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Biomedical subjects

N Verdonschot

Publications and source records attributed to N Verdonschot.

At least 55 records · Page 3Linked to original sources
PubMed2002

Acetabular defect reconstruction with impacted morsellized bone grafts or TCP/HA particles. A study on the mechanical stability of cemented cups in an artificial acetabulum model.

In revision surgery of the acetabulum bone defects can be filled with impacted human morsellized bone grafts. Because of a worldwide limited availability of human bone, alternatives are being considered. In this study we compared the initial stability of acetabular cups after reconstructing a cavitary defect with various compositions of impacted tricalciumphosphate-hydroxyapatite (TCP/HA) particles and mixes of TCP/HA particles and human grafts in a realistic acetabulum model. Primary cemented cups and reconstructions with impacted human cancellous grafts were used as reference. A dynamic load displaced the acetabular cups superomedially. The primary cemented cups showed the highest stability. The cups with impacted human grafts produced the most displacement. All reconstructions with the TCP/HA particles showed a high stability of the cups. However, especially when using large TCP/HA particles this was probably due to a large amount of cement penetration. Mixing TCP/HA particles with human grafts seemed to decrease cement penetration. although still a high stability was obtained. In this perspective, we concluded that TCP/HA particles might be useful as a bone graft extender in the reconstruction of acetabular bone defects.

Acetabulum↗
PubMed2002

Effects of metal-inlay thickness in polyethylene cups with metal-on-metal bearings.

A way to prevent polyethylene wear in total hip replacements is to use metal-on-metal bearings. The cup design of these bearings may be a metal inlay in a polyethylene cup. However, these metal inlays are relatively thin and may deform on loading. The purpose of the current study was to determine whether these potential problems become actual for a realistic range of metal-inlay components having a thickness greater than 1 mm. For this purpose, the effects of thickness variation of a metal inlay in an ultrahigh molecular weight polyethylene cup were determined using three-dimensional finite element techniques. The results showed no indications for jamming of the bearing assuming a realistic inlay thickness (3-5 mm), even with a small clearance (25 microm). The metal inlay acted rigidly beyond a thickness of approximately 5 mm. Metal inlays thinner than 1.5 mm led to a considerable increase in contact area and a reduction in contact peak stress, which may be beneficial for the bearing performance. Currently, these thin liners have too many unknown characteristics and therefore the current authors recommend using rigid metal liners that have a thickness greater than 5 mm.

Biomechanical Phenomena↗
PubMed2002

Do unloading periods affect migration characteristics of cemented femoral components? An in vitro evaluation with the Exeter stem.

Prosthetic migration has been identified as a marker for future revision of cemented total hip reconstructions. This could be tested at a pre-clinical stage with dynamic loading experiments. The purpose of this study was to assess the effects of resting periods, which are a considerable part of the daily activity cycle, on the migration characteristics of femoral cemented stems. Ten polished Exeter stems were implanted in composite femurs and loaded either with a continuous load or a discontinuous load. Continuous loading involved 345,600 loading cycles at 1 Hz, whereas the discontinuous loading involved loading at 1 Hz for 2.5 hours and a resting period of 21.5 hours for a period of four days. Hence, a total of 36,000 loading cycles were applied to these reconstructions. The subsidence patterns of the prostheses were considerably affected by the resting periods. The prostheses exhibited a step-wise migration pattern with migration steps of about 50 microns after every resting period, whereas the continuously loaded prostheses showed a more gradual migration pattern. The final subsidence of the specimens when loaded with resting periods was significantly less than the subsidence measured without resting periods. However, these specimens were loaded with fewer loading cycles. If this was taken into account, the discontinuously loaded specimens had a four fold higher average migration per loading cycle than the specimens that were loaded continuously. In conclusion, the resting periods had a considerable effect on the migration patterns, which should be realized when these stems are analyzed with pre-clinical tests.

Activities of Daily Living↗
PubMed2001

Time-dependent mechanical properties of HA/TCP particles in relation to morsellized bone grafts for use in impaction grafting.

