The vascularized pig fibula bone flap model: effects of multiple segmental osteotomies on growth and viability

Previous work by this laboratory introduced the pig fibula bone flap as a model for the study of the pathophysiology of vascularized bone flaps. Anatomic and hemodynamic studies demonstrated a significant (p < 0.05) decrease in vascular perfusion after a series of segmental osteotomies and rigid fixation (lag screws and miniplates) in the distal end of the flap, suggesting that blood flow to the distal osteotomized segment of the flap may be impaired. Killing the animals after blood flow studies precluded assessment of the effect of these hemodynamic changes on bone healing. Therefore, the aim of this study was to assess the pig fibula bone flap model with respect to viability, healing, and subsequent growth after multiple segmental osteotomies and rigid fixation to contribute to the understanding of vascularized bone flap pathophysiology. Yorkshire pigs (20 to 25 kg) were used for all experiments. Eight pigs underwent unilateral elevation of a vascularized fibula bone flap, which was osteotomized into three segments and orthotopically rigidly fixed using a 2.4-mm mandibular reconstruction plate. The left fibula remained as the control. Fluorochrome labels were injected to assess bone viability and turnover, and both fibulae were assessed for growth radiologically. The fibulae were harvested 21 days postoperatively (when the animals were killed), and bone healing was assessed histologically and clinically. There were no significant differences in preoperative and postoperative lengths of the osteotomized fibulae compared with the controls, suggesting that there was no impairment of growth potential after multiple segmental osteotomies and rigid fixation. Significant (p < 0.05) bony hypertrophy of the osteotomized fibulae was noted when compared with controls. Mobility was observed in 3 of the 32 osteotomies (9 percent), occurring across one proximal and two distal osteotomies in association with failure of fixation. However, histologic and fluorochrome assessment confirmed the viability of all bone segments, as supported by the presence of tetracycline given 2 days postoperatively. The pig fibula bone flap model is well tolerated by the pig. Multiple segmental osteotomies and rigid fixation, previously associated with a significant decrease in blood flow in the distal segment, did not impair either growth potential, viability, or healing ability. It is suggested that the pig fibula is a suitable model for the study of bone flap pathophysiology.     

Effect of simvastatin on fracture healing--an experimental study

Left femur was osteotomized and fixed with K wire in 21 rabbits. One group was fed simvastatin (120 mg/kg body wt/day) orally, whereas another group without medication served as control. Both groups were assessed radiologically, morphologically, histologically and biomechanically at 4, 8 and 12 weeks. An analysis of various parameters of study showed that simvastatin treated group had improved bone healing at 4 and 8 weeks of follow up, however, the difference was not significant statistically at 12 weeks. So it is concluded that Simvastatin favourably hastened the process of fracture healing in the rabbits at earlier phases.     

Mineral and matrix contributions to rigidity in fracture healing

The purpose of this study was to investigate the relationships among selected properties of fracture callus: bending rigidity, tissue density, mineral density, matrix density and mineral-to-matrix ratio. The experimental model was an osteotomized canine radius in which the development of the fracture callus was modified by electrical stimulation with various levels of direct current. This resulted in a range of values for the selected properties of the callus, determined post mortem at 7 weeks after osteotomy. We found that the rigidity (R) of the bone-callus combination obeyed relationships of the form R = axb, where x is the tissue density, mineral density, matrix density or the mineral-to-matrix ratio of the repair tissue. These are analogous to power-law relationships found in studies of compact and cancellous bone. The results suggest that fracture callus at 7 weeks after osteotomy in canine radius behaves more like immature compact bone than cancellous bone in its mechanical and physicochemical properties. The present study demonstrates the feasibility of developing non-invasive in vivo densitometric methods to monitor fracture healing, since models may be developed that can predict mechanical properties from densitometric data. Further studies are needed to develop a refined model based on experimental data on the mechanical and physicochemical properties and microstructure of fracture callus at different stages of healing.     

