francesco Montecchia, Fabio Midulla, Paola Papoff
      Measuring work of breathing (WOB) is an intricate task during high-flow nasal cannula (HFNC) therapy because the continuous unidirectional flow toward the patient makes pneumotachography technically difficult to use. We implemented a new method for measuring WOB based on a differential pneumotachography (DP) system, equipped with one pneumotachograph inserted in the HFNC circuit and another connected to a monitoring facemask, combined with a leak correction algorithm (LCA) that corrects flow measurement errors arising from leakage around the monitoring facemask. To test this system, we used a mechanical lung model that provided data to compare LCA-corrected respiratory flow, volume and time values with effective values obtained with a third pneumotachograph used instead of the LCA to measure mask flow leaks directly. Effective and corrected volume and time data showed high agreement (Bland–Altman plots) even at the highest leak. Studies on two healthy adult volunteers confirmed that corrected respiratory flow combined with esophageal pressure measurements can accurately determine WOB (relative error < 1%). We conclude that during HFNC therapy, a DP system combined with a facemask and an algorithm that corrects errors due to flow leakages allows pneumotachography to measure reliably the respiratory flow and volume data needed for calculating WOB.

      PubDate: 2018-03-08T17:08:50Z
      DOI: 10.1016/j.medengphy.2018.02.004
  • Factors influencing taper failure of modular revision hip stems
    • Authors: A. Krull; M.M. Morlock; N.E. Bishop
      Abstract: Publication date: Available online 2 March 2018
      Source:Medical Engineering & Physics
      Author(s): A. Krull, M.M. Morlock, N.E. Bishop
      Stem modularity of revision hip implant systems offers the advantage of the restoration of individual patient geometry but introduces additional interfaces, which are subjected to repetitive bending loading and have a propensity for fretting corrosion. The male stem taper is the weakest part of the modular junction due to its reduced cross section compared to the outside diameter of the stem. Taper fractures can be the consequence of overloading in combination with corrosion. The purpose of this study was to assess the influence of implant design factors, patient factors, and surgical factors on the risk of taper failure of the modular junction of revision stems. An analytical bending model was used to estimate the strength of the taper connection for pristine, fatigued and corroded conditions. Additionally, a finite element contact model of the taper connection was developed to assess the relative motion and potential for surface damage at the taper interface under physiological loading for varyied assembly and design parameters. Increasing the male taper diameter was shown to be the most effective means for increasing taper strength but would require a concurrent increase in the outer implant diameter to limit a greater risk of total surface damage for a thinner female taper wall. Increasing the assembly force decreases the total surface damage but not local magnitudes, which are probably responsible for crack initiation. It is suggested that in unfavourable loading conditions a monobloc implant system will reduce the risk of failure.

      PubDate: 2018-03-08T17:08:50Z
      DOI: 10.1016/j.medengphy.2018.02.001
  • A computational framework for simultaneous estimation of muscle and joint
           contact forces and body motion using optimization and surrogate modeling
    • Authors: Ilan Eskinazi; Benjamin J. Fregly
      Abstract: Publication date: Available online 2 March 2018
      Source:Medical Engineering & Physics
      Author(s): Ilan Eskinazi, Benjamin J. Fregly
      Concurrent estimation of muscle activations, joint contact forces, and joint kinematics by means of gradient-based optimization of musculoskeletal models is hindered by computationally expensive and non-smooth joint contact and muscle wrapping algorithms. We present a framework that simultaneously speeds up computation and removes sources of non-smoothness from muscle force optimizations using a combination of parallelization and surrogate modeling, with special emphasis on a novel method for modeling joint contact as a surrogate model of a static analysis. The approach allows one to efficiently introduce elastic joint contact models within static and dynamic optimizations of human motion. We demonstrate the approach by performing two optimizations, one static and one dynamic, using a pelvis-leg musculoskeletal model undergoing a gait cycle. We observed convergence on the order of seconds for a static optimization time frame and on the order of minutes for an entire dynamic optimization. The presented framework may facilitate model-based efforts to predict how planned surgical or rehabilitation interventions will affect post-treatment joint and muscle function.