In reconstructive surgery human bone defects are sometimes filled with the use of the impaction bone grafting technique. Currently different types of biomaterial particles are being developed as bone-substitute materials. Before these biomaterials can be applied their mechanical and biological behavior should be characterized. In this study the time-dependent mechanical behavior of biomaterial particles with different tri-calcium-phosphate/hydroxy-apatite (TCP:HA) ratios, particle sizes, and porosities is determined and compared to the behavior of human bone grafts, the latter being the standard material currently used to augment bone defects. The mechanical properties were assessed with the use of dynamic confined compression creep tests with a loading and unloading phase. Different graft material groups were tested, consisting of 100% human bone grafts, 100% biomaterial particles, and 50:50 weight mixtures of human grafts and biomaterial particles. No damage to the particles was observed by the impaction in the test chamber or by the dynamic load. Relative to the human graft material, the biomaterial particles hardly deformed under loading, were much stiffer, and showed almost no viscoelastic behavior. The mixtures showed intermediate results. Particle size and porosity influenced the behavior of the biomaterial particles. TCP:HA ratio did not have a great effect. The conclusion is that the application of these particles should be done with great care, as their mechanical behavior is drastically different than that of the human graft material. Mixing it with human bone grafts gave the material some biphasic, viscoelastic behavior that may be important for its biological response.

Biocompatible Materials↗
PubMed2001

Distal femoral bone mineral density after total knee arthroplasty: a comparison with general bone mineral density.

The bone mineral density (BMD) of the distal femur may decrease after cemented total knee arthroplasty (TKA) as a result of the stress shielding effect of the femoral component. The purpose of the study was to determine the changes in BMD of the distal femur compared with those of the femoral necks and the lumbar spine after cemented TKA. BMD of two regions of interest in the distal femur, both femoral necks and the lumbar spine was measured with dual-energy X-ray absorptiometry in 10 patients (age range 41-80 years, mean 62 years) with 12 TKAs preoperatively and during follow-up for 1 year after surgery. The hip and spine measurements were performed for comparison to assess if general changes in BMD occurred after TKA. The median decrease in BMD in the region behind the anterior flange of the femoral component was 22% (95% CI: 12%-33%), while the average decrease in the region just above the femoral component was 8% (95% CI: 2%-13%). The difference in change of BMD between both regions before and 1 year after TKA was significant (p = 0.03). We found less than 1% difference in BMD of both femoral necks and the lumbar spine on average between the preoperative and 1 year follow-up measurements (not significant). A significant periprosthetic distal femoral bone resorption occurred after TKA. BMD of the femoral necks and lumbar spine did not differ 1 year after TKA.

Aged↗
PubMed2001

Frictional heating of total hip implants. Part 1: measurements in patients.

Hip implants heat up due to friction during long lasting, high loading activities like walking. Thermal damage in the surrounding soft and hard tissues and deteriorated lubrication of synovial fluid could contribute to implant loosening. The goal of this study was to determine the implant temperatures in vivo under varying conditions. Temperatures and contact forces in the joints were measured in seven joints of five patients using instrumented prostheses with alumina ceramic heads and telemetry data transmission. The peak temperature in implants with polyethylene cups rose up to 43.1 degrees C after an hour of walking but varied considerably individually. Even higher temperatures at the joints are probable for patients with higher body weight or while jogging. The peak temperature was lower with a ceramic cup, showing the influence of friction in the joint. During cycling the peak temperatures were lower than during walking, proving the effect of force magnitudes on the produced heat. However, no positive correlation was found between force magnitude and maximum temperature during walking. Other individual parameters than just the joint force influence the implant temperatures. Based on the obtained data and the available literature about thermal damage of biological tissues a detrimental effect of friction induced heat on the stability of hip implants cannot be excluded. Because the potential risk for an individual patient cannot be foreseen, the use and improvement of low friction implant materials is important.

Aged↗
PubMed2001

Hip-joint and abductor-muscle forces adequately represent in vivo loading of a cemented total hip reconstruction.

