Article Aufbau und Validierung einer Methode zur Verschleißmessung von Polyethylen Hüftpfannen mit Metallschale mit Hilfe von Röntgenbildern was published on January 1, 1998 in the journal Biomedical Engineering / Biomedizinische Technik (volume 43, issue s1).

Two identical sets of posterior cruciate retaining total knee replacements were tested for wear on one contemporary knee joint simulator according to the current ISO standards. The first set of implants was tested in load control mode (ISO 14243-1), while the second set was tested in displacement control mode (ISO 14243-3). The type of control mode alludes to the feedback signal of anterior–posterior and internal–external degrees of freedom. Resulting wear scars and rates between the different control mode tests were compared. Significant differences in wear rates were found: the wear rates in displacement control were approximately half of the wear rates in load control mode. This result was mirrored in the wear scars, which were significantly different in size on the medial plateau. Comparing wear rate with wear scar size (area) yielded a positive correlation. Analyzing the motion data of the two tests revealed similar ranges of movement in anterior–posterior translation and internal–external rotation, however the time-scale of the rotational movements differed between the two control types, explaining the differences in wear. This study demonstrated that substantial variability in wear outcome is possible depending on the type of control mode. Future revisions of testing directions should incorporate more implant specific test parameters to produce clinically relevant wear results.

Summary Animal models are necessary to evaluate new options for the treatment of fractures in osteoporotic bone. They permit both the biological response of a living system and the influence of the pathological processes to be taken into account. A sheep model for osteoporosis was established by combining oestrogen deficiency, calcium and vitamin D-deficient diet with steroid medication. Bone mineral density (BMD) was reduced by >30% after 12 weeks of combined treatment. Osteoporosis similar to the human situation with corresponding changes in the micro-architecture and mechanical properties of bone was observed. This publication focuses on the impressive results obtained with the model and contrasts them with considerations of animal welfare. Considerable side-effects associated with steroid medication became manifest. Animals in the treatment groups showed signs of infection of various degrees due to the immunosuppressive effect of the medication. The infections were mostly caused by Corynebacterium pseudotuberculosis. Antibody testing revealed a 100% prevalence of infection in this breed of sheep. A modification of the steroid treatment, i.e. less-frequent injections, reduced the incidence of side-effects. This sheep model shows a significant and reproducible reduction in cancellous BMD of >30%, including relevant changes in biomechanical properties and increased fracture risk. However, the severity of the side-effects cannot be overlooked. The model must be improved if it is to be used in the future. Options to reduce the side-effects are discussed.

Background Crossed k-wire osteosynthesis is a widely used procedure for displaced supracondylar humerus fractures in children, but the rate of secondary displacements is up to 31%. Alternative techniques including casts, elastic stable intramedullary nailing, and the fixateur extern, have been used, but there are no biomechanical data comparing these methods. We developed a biomechanical model to compare four osteosynthesis techniques for stabilizing supracondylar humerus fractures in children.Methods. An osteotomy to simulate a fracture was made in a total of 32 adult cadaver humeri. The pseudofractures were then stabilized by crossed k-wires, elastic nailing, a fixateur extern with either k-wires, or Schanz screws. We measured the stiffness values in flexion and extension and torsion with static loading. The movements in cyclic loading were chosen to resemble the mechanism described in the development of a clinical cubitus varus.Findings. No significant differences were found with static loading. With cyclic loading all methods showed an irreversible torsional deformation less than 20 degrees. Crossed k-wires and elastic nailing showed significantly lower reversible torsional deformation than the external fixateurs.Interpretation. Our biomechanical data reveal that the crossed k-wires have the highest stiffness and lowest loss of reduction under cyclic loading. The external fixators proved to be good alternatives. (c) 2006 Elsevier Ltd. All rights reserved.

