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ABSTRACT: Cementing irregularities have been associated with femoral failures of resurfacing arthroplasties in retrieval studies. We used an in vitro model to measure pressure, temperatures, and cement penetration as a function of 6 different cementing techniques. Filling the component with cement can lead to overpenetration or increase the resistance to component seating with resultant polar cement mass. Both conditions result in high and long-lasting cement pressures, cement defects, as well as peak temperatures higher than 50°C. Manual application of cement provides complete penetration of the available fixation area with the lowest cement pressures, the smallest total cement mass, and a peak temperature of 36.0°C ± 4.1°C. Application of the principles elucidated by this study may reduce the risk of cement overpenetration and incomplete seating.
The Journal of arthroplasty 01/2011; 26(1):144-51. · 1.79 Impact Factor
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ABSTRACT: Cerclage wires are widely used in revision hip surgery to reattach the lid of a femoral osteotomy. The present study compared the influence of multifilaments and monofilaments on primary stability of revision hip stems with different fixation principles.
A standardized extended proximal femoral osteotomy was performed in the anterior cortex of 6 synthetic femora. We used a high-resolution measuring device to explore spatial micromovements of a diaphyseal and a metaphyseal fixating revision stem. Both of these were implanted in 3 femora. The specimens were measured again after consecutive restabilization of osteotomies with multifilaments and monofilaments. The movement graphs generated defined relative micromovements between stems and bones and the stabilizing effect of the two wire systems compared.
Both multifilaments and monofilaments effected a major reduction of relative micromovements for both fixation principles. There were no differences in relative movements between the multifilament and monofilament treatments for the diaphyseal fixating stem. Yet for the metaphyseal fixating stem a significantly better restabilization was observed with multifilaments.
Both multifilaments and monofilaments can support the revision hip stem in bridging the extended proximal femoral osteotomy. Yet, which wiring system should be chosen depends on the fixation principle of the revision stem. Multifilaments seem to be advantageous when used with metaphyseal fixating stems. However, the use of multifilaments with diaphyseal fixating components should be reconsidered as this might constrict the periosteal vascularity.
Clinical biomechanics (Bristol, Avon) 12/2010; 26(3):257-61. · 1.76 Impact Factor
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ABSTRACT: Experimental simulator studies are frequently performed to evaluate wear behavior in total knee replacement. It is vital that the simulation conditions match the physiological situation as closely as possible. To date, few experimental wear studies have examined the effects of joint laxity on wear and joint kinematics and the absence of the anterior cruciate ligament has not been sufficiently taken into account in simulator wear studies. The aim of this study was to investigate different ligament and soft tissue models with respect to wear and kinematics. A virtual soft tissue control system was used to simulate different motion restraints in a force-controlled knee wear simulator. The application of more realistic and sophisticated ligament models that considered the absence of anterior cruciate ligament lead to a significant increase in polyethylene wear (p=0.02) and joint kinematics (p<0.01). We recommend the use of more complex ligament models to appropriately simulate the function of the human knee joint and to evaluate the wear behavior of total knee replacements. A feasible simulation model is presented.
Journal of biomechanics 04/2010; 43(6):1092-6. · 2.66 Impact Factor
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ABSTRACT: Knee wear simulator studies are performed to evaluate the wear behavior of implants. These wear studies simulate in vivo situations as closely as possible. Simulation of the human gait cycle is often carried out continuously according to international standards. However, implants are not loaded continuously in vivo, so it might be advisable to implement resting periods in which no motion occurs.
In the present study the influence of resting periods on the wear behavior of a commercial implant was analyzed using a force-controlled AMTI knee simulator.
The wear rates were 2.27+/-0.23 mg/10(6) cycles for a simulation with resting periods and 2.85+/-0.27 mg/10(6) cycles for a reference simulation without resting periods. There was no significant difference (p=0.22) in wear behavior between these two tests.
The present study shows that continuous simulation without the implementation of resting periods is a valid approach for assessing the wear of knee implants.