      PubDate: 2018-03-08T17:08:50Z
      DOI: 10.1016/j.medengphy.2018.02.002
  • An experimental and computational study of the inferior vena cava
           hemodynamics under respiratory-induced collapse of the infrarenal IVC
    • Authors: Elisabetta Tedaldi; Chiara Montanari; Kenneth I. Aycock; Francesco Sturla; Alberto Redaelli; Keefe B. Manning
      Abstract: Publication date: Available online 2 March 2018
      Source:Medical Engineering & Physics
      Author(s): Elisabetta Tedaldi, Chiara Montanari, Kenneth I. Aycock, Francesco Sturla, Alberto Redaelli, Keefe B. Manning
      Inferior vena cava (IVC) filters have been used for over five decades as an alternative to anticoagulation therapy in the treatment of venous thromboembolic disease. However, complications associated with IVC filters remain common. Though many studies have investigated blood flow in the IVC, the effects of respiration-induced IVC collapse have not been evaluated. Our hypothesis is that IVC collapse may have an influence on IVC filter performance. Therefore, we herein investigate the hemodynamics in uncollapsed and collapsed IVC configurations using in vitro flow experiments and computational simulations. Particle image velocimetry (PIV) is used to measure the hemodynamics in an idealized, compliant model of the human IVC made of silicone rubber. Flow is studied under uncollapsed and collapsed scenarios, with the minor diameter of the IVC reduced by 30% in the collapsed state. Both rest and exercise flow conditions are investigated, corresponding to suprarenal flow rates of 2 lpm and 5.5 lpm, respectively. Finite element analysis simulations are carried out in a computational model of the undeformed, idealized IVC to reproduce the 30% collapse configuration and an additional 50% collapse configuration. Computational fluid dynamics (CFD) simulations are then performed to predict the flow in the uncollapsed and collapsed scenarios, and CFD results are compared to the experimental data. The results show that the collapsed states generate a higher velocity jet at the iliac junction that propagates farther into the lumen of the vena cava in comparison to the jet generated in the uncollapsed state. Moreover, 50% collapse of the IVC causes a shift of the jet away from the IVC wall and towards the center of the vena cava lumen. The area of maximum wall shear stress occurs where the jet impacts the wall and is larger in the collapsed scenarios. Secondary flow is also more complex in the collapsed scenarios. Interestingly, this study demonstrates that a small variation in the flow rate distribution between the right and left iliac veins induces significant variations in the flow characteristics. We speculate that asymmetries in the flow may generate unbalanced forces on the IVC wall and on placed IVC filters that could promote filter tilting and migration, although this requires further investigation. If unbalanced forces are present in vivo, the forces should be considered when determining the optimal placement positions and geometric features for IVC filters. Therefore, these findings motivate further investigation of the in vivo hemodynamics in the infrarenal IVC.

      PubDate: 2018-03-08T17:08:50Z
      DOI: 10.1016/j.medengphy.2018.02.003
  • Dynamic properties of human incudostapedial joint—Experimental
           measurement and finite element modeling
    • Authors: Shangyuan Jiang; Rong Z. Gan
      Abstract: Publication date: Available online 22 February 2018
      Source:Medical Engineering & Physics
      Author(s): Shangyuan Jiang, Rong Z. Gan
      The incudostapedial joint (ISJ) is a synovial joint connecting the incus and stapes in the middle ear. Mechanical properties of the ISJ directly affect sound transmission from the tympanic membrane to the cochlea. However, how ISJ properties change with frequency has not been investigated. In this paper, we report the dynamic properties of the human ISJ measured in eight samples using a dynamic mechanical analyzer (DMA) for frequencies from 1 to 80 Hz at three temperatures of 5, 25 and 37 °C. The frequency–temperature superposition (FTS) principle was used to extrapolate the results to 8 kHz. The complex modulus of ISJ was measured with a mean storage modulus of 1.14 MPa at 1 Hz that increased to 3.01 MPa at 8 kHz, and a loss modulus that increased from 0.07 to 0.47 MPa. A 3-dimensional finite element (FE) model consisting of the articular cartilage, joint capsule and synovial fluid was then constructed to derive mechanical properties of ISJ components by matching the model results to experimental data. Modeling results showed that mechanical properties of the joint capsule and synovial fluid affected the dynamic behavior of the joint. This study contributes to a better understanding of the structure–function relationship of the ISJ for sound transmission.

      PubDate: 2018-02-26T04:34:46Z
      DOI: 10.1016/j.medengphy.2018.02.006
  • Design and experimental force analysis of a novel elliptical vibration
           assisted orthopedic oscillating saw
    • Authors: Liming Shu; Naohiko Sugita; Masaya Oshima; Mamoru Mitsuishi
      Abstract: Publication date: Available online 20 February 2018
      Source:Medical Engineering & Physics
      Author(s): Liming Shu, Naohiko Sugita, Masaya Oshima, Mamoru Mitsuishi
      Orthopedic oscillating saws (OOSs) are widely used for plane processing in orthopedic surgery such as knee and hip replacement. However, sawing has been associated with bone breakthrough and necrosis problems. In this paper, a novel elliptical vibration assisted OOS was designed to achieve a low cutting force under the condition of deepening cut depth and reducing cutting speed, based on the analysis of brittle fractures of the bone and elliptical vibration assisted cutting kinematics. The elliptical vibration was generated using two parallel stacked piezoelectric actuators assembled with the fixture. In order to reduce the large cutting forces due to the large cutting depth, a series of experiments was also conducted to investigate the influence of processing parameters on cutting forces. It was demonstrated that cutting forces are significantly reduced by increasing the vibration frequency and vibration amplitude, and decreasing the sawing speed in the current design. The new design could minimize the cutting forces during sawing and allow surgeons to have better control over the sawing process.

