Wojciech Kowalczyk

University of Duisburg-Essen, Essen, North Rhine-Westphalia, Germany

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Publications (14)15.16 Total impact

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    ABSTRACT: Background Two questions are often addressed by orthopaedists relating to core decompression procedure: 1) Is the core decompression procedure associated with a considerable lack of structural support of the bone? and 2) Is there an optimal region for the surgical entrance point for which the fracture risk would be lowest? As bioresorbable bone substitutes become more and more common and core decompression has been described in combination with them, the current study takes this into account. Methods Finite element model of a femur treated by core decompression with bone substitute was simulated and analysed. In-vitro compression testing of femora was used to confirm finite element results. Findings The results showed that for core decompression with standard drilling in combination with artificial bone substitute refilling, daily activities (normal walking and walking downstairs) are not risky for femoral fracture. The femoral fracture risk increased successively when the entrance point located further distal. The critical value of the deviation of the entrance point to a more distal part is about 20 mm. Interpretation The study findings demonstrate that optimal entrance point should locate on the proximal subtrochanteric region in order to reduce the subtrochanteric fracture risk. Furthermore the consistent results of finite element and in-vitro testing imply that the simulations are sufficient.
    Clinical biomechanics (Bristol, Avon) 01/2014; · 1.76 Impact Factor
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    ABSTRACT: There is still controversy as to whether minimally invasive total hip arthroplasty enhances the postoperative outcome. The aim of this study was to compare the outcome of patients who underwent total hip replacement through an anterolateral minimally invasive (MIS) or a conventional lateral approach (CON). We performed a randomized, prospective study of 75 patients with primary hip arthritis, who underwent hip replacement through the MIS (n=36) or CON (n=39) approach. The Western Ontario and McMaster Universities Osteoarthritis Index and Harris Hip score (HHS) were evaluated at frequent intervals during the early postoperative follow-up period and then after 3.5 years. Pain sensations were recorded. Serological and radiological analyses were performed. In the MIS group the patients had smaller skin incisions and there was a significantly lower rate of patients with a positive Trendelenburg sign after six weeks postoperatively. After six weeks the HHS was 6.85 points higher in the MIS group (P=0.045). But calculating the mean difference between the baseline and the six weeks HHS we evaluated no significant differences. Blood loss was greater and the duration of surgery was longer in the MIS group. The other parameters, especially after the twelfth week, did not differ significantly. Radiographs showed the inclination of the acetabular component to be significantly higher in the MIS group, but on average it was within the same permitted tolerance range as in the CON group. Both approaches are adequate for hip replacement. Given the data, there appears to be no significant long term advantage to the MIS approach, as described in this study.
    Orthopedic Reviews 01/2013; 5(3):e19.
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    Hussam Mansour, Anik Keller, Rolf Gimbel, Wojciech Kowalczyk
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    ABSTRACT: The membrane filtration with inside-out dead-end driven UF-/MF- capillary membranes is an effective process for particle removal in water treatment. Its industrial application increased in the last decade exponentially. To date, the research activities in this field were aimed first of all at the analysis of filtration phenomena disregarding the influence of backwash on the operation parameters of filtration plants. However, following the main hypothesis of this paper, backwash has great potential to increase the efficiency of filtration. In this paper, a numerical approach for a detailed study of fluid dynamic processes in capillary membranes during backwash is presented. The effect of particle size and inlet flux on the backwash process are investigated. The evaluation of these data concentrates on the analysis of particle behavior in the cross sectional plane and the appearance of eventually formed particle plugs inside the membrane capillary. Simulations are conducted in dead-end filtration mode and with two configurations. The first configuration includes a particle concentration of 10% homogeneously distributed within the capillary and the second configuration demonstrates a cake layer on the membrane surface with a packing density of 0:6. Analyzing the hydrodynamic forces acting on the particles shows that the lift force plays the main role in defining the particle enrichment areas. The operation parameters contribute in enhancing the lift force and the heterogeneity to anticipate the clogging of the membrane.