Medical science monitor: international medical journal of experimental and clinical research 11/2009; 15(11):MT143-6. · 1.70 Impact Factor
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ABSTRACT: A periprosthetic femoral fracture after total hip arthroplasty is a serious but uncommon complication, and therefore difficult to analyze clinically in scientifically and statistically valid study samples. With the aim of preventing these fractures the purpose of this study was to investigate potential risk factors associated with cementless hip arthroplasty in a standardized laboratory setup. Additionally, we aimed to clarify if the treatment with a cementless hip stem is fraught with higher risk of periprosthetic fracture for older patients compared to younger patients.
A biomechanical setup was developed to provide analysis on sixteen femoral specimens of different age. A cementless hip stem was implanted into the specimens and loads - representing hip contact forces - were applied under standardized conditions until fracture occurred. The femurs were divided into two age groups (<70 and >or=77 years of age).
The elderly specimens fractured at significantly lower maximum forces (<70: Fmax=5,308N; >or=77: Fmax=2,519N; p<0.01). Maximum fracture loads were found to correlate strongly with age (p=0.01), BMD (e.g. for the Ward's triangle: p<0.01) and BMI (p=0.04).
In patients with advanced age treated with cementless hip stems the risk of suffering a periprosthetic fracture is significantly higher. It increases in patients with an age of 80 years or older, a Ward's triangle BMD below 0.500 g/cm2 and a BMI >33 kg/m2. Whereas one single factor must not be viewed as an exclusion criterion for a cementless hip stem treatment, cumulation of these factors should alert the orthopaedic surgeon.
Medical science monitor: international medical journal of experimental and clinical research 11/2009; 15(11):BR307-12. · 1.70 Impact Factor
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ABSTRACT: Implants with surfaces of various porosities and pore sizes are in clinical use. This article demonstrates how macroscopic porous metal fragments can detach from the implant surface in total hip arthroplasty (THA) and cause significant third-body damage such as deep scratches and indentations in implants' bearing surfaces. Radiographs prior to revision surgery due to aseptic loosening of the acetabular component revealed the presence of numerous small metal fragments approximately 1 to 2 mm in size in the periarticular area. The size, shape, and material of the metal fragments (cobalt-chromium-molybdenum [CoCrMo]) indicated that they originated from the porous metal surface. In this case, the acetabular liner composite material consisted of two-thirds polyurethane and one-third aluminium oxide ceramic. The femoral head was made of aluminium oxide ceramic. The aluminium oxide femoral head, which had been in situ for 21 years, showed no signs of macroscopic indentations or scratches, suggesting that an aluminium oxide bearing surface, which is significantly harder than the CoCrMo debris, is not significantly affected by metal debris embedment in the counterface material. The polyurethane-aluminium oxide composite material used for the acetabular liner is not comparable to a traditional ceramic bearing surface material. Debris damaged the surface of and became embedded in the liner, causing accelerated wear of the femoral head. In porous metal surface THA, ceramic-on-ceramic bearing couples should, due to their superior hardness, be considered to prevent excessive wear, including debris embedment and scratching of the bearing surfaces, especially in revision cases.
Orthopedics 06/2009; 32(5):364. · 2.66 Impact Factor
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ABSTRACT: This article aims to clarify the influence of design- and manufacturing-related parameters on wear of metal-on-metal (MoM) joint bearings. A database search for publications on wear simulator studies of MoM bearings was performed. The results of published studies were normalized; groups with individual parameters were defined and analyzed statistically. Fifty-six investigations studying a total of 200 implants were included in the analysis. Clearance, head size, carbon content, and manufacturing method were analyzed as parameters influencing MoM wear. This meta-analysis revealed a strong influence of clearance on running-in wear for implants of 36-mm diameter and an increase in steady-state wear of heat treated components.
Journal of Orthopaedic Research 06/2009; 27(11):1473-80. · 2.81 Impact Factor
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ABSTRACT: Modular neck implants are an attractive treatment tool in total hip replacement. Concerns remain about the mechanical stability and metal ion release caused by the modular connection. Five different implant designs were investigated in an experimental set-up. In vivo conditions were simulated and the long-term titanium release was measured. Finally, the modular connections were inspected for corrosion processes and signs of fretting. No mechanical failure or excessive corrosion could be identified for the implants tested. The titanium releases measured were extremely low compared to in vivo and in vitro studies and were not in a critical range.