Using finite element analyses, we investigated which muscle groups acting around the hip-joint most prominently affected the load distributions in cemented total hip reconstructions with a bonded and debonded femoral stem. The purpose was to determine which muscle groups should be included in pre-clinical tests, predicting bone adaptation and mechanical failure of cemented reconstructions, ensuring an adequate representation of in vivo loading of the reconstruction. Loads were applied as occurring during heel-strike, mid-stance and push-off phases of gait. The stress/strain distributions within the reconstruction, produced by the hip-joint contact force, were compared to ones produced after sequentially including the abductors, the iliotibial tract and the adductors and vastii. Inclusion of the abductors had the most pronounced effect. They neutralized lateral bending of the reconstruction at heel-strike and increased medial bending at mid-stance and push-off. Bone strains and stem stresses were changed accordingly. Peak tensile cement stresses were reduced during all gait phases by amounts up to 50% around a bonded stem and 11% around a debonded one. Additional inclusion of the iliotibial tract, the adductors and the vastii produced relatively small effects during all gait phases. Their most prominent effect was a slight reduction of bone strains at the level of the stem tip during heel-strike. These results suggest that a loading configuration including the hip-joint contact force and the abductor forces can adequately reproduce in vivo loading of cemented total hip reconstructions in pre-clinical tests.

Biomechanical Phenomena↗
PubMed2001

Frictional heating of total hip implants. Part 2: finite element study.

Due to higher friction artificial hip joints warm up more than natural joints during walking and other continuous activities. This could lead to thermal damage in the surrounding tissues and be a reason for long-term implant loosening, an effect which has not yet been investigated. In vivo measurements with instrumented implants showed temperatures inside the prosthetic head up to 43.1 degrees C (Part 1 of this work). Based on the experimental data a finite element model was developed to calculate the temperatures in the tissues surrounding the hip implant to determine whether these tissues can heat up to critical levels. Various parameters were investigated which could account for the variations in the measured temperatures in the patients, including the perfusion rate in tissues, the volume of synovial fluid, and different implant materials. We found that the synovial fluid is most endangered by thermal damage and consequent deterioration of lubricating properties. Implants with a cobalt-chromium head and a polyethylene cup are unfavourable as they can elevate the temperature in the synovia to more than 46 degrees C. With regard to thermal properties stems made from cobalt-chromium alloys are superior to titanium stems, by better conducting heat to the femur and minimizing the synovial fluid temperature. Factors determining the temperatures during walking are insufficiently known or cannot be determined in the individual patient. Therefore, the risk of a thermally induced implant loosening cannot currently be estimated. Under unfavourable conditions such a risk exists, however. General improvements of implant materials and clinical studies on the possibility of implant loosening due to high temperatures are therefore required.

Alloys↗
PubMed2001

Acetabular revision with impacted freeze-dried cancellous bone chips and a cemented cup: a report of 7 cases at 5 to 9 years' follow-up.

The long-term results of bone impaction grafting with fresh-frozen femoral head allografts and a cemented cup are favorable. Because of intermittent shortage of fresh-frozen femoral heads at our local bone bank, we used processed freeze-dried bone in 7 acetabular revisions operated between 1989 and 1994. All 7 consecutive patients were followed annually. At final review (March 2000), 1 patient had died after 8.5 years of follow-up of a cause not related to the surgery. In 1 hip, a rerevision was performed for septic loosening 5 years after the previous septic loosening. Radiographically the freeze-dried allografts seemed to incorporate in all cases but the reinfected one; progressive radiolucent lines were not seen, although 1 case had a stable line in 1 zone. The overall survival rate for the 7 acetabular reconstructions at an average follow-up of 7 years (range, 5-9 years) was 86%. At midterm follow-up, there was no aseptic loosening. In this limited case report, the results at midterm for freeze-dried allograft bone chips in acetabular reconstructions are acceptable.

Acetabulum↗
PubMed2001

Favorable results of acetabular reconstruction with impacted morsellized bone grafts in patients younger than 50 years: a 10- to 18-year follow-up study of 34 cemented total hip arthroplasties.

We report a long-term review of 41 acetabular reconstructions using impacted morsellized bone grafts and a cemented total hip arthroplasty (THA) in patients younger than 50 (22-49; average 38) years. Reconstruction was performed in 23 primary THA (19 patients) and 18 revision THA (17 patients). 3 patients were lost to follow-up and 3 (4 hips) died within 10 years of surgery; none had a revision. Thus, 34 hips (30 patients) were reviewed with an average follow-up of 13 (10-18) years. In 2 hips, a revision was performed for aseptic loosening of the acetabular component 7 and 11 years after surgery. One additional cup was revised after 12 years during a femoral stem revision due to wear and matching problems, but was well fixed. The survival rate of the acetabular reconstruction technique was 94% (95% CI: 90-98%).

Acetabulum↗
PubMed2000

Creep properties of three low temperature-curing bone cements: a preclinical assessment.

