Biomedical subjects

Thomas Pressel

Publications and source records attributed to Thomas Pressel.

6 recordsLinked to original sources

PubMed2006

[FE-analysis of surface stresses for the tribological system in total hip prostheses].

The implantation of a total hip prosthesis is an operation which is performed frequently due to advanced hip joint damage both in humans and in veterinary medicine in dogs. The long-term result of a hip prosthesis is mainly determined by aseptic loosening of the prosthesis; among other causes, abrasion particles of the tribological pairing are responsible for the loosening. For the analysis of the surface stresses with different tribological pairings, a finite element model was generated which was based on the CAD data of a commercial total hip prosthesis. After transmission of a physiological force in the components of the three tribological pairings ceramic/polyethylene, ceramic/ceramic and metal/polyethylene, stresses were calculated. Stresses in the ceramic/ceramic tribological pairings were conspicuously higher than in the other material pairings. In the future adapted prostheses have to be developed that ensure optimal friction and absorption characteristics of the components.

Arthroplasty, Replacement, Hip↗

PubMed2005

The influence of intraoperative pretensioning on the chondroprotective effect of meniscal transplants.

BACKGROUND: Meniscal replacement has become more common in recent years. The meniscal transplant's ability to transfer load effectively depends on its ability to bear circumferential loading. HYPOTHESIS: Intraoperative pretensioning on the meniscal transplant sutures has a positive influence on meniscal transplants' chondroprotective effect. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-six sheep were divided into 6 groups (n = 6), subjected to a sham operation (group A), a meniscectomy (group B), or a meniscal autograft using tag sutures with different levels of pretensioning (group C, 0 N; group D, 20 N; group E, 40 N; group F, 60 N). Macroscopic (International Cartilage Repair Society score) and histologic evaluations (Mankin score) of the articular cartilage were performed after 6 months. RESULTS: Higher suture pretension (40 N, 60 N) resulted in less cartilage degeneration than in meniscectomized (P =.047; P =.036) and nonpretensioned (P =.028; P =.015) knees, with International Cartilage Repair Society scores of 1.63 +/- 0.57 and 1.66 +/- 0.51 in groups E and F, respectively, and scores of 2.40 +/- 0.27 and 2.68 +/- 0.46 observed after meniscectomy and meniscal transplantation with no pretensioning, respectively. Group F had a significantly better Mankin score of 6.66 +/- 2.15 (P =.05) compared with group D. Regarding criterion cells, trends toward less degeneration compared with meniscectomized and nonpretensioned knees (P = .054 and P =.055) were found. The coefficient of variation of the Mankin scores was greater than that of the International Cartilage Repair Society score. Group A had significantly better cartilage than all other groups. CONCLUSION: Adequate intraoperative pretensioning has a significant influence on the chondroprotective effect of meniscal transplants but did not prevent the development of articular cartilage degeneration. CLINICAL RELEVANCE: The results suggest that intraoperative pretensioning could improve the chondroprotective effect of meniscal transplantation.

Animals↗

PubMed2005

The effect of functional splinting on mild dysplastic hips after walking onset.

BACKGROUND: For treatment of Graf class IIb dysplastic hips at walking onset a treatment concept with abduction splints allowing patterns as walking and crawling under constant abduction control was investigated. However, as the splint still incapacitates child movements the research question remains whether the physiologically progressing maturation of hips can be significantly altered using such abduction splints for walking children. METHODS: Of 106 children showing late hip dysplasia, 68 children treated with the Hoffman-Daimler (HD-splint) abduction splint were compared with 38 children with neglect of the abduction treatment in this retrospective study. Radiographic analyses were performed measuring the development of the age dependent acetabular angle. RESULTS: The regression analysis for splint treatment showed a significant linear regression for both splint treatment and no splint treatment group (r2 = 0.31 respectively r2 = 0.33). No statistical difference between both treatment groups was apparent. CONCLUSION: Considering the characteristics of this study, there seems to be no strong rationale supporting the use of an abduction device in growing children. As no significant difference between treatment groups is apparent, a future controlled prospective study on splinting effects can be considered ethically allowed.

Hip Dislocation, Congenital↗

PubMed2005

Femoral strain changes after total hip arthroplasty--patient-specific finite element analyses 12 years after operation.