Determining the most important cellular characteristics for fracture healing using design of experiments methods

Computational models are employed as tools to investigate possible mechanoregulation pathways for tissue differentiation and bone healing. However, current models do not account for the uncertainty in input parameters, and often include assumptions about parameter values that are not yet established. The objective of this study was to determine the most important cellular characteristics of a mechanoregulatory model describing both cell phenotype-specific and mechanobiological processes that are active during bone healing using a statistical approach. The computational model included an adaptive two-dimensional finite element model of a fractured long bone. Three different outcome criteria were quantified: (1) ability to predict sequential healing events, (2) amount of bone formation at early, mid and late stages of healing and (3) the total time until complete healing. For the statistical analysis, first a resolution IV fractional factorial design (L₆₄) was used to identify the most significant factors. Thereafter, a three-level Taguchi orthogonal array (L₂₇) was employed to study the curvature (non-linearity) of the 10 identified most important parameters. The results show that the ability of the model to predict the sequences of normal fracture healing was predominantly influenced by the rate of matrix production of bone, followed by cartilage degradation (replacement). The amount of bone formation at early stages was solely dependent on matrix production of bone and the proliferation rate of osteoblasts. However, the amount of bone formation at mid and late phases had the rate of matrix production of cartilage as the most influential parameter. The time to complete healing was primarily dependent on the rate of cartilage degradation during endochondral ossification, followed by the rate of cartilage formation. The analyses of the curvature revealed a linear response for parameters related to bone, where higher rates of formation were more beneficial to healing. In contrast, parameters related to fibrous tissue and cartilage showed optimum levels. Some fibrous connective tissue- and cartilage formation was beneficial to bone healing, but too much of either tissue delayed bone formation. The identified significant parameters and processes are further confirmed by in vivo animal experiments in the literature. This study illustrates the potential of design of experiments methods for evaluating computational mechanobiological model parameters and suggests that further experiments should preferably focus at establishing values of parameters related to cartilage formation and degradation.     

Prediction of the Time Course of Callus Stiffness as a Function of Mechanical Parameters in Experimental Rat Fracture Healing Studies - A Numerical Study

Numerous experimental fracture healing studies are performed on rats, in which different experimental, mechanical parameters are applied, thereby prohibiting direct comparison between each other. Numerical fracture healing simulation models are able to predict courses of fracture healing and offer support for pre-planning animal experiments and for post-hoc comparison between outcomes of different in vivo studies. The aims of this study are to adapt a pre-existing fracture healing simulation algorithm for sheep and humans to the rat, to corroborate it using the data of numerous different rat experiments, and to provide healing predictions for future rat experiments. First, material properties of different tissue types involved were adjusted by comparing experimentally measured callus stiffness to respective simulated values obtained in three finite element (FE) models. This yielded values for Young’s moduli of cortical bone, woven bone, cartilage, and connective tissue of 15,750 MPa, 1,000 MPa, 5 MPa, and 1 MPa, respectively. Next, thresholds in the underlying mechanoregulatory tissue differentiation rules were calibrated by modifying model parameters so that predicted fracture callus stiffness matched experimental data from a study that used rigid and flexible fixators. This resulted in strain thresholds at higher magnitudes than in models for sheep and humans. The resulting numerical model was then used to simulate numerous fracture healing scenarios from literature, showing a considerable mismatch in only 6 of 21 cases. Based on this corroborated model, a fit curve function was derived which predicts the increase of callus stiffness dependent on bodyweight, fixation stiffness, and fracture gap size. By mathematically predicting the time course of the healing process prior to the animal studies, the data presented in this work provides support for planning new fracture healing experiments in rats. Furthermore, it allows one to transfer and compare new in vivo findings to previously performed studies with differing mechanical parameters.     

Automatic allograft bone selection through band registration and its application to distal femur

Clinical reports suggest that large bone defects could be effectively restored by allograft bone transplantation, where allograft bone selection acts an important role. Besides, there is a huge demand for developing the automatic allograft bone selection methods, as the automatic methods could greatly improve the management efficiency of the large bone banks. Although several automatic methods have been presented to select the most suitable allograft bone from the massive allograft bone bank, these methods still suffer from inaccuracy. In this paper, we propose an effective allograft bone selection method without using the contralateral bones. Firstly, the allograft bone is globally aligned to the recipient bone by surface registration. Then, the global alignment is further refined through band registration. The band, defined as the recipient points within the lifted and lowered cutting planes, could involve more local structure of the defected segment. Therefore, our method could achieve robust alignment and high registration accuracy of the allograft and recipient. Moreover, the existing contour method and surface method could be unified into one framework under our method by adjusting the lift and lower distances of the cutting planes. Finally, our method has been validated on the database of distal femurs. The experimental results indicate that our method outperforms the surface method and contour method.     