The goal of our study was to evaluate two newly developed implant designs and their behavior in terms of subsidence in lumbar vertebral bodies under cyclic loading. The new implants were evaluated in two different configurations (two small prototypes vs. one large prototype with similar load-bearing area) in comparison to a conventional screw-based implant (MACS TL). A pool of 13 spines with a total of 65 vertebrae was used to establish five testing groups of similar bone mineral density (BMD) distribution with eight lumbar vertebrae each. In additional to BMD assessment via dual-energy X-ray absorptiometry, cancellous BMD and structural parameters were determined using a new generation in vivo 3D-pQCT. The specimens were loaded sinusoidally in force control at 1 Hz for 1000 cycles at three load levels (100, 200, and 400 N). A survival analysis using the number of cycles until failure (Cox regression with covariates) was applied to reveal differences between implant groups. All new prototype configurations except the large cylinder survived significantly longer than the control group. The number of cycles until failure was significantly correlated with the structural parameter Tb.Sp. and similarly with the cancellous BMD for three of five implants. In both large prototypes the cycle number until failure significantly correlated with the preoperative distance to the upper endplates. Although the direct relationship between bone structure or density and mechanical breakage behavior cannot be conclusively proven, all the prototypes adapted for poor bone structure performed better than the comparable conventional implant.

Incidences of infection following elective orthopedic surgery are low and range from 0.7−4.2%, depending on the type of operation, soft-tissue status, general patient condition, and prophylactic use of antibiotics. Patients with open fractures clearly show a higher risk of infection (5−33%) due to bacterial contamination and soft tissue damage. The consequences of such infections can be devastating, leading to prolonged hospitalization, poor functional outcome, and sepsis. Bone infections associated with foreign bodies such as prostheses or osteosynthetic devices are especially difficult to treat. Procedures frequently required include removal of the infected device, long-term systemic antibiotic therapy with possible side effects, and multiple revisions with radical debridement. Systemically administered antibiotics are necessary and effective in therapy in addition to surgical revision. A serious problem is the increasing number of implants infected by (methicillinresistant Staphyloccus aureus) MRSA and chronic Staphyloccus epidermidis. Due to disturbed tissue function caused by surgical trauma at the implant/tissue interface, bacteria seeded during surgery may cause later infection. Mainly S. epidermidis, but also certain strains of S. aureus, tend to produce an extracellular polysaccharide matrix (biofilm) if they attach to foreign body surfaces. Biofilm formation makes eradication of these microorganisms nearly impossible without removing the implant. S. aureus and coagulase negative staphylococci (S. epidermidis) can be isolated from deep wound infections in up to 70−90% of cases. Systemic perioperative application of antibiotics is routinely performed in orthopedic and trauma surgery, the efficacy of which has clearly been proven. High levels of tissue protection are achieved during surgery to prevent deep wound infection caused possibly by contaminating bacteria. In addition to systemic prophylaxis, various local antibiotic delivery techniques are in clinical use to reduce the rate of infection (antibiotic-loaded bone cements, antibiotic-impregnated collagen sponges or polymethylmethacrylate beads). Local application of antibiotics is advantageous in that high levels can be achieved around the implant without systemic toxicity. However, low drug levels provided over a long period could be disadvantageous and might cause the development of drugresistant bacterial strains. In several in vitro and in vivo studies and first clinical cases, it has been proven that locally delivered gentamicin from a biodegradable poly (D, L-lactide) (PDLLA) coating of implants with an initial burst release at high concentration could be an effective supplement for prophylaxis of implant-related infection in orthopedic and trauma surgery. This new approach in addition to established systemic antibiotic prophylaxis could reduce the infection rate especially in open-fracture situations. Antiseptics and antibiotics on implants

INTRODUCTION:Osteoporosis is not only responsible for an increased number of metaphyseal and spinal fractures but it also complicates their treatment. To prevent the initial loosening, we developed a new implant with an enlarged implant/bone interface based on the concept of perforated, hollow cylinders. We evaluated whether osseointegration of a hollow cylinder based implant takes place in normal or osteoporotic bone of sheep under functional loading conditions during anterior stabilization of the lumbar spine.MATERIALS AND METHODS:Osseointegration of the cylinders and status of the fused segments (ventral corpectomy, replacement with iliac strut, and fixation with testing implant) were investigated in six osteoporotic (age 6.9 +/- 0.8 years, mean body weight 61.1 +/- 5.2 kg) and seven control sheep (age 6.1 +/- 0.2 years, mean body weight 64.9 +/- 5.7 kg). Osteoporosis was introduced using a combination protocol of ovariectomy, high-dose prednisone, calcium and phosphor reduced diet and movement restriction. Osseointegration was quantified using fluorescence and conventional histology; fusion status was determined using biomechanical testing of the stabilized segment in a six-degree-of-freedom loading device as well as with radiological and histological staging.RESULTS:Intact bone trabeculae were found in 70% of all perforations without differences between the two groups (P = 0.26). Inside the cylinders, bone volume/total volume was significantly higher than in the control vertebra (50 +/- 16 vs. 28 +/- 13%) of the same animal (P<0.01), but significantly less (P<0.01) than in the near surrounding (60 +/- 21%). After biomechanical testing as described in Sect. "Materials and methods", seven spines (three healthy and four osteoporotic) were classified as completely fused and six (four healthy and two osteoporotic) as not fused after a 4-month observation time. All endplates were bridged with intact trabeculae in the histological slices.CONCLUSIONS:The high number of perforations, filled with intact trabeculae, indicates an adequate fixation; bridging trabeculae between adjacent endplates and tricortical iliac struts in all vertebrae indicates that the anchorage is adequate to promote fusion in this animal model, even in the osteoporotic sheep.