    Membranes. 01/2013; 3(4):249-65.
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    ABSTRACT: Aseptic necrosis of the femoral head (AVN) leads to destruction of the affected hip joint, predominantly in younger patients. Advanced core decompression (ACD) is a new technique that may allow better removal of the necrotic tissue by using a new percutaneous expandable reamer. A further modification is the refilling of the drill hole and the defect with an injectable, hard-setting, composite calcium sulphate (CaSO(4) )-calcium phosphate (CaPO(4) ) bone graft substitute. Compression tests were performed on seven pairs of femoral cadaver bones. One femur of each pair was treated with ACD, while the opposite side remained untreated. Clinically, the postoperative outcome of 27 hips in 23 patients was performed by physical examination 6 weeks after ACD and at average follow-up of 9.69 months, and compared with the preoperative results. MRI was used to assess the removal of the necrotic tissue, any possible progression of AVN and evaluation of collapse. In the biomechanical analysis, the applied maximum compression force that caused the fracture did not significantly differ from the untreated opposite side. The overall results of postoperative physical examinations were significantly better than preoperatively. Five hips (18.5%) were converted to a total hip replacement. The follow-up MRIs of the other patients showed no progression of the necrotic area. The first follow-up results of ACD have been encouraging for the early stages of aseptic necrosis of the femoral head. In our opinion, an assured advantage is the high stability of the femoral neck after ACD, which allows quick rehabilitation. Copyright © 2012 John Wiley & Sons, Ltd.
    Journal of Tissue Engineering and Regenerative Medicine 04/2012; · 4.43 Impact Factor
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    ABSTRACT: The aim of the present study was to evaluate and compare the in vitro and flow dynamics of the Magna (MB) and the Magna Ease aortic valve bioprosthesis (MEB) within the ascending aorta. A 2D-particle-image-velocimetry (2D-PIV) study was performed to compare the flow dynamics induced by each pericardial Carpentier-Edwards Magna and Magna Ease aortic valve prosthesis in the aortic flow field directly behind the valve. Both prostheses (diameter 23 mm) were placed inside an artificial aorta under pulsatile flow conditions (70 Hz and 70 ml stroke volume). The flow field was evaluated according to velocity, shear strength, and vorticity. Both prostheses showed a jet flow type profile with a maximum velocity of 0.97±0.09 m/s for MB and 0.83±1.8 m/s for MEB. Flow fields of both valves were similar in acceleration, peak flow deceleration and leakage phase. Maximum shear strength was 20,285±11,774 l/s2 for MB and 17,006±8453 l/s2 for MEB. Vorticity was nearly similar for counterclockwise and clockwise rotation in both prostheses, but slightly higher with MB (251±41 l/s and -250±39 l/s vs. 225±48 l/s and -232±48 l/s). The point-of-interest (POI)-analysis revealed a higher velocity for left-sided aortic wall compared to right-sided at MB (0.12±0.09 m/s vs. 0.18±0.10 m/s, p<0.001), but was consistent at MEB (0.09±0.05 m/s vs. 0.08±0.04 m/s, p=0.508), respectively. Velocity, shear strength and vorticity in an in vitro test set-up are lower with MEB compared to MB, thus resulting in improved flow dynamics with a similar flow field, which might have a positive influence on blood rheology and potential valve degeneration.
    Biomedizinische Technik/Biomedical Engineering 01/2012; 57(2):97-106. · 1.16 Impact Factor
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    ABSTRACT: There is still a lack of quantitative information concerning optimal blood flow in the aorta and in the carotid arteries during extracorporeal circulation (ECC). Problems are not only based on the location of the aortic cannula, they are furthermore associated with the cannula design itself and the effects on blood cells and aortic wall shear stresses. We simulated a two-phase fluid flow induced by different cannulas in the ascending aorta during ECC. Three commercially available cannulas were examined according to their influence on red blood cells (RBC). Additionally, mass flow in the carotid vessels and wall shear stresses acting on the aortic wall were evaluated. A constant volume flow of blood (3.4 L/min) was applied. Numerical results demonstrate a strong relation between the mass flow rate in the carotid vessels and the geometry of the aortic outflow cannula. RBC distributions both in the aorta and the carotid vessels changed depending on cannula geometry. Maximum blood velocities, shear stresses on the aortic wall, and the fluid mechanical load acting on RBCs varied depending on each cannula design. This numerical approach demonstrates the significant influence of the cannula design on the distribution of RBCs in the carotid vessels during ECC.
    Minimally invasive therapy & allied technologies: MITAT: official journal of the Society for Minimally Invasive Therapy 04/2011; 20(2):125-31. · 1.33 Impact Factor