Gene expression of TGF-beta, TGF-beta receptor, and extracellular matrix proteins during membranous bone healing in rats

Poorly healing mandibular fractures and osteotomies can be troublesome complications of craniomaxillofacial trauma and reconstructive surgery. Gene therapy may offer ways of enhancing bone formation by altering the expression of desired growth factors and extracellular matrix molecules. The elucidation of suitable candidate genes for therapeutic intervention necessitates investigation of the endogenously expressed patterns of growth factors during normal (i.e., successful) fracture repair. Transforming growth factor beta1 (TGF-beta1), its receptor (Tbeta-RII), and the extracellular matrix proteins osteocalcin and type I collagen are thought to be important in long-bone (endochondral) formation, fracture healing, and osteoblast proliferation. However, the spatial and temporal expression patterns of these molecules during membranous bone repair remain unknown. In this study, 24 adult rats underwent mandibular osteotomy with rigid external fixation. In addition, four identically treated rats that underwent sham operation (i.e., no osteotomy) were used as controls. Four experimental animals were then killed at each time point (3, 5, 7, 9, 23, and 37 days after the procedure) to examine gene expression of TGF-beta1 and Tbeta-RII, osteocalcin, and type I collagen. Northern blot analysis was used to compare gene expression of these molecules in experimental animals with that in control animals (i.e., nonosteotomized; n = 4). In addition, TGF-beta1 and T-RII proteins were immunolocalized in an additional group of nine animals killed on postoperative days 3, 7, and 37. The results of Northern blot analysis demonstrated a moderate increase (1.7 times) in TGF-beta1 expression 7 days postoperatively; TGF-beta1 expression returned thereafter to near baseline levels. Tbeta-RII mRNA expression was downregulated shortly after osteotomy but then increased, reaching a peak of 1.8 times the baseline level on postoperative day 9. Osteocalcin mRNA expression was dramatically downregulated shortly after osteotomy and remained low during the early phases of fracture repair. Osteocalcin expression trended slowly upward as healing continued, reaching peak expression by day 37 (1.7 times the control level). In contrast, collagen type IalphaI mRNA expression was acutely downregulated shortly after osteotomy, peaked on postoperative days 5, and then decreased at later time points. Histologic samples from animals killed 3 days after osteotomy demonstrated TGF-beta1 protein localized to inflammatory cells and extracellular matrix within the fracture gap, periosteum, and peripheral soft tissues. On postoperative day 7, TGF-beta1 staining was predominantly localized to the osteotomized bone edges, periosteum, surrounding soft tissues, and residual inflammatory cells. By postoperative day 37, complete bony healing was observed, and TGF-beta1 staining was localized to the newly formed bone matrix and areas of remodeling. On postoperative day 3, Tbeta-RII immunostaining localized to inflammatory cells within the fracture gap, periosteal cells, and surrounding soft tissues. By day 7, Tbeta-RII staining localized to osteoblasts of the fracture gap but was most intense within osteoblasts and mesenchymal cells of the osteotomized bone edges. On postoperative day 37, Tbeta-RII protein was seen in osteocytes, osteoblasts, and the newly formed periosteum in the remodeling bone. These observations agree with those of previous in vivo studies of endochondral bone formation, growth, and healing. In addition, these results implicate TGF-beta1 biological activity in the regulation of osteoblast migration, differentiation, and proliferation during mandibular fracture repair. Furthermore, comparison of these data with gene expression during mandibular distraction osteogenesis may provide useful insights into the treatment of poorly healing fractures because distraction osteogenesis has been shown to be effective in the management of these difficult clinical cases.     

