Showing papers by "Georg N. Duda published in 2006"
TL;DR: A new method is proposed, the symmetrical CoR estimation or SCoRE, in which the coordinates of the joint centre must only remain constant relative to each segment, thus not requiring the assumption that one segment should remain at rest.
387 citations
TL;DR: Evidence is provided that less rigid fixation increased the time required for healing, and the process of intramembranous ossification appeared during the initial stages of healing to be independent of mechanical stability.
148 citations
TL;DR: A better understanding of the mechanical loading environment that occurs in sheep is provided and this has important implications for the interpretation of knee studies in quadrupeds and their relevance to the clinical situation.
127 citations
01 Jan 2006
TL;DR: In this paper, the osteoclastic number was counted, the area of mineralised bone tissue was measured histomorphometrically and density of osteoclasts per square millimetre mineralised tissue was calculated.
Abstract: Osteoclasts are specialised bone-resorbing cells. This particular ability makes osteoclasts irreplaceable for the continual physiological process of bone remodelling as well as for the repair process during bone healing. Whereas the effects of systemic diseases on osteoclasts have been described by many authors, the spatial and temporal distribution of osteoclasts during bone healing seems to be unclear so far. In the present study, healing of a tibial osteotomy under standardised external fixation was examined after 2, 3, 6 and 9 weeks (n = 8) in sheep. The osteoclastic number was counted, the area of mineralised bone tissue was measured histomorphometrically and density of osteoclasts per square millimetre mineralised tissue was calculated. The osteoclastic density in the endosteal region increased, whereas the density in the periosteal region remained relatively constant. The density of osteoclasts within the cortical bone increased slightly over the first 6 weeks, however, there was a more rapid increase between the sixth and ninth weeks. The findings of this study imply that remodelling and resorption take place already in the very early phase of bone healing. The most frequent remodelling process can be found in the periosteal callus, emphasising its role as the main stabiliser. The endosteal space undergoes resorption in order to recanalise the medullary cavity, a process also started in the very early phase of healing at a low level and increasing significantly during healing. The cortical bone adapts in its outward appearance to the surrounding callus structure. This paradoxic loosening is caused by the continually increasing number and density of osteoclasts in the cortical bone ends. This study clearly emphasises the osteoclastic role especially during early bone healing. These cells do not simply resorb bone but participate in a fine adjusted system with the bone-producing osteoblasts in order to maintain and improve the structural strength of bone tissue.
115 citations
TL;DR: The findings of this study imply that remodelling and resorption take place already in the very early phase of bone healing, particularly during early bone healing of a tibial osteotomy under standardised external fixation.
108 citations
TL;DR: This study found that the mechanical stimuli generated by interfragmentary shear and torsion differed from those produced by axial interfragenary movements, and the initial tissue formation was dominated by the deformation stimulus.
97 citations
TL;DR: Autologous BMD cell grafting leads to an increase in contraction force, 14% in tetanic and 13% in fast twitch stimulation, demonstrating its potential to improve functional outcome after skeletal muscle crush injury.
Abstract: Insufficient post-traumatic skeletal muscle regeneration with consecutive functional deficiency continues to be a serious problem in orthopedic and trauma surgery. Transplantation of autologous muscle precursor cells has shown encouraging results in muscle trauma treatment but is associated with significant donor site morbidity. In contrast to this, bone marrow-derived (BMD) cells can be obtained without any functional deficit by puncture. The goal of this study was to examine whether regular muscle regeneration can be improved by local application of autologous BMD cells in a rat model of blunt skeletal muscle trauma. One week after standardized open blunt crush injury to the left soleus muscle, 10(6) autologous BMD cells were injected into the traumatized muscle of male Sprague Dawley rats. Rats of the control group received saline solution as treatment. Three weeks after application, the fast twitch and tetanic contraction capacity of the soleus muscles was measured bilaterally by stimulating the sciatic nerves. Contraction forces of injured soleus muscles in control animals recovered to 39 +/- 10% (tetanic) and 59 +/- 12% (fast twitch) of the contralateral noninjured soleus muscles (p < 0.001). In contrast, autologous BMD cell injection significantly restored contractile forces to 53 +/- 8% (tetanic) and 72 +/- 13% (fast twitch) compared to those observed in contralateral noninjured soleus muscles. Thus, muscle function was significantly increased by BMD cell treatment (tetanic, p = 0.014; fast twitch, p = 0.05). In conclusion, autologous BMD cell grafting leads to an increase in contraction force, 14% in tetanic and 13% in fast twitch stimulation, demonstrating its potential to improve functional outcome after skeletal muscle crush injury.
