Biomedical subjects

P Büchler

Publications and source records attributed to P Büchler.

13 recordsLinked to original sources

PubMed2004

Benefits of an anatomical reconstruction of the humeral head during shoulder arthroplasty: a finite element analysis.

OBJECTIVE: To study the influence of the shape of the prosthetic humeral head on shoulder biomechanics and then to evaluate the benefits of an anatomical reconstruction of the humeral head after shoulder arthroplasty. DESIGN: A 3D numerical model of a healthy shoulder was reconstructed. The model included the proximal humerus, the scapula and, for stability purposes, the subscapularis, infraspinatus and supraspinatus rotator cuff muscles. BACKGROUND: Shoulder prostheses used nowadays, called third generation, allow for a better adaptation of the implant to the anatomy of the proximal humerus than previously used implants. However, no biomechanical study has shown the benefits of this anatomical reconstruction of the humeral head. METHODS: The model was used to compare the biomechanics of a shoulder without implant with the biomechanics of the same shoulder after humeral hemiarthroplasty. Two humeral components were tested: a second-generation prosthesis and an implant with an anatomically reconstructed humeral head. RESULTS: The anatomical reconstruction of the humeral head restored the physiological motions and limited eccentric loading of the glenoid. Conversely, the second-generation implant produced contact forces in the superior extremity of the glenoid surface leading to bone stresses up to 8 times higher than for the intact shoulder. CONCLUSIONS: This analysis provided insights into the mechanical effects of different reconstructions of the humeral head and highlighted the advantages of anatomical reconstructions of the humeral head during shoulder arthroplasty.

Arthroplasty, Replacement↗

PubMed2003

[Central case management in surgery].

Up to now, in most surgical departments there has been no central patient management coordinating the admission, the diagnostic work-up, and the surgical procedures of patients with the resources available in the hospital. In future, however, it will be essential for surgical departments to establish such a central patient management, not only in view of the importance of patient-oriented medicine but also considering the planned introduction of diagnosis related groups. A central patient management will reduce preoperative and overall length of stay through adequate organisation and communication structures. In addition, a central patient management will make optimal use of the available resources in terms of operation rooms and hospital beds. In this article, we will present our basic concept of a central patient management in a surgical university department.

Diagnosis↗

PubMed2003

Biphasic constitutive laws for biological interface evolution.

A model of tissue differentiation at the bone-implant interface is proposed. The basic hypothesis of the model is that the mechanical environment determines the tissue differentiation. The stimulus chosen is related to the bone-implant micromotions. Equations governing the evolution of the interfacial tissue are proposed and combined with a finite element code to determine the evolution of the fibrous tissue around prostheses. The model is applied to the case of an idealized hip prosthesis.

Algorithms↗

PubMed2002

[Central patient management in surgery].

Diagnosis-Related Groups↗

PubMed2002

Adjuvant therapy in operable pancreatic cancer.

Adenocarcinoma of the pancreas remains a highly lethal disease with one of the worst mean survival rates of all solid malignancies. Even with improvements in surgical techniques in the last decades, the five-year survival rate of patients following resection is still under 20 percent. Various additional treatment concepts have been introduced based on encouraging results for adjuvant chemoradiotherapy obtained in a small randomized-controlled trial more than 15 years ago. The purpose of this article is to review the results of several trials investigating adjuvant therapy for pancreatic cancer. We will discuss recent studies of EORTC (European Organization for Research and Treatment of Cancer), ESPAC (European Study Group for Pancreatic Cancer) and others and will also focus on future alternative treatment options for pancreatic cancer.

Adenocarcinoma↗

PubMed2002

Virtual power based algorithm for decoupling large motions from infinitesimal strains: application to shoulder joint biomechanics.

New trends of numerical models of human joints require more and more computation of both large amplitude joint motions and fine bone stress distribution. Together, these problems are difficult to solve and very CPU time consuming. The goal of this study is to develop a new method to diminish the calculation time for this kind of problems which include calculation of large amplitude motions and infinitesimal strains. Based on the Principle of Virtual Power, the present method decouples the problem into two parts. First, rigid body motion is calculated. The bone micro-deformations are then calculated in a second part by using the results of rigid body motions as boundary conditions. A finite element model of the shoulder was used to test this decoupling technique. The model was designed to determine the influence of humeral head shape on stress distribution in the scapula for different physiological motions of the joint. Two versions of the model were developed: a first version completely deformable and a second version based on the developed decoupling method. It was shown that biomechanical variables, as mean pressure and von Mises stress, calculated with the two versions were sensibly the same. On the other hand, CPU time needed for calculating with the new decoupled technique was more than 6 times less than with the completely deformable model.

Algorithms↗

PubMed2002

Surgical treatment of hepatic and pulmonary metastases from non-colorectal and non-neuroendocrine carcinoma.