Sensitivity of tissue differentiation and bone healing predictions to tissue properties

Computational models are employed as tools to investigate possible mechano-regulation pathways for tissue differentiation and bone healing. However, current models do not account for the uncertainty in input parameters, and often include assumptions about parameter values that are not yet established. The aim was to clarify the importance of the assumed tissue material properties in a computational model of tissue differentiation during bone healing. An established mechano-biological model was employed together with a statistical approach. The model included an adaptive 2D finite element model of a fractured long bone. Four outcome criteria were quantified: (1) ability to predict sequential healing events, (2) amount of bone formation at specific time points, (3) total time until healing, and (4) mechanical stability at specific time points. Statistical analysis based on fractional factorial designs first involved a screening experiment to identify the most significant tissue material properties. These seven properties were studied further with response surface methodology in a three-level Box–Behnken design. Generally, the sequential events were not significantly influenced by any properties, whereas rate-dependent outcome criteria and mechanical stability were significantly influenced by Young's modulus and permeability. Poisson's ratio and porosity had minor effects. The amount of bone formation at early, mid and late phases of healing, the time until complete healing and the mechanical stability were all mostly dependent on three material properties; permeability of granulation tissue, Young's modulus of cartilage and permeability of immature bone. The consistency between effects of the most influential parameters was high. To increase accuracy and predictive capacity of computational models of bone healing, the most influential tissue mechanical properties should be accurately quantified.     

Geometry and respiratory displacement of human ribs

The three-dimensional coordinates of points in the ribs of two supine relaxed males, holding their breath at functional residual capacity (FRC) and with their glottis closed at total lung capacity (TLC), were obtained from volumetric X-ray computed tomographical images. The orientation of planes that best fit the data for each rib at each lung volume and the circular arcs that fit the points in the planes of the ribs were determined, and average values of these geometrical parameters for ribs 3-7 are reported. The planes of the ribs at TLC can be described as displaced from the planes at FRC by a rotation about an axis that passes near the spine. The pump handle and bucket handle components of rotation are 11 and 13 degrees, respectively, for rib 3 and both decrease with increasing rib number to 7 and 10 degrees at rib 7. The angles between the axes of rotation and the midplane are approximately 35 degrees for all 5 ribs. The radii of the circular arcs fit to the data at TLC are slightly larger than those at FRC, and this suggests that there is a small component of rotation normal to the plane of the rib.     

DEXA对骨髓炎骨缺损治疗中骨痂密度的评价

目的：探讨DEXA对骨髓炎骨缺损治疗中骨痂密度的评价及意义。方法：严格按照纳入排除标准,选取21例骨髓炎清创后伴大段皮质骨缺损一期植骨的病人。术后4,6,8,10个月后对骨折端骨痂行双能X线骨密度仪检测,并进行X摄片以及Enneking评分,从而明确植骨区愈合骨痂的密度变化趋势,骨愈合情况以及症状改善情况。结果：（1）X线摄片结果显示：4个月后：骨缺损区依然清晰可见,内有少量稀疏骨痂通过,少量外骨痂形成。6个月后：植骨区内骨痂含量明显增多,且外骨痂膨大。8个月：缺损区模糊,有较致密骨痂生成,且外骨痂逐渐减少。10个月：植骨区骨痂更加致密,且部份髓腔再通。（2）Enneking评分：患者术后第10个月功能恢复情况评估正常功能20例,20分以下的患者1例。（3）BMD测定：骨折端的骨密度及骨密度比率随时间延长而增加,植骨10个月后患侧的骨密度已可基本上达到正常对照侧的骨密度水平。结论：双能X线骨密度测量从一定程度上反映出骨痂的力学强度特性。在感染性骨缺损治疗中可以作为检测植骨区的恢复情况的参考。     

Development of a locking femur nail for mice

We herein report on a novel locking intramedullary nail system in a murine closed femur fracture model. The nail system consists of a modified 24-gauge injection needle and a 0.1-mm-diameter tungsten guide wire. Rotation stability was accomplished by flattening the proximal and distal end of the needle. Torsional mechanical testing of the implants in osteotomized cadaveric femora revealed a superiority of the locking nail (3.9+/-1.0 degrees rotation at a torque of 0.9 Nmm, n=10) compared to the unmodified injection needle (conventional nail; 52.4+/-3.2 degrees, n=10, p<0.05). None of the implants, however, achieved the rotation stability of unfractured femora (0.3+/-0.5 degrees, n=10). In a second step, we tested the feasibility of the in vivo application of the locking nail to stabilize a closed femoral midshaft fracture in C57BL/6 mice. Of interest, none of the 10 animals showed a dislocation of the locking nail over a 5-week period, while 3 of 4 animals with conventional nail fracture stabilization showed a significant pin dislocation within the first 3 days (p<0.05). Mechanical testing after 5-weeks stabilization with the locking nail revealed an appropriate bone healing with a torque at failure of 71.6+/-3.4% and a peak rotation before failure of 68.4+/-5.3% relative to the unfractured contralateral femur. With the advantage that closed fractures can be fixed with rotation stability, the herein introduced model may represent an ideal tool to study bone healing in transgenic and knockout mice.     