Osteoporosis is a common problem in orthopedic surgery. The purpose of this review of the literature was to examine whether osteoporosis is also an important factor in patient treatment in the field of craniomaxillofacial surgery. Emphasis was given to the consequences of osteoporosis for the maxilla and mandible, the influence of osteoporosis on fracture treatment, the use of dental implants, the importance of soft tissues and the effect of osteoporosis therapies. It was found that osteoporosis does affect the bones of the skull. The effect of osteoporosis on treatment, however, is controversial and necessitates better ways of quantifying bone loss. Large inter-individual and site-specific differences in bone density, as well as other effects such as removal of teeth, periodontitis, implant insertion, augmentation procedures and altered loading with dystrophic consequences need to be considered in future studies. Special attention should be given to osteoporosis during fracture treatment.

Critical size defects of bone and delayed fracture healing due to metabolic disorders are still problems in orthopaedic surgery. Adenoviral vectors encoding bone morphogenetic protein-2 (Ad.BMP-2) have been used to stimulate bone formation in small animals. The present study evaluated the use of direct adenoviral gene transfer for inducing bone formation in a large animal. Standardized iliac crest defects were created surgically on both sides of the pelvic bone of white mountain sheep. The efficiency of gene transfer was evaluated using recombinant adenoviruses carrying the cDNA for luciferase. High levels of transgene expression, restricted to the site of injection, were found for the 1st week. Transgene expression then fell considerably, but could still be detected for up to 5 weeks. To investigate the effect on bone healing, Ad.BMP-2 (1011 particles in 200 μl saline) was unilaterally injected into iliac crest defects and into tibial osteotomies. The contralateral defects remained untreated to evaluate possible systemic effects. The controls were treated with saline solution. Bone formation within the defect, assessed by micro-computed tomography (CT) measurement at 8 weeks, and callus formation after osteotomy were significantly reduced following direct application of Ad.BMP-2. The retardation compared to untreated control animals was additionally found at the contralateral iliac crest indicating a systemic inhibitory effect. Histological analysis confirmed the CT measurement and showed an increased number of inflammatory cells within both defects. Antibodies against the adenovirus and the transgene product were detected in all treated animals. These data show a systemic retardation of bone formation following a single local injection of Ad.BMP-2 in sheep. This finding stands in contrast to the data obtained from small animal models. Further studies are needed to determine the contribution of the immune response to these results, and whether a lower dose of Ad.BMP-2 would be advantageous.

Osteoporosis, a major public health burden, is associated with increased fracture risk. Fracture healing in osteoporosis is delayed, with reduced callus formation and impaired biomechanical properties of newly formed bone leading to high risk of fixation failure. Adenoviral gene transfer of bone morphogenetic protein-2 (BMP-2) has been shown to enhance fracture healing. This study evaluated the ability of gene transfer to enhance bone healing in osteoporosis. An established sheep model of osteoporosis with well-characterized alterations in fracture healing was used. Osteotomies were created surgically in the tibias of adult female sheep and monitored for 8 weeks, using radiographic, biomechanical, and histological methods. For pilot experiments, primary ovine osteoblasts and mesenchymal stem cells were transduced with a recombinant adenovirus carrying BMP-2 cDNA (Ad.BMP-2). Large increases in alkaline phosphatase production and mineralization confirmed the ability of human BMP-2 to stimulate osteoblastic differentiation in sheep. In vivo bending stiffness measurements during fracture healing as well as ex vivo torsional stiffness measurements demonstrated stiffer callus tissue after treatment with Ad.BMP-2. The differences were found mainly in the early fracture-healing period. Computed tomography demonstrated that animals receiving the BMP-2 cDNA had larger cross-sectional callus area and higher callus density. Histological examination of the tibias confirmed enhanced callus formation. Direct, local adenoviral delivery of an osteogenic gene thus led to enhanced healing of fractures in an ovine model of osteoporosis. These promising data encourage the further development of genetic approaches to enhance bone healing in patients suffering osteoporosis-associated fractures.