International Orthopaedics 03/2009; 33(6):1531-6. · 2.03 Impact Factor
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ABSTRACT: Evaluation of patient activity is essential for clinical decision making before THA. To correlate age progression to patient activity after THA, we determined the number of walking cycles of 105 patients in different age groups by decades. Patients on average performed 6144 walking cycles per day (2.24 million cycles per year). Men were more active than women. The highest activity occurred in patients between 50 and 59 years of age, with a constant decrease in activity with advancing age. However, within age groups, we observed up to sixfold differences in the number of walking cycles per day. In addition to declining activity with advancing age, higher body mass index correlated with lower step counts. The high mean measured number of walking cycles, which were even higher than those reported for subjects without an arthroplasty, suggests patients benefit from THA. Female gender, advanced age, and obesity correlated with lower activity. Owing to the high intragroup variability of our results, preoperative evaluation of patient activity levels, individual patient factors, and patient demands, should be considered in clinical practice.
Clinical Orthopaedics and Related Research 03/2009; 467(8):2053-8. · 2.53 Impact Factor
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ABSTRACT: Hip resurfacing is extremely technique-sensitive, yet scientific investigations into cementing techniques are lacking. In this study, we tested open-cell, reticulated, carbon-foam materials in comparison with paired human femoral heads to validate a laboratory cementing model for resurfacing arthroplasty.
Paired human femoral heads prepared for resurfacing were compared with thirty and sixty-pore-per-inch fat-filled foam specimens. Two different cementing techniques were analyzed: manual application of high-viscosity cement, and half component-filling with low-viscosity cement. Real-time measurements were made of cement pressure and temperature. Cement penetration areas and depths were quantified.
We found no significant differences between the human femoral heads and the fat-filled thirty-pore-per-inch foam models in all measured variables (pressures at the top, chamfer and outer wall, temperature at the 5-mm and 15-mm subsurface). There was no significant difference in the cement penetration of the human femoral heads and the fat-filled thirty-pore-per-inch foam models. There were a number of significant differences between the human femoral heads and the sixty-pore-per-inch foam models with use of the low-viscosity cement technique. The differences between the cementing techniques were greater than those between the three materials for most of the measurements.
Fat-filling (to emulate bone marrow) of lower-density carbon foam more closely simulates the cement penetration resistance and thermal properties of human femoral heads than does the denser (unfilled) material. This model is sensitive to differences in cementing technique.
The Journal of Bone and Joint Surgery 09/2008; 90 Suppl 3:102-10. · 3.27 Impact Factor
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ABSTRACT: Bone stock losses in cementless femoral stem revisions compromise a stable fixation. The surgeon has to rely on his wealth of experience in deciding which stem shape to use. The aim of our study was to compare the primary rotational stability of cylindrical and conical revision hip stems subjected to femoral defects. Four current prostheses (two cylindrical, two conical) were implanted into four synthetic femora. Micro-motion was measured under torque application and femoral neck osteotomy and segmental AAOS Type I and III defects were simulated. The relative movements of all prostheses were significantly influenced by the extent of bone loss (p<0.01). Major differences were seen in fixation behavior (p<0.01). The main fixation area of conical stems is within the distal femoral isthmus, whereas cylindrical implants are dependent on proximal bone stock. In our study, cylindrical stems are advantageous for minor defects because they provide a proximal fixation. In cases of extensive substance loss, the conical implants showed lesser relative movements. These findings should be taken into account for clinical decisions.
Journal of Biomechanics 09/2008; 41(14):3078-84. · 2.43 Impact Factor
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ABSTRACT: Metal-on-metal total hip resurfacing arthroplasty is increasingly being performed in young and active patients. Preclinical in vitro testing of implants is usually performed with use of hip simulators, and the serum metal ion concentration is determined for the purpose of monitoring the patients. The goal of this study was to characterize the early running-in period in vivo and in vitro by characterizing metal ion levels.