Temporal changes in the physical properties of healing fractures in rabbits

Temporal changes in the physical properties of healing fractures in rabbits were studied. The mechanical environment at the fracture site was measured and monitored during healing. Animals were sacrificed after 3 to 8 weeks. The results of healing were quantified by whole bone dynamic torsional strength tests. Torque-angle curves were recorded by computer. At maximum torque four parameters were calculated: torque, angle, energy absorbed and stiffness. Torque and stiffness increased while energy remained constant and angle decreased with time. However, values calculated by a constant deformation criteria showed the three strength parameters to increase with time. The rate of increase was highest for stiffness followed by torque and energy.     

The effects of gelatin,fibrin-platelet glue and their combination on healing of the experimental critical bone defect in a rat model: radiological,histological, scanning ultrastructural and biomechanical evaluation

Fibrin-platelet glue (FPG) is a blood derivative, in which platelets and fibrinogen are concentrated in a small plasma volume, by differential centrifugation and precipitation. It can form a three-dimensional and biocompatible fibrin scaffold with a myriad of growth factors and proteins that are released progressively to the local environment and contribute to the accelerated postoperative bone healing. Gelatin (Gel) is a derivative of collagen and can promote cell adhesion and proliferation due to its unique sequence of amino acids, so it is suitable for bone tissue applications. This study examined the effects of Gel, FPG and their combinations as bone scaffold on the healing of surgically created critical-size defects in rat radius. Fifty critical size defects of 5 mm long were bilaterally created in the radial diaphysis of 25 rats. The animals were randomly divided into five equal groups as empty defect, autograft, Gel, FPG and Gel–FPG groups (n = 10 in each group). Radiographs of each forelimb were taken postoperatively on the 1st day and then at the 28th and 56th days post injury to evaluate bone formation, union and remodeling of the defect. After 56 days, the rats were euthanized and their harvested healing bone samples were evaluated by histopathology, scanning electron microscopy (SEM) and biomechanical testing. The results of present study showed that the Gel alone did not significantly affect bone healing and regeneration; however, the Gel treated defects promoted healing more than those that were left untreated (negative control). Furthermore, the FPG-enhanced grafts provided a good scaffold containing numerous growth factors for proliferation of osteoinduction and was effective in improving the structural and functional properties of the newly formed bone more than that of the untreated and also the Gel treated groups. Incorporation of Gel into the FPG scaffold improved healing potential of the FPG scaffold; however, it was still inferior to the autograft (positive control). Although the Gel–FPG scaffolds had best effectiveness during bone regeneration, it still needs to be further enhanced by incorporation of the ceramic and osteoinductive biomaterials.     

Creating Rigidly Stabilized Fractures for Assessing Intramembranous Ossification,Distraction Osteogenesis,or Healing of Critical Sized Defects

Assessing modes of skeletal repair is essential for developing therapies to be used clinically to treat fractures. Mechanical stability plays a large role in healing of bone injuries. In the worst-case scenario mechanical instability can lead to delayed or non-union in humans. However, motion can also stimulate the healing process. In fractures that have motion cartilage forms to stabilize the fracture bone ends, and this cartilage is gradually replaced by bone through recapitulation of the developmental process of endochondral ossification. In contrast, if a bone fracture is rigidly stabilized bone forms directly via intramembranous ossification. Clinically, both endochondral and intramembranous ossification occur simultaneously. To effectively replicate this process investigators insert a pin into the medullary canal of the fractured bone as described by Bonnarens⁴. This experimental method provides excellent lateral stability while allowing rotational instability to persist. However, our understanding of the mechanisms that regulate these two distinct processes can also be enhanced by experimentally isolating each of these processes. We have developed a stabilization protocol that provides rotational and lateral stabilization. In this model, intramembranous ossification is the only mode of healing that is observed, and healing parameters can be compared among different strains of genetically modified mice ^5-7, after application of bioactive molecules ^8,9, after altering physiological parameters of healing ¹⁰, after modifying the amount or time of stabilization ¹¹, after distraction osteogenesis ¹², after creation of a non-union ¹³, or after creation of a critical sized defect. Here, we illustrate how to apply the modified Ilizarov fixators for studying tibial fracture healing and distraction osteogenesis in mice.     