The mechanical characteristics of new bone cements should be assessed before these cements are released on the orthopedic market in great quantities. In this study, we present the deformational response of 3 relatively new, low-curing temperature bone cements (Cemex RX, Cemex System, and Cemex Isoplastic) to a dynamic compressive force in comparison to Simplex P bone cement. For this purpose, dynamic compressive creep tests were performed on cylindrical shaped specimens at a maximal load level of 20 MPa for a period of 250,000 cycles. The results showed that Cemex System and Cemex RX produced creep rates that were higher (20% and 30%, respectively) as compared to Simplex P bone cement. The creep behavior of Cemex Isoplastic was very similar to that of Simplex P. It was concluded that although Cemex RX and Cemex System produced higher creep rates than Simplex P, these differences were not considered excessive. Hence, although other tests are required to assess the safety and efficacy of these new cements, the dynamic creep properties under compression can be considered adequate for clinical use.

Biocompatible Materials↗
PubMed2000

Acetabular reconstruction with impacted morcellized cancellous bone autograft and cemented primary total hip arthroplasty: a 10- to 17-year follow-up study.

During the period 1979 through 1986, 69 acetabular reconstructions in 63 patients were performed with the use of autologous morcellized bone-grafts because of acetabular bone stock loss. Nine cases (10 hips) were lost to follow-up. Eleven patients (12 hips) died <10 years after surgery; none had a revision. The results for the remaining 43 patients (47 hips) were reviewed at an average interval of 12.3 years (range, 10-17 years). No preoperative Harris hip score was available. The average Harris hip score at follow-up was 88 (range, 60-100). Radiographically, all grafts united. One hip developed a deep infection. Three other hips (6%) were revised because of aseptic loosening of the acetabular component. An additional 3 acetabular components were considered radiographic failures. Excluding the infected case, the overall survival rate of these acetabular reconstructions with a revision as endpoint was 94% at an average follow-up of 12.3 years. Reconstruction of acetabular bone stock loss with autologous morcellized bone-grafts is an attractive technique with a good potential for long-term success.

Acetabulum↗
PubMed2000

The role of femoral stem extension in total knee arthroplasty.

Although stemmed femoral components often are used in revision total knee arthroplasty, no quantitative comparison of the relative stability of a femoral component with and without a stem has been performed previously. A radiostereophotogrammetric analysis was performed to determine the influence of stem extension on mechanical stability in a laboratory experiment. In addition, the contribution of impacted morselized bone graft used for reconstruction of bone defects to stability was determined. Ten fresh frozen distal femoral specimens, of which the bone mineral density was measured, were prepared to fit a cemented femoral component with an uncemented stem. A cyclic axial load of 750 N was applied to the medial part of the femoral component. The loading test was repeated after creation of a standard, unicondylar, uncontained medial bone defect, after reconstruction of the defect with impacted morselized bone graft, after disconnecting the stem from the component, and after removal of the morselized bone graft. A significant difference was found in rotation and translation of the femoral component with the stem and after its functional removal. The femoral component rotated significantly into varus and internal rotation, and the tip of the stem translated significantly laterally after disconnection of the stem. A linear correlation between bone mineral density in the femoral neck and the radiostereophotogrammetric motion data was absent, but a bone mineral density threshold level of 0.55 g/cm2 was present, below which stability decreased considerably. Morselized bone graft provided only a minor contribution to stability compared with a stem.

Arthroplasty, Replacement, Knee↗
PubMed2000

Autologous morsellised bone grafting restores uncontained femoral bone defects in knee arthroplasty. An in vivo study in horses.

The properties of impacted morsellised bone graft (MBG) in revision total knee arthroplasty (TKA) were studied in 12 horses. The left hind metatarsophalangeal joint was replaced by a human TKA. The horses were then randomly divided into graft and control groups. In the graft group, a unicondylar, lateral uncontained defect was created in the third metatarsal bone and reconstructed using autologous MBG before cementing the TKA. In the control group, a cemented TKA was implanted without the bone resection and grafting procedure. After four to eight months, the animals were killed and a biomechanical loading test was performed with a cyclic load equivalent to the horse's body-weight to study mechanical stability. After removal of the prosthesis, the distal third metatarsal bone was studied radiologically, histologically and by quantitative and micro CT. Biomechanical testing showed that the differences in deformation between the graft and the control condyles were not significant for either elastic or time-dependent deformations. The differences in bone mineral density (BMD) between the graft and the control condyles were not significant. The BMD of the MBG was significantly lower than that in the other regions in the same limb. Micro CT showed a significant difference in the degree of anisotropy between the graft and host bone, even although the structure of the area of the MBG had trabecular orientation in the direction of the axial load. Histological analysis revealed that all the grafts were revascularised and completely incorporated into a new trabecular structure with few or no remnants of graft. Our study provides a basis for the clinical application of this technique with MBG in revision TKA.