      PubDate: 2018-02-26T04:34:46Z
      DOI: 10.1016/j.medengphy.2018.02.005
  • Post-operative ventricular flow dynamics following atrioventricular valve
           surgical and device therapies: A review
    • Authors: Yen Ngoc Nguyen; Munirah Ismail; Foad Kabinejadian; Edgar Lik Wui Tay; Hwa Liang Leo
      Abstract: Publication date: Available online 14 February 2018
      Source:Medical Engineering & Physics
      Author(s): Yen Ngoc Nguyen, Munirah Ismail, Foad Kabinejadian, Edgar Lik Wui Tay, Hwa Liang Leo
      Intra-ventricular flow dynamics has recently emerged as an important evaluation and diagnosis tool in different cardiovascular conditions. The formation of vortex pattern during the cardiac cycle has been suggested to play important epigenetic and energy-modulation roles in cardiac remodelling, adaptations and mal-adaptations. In this new perspective, flow alterations due to different cardiovascular procedures can affect the long-term outcome of those procedures. Especially, repairs and replacements performed on atrioventricular valves are likely to exert direct impact on intra-ventricular flow pattern. In this review, current consensus around the roles of vortex dynamics in cardiac function is discussed. An overview of physiological vortex patterns found in healthy left and right ventricles as well as post-operative ventricular flow phenomenon owing to different atrioventricular valvular procedures are reviewed, followed by the summary of different vortex identification schemes used to characterise intraventricular flow. This paper also emphasises on future research directions towards a comprehensive understanding of intra-cardiac flow and its clinical relevance. The knowledge could encourage more effective pre-operative planning and better outcomes for current clinical practices.

      PubDate: 2018-02-16T03:25:27Z
      DOI: 10.1016/j.medengphy.2018.01.007
  • Towards the enhancement of body standing balance recovery by means of a
           wireless audio-biofeedback system
    • Authors: Giovanni Costantini; Daniele Casali; Fabio Paolizzo; Marco Alessandrini; Alessandro Micarelli; Andrea Viziano; Giovanni Saggio
      Abstract: Publication date: Available online 10 February 2018
      Source:Medical Engineering & Physics
      Author(s): Giovanni Costantini, Daniele Casali, Fabio Paolizzo, Marco Alessandrini, Alessandro Micarelli, Andrea Viziano, Giovanni Saggio
      Human maintain their body balance by sensorimotor controls mainly based on information gathered from vision, proprioception and vestibular systems. When there is a lack of information, caused by pathologies, diseases or aging, the subject may fall. In this context, we developed a system to augment information gathering, providing the subject with warning audio-feedback signals related to his/her equilibrium. The system comprises an inertial measurement unit (IMU), a data processing unit, a headphone audio device and a software application. The IMU is a low-weight, small-size wireless instrument that, body-back located between the L2 and L5 lumbar vertebrae, measures the subject's trunk kinematics. The application drives the data processing unit to feeding the headphone with electric signals related to the kinematic measures. Consequently, the user is audio-alerted, via headphone, of his/her own equilibrium, hearing a pleasant sound when in a stable equilibrium, or an increasing bothering sound when in an increasing unstable condition. Tests were conducted on a group of six older subjects (59y-61y, SD = 2.09y) and a group of four young subjects (21y-26y, SD = 2.88y) to underline difference in effectiveness of the system, if any, related to the age of the users. For each subject, standing balance tests were performed in normal or altered conditions, such as, open or closed eyes, and on a solid or foam surface. The system was evaluated in terms of usability, reliability, and effectiveness in improving the subject's balance in all conditions. As a result, the system successfully helped the subjects in reducing the body swaying within 10.65%-65.90%, differences depending on subjects’ age and test conditions.

      PubDate: 2018-02-16T03:25:27Z
      DOI: 10.1016/j.medengphy.2018.01.008
  • Numerical validation of a subject-specific parameter identification
           approach of a quadriceps femoris EMG-driven model
    • Authors: Cláudio Bastos Heine; Luciano Luporini Menegaldo
      Abstract: Publication date: Available online 1 February 2018
      Source:Medical Engineering & Physics
      Author(s): Cláudio Bastos Heine, Luciano Luporini Menegaldo
      Muscle models can be used to estimate muscle forces in motor tasks. Muscle model parameters can be estimated by optimizing cost functions based on error between measured and model-estimated joint torques. This paper is a numerical simulation study addressing whether this approach can accurately identify the parameters of the quadriceps femoris. The simulated identification task is a single joint maximum voluntary knee concentric–eccentric extension in an isokinetic dynamometer, keeping the hip fixed at a neutral position. A curve considered as the nominal torque was obtained by simulating the quadriceps femoris model exerting a maximum knee extension torque using a set of known parameter values. Three parameters, with different expected sensitivities of force estimations by Hill-type muscle models, were studied: very sensitive, sensitive and not sensitive, corresponding to slack tendon length, maximum isometric force, and pennation angle, respectively. The initial values of the parameters were randomly changed, simulating an ignorance of nominal values. EMG generation and torque measurement error models were used to obtain realistic simulated data corrupted by noise. Simulated annealing was chosen as the optimization algorithm. Different sequences of parameter identification and cost functions were tested. The best nominal torque curve reconstruction was obtained by optimizing the parameters sequentially, starting from slack tendon length using the Euclidean norm cost function. However, the simultaneous estimation of all parameters resulted in the most accurate values for the parameters, although dispersion was relatively large. In conclusion, in the present simulation study using realistic synthetic torque and EMG data, the optimization approach based on torque error curve was able to closely approximate the parameter values of the model's quadriceps femoris muscle.