Bone Fracture Healing using a Capacitatively Coupled Rffield

A new pulsed radio frequency electric field pattern evolved from bone studies was adopted to accelerate fracture healing in rats. The output of a specially designed signal generator was ca-pacitatively coupled to the fracture site using a pair of stainless steel electrodes. In a series of experiments performed on rats, fractures were induced in the femoral shafts and electrical stimulations were applied to one leg. Bone mass formed in the gap was estimated by measurement of the cortical thickness and by ultrasonic attenuation. We found that the stimulated side showed greater bone mass than the contralateral control. We suggest that. this device offers a simple and reliable method of acclerated healing, immediately after fracture.     

Effects of chronic physical activity and of ultrasound treatment on bone consolidation

The objective of this study was to investigate the effects of ultrasound treatment and physical exercise on the velocity of bone consolidation and resistance to deformation. We performed osteotomy in the upper third of the right tibia of rats. Physical training consisted of swimming 1 h per day with a load of 5% b.w. for 30 days. Therapy with medium-intensity ultrasound was applied daily on the damaged area. Wistar rats were divided into the following groups: osteotomized sedentary animals with no ultrasound treatment (1.OSnUS), osteotomized trained animals with no ultrasound treatment (2.OTnUS), osteotomized sedentary animals with ultrasound treatment (3.OSwUS), and osteotomized trained animals with ultrasound treatment (4.OTwUS). The animals were sacrificed for the following analyses: muscle glycogen, serum alkaline phosphatase at the 5th, 10th, 20th, and 30th days, test of maximum resistance to flexion, rupture flexion and mean tibial rigidity at the 30th day. Muscle glycogen was increased at the 20th day; alkaline phosphatase was elevated at the 5th and 20th days in groups 3.OSwUS and 4.OTwUS, and decreased at the 10th day. Groups 1.OSnUS and 2.OTnUS did not show significant variations. In the mechanical resistance tests, we noted that ultrasound therapy and the association of physical activity used in the present study showed significant differences in bone resistance and bone rigidity after 30 days of treatment. These facts suggest that ultrasound or physical activity, or their combination may accelerate the process of bone tissue repair.     

Molecular aspects of embryonic mouse haemoglobin ontogeny.

Embryos from C57BL/6J mice between the gestational ages of 9 and 16 days possess three embryonic haemoglobins EI, EII and EIII, the proportions of which change as a function of gestational age. Component EI, originally present at approx. 65% at day 9, decreases to approx. 20% by day 16, while component EII increases in an inverse manner to that of component EI. During this period component EIII remains essentially constant at approx. 25%. Separation of these species by ion-exchange chromatography has allowed the characterization of the Hill coefficient, Bohr effect, heat of oxygenation and binding of allosterically active organic phosphates for each component. The three components show marked functional heterogeneity and also differ from maternal haemoglobin. Oxygenation curves for whole embryonic blood show distinct deviations from simple binding behaviour. The presence of a high-affinity component within the blood samples may be accounted for by the presence of haemoglobin EI. By using parameters obtained from the study of the isolated components it has been possible to synthesize mathematically the O2-binding curves, obtained experimentally, throughout the gestational period. The characteristics of the isolated haemoglobin components of embryonic mouse blood are discussed in terms of the changing demands for O2 likely to be encountered by the developing embryo.     