BACKGROUND: Surgical resection is standard treatment for colorectal and neuroendocrine liver metases provided the tumor can be removed completely. The same is true for isolated pulmonary metastases. To date, only few reports have addressed the value of surgical resection of organ metastases from other solid tumors. METHODS: The literature was searched by Medline, conference proceedings and cross-referencing of published articles for information pertaining to the long-term results of surgical treatment of non-colorectal and non-neuroendocrine (NCNN) liver or lung metastases. RESULTS: Resection of hepatic and pulmonary metastases is increasingly performed in non-colorectal and non-neuroendocrine malignancies. Mortality and morbidity of hepatic and pulmonary resection are low and 5 year survival can be expected to reach some 20-30 percent, irrespective of the histological type of the primary tumor. CONCLUSION: Resection of hepatic or pulmonary metastasis should be considered in all patients with low operative risk provided that complete resection is possible.

Humans↗

PubMed2001

Real-time quantitative PCR of telomerase mRNA is useful for the differentiation of benign and malignant pancreatic disorders.

The presence of telomerase activity has been proposed as a specific and sensitive marker for malignant tissue, and positivity rates of up to 95% have been reported in pancreatic cancer. In the present study telomerase activity analysis was reevaluated in 29 pancreatic cancer tissues compared with 36 chronic pancreatitis tissues and 21 normal controls, and a study was made of whether malignant and benign pancreatic disorders can be better differentiated using a novel technique real-time quantitative PCR analysis-analyzing telomerase mRNA expression. Telomerase activity was present in 35% (10 of 29) of pancreatic cancer samples, 3% (one of 36) of chronic pancreatitis samples, and none of the normal pancreatic tissue samples in the TRAP assay. Real-time quantitative PCR analysis revealed the presence of telomerase mRNA expression in 50% (10 of 20) of normal, 86% (31 of 36) of chronic pancreatitis, and 90% (26 of 29) of pancreatic cancer samples. However, quantification of the expression data revealed that the relative increase above normal was 5.5 (range, 3.5-8.6) for chronic pancreatitis and 23.9 (range, 18.6-30.7) for pancreatic cancer samples (p < 0.01). No relationship was found between telomerase activity and the fold increase of telomerase mRNA above normal and gender, patient age, tumor stage, or tumor grade. These data indicate that detection of telomerase activity using the TRAP assay has limitations in differentiating benign and malignant pancreatic disorders. However, telomerase mRNA analysis by real-time quantitative PCR analysis allows a highly sensitive detection and differentiation of pancreatic cancer from normal pancreas and chronic pancreatitis and thereby may serve as a new reliable, easy, and effective diagnostic tool for cancer diagnosis.

Adult↗

PubMed1999

Surgical approach in patients with acute pancreatitis. Is infected or sterile necrosis an indication--in whom should this be done, when, and why?

The morbidity and mortality rates of severe acute pancreatitis are related to the degree of pancreatic necrosis that accompanies the attack and to the presence of infection. The decision about whether and when to operate on these patients is often difficult, and it requires mature clinical judgment. Proven infection of pancreatic necrosis is an absolute indication for surgical intervention, at which time surgical doffebridement and drainage should be performed. Most patients with sterile necrosis eventually respond to conservative nonsurgical medical management. In patients who remain critically ill for weeks or whose clinical course deteriorates despite maximal intensive care, surgery may be appropriate. Even when these guidelines are followed, the mortality (15% to 40%) and morbidity (approximately 80%) rates remain high.

Debridement↗

PubMed1999

Overexpression of Smad2 and colocalization with TGF-beta1 in human pancreatic cancer.

Smad2 belongs to a family of cytoplasmic molecules that are critical components in the transforming growth factor beta (TGF-beta) signaling pathway. Upon ligand binding, the type II TGF-beta receptor (TbetaRII) heterodimerizes with and activates TGF-beta receptor type I (TbetaRI). Activated TbetaRI phosphorylates Smad2, which then heterodimerizes with Smad4, translocates into the nucleus, and subsequently effects gene transcription. Previously we have shown that pancreatic cancers overexpress TGF-betas and TbetaRII. Here, we show by northern blot analysis that Smad2 mRNA levels are significantly increased in pancreatic cancer samples in comparison with normal pancreatic tissues. By immunohistochemistry, Smad2 is present in the cancer cells of 67% of the pancreatic cancer samples. Analysis of serial sections reveals coexpression of Smad2 and TGF-beta1 in the cancer cells. Furthermore, TGF-beta1 increases steady-state levels of Smad2 mRNA in the TGF-beta1-sensitive pancreatic cancer cell line COLO-357. It is suggested that pancreatic cancer cells have the capacity to up-regulate Smad2 expression, which may lead to excessive activation of specific components of the TGF-beta-signaling pathway.