      PubDate: 2018-02-05T07:32:29Z
      DOI: 10.1016/j.medengphy.2018.01.006
  • A finite element modeling study of peripheral nerve recruitment by
           percutaneous tibial nerve stimulation in the human lower leg
    • Authors: Christopher W. Elder; Paul B. Yoo
      Abstract: Publication date: Available online 1 February 2018
      Source:Medical Engineering & Physics
      Author(s): Christopher W. Elder, Paul B. Yoo
      Percutaneous tibial nerve stimulation (PTNS) is a clinical therapy for treating overactive bladder (OAB), where an un-insulated stainless steel needle electrode is used to target electrically the tibial nerve (TN) in the lower leg. Recent studies in anesthetized animals not only confirm that bladder-inhibitory reflexes can be evoked by stimulating the TN, but this reflex can also be evoked by stimulating the adjacent saphenous nerve (SAFN). Although cadaver studies indicate that the TN and major SAFN branch(es) overlap at the location of stimulation, the extent to which SAFN branches are co-activated is unknown. In this study, we constructed a finite element model of the human lower leg and applied a numeric axon model (MRG model) to simulate the electrical recruitment of TN and SAFN fibers during PTNS. The model showed that up to 80% of SAFN fibers (located at the level of the needle electrode) can be co-activated when electrical pulses are applied at the TN activation threshold, the standard therapeutic amplitude. Both the location of the inserted electrode and stimulation amplitude were important variables that affected the recruitment of SAFN branches. This study suggests further work is needed to investigate the potential therapeutic effects of SAFN stimulation in OAB patients.

      PubDate: 2018-02-05T07:32:29Z
      DOI: 10.1016/j.medengphy.2018.01.004
  • Constitutive modeling of compressible type-I collagen hydrogels
    • Authors: Brooks A. Lane; Katrina A. Harmon; Richard L. Goodwin; Michael J. Yost; Tarek Shazly; John F. Eberth
      Abstract: Publication date: Available online 1 February 2018
      Source:Medical Engineering & Physics
      Author(s): Brooks A. Lane, Katrina A. Harmon, Richard L. Goodwin, Michael J. Yost, Tarek Shazly, John F. Eberth
      Collagen hydrogels have been used ubiquitously as engineering biomaterials with a biphasic network of fibrillar collagen and aqueous-filled voids that contribute to a complex, compressible, and nonlinear mechanical behavior - not well captured within the infinitesimal strain theory. In this study, type-I collagen, processed from a bovine corium, was fabricated into disks at 2, 3, and 4% (w/w) and exposed to 0, 105, 106, and 107 microjoules of ultraviolet light or enzymatic degradation via matrix metalloproteinase-2. Fully hydrated gels were subjected to unconfined, aqueous, compression testing with experimental data modeled within a continuum mechanics framework by employing the uncommon Blatz–Ko material model for porous elastic materials and a nonlinear form of the Poisson's ratio. From the Generalized form, the Special Blatz–Ko, compressible Neo–Hookean, and incompressible Mooney–Rivlin models were derived and the best-fit material parameters reported for each. The average root-mean-squared (RMS) error for the General (RMS = 0.13 ± 0.07) and Special Blatz–Ko (RMS = 0.13 ± 0.07) were lower than the Neo–Hookean (RMS = 0.23 ± 0.10) and Mooney–Rivlin (RMS = 0.18 ± 0.08) models. We conclude that, with a single fitted-parameter, the Special Blatz–Ko sufficiently captured the salient features of collagen hydrogel compression over most examined formulations and treatments.

      PubDate: 2018-02-05T07:32:29Z
      DOI: 10.1016/j.medengphy.2018.01.003
  • Kinematic measures for upper limb robot-assisted therapy following stroke
           and correlations with clinical outcome measures: A review
    • Authors: Vi Do Tran; Paolo Dario; Stefano Mazzoleni
      Abstract: Publication date: Available online 1 February 2018
      Source:Medical Engineering & Physics
      Author(s): Vi Do Tran, Paolo Dario, Stefano Mazzoleni
      Aim of the study This review classifies the kinematic measures used to evaluate post-stroke motor impairment following upper limb robot-assisted rehabilitation and investigates their correlations with clinical outcome measures. Methods An online literature search was carried out in PubMed, MEDLINE, Scopus and IEEE-Xplore databases. Kinematic parameters mentioned in the studies included were categorized into the International Classification of Functioning, Disability and Health (ICF) domains. The correlations between these parameters and the clinical scales were summarized. Results Forty-nine kinematic parameters were identified from 67 articles involving 1750 patients. The most frequently used parameters were: movement speed, movement accuracy, peak speed, number of speed peaks, and movement distance and duration. According to the ICF domains, 44 kinematic parameters were categorized into Body Functions and Structure, 5 into Activities and no parameters were categorized into Participation and Personal and Environmental Factors. Thirteen articles investigated the correlations between kinematic parameters and clinical outcome measures. Some kinematic measures showed a significant correlation coefficient with clinical scores, but most were weak or moderate. Conclusions The proposed classification of kinematic measures into ICF domains and their correlations with clinical scales could contribute to identifying the most relevant ones for an integrated assessment of upper limb robot-assisted rehabilitation treatments following stroke. Increasing the assessment frequency by means of kinematic parameters could optimize clinical assessment procedures and enhance the effectiveness of rehabilitation treatments.