70 citations
TL;DR: The presented method allows simulation of cell and tissue differentiation during the early phase of fracture healing using a mixed construct composed of lyophilized cancellous bone and a fibrin matrix in a sandwich configuration to serve as an in vitro model for the examination of mechanical and pharmacological influences during theEarly phase of bone healing on a cellular level.
Abstract: Cell differentiation during bone healing following a fracture is influenced by various biological and mechanical factors We introduce a method for the examination of cell and tissue differentiation simulating a fracture gap in vitro A closed bioreactor system allows the imitation of the biological, mechanical, and biochemical conditions in vitro The initial hematoma formed in a fracture is simulated with a mixed construct composed of lyophilized cancellous bone and a fibrin matrix in a sandwich configuration The construct may be loaded with osteoprogenitor cells Exemplarily, constructs were loaded with rabbit periosteal cells and cultivated under mechanical loading with 7 kPa at 005 Hz for up to two weeks During the observation period, cell morphology and correlating protein synthesis changed under mechanical stimulation Cell differentiation differed between the various regions of the constructs The periosteal cells were arranged perpendicularly to the mechanical loading and differentiated to ost
55 citations
TL;DR: The hypothesis of the present study was that decreased fixation stability, which leads to a delay in healing, would lead to reduced CYR61 protein expression in fracture callus, and the results supply further evidence that CYR 61 may serve as an important regulator of bone healing.
49 citations
TL;DR: The sequences identified are a valuable resource for future studies on musculoskeletal healing and regeneration using sheep and represent an important head-start for genomic sequencing projects for Ovis aries, with partial or complete sequences being made available for over 5,800 previously unsequenced sheep genes.
Abstract: The sheep is an important model animal for testing novel fracture treatments and other medical applications. Despite these medical uses and the well known economic and cultural importance of the sheep, relatively little research has been performed into sheep genetics, and DNA sequences are available for only a small number of sheep genes. In this work we have sequenced over 47 thousand expressed sequence tags (ESTs) from libraries developed from healing bone in a sheep model of fracture healing. These ESTs were clustered with the previously available 10 thousand sheep ESTs to a total of 19087 contigs with an average length of 603 nucleotides. We used the newly identified sequences to develop RT-PCR assays for 78 sheep genes and measured differential expression during the course of fracture healing between days 7 and 42 postfracture. All genes showed significant shifts at one or more time points. 23 of the genes were differentially expressed between postfracture days 7 and 10, which could reflect an important role for these genes for the initiation of osteogenesis. The sequences we have identified in this work are a valuable resource for future studies on musculoskeletal healing and regeneration using sheep and represent an important head-start for genomic sequencing projects for Ovis aries, with partial or complete sequences being made available for over 5,800 previously unsequenced sheep genes.
26 citations
Journal Article•
TL;DR: Dexamethasone was found to inhibit the [Ca2+]i increase in MG-63 cells following stimulation and to reduce considerably COX-2 expression via the genomic pathway, while celecoxib did not show any measurable short-term or long-term effects on the parameters of bone physiology measured.
Abstract: Objective Glucocorticoids and selective COX-2 inhibitors are potent anti-inflammatory agents They are also suggested to influence bone physiology and remodeling Here we searched for effects of dexamethasone and celecoxib on crucial parameters of bone physiology that could be therapeutically relevant Methods The human osteosarcoma cell line MG-63 was used to measure effects of these drugs on (i) intracellular calcium concentration ([Ca 2+ ] i ) using a microfluorometric technique, (ii) alkaline phosphatase and osteocalcin levels (EIA) and (iii) the expression of cox-2 mRNA (quantitative real time PCR) Measurements were performed in Vitamine D-incubated quiescent cells and in cells stimulated with TNF-α and IL-1β
01 Jan 2006
TL;DR: Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome.