Periprosthetic stress-shielding after total hip arthroplasty (THA) is a well-known phenomenon. Many authors have used the finite element (FE) method to show the effects of THA on animal or human femora. In most cases they have performed cadaver experiments. The current project is a FE analysis based on a retrospective computerized tomography (CT) in vivo data set of 11 patients 12 years after THA. In order to control the analysis, a computationally created stem was implanted at the femur model of the not operated contralateral side. In comparison to the not operated side, there was a significant reduction of the strain energy density (SED) values in all regions of interest (ROI) with the greatest effect near the distal tip of the stem. Only zone 1 showed no clear trend which may be due to load application at the greater trochanter causing local strain peaks. The median SED values changed by -31.65% (ROI 1), -25.64% (ROI 2), -30.82% (ROI 3), -12.35% (ROI 4), -40.10% (ROI 5), -30.37% (ROI 6) and -43.38% (ROI 7). As far as we are aware, the current combination of in vivo CT density data with FE strain analyses after THA is based on the largest number of patients and the longest follow-up period. This combination enables analysis and prediction of the influence of implantation upon bone and can be compared with of remodelling theories. The assessment of mechanical strain data during a follow-up trial could be a new approach for analyzing different hip stems in clinical biomechanics.

Adult↗

PubMed2005

Mechanical properties of femoral trabecular bone in dogs.

BACKGROUND: Studying mechanical properties of canine trabecular bone is important for a better understanding of fracture mechanics or bone disorders and is also needed for numerical simulation of canine femora. No detailed data about elastic moduli and degrees of anisotropy of canine femoral trabecular bone has been published so far, hence the purpose of this study was to measure the elastic modulus of trabecular bone in canine femoral heads by ultrasound testing and to assess whether assuming isotropy of the cancellous bone in femoral heads in dogs is a valid simplification. METHODS: From 8 euthanized dogs, both femora were obtained and cubic specimens were cut from the centre of the femoral head which were oriented along the main pressure and tension trajectories. The specimens were tested using a 100 MHz ultrasound transducer in all three orthogonal directions. The directional elastic moduli of trabecular bone tissue and degrees of anisotropy were calculated. RESULTS: The elastic modulus along principal bone trajectories was found to be 11.2 GPa +/- 0.4, 10.5 +/- 2.1 GPa and 10.5 +/- 1.8 GPa, respectively. The mean density of the specimens was 1.40 +/- 0.09 g/cm3. The degrees of anisotropy revealed a significant inverse relationship with specimen densities. No significant differences were found between the elastic moduli in x, y and z directions, suggesting an effective isotropy of trabecular bone tissue in canine femoral heads. DISCUSSION: This study presents detailed data about elastic moduli of trabecular bone tissue obtained from canine femoral heads. Limitations of the study are the relatively small number of animals investigated and the measurement of whole specimen densities instead of trabecular bone densities which might lead to an underestimation of Young's moduli. Publications on elastic moduli of trabecular bone tissue present results that are similar to our data. CONCLUSION: This study provides data about directional elastic moduli and degrees of anisotropy of canine femoral head trabecular bone and might be useful for biomechanical modeling of proximal canine femora.

Animals↗

PubMed2002

Validation data for periprosthetic bone remodelling theories.

Periprosthetic adaptive bone remodelling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodelling theory with finite element analysis. Unfortunately, there still subsist a lack of clinical data, which are necessary for validation of these simulation results. Therefore, the objective of the current project is to collect prospective volumetric bone density data with a clinical computerized tomography study in seven patients after THA. A retrospective study 12 years after implantation in 11 patients was added. A data set of about 100000 bone voxels for each femur was collected. In all prospective cases, the predominant change is seen during the first year. The average density reduction in the horizontal slices was between 50 and 150 Hounsfield units (HU) (approx. 10%; p<0.001) after 2 years. Loss of density is particularly strong distal of the minor trochanter and decreases from proximal to distal. For the 12 years retrospective study, the contralateral femur provided the control. Similar trends comparable to the prospective 2-year follow-up CT density values were seen in most cases with density reductions of up to 400 HU (30%). However, in one of these cases there was no difference between the operated and the control density. As far as we are aware, this is the first collection of fully prospective 3D validation data in vivo for periprosthetic adaptive bone remodelling theories. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and individual weight-related loading.

Absorptiometry, Photon↗