      PubDate: 2018-02-05T07:32:29Z
      DOI: 10.1016/j.medengphy.2017.12.005
  • Mechanical properties of cancellous bone from the acetabulum in relation
           to acetabular shell fixation and compared with the corresponding femoral
    • Authors: Rianne van Ladesteijn; Holly Leslie; William A Manning; James P Holland; David J Deehan; Thomas Pandorf; Richard M Aspden
      Abstract: Publication date: Available online 1 February 2018
      Source:Medical Engineering & Physics
      Author(s): Rianne van Ladesteijn, Holly Leslie, William A Manning, James P Holland, David J Deehan, Thomas Pandorf, Richard M Aspden
      To gain initial stability for cementless fixation the acetabular components of a total hip replacement are press-fit into the acetabulum. Uneven stiffness of the acetabular bone will result in irregular deformation of the shell which may hinder insertion of the liner or lead to premature loosening. To investigate this, we removed bone cores from the ilium, ischium and pubis within each acetabulum and from selected sites in corresponding femoral heads from four cadavers for mechanical testing in unconfined compression. From a stress-relaxation test over 300 s, the residual stress, its percentage of the initial stress and the stress half-life were calculated. Maximum modulus, yield stress and energy to yield (resilience) were calculated from a load-displacement test. Acetabular bone had a modulus about 10–20%, yield stress about 25% and resilience about 40% of the values for the femoral head. The stress half-life was typically between 2–4 s and the residual stress was about 60% of peak stress in both acetabulum and femur. Pubic bone was mechanically the poorest. These results may explain uneven deformation of press-fit acetabular shells as they are inserted. The measured half-life of stress-relaxation indicates that waiting a few minutes between insertion of the shell and the liner may allow seating of a poorly congruent liner.

      PubDate: 2018-02-05T07:32:29Z
      DOI: 10.1016/j.medengphy.2018.01.005
  • Spring assisted cranioplasty: A patient specific computational model
    • Authors: Alessandro Borghi; Naiara Rodriguez-Florez; Will Rodgers; Gregory James; Richard Hayward; David Dunaway; Owase Jeelani; Silvia Schievano
      Abstract: Publication date: Available online 19 January 2018
      Source:Medical Engineering & Physics
      Author(s): Alessandro Borghi, Naiara Rodriguez-Florez, Will Rodgers, Gregory James, Richard Hayward, David Dunaway, Owase Jeelani, Silvia Schievano
      Implantation of spring-like distractors in the treatment of sagittal craniosynostosis is a novel technique that has proven functionally and aesthetically effective in correcting skull deformities; however, final shape outcomes remain moderately unpredictable due to an incomplete understanding of the skull-distractor interaction. The aim of this study was to create a patient specific computational model of spring assisted cranioplasty (SAC) that can help predict the individual overall final head shape. Pre-operative computed tomography images of a SAC patient were processed to extract a 3D model of the infant skull anatomy and simulate spring implantation. The distractors were modeled based on mechanical experimental data. Viscoelastic bone properties from the literature were tuned using the specific patient procedural information recorded during surgery and from x-ray measurements at follow-up. The model accurately captured spring expansion on-table (within 9% of the measured values), as well as at first and second follow-ups (within 8% of the measured values). Comparison between immediate post-operative 3D head scanning and numerical results for this patient proved that the model could successfully predict the final overall head shape. This preliminary work showed the potential application of computational modeling to study SAC, to support pre-operative planning and guide novel distractor design.

      PubDate: 2018-01-27T06:57:28Z
      DOI: 10.1016/j.medengphy.2018.01.001
  • Instantaneous VO2 from a wearable device
    • Authors: Andrew J. Cook; Ben Ng; Gaetano D. Gargiulo; Diane Hindmarsh; Mark Pitney; Torsten Lehmann; Tara Julia Hamilton
      Abstract: Publication date: Available online 17 January 2018
      Source:Medical Engineering & Physics
      Author(s): Andrew J. Cook, Ben Ng, Gaetano D. Gargiulo, Diane Hindmarsh, Mark Pitney, Torsten Lehmann, Tara Julia Hamilton
      We present a method for calculating instantaneous oxygen uptake (VO2) through the use of a non-invasive and non-obtrusive (i.e. without a face mask) wearable device, together with its clinical evaluation against a standard technique based upon expired gas calorimetry. This method can be integrated with existing wearable devices, we implemented it in the “Device for Reliable Energy Expenditure Monitoring” (DREEM). The DREEM comprises a single lead electrocardiogram (ECG) device combined with a tri-axial accelerometer and is worn around the waist. Our clinical evaluation tests the developed method against a gold standard for VO2, expired gas calorimetry, using an ethically approved protocol comprising active exercise and sedentary periods. The study was performed on 42 participants from a wide sample population including healthy people, athletes and an at-risk health group including persons affected by obesity. We developed an algorithm combining heart rate (HR) and the integral of absolute acceleration (IAA), with results showing a correlation of r = 0.93 for instantaneous VO2, and r = 0.97 for 3 min mean VO2, this is a considerably improved estimation of VO2 in comparison to methods utilising HR and IAA independently.