Parasternal and external intercostal muscle shortening during eupneic breathing

The interosseous external intercostal (EI) muscles of the upper rib cage are electrically active during inspiration, but the mechanical consequence of their activation is unclear. In 16 anesthetized dogs, we simultaneously measured EI (3rd and 4th interspaces) and parasternal intercostal (PA) (3rd interspace) electromyogram and length. Muscle length was measured by sonomicrometry and expressed as a percentage of resting length (%LR). During resting breathing, each muscle was electrically active and shortened to a similar extent. Sequential EI muscle denervation (3rd and 4th interspaces) followed by PA denervation (3rd interspace) demonstrated significant reductions in the degree of inspiratory shortening for each muscle. Mean EI muscle shortening of the third and fourth interspaces decreased from -3.4 +/- 0.5 and -3.0 +/- 0.4% LR (SE) under control conditions to -0.2 +/- 0.2 and -0.8 +/- 0.3% LR, respectively, after selective denervation of each of these muscles (P less than 0.001 for each). After selective denervation of the PA muscle, its shortening decreased from -3.5 +/- 0.3 to +0.6% LR (SE) (P less than 0.001). PA muscle denervation also caused the EI muscle in the third interspace to change from inspiratory shortening of -0.2% to inspiratory lengthening of +0.2% +/- 0.2 (P less than 0.05). We conclude that during eupneic breathing 1) the EI muscles of the upper rib cage, like the PA muscles, are inspiratory agonists and actively contribute to rib cage expansion and 2) PA muscle contraction contributes to EI muscle shortening.     

Effect of guided bone regeneration on bone quality surrounding dental implants

Bone quality as well as its quantity at the implant interface is responsible for determining stability of the implant system. The objective of this study is to examine the nanoindentation based elastic modulus (E) at different bone regions adjacent to titanium dental implants with guided bone regeneration (GBR) treated with DBM and BMP-2 during different post-implantation periods. Six adult male beagle dogs were used to create circumferential defects with buccal bone removal at each implantation site of mandibles. The implant systems were randomly assigned to only GBR (control), GBR with demineralized bone matrix (DBM), and GBR with DBM + recombinant human bone morphogenetic protein-2 (rhBMP-2) (BMP) groups. Three animals were sacrificed at each 4 and 8 weeks of post-implantation healing periods. Following buccolingual dissection, the E values were assessed at the defects (Defect), interfacial bone tissue adjacent to the implant (Interface), and pre-existing bone tissue away from the implant (Pre-existing). The E values of BMP group had significantly higher than control and DBM groups for interface and defect regions at 4 weeks of post-implantation period and for the defect region at 8 weeks (p < 0.043). DBM group had higher E values than control group only for the defect region at 4 weeks (p < 0.001). The current results indicate that treatment of rhBMP-2 with GBR accelerates bone tissue mineralization for longer healing period because the GBR likely facilitates a microenvironment to provide more metabolites with open space of the defect region surrounding the implant.     

The peptidoglycan crosslinking enzyme system in Streptomyces strains R61, K15 and rimosus. Kinetic coefficients involved in the interactions of the membrane-bound transpeptidase with peptide substrates and beta-lactam antibiotics

The transpeptidation reaction performed by the membranes of Streptomyces strain R61 fits the general rate equation for an enzyme-catalysed bimolecular reaction. The same membranes (E) interact with beta-lactams (I) to form inactive penicillin-enzyme-membrane complexes (EI) of rather high stability, which subsequently break down (E + I leads to EI leads to E + degradation products). The enzyme is regenerated and the antibiotic is released in the form of an inactive metabolite. With benzylpenicillin, the degradation product is benzylpenicilloic acid. The reaction is heat-labile. The first step of the reaction (E + I leads to EI) is characterized by a second-order rate constant (kformation in M-1 s-1) and the second step (EI leads to E + degradation products) by a first-order rate constant (kbreakdown in s-1). The effects in vitro of various beta-lactams on the membrane-bound transpeptidase, as expressed by the relevant kformation and kbreakdown values, parallel the effects in vivo of the same antibiotics as expressed by their ability to prevent the germination and growth of conidiospores. The kinetic parameters of the transpeptidase that was solubilized with N-cetyl-N,N,N-trimethylammonium bromide with respect to its interaction with both peptide substrates and beta-lactam antibiotics are quantitatively different from those of the membrane-bound enzyme. Moreover, the solubilized enzyme fragments benzylpenicillin with formation of phenylacetylglycine, a reaction which is similar to that catalysed by the exocellular R61 enzyme. The membranes of Streptomyces strains rimosus and K15 possess an active 'classic' penicillinase. They were not studied but the kinetic coefficients of the corresponding solubilized transpeptidases were determined and compared with those of the solubilized enzyme from strain R61.