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    ABSTRACT: To date, cardiac valve diseases are considered as a major public health problem and most frequently, the aortic valve is affected. To treat high-risk patients, catheter-based techniques have been developed recently, avoiding open heart surgery and/or cardiopulmonary bypass. Although these sophisticated and rapidly emerging catheter-based technologies do allow a minimally invasive treatment option of high-risk patients on the one hand, further developments and in vitro testing under physiological conditions are necessary, on the other hand, in order to further optimize them for clinical routines. Therefore, we present the concept of a new multifunctional flow channel, offering (i) the possibility of transapical access; (ii) the simulation of physiological flow conditions; and (iii) the evaluation of the fluid flow by 2D particle image velocimetry within a wide range of parameters.
    Artificial Organs 03/2011; 35(3):E59-64. · 1.96 Impact Factor
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    ABSTRACT: The study aim was to evaluate the hemodynamic performance of the Sapien transcatheter heart valve (THV) in the ascending aorta, and its influence on the aortic wall in an in-vitro set-up. A two-dimensional particle image velocimetry (2D-PIV) study was conducted to evaluate the hemodynamic performance of the Edwards Sapien THV in the aortic flow field (image rate 15 Hz). The prosthesis (diameter 23 mm) was placed inside a mock aorta under pulsatile flow conditions. The velocities, shear strength, vorticity and strain rate were obtained and calculated with a fixed frequency (70 Hz) at constant stroke volume (70 ml). The Sapien THV showed a jet flow-type profile with a maximum velocity of 0.87 +/- 0.16 m/s during peak flow phase (PFP). The jet flow was surrounded by ambilateral vortices with a higher percentage of counterclockwise than clockwise vorticity (335 +/- 66/s versus 277 +/- 44.1/s), analogous to the strain rate (261 +/- 55/s for elongation versus -168 +/- 25/s for contraction). The maximum shear strength was 26,284 +/- 11,550/s2, while the point-of-interest analysis revealed a higher velocity for the bottom aortic wall compared to the upper aortic wall (0.25 +/- 0.05 m/s versus 0.30 +/- 0.04 m/s; p = 0.014). All values were lower during the acceleration and deceleration phases compared to PFP. The peak flow of the Sapien THV seems to be slightly higher than that of the native aortic valve, thus imitating near-physiological conditions. That the shear strength, vorticity and strain rate were high during peak flow phase, but low during other phases, might also have an influence on the aortic wall.
    The Journal of heart valve disease 01/2011; 20(1):53-63. · 1.07 Impact Factor
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    ABSTRACT: : Currently, sutureless heart valves (SHV) reveal good clinical results during aortic valve replacement. The aim of this study was to evaluate the fluid dynamics of the ATS 3F Enable SHV in the ascending aorta and their influence on the aortic wall in an in vitro setup. : A two-dimensional particle image velocimetry study with an image rate of 15 Hz was conducted to evaluate the fluid dynamics of the SHV in the aortic flow field. The prosthesis (diameter, 23 mm) was placed inside a silicone mock aorta under pulsatile flow conditions. Velocities, vorticity, and strain rate were obtained and calculated with a fixed frequency (70 Hz) at constant stroke volume (70 mL). : 3F Enable showed a jet flow type profile with a maximum velocity of 1.01 ± 0.13 m/s during peak flow phase (PFP). The jet flow was surrounded by ambilateral vortices with a slightly higher percentage of clockwise than counterclockwise vorticity (377 ± 57/s vs 389 ± 76/s), strain rate (370 ± 79/s for elongation vs -370 ± 102/s for contraction) was nearly similar. The point-of-interest analysis revealed a higher velocity for bottom compared with upper aortic wall (0.28 ± 0.07 m/s vs 0.31 ± 0.06 m/s, P = 0.024). All values were lower during acceleration and deceleration phase compared with PFP. : The peak flow of the 3F Enable SHV seems to be little higher compared with native aortic valves, thus simulating nearly physiologic conditions. Vorticity and strain rate are high during PFP and low during other phases and might have an influence on the aortic wall as well.
    Innovations Technology and Techniques in Cardiothoracic and Vascular Surgery 01/2011; 6(1):37-44.
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    Hussam Mansour, Wojciech Kowalczyk
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    ABSTRACT: The purpose of this contribution is to compare the shear and the normal stresses in two different types of bioreactors. In the first one (SBR), the granules are generated by liquid and bubbles flow, whereas in the second one (SF-SBR), the shear rate is achieved by installing a rotating cylinder inside the reactor. Such shear flow can be applied for anaerobic process in the wastewater treatment. The results demonstrate the effective role of the process parameters and the reactor geometry on the shear and normal stresses and consequently on the granulation process. Hereby, the different tendencies of the velocity fields, the particle sedimentation as well as Taylor vortices in (SF-SBR), are observed. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)