A well-functioning total hip resurfacing prosthesis was implanted in fifteen consecutive patients, and the serum metal ion concentrations in these patients were then determined preoperatively and at intervals during the first postoperative year (at one, six, twelve, twenty-four, and fifty-two weeks). The number of walking cycles was measured with use of a computerized accelerometer in order to compare walking cycles to hip simulator cycles. In vitro, five similar components were investigated for 3 million cycles with use of a hip simulator. Serum samples were obtained at different time points, and wear was measured by quantifying wear particles and ions in the samples. All patient and simulation serum samples were analyzed with use of inductively coupled plasma-mass spectrometry. One simulator implant was investigated with use of scanning electron microscopy.
The serum chromium and cobalt levels of the patients continuously increased during the first six months and showed an insignificant decrease thereafter. The molybdenum concentration was unchanged compared with preoperative values. In contrast, the simulator measurements showed a different wear pattern with a high-wear running-in period and a low-wear steady-state phase. The running-in period was delayed by 300,000 cycles and lasted up to 1 million cycles. Scanning electron microscopic analysis showed a carbon-rich protein film predominantly in the early phases of simulation. Scratches were detected originating from pits filled with aluminum oxide and silicon oxide and from pulled-out carbides that were causing third-body wear.
The simulator study allowed an exact characterization of the running-in period and showed a delayed onset of running-in wear. In contrast, the clinical data showed a slow increase in measured ion concentrations. These different wear patterns are probably due to the effects of distribution, accumulation, and excretion of particles and ions in vivo.
The Journal of Bone and Joint Surgery 09/2008; 90 Suppl 3:125-33. · 3.27 Impact Factor
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ABSTRACT: We previously reported wear data at a minimum of two years following thirty-four total hip replacements with a Marathon cross-linked polyethylene liner and twenty-four replacements with a conventional (gamma-sterilized-in-air) Enduron polyethylene liner. In this current study, with sequential five-year radiographs, wear rates were determined with use of linear regression analysis. The Marathon polyethylene had average wear rates of 15.4 mm(3)/yr and 8.0 mm(3)/million cycles. The Enduron polyethylene had average wear rates of 55.5 mm(3)/yr and 29.9 mm(3)/million cycles. The adjusted volumetric wear rate of the Marathon polyethylene was 73% lower than that of the Enduron polyethylene (p = 0.001). Osteolysis developed in eight of the twenty-four hips with an Enduron liner but was not apparent in any hip with a Marathon liner.
The Journal of Bone and Joint Surgery 08/2008; 90(7):1487-91. · 3.27 Impact Factor
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ABSTRACT: This study gives an overview of the main macro- and microstructural differences of ten commercially available total hip resurfacing implants. The heads and cups of resurfacing hip implants from ten different manufacturers were analysed. The components were measured in a coordinate measuring machine. The microstructure of the heads and cups was inspected by scanning electron microscopy. The mean radial clearance was 84.86 microm (range: 49.47-120.93 microm). The implants were classified into three groups (low, medium and high clearance). All implants showed a deviation of roundness of less than 10 microm. It was shown that all implants differ from each other and a final conclusion about the ideal design and material combination cannot be given based on biomechanical data. Widespread use of specific designs can only be recommended if clinical long-term follow-up studies are performed and analysed for each design.
International Orthopaedics 08/2008; 33(4):939-43. · 2.03 Impact Factor
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ABSTRACT: The causes of periprosthetic fractures of the femur due to the design of the prosthesis and the individual parameters of the patient are unexplored. By different anchorage techniques in cementless total hip arthroplasties, it is assumed that there are various load limits of the implant's bearing femur.
In the present study, we compared a standard hip stem (cementless Spotorno) and a short-stemmed design (Mayo) by an artificial reproduction of periprosthetic fractures in 20 femur specimens.
The measured fracture loads showed an extensive range, with higher maximum loads in the standard stem group. The bone mineral density and the subsiding pattern of the standard stems showed a significant correlation to the incidence of the periprosthetic fractures. In the experimental setup, a slightly lower fracture resistance was shown for the short-stemmed prosthesis. Additionally, it was shown that donors with a higher body mass index had a significantly increased fracture risk.
