Biomedical subjects

G Harry van Lenthe

Publications and source records attributed to G Harry van Lenthe.

6 recordsLinked to original sources

PubMed2006

In vivo behavior of calcium phosphate scaffolds with four different pore sizes.

The goal of the present study was to assess the effect of macropore size on the in vivo behavior of ceramic scaffolds. For that purpose, beta-tricalcium phosphate (beta-TCP) cylinders with four different macropore sizes (150, 260, 510, and 1220 microm) were implanted into drill hole defects in cancellous bone of sheep and their resorption behavior was followed for 6, 12 and 24 weeks. The scaffolds were evaluated for biocompatibility, and new bone formation was observed macroscopically, histologically and histomorphometrically. Histomorphometrical measurements were performed for the whole defect area and for the area subdivided into three concentric rings (outer, medial, and inner ring). All implants were tolerated very well as evidenced by the low amount of inflammatory cells and the absence of macroscopic signs of inflammation. Resorption proceeded fast since less than 5% ceramic remained at 24-week implantation. Hardly any effect of macropore size was observed on the in vivo response. Samples with an intermediate macropore size (510 microm) were resorbed significantly faster than samples with smaller macropore sizes (150 and 260 microm). However, this fast resorption was associated with a lower bone content and a higher soft tissue content. At 12 and 24 weeks, the latter differences had disappeared. Bone was more abundant in the outer ring than in the rest of the blocks at 6 weeks, and in the outer and medial ring compared to the inner ring at 12 weeks.

Animals↗

PubMed2006

Importance of individual rods and plates in the assessment of bone quality and their contribution to bone stiffness.

UNLABELLED: Local morphometry based on the assessment of individual rods and plates was applied to 42 human vertebral trabecular bone samples. Results showed that multiple linear regression models based on local morphometry as a measure for bone microstructure helped improving our understanding of the role of local structural changes in the determination of bone stiffness as assessed from direct and computational biomechanics. INTRODUCTION: In a recent study, we proposed a method for local morphometry of trabecular bone, i.e., morphometry as applied to individual rods and plates. In this study, we used this method to study the relative importance of local morphometry in the assessment of bone architecture and its relative contribution to the stiffness of human vertebral bone. MATERIALS AND METHODS: We extracted 42 human trabecular bone autopsies from nine intact spinal columns. The cylindrical samples were imaged with muCT to assess bone microstructure. From these images, global and local morphometric indices were derived and related to Young's modulus as assessed by experimental uniaxial compression testing (Emeas) and computational finite element analysis (EFE). RESULTS: We found the best single predictor for Young's modulus to be apparent bone volume density (BV/TV), which explained 89% of the variance in EFE when fitted with a power law. A multiple linear regression model combining mean trabecular spacing (Tb.Sp), mean slenderness of the rods ( ), and the relative amount of rod volume to total bone volume (Ro.BV/BV) was able to explain 90% of the variance in EFE. This model could not be improved by adding BV/TV as an independent variable. Furthermore, we found that mean trabecular thickness of the rods was significantly related to EFE (r2 = 0.42), whereas mean trabecular thickness of plates had no correlation to Young's modulus. Because the globally determined trabecular thickness does not discriminate between rods and plates, this index had only a poor predictive power for EFE (r2 = 0.09), showing the importance of local analysis of individual rods and plates. CONCLUSIONS: From these results, we conclude that models based on local morphometry help improving our understanding of the relative importance of local structural changes in the determination of the stiffness of bone. Separate analysis of individual rods and plates may help to better predict age and disease-related fractures as well as to shed new light on the effect of pharmaceutical intervention in the prevention of such fractures beyond BMD.

Biomechanical Phenomena↗

PubMed2006

Local delivery of bisphosphonate from coated orthopedic implants increases implants mechanical stability in osteoporotic rats.

Patients with osteoporosis and joint disabilities represent a constant growing and challenging population to be treated in the musculoskeletal clinical field. Especially in the case of total hip arthroplasty, new solutions should be developed to compensate for the double negative factors, peri-implant osteolysis, and osteoporotic bone loss, affecting the quality of implant outcome. The goal of this study was then to establish a proof of concept for orthopedic implant used as Zoledronate delivery in osteoporotic rats, and in particular, to verify if this approach could increase the initial implant stability. Twenty-five female 6-month-old Wistar rats were ovariectomized 6 weeks before the implantation to induce osteoporosis. The animals were randomly separated in five groups representing the different Zoledronate concentrations in the HA coating: 0, 0.2, 2.1, 8.5, and 16 microg/implant. Histomorphometric measures and peri-implant bone volume fraction were assessed and mechanical stability tests were performed. Bone volume fraction and biomechanical results clearly illustrate the positive effect of Zoledronate coated implants in the osteoporotic rats. A remarkable result was to show the existence of a window of Zoledronate content (0.2 to 8.5 microg/implant) in which the mechanical fixation of the implant increased. We were able to establish the proof of concept for orthopedic implants used as a drug delivery system in osteoporotic rats. The local bisphosphonate delivery from a calcium phosphate coating allowed increase of the mechanical fixation of an orthopedic implant. This study shows that orthopedic implants containing bisphosphonates could be beneficial for osteoporotic patients in need of a total joint replacement.