Animals↗
PubMed1999

Morsellized bone grafting compensates for femoral bone loss in revision total knee arthroplasty. An experimental study.

This study was undertaken to examine the contribution of uncontained morsellized bone graft to the structural properties of a femoral reconstruction in total knee arthroplasty and to serve as a basis for an in vivo animal study. Ten human distal femora with a standard unicondylar uncontained medial bone defect were prepared to fit a femoral component of a cruciate sacrificing TKA. A cyclic axial load of 750 N was applied to the medial part of the femoral component in the presence of impacted morsellized bone graft. After removal of the bone graft, the cyclic loading was repeated for the unsupported situation. None of the grafts collapsed and all cement mantles stayed intact during the experiments. Elastic deformation during cyclic loading was significantly less when graft was added while time-dependent deformation was not affected. We conclude that impacted morsellized bone graft, used for reconstruction of uncontained femoral bone loss in revision knee arthroplasty, may improve the structural resistance against loading. Further animal experimentation for in vivo application is warranted.

Animals↗
PubMed1999

A combined finite element method and continuum damage mechanics approach to simulate the in vitro fatigue behavior of human cortical bone.

The fatigue of bone, in particular the associated modulus degradation and accumulation of permanent strain, has been implicated as the cause of femoral neck fractures and the migration of total joint replacements. The objective of this study was to develop a technique to simulate the tensile fatigue behavior of human cortical bone. A combined continuum damage mechanics (CDM) and finite element analysis (FEA) approach was used to predict the number of cycles to failure, modulus degradation and accumulation of permanent strain of human cortical bone specimens. The simulation of fatigue testing of eight dumb-bell specimens of cortical bone were performed and the predictions compared with existing experimental data. The predictions from the finite element models were in close agreement with the experimental data. The models predicted similar development of modulus degradation and permanent strain as observed in the experimental tests. The technique is capable of predicting the accumulation of permanent strain without the need for simulating every single load step. These findings suggest that the complex fatigue behavior of human cortical bone can be simulated using the described approach and forms the first step for simulating the more complex mechanisms associated with femoral neck fractures and implant migration.

Journal Article↗
PubMed1999

Mechanical characteristics of impacted morsellised bone grafts used in revision of total hip arthroplasty.

The use of impacted, morsellised bone grafts has become popular in revision total hip arthroplasty (THA). The initial stability of the reconstruction and the effectiveness of any subsequent process of revitalisation and incorporation will depend on the mechanical integrity of the graft. Our aim in this study was to document the time-dependent mechanical properties of the morsellised graft. This information is useful in clinical application of the graft, in studies of migration of the implant and in the design of the joint. We used 16 specimens of impacted, morsellised cancellous bone from the sternum of goats to assess the mechanical properties by confined compression creep tests. Consideration of the graft material as a porous, permeable solid, filled with fluid, allowed determination of the compressive modulus of the matrix, and its permeability to fluid flow. In all specimens the compression tests showed large, irreversible deformations, caused by flow-independent creep behaviour as a result of rolling and sliding of the bone chips. The mean permeability was 8.82 *10(-12) m4/Ns (SD 43%), and the compressive modulus was 38.7 MPa (SD 34%). No correlation was found between the apparent density and the permeability or between the apparent density and the compressive modulus. The irreversible deformations in the graft could be captured by a creep law, for which the parameters were quantified. We conclude that in clinical use the graft is bound to be subject to permanent deformation after operation. The permeability of the material is relatively high compared with, for example, human cartilage. The confined compression modulus is relatively low compared with cancellous bone of the same apparent density. Designs of prostheses used in revision surgery must accommodate the viscoelastic and permanent deformations in the graft without causing loosening at the interface.

Animals↗