Short-stemmed prostheses, especially the Mayo hip, do not constitute a higher fracture risk. In general, an increased body mass index among patients with a cementless hip stem is associated with an increased fracture risk, particularly at high load values, i.e., resulting from a step during stumbling. Taking into account the ascertained results, the danger of provoking a femoral periprosthetic fracture can be reduced.
Archives of Orthopaedic and Trauma Surgery 07/2008; 129(6):849-55. · 1.37 Impact Factor
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ABSTRACT: Clinical success of bone implants is critically related to the interaction between the implant surface and the surrounding tissue. The polymer poly(bis(trifluoroethoxy)phosphazene) (PTFEP) is a promising, highly biocompatible surface coating which also inhibits the adsorption of granulocytes, macrophages, inflammatory cells, bacteria, and platelets. However, there is limited clinical experience of PTFEP as a coating for bone implants. Therefore PTFEP-coated titanium implants in an animal model were examined.
PTFEP-coated titanium cylinders were implanted into the lateral femoral condyles of rabbits. Osseointegration was examined six weeks and six months after implantation using a non-destructive mechanical pull-out measurement and a histological analysis.
The results indicate improved osseointegration of PTFEP-coated implants. Six weeks after implantation, the PTFEP-coated implants showed a higher stiffness (pull-out length [pol]=7.1+/-2.0 microm) compared with uncoated cylinders (pol=10.2+/-3.4 microm, p<0.05). Six months after implantation, the mechanical properties of both implants had adjusted, and histological analysis revealed an increased bone-implant interface of PTFEP-coated cylinders compared with the first 6 weeks (17.5% vs. 8.2% in controls, p<0.05).
Taken together, the results of this preliminary study indicate promising applications of PTFEP as a coating material for bone implants.
Medical science monitor: international medical journal of experimental and clinical research 03/2008; 14(2):BR35-40. · 1.70 Impact Factor
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The Journal of Bone and Joint Surgery 01/2008; 89(12):2758-63. · 3.27 Impact Factor
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ABSTRACT: The aim of this study was to determine the diagnostic value of systemic biochemical markers of bone turnover in aseptic loosening in hip arthroplasty, namely the urine levels of three bone resorption peptides - crosslinked n-telopeptides (NTX), c-telopeptides (CTX I) and deoxypyridinoline (DPD). We compared 52 patients with surgically proven component loosening with 52 patients without clinical or radiological signs of endoprosthetic loosening and 52 healthy individuals. All three markers were measured using commercially available enzyme-linked immunoassays. We found significantly increased levels of DPD in the loosening group (p < 0.05), but there was no significant difference between the loosening group and the two reference groups for the other two markers tested. Our data suggest that DPD can be used as an additional tool in the diagnosis of aseptic loosening in hip arthroplasty but CTX I and NTX have no predictive value in this context.
International Orthopaedics 12/2007; 33(1):77-82. · 2.03 Impact Factor
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ABSTRACT: We occasionally noticed excessive distal plug position in our clinical routine of cemented hip arthroplasties. We therefore performed an analysis of risk factors for migration of a biodegradable intramedullary gelatine plug.
The performance of a cement restrictor was studied in 100 consecutive cemented total hip arthroplasties implanted with third-generation cementing techniques. In a radiographic analysis anatomical parameters, cement mantle quality, and mechanisms and factors for restrictor failure were evaluated.
40 restrictors showed inadequate performance: 5 cases of tilting, 22 cement leakages, 16 excessive migrations, 2 excessive migrations plus leakages, and 1 case of leakage plus tilting. excessive migration (< 5 cm) was more common in large intramedullary canals (p = 0.04) and cement leakage was more common in patients with a proximally located isthmus (p = 0.04). Half of the hips showed a complete or almost complete filling of the intramedullary cavity, which was more often found in operations carried out by experienced surgeons.
A more reliable plug design should be considered for patients with wide intramedullary canals and a high isthmus, to minimize the risk of plug migration and poor cement mantle quality.
Acta Orthopaedica 09/2007; 78(4):485-90. · 2.17 Impact Factor
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Orthopedics 06/2007; 30(5):352-7. · 2.66 Impact Factor