Aged↗

PubMed1998

Structural and functional analysis of the BMP-4 promoter in early embryos of Xenopus laevis.

The Xenopus laevis BMP-4 gene shows an evolutionary conserved structure containing two coding exons and a leader exon. The transcripts which are detected after zygotic activation of the gene in ventral mesoderm of late blastula stage embryos do either contain the leader exon or begin within the first intron. Luciferase reporter/promoter studies revealed multiple elements being required for the activation and for the spatial control of transcription. These elements are located within the upstream region and within the second intron and they interact with a most proximal located basal promoter being indispensable for transcriptional activation. The auto-activatory capacity of BMP-4 is mediated by several enhancer elements being responsive not only to BMP-4 but also to BMP-2 signaling. BMP-2 might thus function as a natural activator of the BMP-4 gene in the early embryo. Since reporter activity obtained with distinct BMP-2/4 responsive promoter deletion mutants is simultaneously inhibited by the dominant negative BMP receptor as well as by chordin, we suggest that down-regulation of the BMP-4 gene by chordin results from an interference with the auto-regulatory loop at the level of protein-protein interactions.

Amino Acid Sequence↗

PubMedDate not supplied

A finite element model of the shoulder: application to the comparison of normal and osteoarthritic joints.

OBJECTIVE: The objective of the present study was to develop a numerical model of the shoulder able to quantify the influence of the shape of the humeral head on the stress distribution in the scapula. The subsequent objective was to apply the model to the comparison of the biomechanics of a normal shoulder (free of pathologies) and an osteoarthritic shoulder presenting primary degenerative disease that changes its bone shape. DESIGN: Since the stability of the glenohumeral joint is mainly provided by soft tissues, the model includes the major rotator cuff muscles in addition to the bones. BACKGROUND: No existing numerical model of the shoulder is able to determine the modification of the stress distribution in the scapula due to a change of the shape of the humeral head or to a modification of the glenoid contact shape and orientation. METHODS: The finite element method was used. The model includes the three-dimensional computed tomography-reconstructed bone geometry and three-dimensional rotator cuff muscles. Large sliding contacts between the reconstructed muscles and the bone surfaces, which provide the joint stability, were considered. A non-homogenous constitutive law was used for the bone as well as non-linear hyperelastic laws for the muscles and for the cartilage. Muscles were considered as passive structures. Internal and external rotations of the shoulders were achieved by a displacement of the muscle active during the specific rotation (subscapularis for internal and infrapinatus for external rotation). RESULTS: The numerical model proposed is able to describe the biomechanics of the shoulder during rotations. The comparison of normal vs. osteoarthritic joints showed a posterior subluxation of the humeral head during external rotation for the osteoarthritic shoulder but no subluxation for the normal shoulder. This leads to important von Mises stress in the posterior part of the glenoid region of the pathologic shoulder while the stress distribution in the normal shoulder is fairly homogeneous. CONCLUSION: This study shows that the posterior subluxation observed in clinical situations for osteoarthritic shoulders may also be cause by the altered geometry of the pathological shoulder and not only by a rigidification of the subscapularis muscle as often postulated. This result is only possible with a model including the soft tissues provided stability of the shoulder. RELEVANCE: One possible cause of the glenoid loosening is the eccentric loading of the glenoid component due to the translation of the humeral head. The proposed model would be a useful tool for designing new shapes for a humeral head prosthesis that optimizes the glenoid loading, the bone stress around the implant, and the bone/implant micromotions in a way that limits the risks of loosening.

Computer Simulation↗

PubMedDate not supplied

Therapy for pancreatic cancer with a recombinant humanized anti-HER2 antibody (herceptin).

The HER2/neu oncogene is overexpressed in human pancreatic cancer, but the clinical significance of that overexpression is uncertain. In the present study we investigated the antitumor efficacy of Herceptin, a new recombinant humanized anti-HER2/neu antibody, which exhibits cytostatic activity on breast and prostate cancer cells that overexpress the HER2 oncogene. That antibody may retard tumor growth in certain patients with those diseases. We quantified HER2 expression in various human pancreatic cancer cell lines and studied the bioactivity of this antibody both in vitro and in vivo. Growth inhibition by Herceptin was observed in vitro in cell lines with high levels of HER2/neu expression. Cell lines with low levels of this protein did not respond significantly to the antibody. In vivo we studied two different pancreatic cancer cell lines in an orthotopic mouse model of the disease. Herceptin treatment suppressed tumor growth in the MIA PaCa-2 tumor cell line, which expressed high levels of HER2/neu. These data suggest that Herceptin treatment of patients with pancreatic cancer who express high levels of the HER2/neu oncogene may be reasonable.

Adenocarcinoma↗