    PAMM 12/2010; 10(1).
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    ABSTRACT: Aortic dissection is one of the most life-threatening diseases of the human cardiovascular system. Since the fluid dynamic behavior of several blood elements in false and true lumen is not well understood so far, in this paper modeling and numerical simulations of the multiphase flow in the aorta without dissection as well as with dissections Stanford type A and B are presented. Additionally, influence of the biological heart valve prosthesis on the blood flow is shown. The blood is modeled as a multiphase medium that consists of three phases: plasma, red blood cells (RBCs) and leukocytes. The non-Newtonian behavior of the fluid depends not only on the shear rate but also on the volume fraction of RBCs. The numerical simulations are carried out with the RBC volume fraction of 38 % and 44 %. In order to model physiological conditions in the computational domain, a pulsatile flow with the maximum stroke volume of 70 ml and 120 ml is considered. The results reveal significant influence of the process parameters and the heart valve prosthesis on the blood flow characteristics and the hematocrit distribution in dissections and true lumen. The RBC distribution in the false lumen varies in a very wide range in the upper and the lower part of dissection. It is clearly seen that hematocrit has a tendency to separate from plasma as well as sediment and coagulate at the bottom of the false lumen.
    07/2010;
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    ABSTRACT: Diseases of the aortic valve belong to the most common health problems. The aortic valve maintains the blood flow in one direction and serves to prevent retrograde flow from aorta to the left ventricle. To date, new bio-prosthetic, suturless heart valves have been designed. The purpose of the present study is therefore to evaluate their influence on hemodynamics in the cardiovascular system. Especially the blood flow in the vicinity of the aortic valve, in the sinus of Valsalva and the ascending aorta becomes on importance from the fluid dynamical point of view. The three-dimensional geometrical model is generated after segmentation of CT data of the 3F-Enable aortic valve prosthesis. A set of simulations with different initial velocity profiles and pulse frequencies has been created to examine the transient behavior of the fluid flow and the heart valve prosthesis. The function of heart valve system, however, involves an analysis of fluid-structure interaction to predict the motion of leaflets. Hence, the separation of the soft tissue and the hard nitinol-based frame is carried out. The results reveal pressure and velocity distributions as well as normal and shear stresses acting on the wall of the prosthesis and aorta. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)
    PAMM 12/2009; 9(1).
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    ABSTRACT: In complex thoracic aortic procedures, proximal repair and antegrade stent grafting of the descending aorta is an emerging technique to achieve one-stage treatment of the thoracic aorta. To overcome problems of proximal endoleak, a hybrid stent graft was designed and used. This study assessed technical feasibility and early results. From Jan 2005 to May 2008, 41 patients (age, 60 +/- 13 years) comprising 35 aortic dissections (AD) and 6 aortic aneurysms underwent arch replacement and antegrade stent grafting of the descending aorta using the hybrid stent graft. Endoleaks were evaluated by computed tomography (CT) scans. In AD cases, the false lumen (FL) was evaluated with CT volume measurements. Combined arch replacement and antegrade stent grafting was technically successful. One proximal endoleak was observed, which was not related to the hybrid prosthesis (40 of 41, 98%). Three patients died (7%). No paraplegia occurred. Incidence of immediate FL thrombosis was 97% at the proximal and 80% at the distal stent graft level. During follow-up (17 +/- 11 months), complete thrombosis of the perigraft space was 91%. FL volume shrinkage was documented (p < 0.01). No perfusion of the perigraft space was observed in aneurysm cases. Intermediate survival was 33 of 38 (87%). One-stage repair of complex thoracic aortic disease using a hybrid stent graft can be reliably performed with low hospital mortality. Proximal endoleak can be definitely avoided; in AD, exclusion and ongoing significant shrinkage of the FL can be achieved.
    The Annals of thoracic surgery 09/2009; 88(3):773-9. · 3.45 Impact Factor
  • Thoracic and Cardiovascular Surgeon - THORAC CARDIOVASC SURG. 01/2009; 56.

Publication Stats

22 Citations
15.16 Total Impact Points

Institutions

  • 2009–2014
    • University of Duisburg-Essen
      • • Lehrstuhl für Mechanik und Robotik
      • • Institut für Mechatronik und Systemdynamik
      Essen, North Rhine-Westphalia, Germany
  • 2011–2012
    • University Hospital Essen
      • Klinik für Thorax- und Kardiovaskuläre Chirurgie
      Essen, North Rhine-Westphalia, Germany