      PubDate: 2018-01-27T06:57:28Z
      DOI: 10.1016/j.medengphy.2017.12.008
  • An adaptive, real-time cadence algorithm for unconstrained sensor
    • Authors: B.T. van Oeveren; C.J. de Ruiter; P.J. Beek; S.M. Rispens; J.H. van Dieën
      Abstract: Publication date: Available online 17 January 2018
      Source:Medical Engineering & Physics
      Author(s): B.T. van Oeveren, C.J. de Ruiter, P.J. Beek, S.M. Rispens, J.H. van Dieën
      This paper evaluates a new and adaptive real-time cadence detection algorithm (CDA) for unconstrained sensor placement during walking and running. Conventional correlation procedures, dependent on sensor position and orientation, may alternately detect either steps or strides and consequently suffer from false negatives or positives. To overcome this limitation, the CDA validates correlation peaks as strides using the Sylvester's criterion (SC). This paper compares the CDA with conventional correlation methods. 22 volunteers completed 7 different circuits (approx. 140 m) at three gaits-speeds: walking (1.5 m s− 1), running (3.4 m s− 1), and sprinting (5.2 and 5.7 m s− 1), disturbed by various gait-related activities. The algorithm was simultaneously evaluated for 10 different sensor positions. Reference strides were obtained from a foot sensor using a dedicated offline algorithm. The described algorithm resulted in consistent numbers of true positives (85.6–100.0%) and false positives (0.0–2.9%) and showed to be consistently accurate for cadence feedback across all circuits, subjects and sensors (mean ± SD: 98.9 ± 0.2%), compared to conventional cross-correlation (87.3 ± 13.5%), biased (73.0 ± 16.2) and unbiased (82.2 ± 20.6) autocorrelation procedures. This study shows that the SC significantly improves cadence detection, resulting in robust results for various gaits, subjects and sensor positions.

      PubDate: 2018-01-27T06:57:28Z
      DOI: 10.1016/j.medengphy.2017.12.007
  • Design, optimisation and testing of a compact, inexpensive elastic element
           for series elastic actuators
    • Authors: Cornelius Irmscher; Elmar Woschke; Erik May; Christian Daniel
      Abstract: Publication date: Available online 17 January 2018
      Source:Medical Engineering & Physics
      Author(s): Cornelius Irmscher, Elmar Woschke, Erik May, Christian Daniel
      This paper presents the development of a compact torsion spring for use as an elastic element in a lightweight series elastic actuator for an active orthosis. This orthosis is going to be utilised as an assistive device for motorically impaired stroke-patients. In the design a two-step optimisation strategy was implemented to meet all requirements for the torsion spring. The first step was to identify a promising topology for the element. In the second step, the shape was optimised based on a finite element model using two different optimisation methods in order to minimise the von Mises equivalent stresses. Four promising variants of the identified topology were extracted from these calculations, one of which was then chosen as the final design. A prototype was manufactured by a laser cutting process, which is a new procedure in the context of elastic elements for series elastic actuators. The calculation results were validated successfully by measurement of the spring properties of this prototype.

      PubDate: 2018-01-27T06:57:28Z
      DOI: 10.1016/j.medengphy.2017.12.004
  • Automatic recognition of gait patterns in human motor disorders using
           machine learning: A review
    • Authors: Joana Figueiredo; Cristina P. Santos; Juan C. Moreno
      Abstract: Publication date: Available online 17 January 2018
      Source:Medical Engineering & Physics
      Author(s): Joana Figueiredo, Cristina P. Santos, Juan C. Moreno
      Background automatic recognition of human movement is an effective strategy to assess abnormal gait patterns. Machine learning approaches are mainly applied due to their ability to work with multidimensional nonlinear features. Purpose to compare several machine learning algorithms employed for gait pattern recognition in motor disorders using discriminant features extracted from gait dynamics. Additionally, this work highlights procedures that improve gait recognition performance. Methods we conducted an electronic literature search on Web of Science, IEEE, and Scopus, using “human recognition”, “gait patterns’’, and “feature selection methods” as relevant keywords. Results analysis of the literature showed that kernel principal component analysis and genetic algorithms are efficient at reducing dimensional features due to their ability to process nonlinear data and converge to global optimum. Comparative analysis of machine learning performance showed that support vector machines (SVMs) exhibited higher accuracy and proper generalization for new instances. Conclusions automatic recognition by combining dimensional data reduction, cross-validation and normalization techniques with SVMs may offer an objective and rapid tool for investigating the subject's clinical status. Future directions comprise the real-time application of these tools to drive powered assistive devices in free-living conditions.