Animals↗

PubMed2006

Trabecular bone failure at the microstructural level.

Although biomedical imaging technology is now readily available, few attempts have been made to expand the capabilities of these systems by adding not only quantitative but also functional analysis tools combining microimaging with time-lapsed mechanical testing. An area of special interest is multiscale functional imaging of trabecular bone to assess the relative importance of bone "quality" in the assessment of the mechanical competence of bone. First, relevant studies dealing with hierarchical imaging of trabecular bone and classic analyses such as quantitative morphometry and finite-element analysis to predict bone strength are reviewed. Second, studies are presented investigating failure mechanisms of three-dimensional trabecular bone through dynamic, time-lapsed microimaging, including image-guided techniques developed for this purpose and utilizing microcompression. For the first time, these allow the direct three-dimensional visualization and quantification of failure initiation and progression at the microstructural level.

Biomechanical Phenomena↗

PubMed2006

Evaluation of an in situ formed synthetic hydrogel as a biodegradable membrane for guided bone regeneration.

The aim of the present study was to test whether or not the application of an in situ formed synthetic hydrogel made of polyethylene glycol (PEG) used as a biodegradable membrane for guided bone regeneration will result in the same amount of bone regeneration as with the use of an expanded polytetrafluoro-ethylene (ePTFE) membrane. In eight New Zealand White rabbits, four evenly distributed 6 mm diameter defects were drilled into the calvarial bone. Three treatment modalities were evenly distributed among the 32 defects: hydroxyapatite (HA)/tricalciumphosphate (TCP) granules covered at the outer and inner surface with a PEG membrane (test), HA/TCP granules covered at the outer and inner surface with an ePTFE membrane (positive control) and HA/TCP granules alone without membranes (negative control). After 4 weeks, the animals were sacrificed and the calvarial bones were removed. The area fraction of newly formed bone was determined by histomorphometrical analysis of the vertical sections from the middle of the defect and by micro-computed tomography of the entire defect. Multiple regression analysis (SAS GLM) was used to model the amount of new bone formation. The quantitative histomorphometric analysis clearly revealed higher values of newly formed bone for the two membrane groups compared with the negative control group. The average area fractions of newly formed bone measured within the former defect amounted to 20.3+/-9.5% for the PEG membrane, 18.9+/-9.9% for the ePTFE membrane, and 7.3+/-5.3% for the sites with no membrane. The micro-computed tomography also showed higher values of new bone formation for the PEG and for the ePTFE groups compared with the negative control group. The GLM revealed a highly significant effect of the treatment on the amount of bone formation (P=0.0048). The values for the negative control group were significantly lower than the ones found in the PEG membrane group (P=0.0017), whereas the ePTFE membrane group showed no significant difference from the PEG membrane group. It is concluded that the PEG membrane can be used successfully as a biodegradable barrier membrane in the treatment of non-critical-size defects in the rabbit skull, and leads to similar amounts of bone regeneration as an ePTFE membrane.

Absorbable Implants↗

PubMed2002

Stemmed femoral knee prostheses: effects of prosthetic design and fixation on bone loss.

Although the revision rates for modern knee prostheses have decreased drastically, the total number of revisions a year is increasing because many more primary knee replacements are being done. At the time of revision, bone loss is common, which compromises prosthetic stability. To improve stability, intramedullary stems are often used. The aim of this study was to estimate the effects of a stem, its diameter and the interface bonding conditions on patterns of the bone remodeling in the distal femur. We created finite element models of the distal half of a femur in which 4 types of knee prostheses were placed. The bone remodeling process was simulated using a strain-adaptive bone remodeling theory. The amount of such remodeling was determined by calculating the changes in bone mineral density in 9 regions of interest from simulated DEXA scans. The computer simulation model showed that revision prostheses tend to cause more bone resorption than primary ones, especially in the most distal regions. Predicted long-term bone loss due to a revision prosthesis with a thin stem equalled that around a prosthesis with an intercondylar box. However, strong regional differences were found--the stemmed prostheses having more bone loss in the most distal areas and some bone gain in the more proximal ones. A prosthesis with a thick stem led to an increase in bone loss. When the prosthesis-cement interface was bonded, more bone loss was predicted than with an unbonded interface. These results suggest that a stem which increases stability initially may reduce stability in the long term. This is due to an increase in stress shielding and bone resorption.

Bone Remodeling↗