INTRODUCTION:Failure of pedicle screws by loosening and back out remains a significant clinical problem. Pedicle screw fixation is determined by bone mineral density, pedicle morphology and screw design. The objective of this study was to compare the holding strength of newly developed dual core pedicle screws having a cylindrical design in terms of outer diameter and two cylindrical inner core regions connected by a conical transition with conventional cylindrical pedicle screws.MATERIALS AND METHODS:Fifty bovine lumbar vertebrae and 40 human lumbar vertebrae were used. Five different screws were tested in nine experimental "settings" and ten specimens each. The screws were tested for cranial displacement and pullout strength before and after 5,000 cycles of cranio-caudal loading. The tests included a setting with fully inserted and 4 mm backed out screws. For statistical analysis the incomplete balanced block design was used.RESULTS:Cyclic loading led to a decrease of pullout force between 24 and 31% and a 9% increase of displacement. The cylindrical screw designs were affected more than the dual core designs. The pullout force of cylindrical screws was smaller than of dual core screws. Even in a backed out condition dual core screws showed a significantly smaller displacement than cylindrical screws.CONCLUSION:Pedicle screws with the dual core design provide good anchorage in the vertebra.

Slip velocities between the condyle and tibial plateau in total knee replacements are suspected to play a major role in wear generation. In this study, the velocity profiles from three different sources were calculated: directly from the input of the international standard ISO 14243-3 (knee wear testing in displacement control), from the kinetics of a simulator running under ISO 14243-1 (load control), and from data derived from three gait tested patients. Slip velocity and contact load showed similar patterns for all three sources, resulting in only moderate differences in the product of both, the force-velocity profile. Based on these finding, a constant vertical load and three different velocity ranges were applied onto three UHMWPE specimens in a wheel-on-flat simulator set-up. After 1 million cycles of testing, optoelectronic measurements revealed more wear in areas of high slip velocity and near zero slip velocity where a transition from rolling to sliding took place. Further, it was found that the coefficient of friction was influenced by the total velocity range.

Fracture fixation in severe osteoporotic bone by means of implants that rely on screw anchorage is still a clinical problem. So far, a sufficiently accurate prediction of the holding capacity of screws as a function of local bone morphology has not been obtained. In this study the ultimate pullout loads of screws in the epi-, meta-, and diaphyseal regions of human tibiae were correlated to the cortical thicknesses and cancellous bone mineral densities at the screw axes determined from QCT densitometric data. Stepwise multiple linear regression showed that in regions with cortical thicknesses below 1.5 mm, cancellous density determined the ultimate pullout load (R2=0.85, p <0.001), while in regions with cortices above 1.5 mm, cortical thickness alone significantly influenced the holding capacity of a screw (R2=0.90, p <0.001). The findings of this study provide a basis for a bone morphology-related pre-operative estimation of the holding capacity of screws, which could help to improve their proper application in osteoporotic bone.

Kurzfassung Die von Metallpartikeln ausgekratzten Ablagerungen lassen darauf schließen, dass diese durch den alltäglichen Betrieb in vivo erzeugt wurden und die Kontaktflächen vollständig oder teilweise bedeckten. Damit handelt es sich um tribochemisch erzeugte Reaktionsschichten und nicht etwa um chemische Ablagerungen. Es wird spekuliert, dass diese den direkten Metall-Metall-Kontakt und damit die Adhäsion („Fressen“) der identischen Kontaktpartner verhindern und somit als Festschmierstoff dienen. Über die Höhe der Verschleiß reduzierenden Wirkung ist jedoch bislang wenig bekannt und dies wird Gegenstand zukünftiger Forschungsarbeiten sein.

This study examines the effect of long-term ICV administration of leptin in ewes. We found that central application significantly decreased osteoblast activity as measured by serum analysis as well as by histomorphometry, resulting in decreased trabecular bone volume. These data provide additional evidence that bone formation and therefore bone remodeling is at least in part centrally controlled.