      PubDate: 2018-01-27T06:57:28Z
      DOI: 10.1016/j.medengphy.2017.12.006
  • Sin-quadratic model for chest tomosynthesis respiratory signal analysis
           and its application in four dimensional chest tomosynthesis reconstruction
    • Authors: Xi Tao; Hua Zhang; Genggeng Qin; Jianhua Ma; Qianjin Feng; Wufan Chen
      Abstract: Publication date: Available online 12 January 2018
      Source:Medical Engineering & Physics
      Author(s): Xi Tao, Hua Zhang, Genggeng Qin, Jianhua Ma, Qianjin Feng, Wufan Chen
      Chest tomosynthesis (CTS) is a newly developed imaging technique which provides pseudo-3D volume anatomical information of thorax from limited-angle projections and contains much less of superimposed anatomy than the chest X-ray radiography. One of the relatively common problems in CTS is the patient respiratory motion during image acquisition, which negatively impacts the detectability. In this work, we propose a sin-quadratic model to analyze the respiratory motion during CTS scan, which is a real time method where the respiratory signal is generated by extracting the motion of diaphragm from projection radiographs. According to the estimated respiratory signal, the CTS projections were then amplitude-based sorted into four to eight phases, and an iterative reconstruction strategy with total variation regularization was adopted to reconstruct the CTS images at each phase. Simulated digital XCAT phantom data and three sets of patient data were adopted for the experiments to validate the performance of the sin-quadratic model and its application in four dimensional (4D) CTS reconstruction. Results of the XCAT phantom simulation study show that the correlation coefficient between the extracted respiratory signal and the originally designed respiratory signal is 0.9964, which suggests that the proposed model could exactly extract the respiratory signal from CTS projections. The 4D CTS reconstructions of both the phantom data and the patient data show clear reduction of motion-induced blur.

      PubDate: 2018-01-27T06:57:28Z
      DOI: 10.1016/j.medengphy.2017.12.003
  • Acknowledgement to Reviewers 2017
    • Abstract: Publication date: January 2018
      Source:Medical Engineering & Physics, Volume 51

      PubDate: 2018-01-05T20:47:59Z
  • In vitro simulation of fretting-corrosion in hip implant modular
           junctions: The influence of pH
    • Authors: Dmitry Royhman; Megha Patel; Joshua J. Jacobs; Markus A. Wimmer; Nadim J. Hallab; Mathew T. Mathew
      Abstract: Publication date: Available online 29 December 2017
      Source:Medical Engineering & Physics
      Author(s): Dmitry Royhman, Megha Patel, Joshua J. Jacobs, Markus A. Wimmer, Nadim J. Hallab, Mathew T. Mathew
      Background The fretting-corrosion behavior of mixed metal contacts is affected by various mechanical and electrochemical parameters. Crevice conditions at the junction and patient-specific pathologies can affect the pH of the prosthetic environment. The main objective of this study is to understand the effect of pH variation at the stem/head junction of the hip implant under fretting corrosion exposure. We hypothesized that pH will have a significant influence on the fretting-corrosion behavior hip implant modular junctions. Materials and methods A custom-made setup was used to evaluate the fretting corrosion behavior of hip implant modular junctions. A Newborn calf serum solution (30 g/L protein content) was used to simulate the synovial fluid environment. A sinusoidal fretting motion, with a displacement amplitude of +50 µm, was applied to the Ti alloy rod. The effects of pathology driven, periprosthetic pH variation were simulated at four different pH levels (3.0, 4.5, 6.0 and 7.6). Electrochemical and mechanical properties were evaluated before, during, and after the applied fretting motion. Results The impedance of the system was increased in response to the fretting motion. The hysteresis tangential load/displacement behavior was not affected by pH level. The worn surfaces of CoCrMo pins exhibited the presence of tribolayer or organic deposits, in the pH 4.5 group, which may explain the lower drop in potential and mass loss observed in that group. Mechanically dominated wear mechanisms, namely, adhesive wear was shown in the pH 7.6 group, which may account for a higher potential drop and metal content loss. Conclusions This study suggests that the fretting-corrosion mechanisms in hip implant are affected by the pH levels of the surrounding environment and patient-specific factors.
      Graphical abstract image