Abstract: Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome. We hypothesised that mechanical conditions influence not only the healing outcome, but also the early phase of fracture healing. Additionally, it was hypothesised that decreased fixation stability characterised by an increased shear interfragmentary movement results in a delay in healing. Sixty-four sheep underwent a mid-shaft tibial osteotomy which was treated with either a rigid or a semi-rigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture callus was analysed using radiological, biomechanical and histological techniques. The tibia treated with semi-rigid fixation showed inferior callus stiffness and quality after 6 weeks. At 9 weeks, the calluses were no longer distinguishable in their mechanical competence. The calluses at 9 weeks produced under rigid fixation were smaller and consisted of a reduced fibrous tissue component. These results demonstrate that the callus formation over the course of healing differed both morphologically and in the rate of development. In this study, we provide evidence that the course of healing is influenced by the initial fixation stability. The semi-rigid fixator did not result in delayed healing, but a less optimal healing path was taken. An upper limit of stability required for successful healing remains unknown, however a limit by which healing is less optimal has been determined.
01 Mar 2006
TL;DR: It is concluded that DC is an important element of early fracture healing by increasing the expression of OPN and thereby modulating progenitor cell differentiation immediately after mechanical instability caused by a fracture.
Abstract: Background Osteopontin (OPN), also known as bone sialoprotein I or secreted phosphoprotein 1, is a major non-collagenous bone matrix protein. A broad distribution has been detected in embryonic bone, osteoid, and fracture callus [Nomura et al. 2000] pointing out its central role in bone development and healing. It remains unclear weather mechanical conditions influence OPN synthesis and thereby osteoprogenitor cell differentiation. We investigated OPN mRNA-levels of bone marrow derived mesenchymal stem cells (bm-MSC) cultured in a previously described compression bioreactor (CBR) [Matziolis et al. under review] under dynamic compression (DC). Materials Bm-MSCs of 5 different individuals (mean age 61y) were seeded in a fibrin-alginate mix-matrix placed between two slices of lyophyliced cancellous bone. One group of constructs (n=10) underwent DC with 7kPa at 0.05 Hz, resulting in a matrix compression of 1mm at an heigh of 5mm, for 24 hours in the CBR. Constructs cultured under similar conditions but without DC served as control group (n=10). mRNA was extracted out of each construct after ending the DC, following the Trizol®-protocol. After cDNA-synthesis, GEArray Q series (Human Osteogenesis Gene Arrays) were performed and normalized versus GAPDH. Results We found an increase of OPN-expression in all dynamically compressed matrices. In the DC-group we found a mean of 5-fold increase of OPN mRNA compared to the control group (median: 0.43 vs. 0.09, p Discussion and Conclusion The results of this study demonstrate that an in vitro DC of bm-MSCs for 24 hours leads to an increased expression of OPN. We conclude that DC is an important element of early fracture healing by increasing the expression of OPN and thereby modulating progenitor cell differentiation immediately after mechanical instability caused by a fracture.
01 Jan 2006
TL;DR: In dieser Arbeit wird ein Verfahren vorgestellt, das mithilfe eines statistischen 3D-Formmodells (SFM) des Beckens die geometrisch sowie toplogisch komplexe3D- form aus wenigen Rontgenbildern rekonstruiert.
Abstract: Haufig liegt einer computergestutzten Operationsplanung lediglich ein Satz von wenigen 2D-Rontgenbildern zugrunde. Dennoch ist es ein Anliegen, auf Basis solcher Daten Ruckschlusse auf die dreidimensionale Anatomie des Patienten zu ziehen. In dieser Arbeit wird ein Verfahren vorgestellt, das mithilfe eines statistischen 3D-Formmodells (SFM) des Beckens die geometrisch sowie toplogisch komplexe 3D-Form aus wenigen Rontgenbildern rekonstruiert. Dies geschieht durch eine Optimierung, welche den Abstand der Silhouette des Modells in den Projektionsebenen zur Silhouette des Objekts in den Rontgenbildern minimiert. Das Verfahren wird an 23 synthetisch erzeugten Datensatzen validiert.