Demographic changes in the age structure of occidental populations are giving rise to osteoporosis and associated fractures, which are becoming a major public health burden. Various animal models have been established and used to investigate the pathogenesis of osteoporosis and to facilitate the preclinical testing of new treatment options such as antiresorptive drugs. Although osteoporosis can be induced in animals, spontaneous fractures without adequate trauma were only found in nonhuman primates. An animal model designed to investigate new ways to treat fractures of osteoporotic bone has to fulfill requirements that are very different from those of pharmacological testing. The aspects of major interest in orthopedic applications are bone fragility, efficacy of implant fixation and bone healing. Existing animal models for osteoporosis were critically reviewed focusing on these aspects. The advantages and disadvantages of the models with regard to their application in the testing of new fracture-fixation devices or biological approaches to stimulate bone healing are discussed. Ovariectomy alone does not cause the bone loss seen in osteoporotic human patients. New models to simulate fracture of osteoporotic bone need to be explored and used to address the specific aims of an experiment.

Wear of total knee replacements is determined gravimetrically in simulator studies. A mix of bovine serum, distilled water, and additives is intended to replicate the lubrication conditions in vivo. Weight gain due to fluid absorption during testing is corrected using a load soak station. In this study, three sets of ultrahigh molecular weight polyethylene tibial plateau were tested against highly polished titanium condyles. Test 1 was performed in two different institutions on the same simulator according to the standard ISO 14243-1, using two testing lubricants. Test 2 and test 3 repeated both previous test sections. The wear and load soak rates changed significantly with the lubricant. The wear rate decreased from 16.9 to 7.9 mg weight loss per million cycles when switching from fluid A to fluid B. The weight gain of the load soak specimen submersed in fluid A was 6.1 mg after 5 × 106 cycles, compared with 31.6 mg for the implant in fluid B after the same time period.Both lubricants were mixed in accordance with ISO 14243 ( Implants for surgery - wear of total knee-joint prostheses), suggesting that calf serum should be diluted to 25 ± 2 per cent with deionized water and a protein mass concentration of not less than 17 g/1. The main differences were the type and amount of additives that chemically stabilize the lubricant throughout the test. The results suggest that wear rates can only be compared if exactly the same testing conditions are applied. An agreement on detailed lubricant specifications is desirable.

Demographic changes in the age structure of occidental populations are giving rise to osteoporosis and associated fractures, which are becoming a major public health burden. Various animal models have been established and used to investigate the pathogenesis of osteoporosis and to facilitate the preclinical testing of new treatment options such as antiresorptive drugs. Although osteoporosis can be induced in animals, spontaneous fractures without adequate trauma were only found in nonhuman primates. An animal model designed to investigate new ways to treat fractures of osteoporotic bone has to fulfill requirements that are very different from those of pharmacological testing. The aspects of major interest in orthopedic applications are bone fragility, efficacy of implant fixation and bone healing. Existing animal models for osteoporosis were critically reviewed focusing on these aspects. The advantages and disadvantages of the models with regard to their application in the testing of new fracture-fixation devices or biological approaches to stimulate bone healing are discussed. Ovariectomy alone does not cause the bone loss seen in osteoporotic human patients. New models to simulate fracture of osteoporotic bone need to be explored and used to address the specific aims of an experiment.

Osteoporosis-associated fractures impair a patient’s function and quality of life and represent one of the major public health burdens. Demographic changes predict a dramatic increase in osteoporotic fractures. Experimental data have shown that osteoporosis impairs fracture healing. Clinical observations demonstrate high failure rates of implant fixation in osteoporosis. The reduced healing capacity, including impaired bone formation, in osteoporotic humans might be due to defects in mesenchymal stem cells that lead to reduced proliferation and osteoblastic differentiation. Growth factors show remarkable promise as agents that can improve the healing of bone or increase the proliferation and differentiation capacities of mesenchymal stem cells. Their clinical utility is limited by delivery problems. The attraction of gene-transfer approaches is the unique ability to deliver authentically processed gene products to precise anatomical locations at therapeutic levels for sustained periods of time. Unlike the treatment of chronic diseases, it is neither necessary nor desirable for transgene expression to persist beyond the few weeks or months needed to achieve healing. This review presents different approaches of gene therapy to enhance fracture healing and summarizes the promising results of preclinical studies. It focuses on applications of this new technique to fracture healing in osteoporosis. In our opinion, these applications represent some of the few examples in which gene therapy has a good chance of early clinical success.