      PubDate: 2018-01-05T20:47:59Z
      DOI: 10.1016/j.medengphy.2017.10.016
  • In vitro validation of measurement of volume elastic modulus using
    • Authors: Haneen Njoum; Panayiotis A Kyriacou
      Abstract: Publication date: Available online 28 December 2017
      Source:Medical Engineering & Physics
      Author(s): Haneen Njoum, Panayiotis A Kyriacou
      Arterial stiffness (AS) is one of the earliest detectable symptoms of cardiovascular diseases and their progression. Current AS measurement methods provide an indirect and qualitative estimation of AS. The purpose of this study is to explore the utilisation of Photoplethysmography (PPG) as a measure of volumetric strain in providing a direct quantification of the Volume Elastic modulus (Ev ). An in vitro experimental setup was designed using an arterial model to simulate the human circulation in health (Model 2) and disease (Model 1). Flow, pressure, and PPG signals were recorded continuously under varied conditions of flow dynamics. The obtained Ev values were validated with the gold standard mechanical testing techniques. Values obtained from both methods had no significant difference for both models with a percent error of 0.26% and 1.9% for Model 1 and Model 2, respectively. This study shows that PPG and pressure signals can provide a direct measure of AS in an in vitro setup. With emerging noninvasive pressure measurement methods, this research paves the way for the direct quantification of AS in vivo.

      PubDate: 2018-01-05T20:47:59Z
      DOI: 10.1016/j.medengphy.2017.11.011
  • 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)
  • Concurrent prediction of ground reaction forces and moments and
           tibiofemoral contact forces during walking using musculoskeletal modelling
    • Authors: Yinghu Peng; Zhifeng Zhang; Yongchang Gao; Zhenxian Chen; Hua Xin; Qida Zhang; Xunjian Fan; Zhongmin Jin
      Abstract: Publication date: Available online 19 December 2017
      Source:Medical Engineering & Physics
      Author(s): Yinghu Peng, Zhifeng Zhang, Yongchang Gao, Zhenxian Chen, Hua Xin, Qida Zhang, Xunjian Fan, Zhongmin Jin
      Ground reaction forces and moments (GRFs and GRMs) measured from force plates in a gait laboratory are usually used as the input conditions to predict the knee joint forces and moments via musculoskeletal (MSK) multibody dynamics (MBD) model. However, the measurements of the GRFs and GRMs data rely on force plates and sometimes are limited by the difficulty in some patient's gait patterns (e.g. treadmill gait). In addition, the force plate calibration error may influence the prediction accuracy of the MSK model. In this study, a prediction method of the GRFs and GRMs based on elastic contact element was integrated into a subject-specific MSK MBD modelling framework of total knee arthroplasty (TKA), and the GRFs and GRMs and knee contact forces (KCFs) during walking were predicted simultaneously with reasonable accuracy. The ground reaction forces and moments were predicted with an average root mean square errors (RMSEs) of 0.021 body weight (BW), 0.014 BW and 0.089 BW in the antero–posterior, medio–lateral and vertical directions and 0.005 BW•body height (BH), 0.011 BW•BH, 0.004 BW•BH in the sagittal, frontal and transverse planes, respectively. Meanwhile, the medial, lateral and total tibiofemoral (TF) contact forces were predicted by the developed MSK model with RMSEs of 0.025–0.032 BW, 0.018–0.022 BW, and 0.089–0.132 BW, respectively. The accuracy of the predicted medial TF contact force was improved by 12% using the present method. The proposed method can extend the application of the MSK model of TKA and is valuable for understanding the in vivo knee biomechanics and tribological conditions without the force plate data.

      PubDate: 2017-12-23T19:11:50Z
      DOI: 10.1016/j.medengphy.2017.11.008
  • A surface-based approach to determine key spatial parameters of the
           acetabulum in a standardized pelvic coordinate system
    • Authors: Xiaojun Chen; Pengfei Jia; Yiping Wang; Henghui Zhang; Liao Wang; Alejandro F. Frangi; Zeike A. Taylor
      Abstract: Publication date: Available online 18 December 2017
      Source:Medical Engineering & Physics
      Author(s): Xiaojun Chen, Pengfei Jia, Yiping Wang, Henghui Zhang, Liao Wang, Alejandro F. Frangi, Zeike A. Taylor
      Accurately determining the spatial relationship between the pelvis and acetabulum is challenging due to their inherently complex three-dimensional (3D) anatomy. A standardized 3D pelvic coordinate system (PCS) and the precise assessment of acetabular orientation would enable the relationship to be determined. We present a surface-based method to establish a reliable PCS and develop software for semi-automatic measurement of acetabular spatial parameters. Vertices on the acetabular rim were manually extracted as an eigenpoint set after 3D models were imported into the software. A reliable PCS consisting of the anterior pelvic plane, midsagittal pelvic plane, and transverse pelvic plane was then computed by iteration on mesh data. A spatial circle was fitted as a succinct description of the acetabular rim. Finally, a series of mutual spatial parameters between the pelvis and acetabulum were determined semi-automatically, including the center of rotation, radius, and acetabular orientation. Pelvic models were reconstructed based on high-resolution computed tomography images. Inter- and intra-rater correlations for measurements of mutual spatial parameters were almost perfect, showing our method affords very reproducible measurements. The approach will thus be useful for analyzing anatomic data and has potential applications for preoperative planning in individuals receiving total hip arthroplasty.

      PubDate: 2017-12-23T19:11:50Z
      DOI: 10.1016/j.medengphy.2017.11.009
  • 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
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