The bone pencil and the bone surgeon

While helpful for preoperative skin markings, methylene blue is washed away by irrigation and tissue fluids during bony reconstruction. The bone pencil is an ideal marker for hard tissue because it is indelible to irrigation. Further, the surgeon may draw with ease in areas of limited access (i.e., sagittal split and intraoral vertical ramus osteotomies). The pencil can be obtained from most art suppliers. No adverse effects from use of the pencil have been noted in any of our patients.     

Morpho-functional correlations of the structure of bone cells and adjoining bone matrix in the developing bone

By means of scanning and transmissive electron microscopy methods structure of the developing bone has been studied. Interconnection of the cell structure and spatial organization of the adjoining matrix has been demonstrated. On the surface of the growing bone not only forming areas have been revealed, where under osteoblasts at various functional states, osteoid layer is determined, but also areas of resorption and completed osteogenesis. This demonstrates an interrupted character of osteogenesis at modelling. At the same time for the remodelling process presence of erosive lacunae is specific; they are filled with a newly deposited collagenous matrix. Therefore, it is possible to suppose that formation of the bone as an organ during the postnatal development includes in itself both mechanisms supporting its form at outgrowth of the osseous matrix volume (modeling) and its continuous rearrangement and adaptation to real conditions of functioning (remodelling).     

Stromal cells of the bone marrow in growing bone

By means of electron microscopy, cytochemistry and radioautography with 3H-thymidine, the bone marrow stromal cells have been studied in the zones of endochondral osteogenesis in the rabbit and rat femoral bones. In the stromal cells demonstrating a high alkaline phosphatase activity are distinguished: perivascular, reticular fibroblastic, osteogenic cells. Populations of the perivascular phosphatase-positive cells include poorly differentiated DNA-synthesizing forms, as well as cells with signs of differentiation into stromal fibroblasts. Cleft-like spaces in cytoplasm of the fibroblastic reticular cells are, probably, formed as a result of lymphocyte-like mononuclears passing through. Phagocyting stromal elements are presented by macrophages, having perivascular localization and including into composition of erythroblastic islets. Mononuclear macrophages are revealed also on the surface of osseous trabecules, where they participate in destruction of hemopoetic and osteogenic cells.     

Sinusoids of the bone marrow stroma in the human iliac bone

Results of histological and ultramicroscopic investigations of sinusoid vessels are presented. Interrupted structure of the basal membrane and continuous endothelial lining are revealed. Endotheliocytes of two types are described. At places of blood cells migration functional activity of endothelium is increased and the basal membrane is absent. A suggestion is made that the endothelial cells directly influence hemopoiesis.     

Endosteal cells of the bone marrow stroma in human iliac bone

The data on histological and electron microscopical investigation of the endosteal cells of the human iliac bone are presented. Three types of stromal elements in the endosteum, differing in their ultrastructural organization have been revealed. In the endosteal areas young hemopoietic cells are present, they are closely connected with the stroma. A suggestion is made on an important role of the endosteum in processes of proliferation and differentiation of hemopoietic predecessors.     

The role of bone sialoprotein in the tendon–bone insertion

Tendons/ligaments insert into bone via a transitional structure, the enthesis, which is susceptible to injury and difficult to repair. Fibrocartilaginous entheses contain fibrocartilage in their transitional zone, part of which is mineralized. Mineral-associated proteins within this zone have not been adequately characterized. Members of the Small Integrin Binding Ligand N-linked Glycoprotein (SIBLING) family are acidic phosphoproteins expressed in mineralized tissues. Here we show that two SIBLING proteins, bone sialoprotein (BSP) and osteopontin (OPN), are present in the mouse enthesis. Histological analyses indicate that the calcified zone of the quadriceps tendon enthesis is longer in Bsp^−/− mice, however no difference is apparent in the supraspinatus tendon enthesis. In an analysis of mineral content within the calcified zone, micro-CT and Raman spectroscopy reveal that the mineral content in the calcified fibrocartilage of the quadriceps tendon enthesis are similar between wild type and Bsp^−/− mice. Mechanical testing of the patellar tendon shows that while the tendons fail under similar loads, the Bsp^−/− patellar tendon is 7.5% larger in cross sectional area than wild type tendons, resulting in a 16.5% reduction in failure stress. However, Picrosirius Red staining shows no difference in collagen organization. Data collected here indicate that BSP is present in the calcified fibrocartilage of murine entheses and suggest that BSP plays a regulatory role in this structure, influencing the growth of the calcified fibrocartilage in addition to the weakening of the tendon mechanical properties. Based on the phenotype of the Bsp^−/− mouse enthesis, and the known in vitro functional properties of the protein, BSP may be a useful therapeutic molecule in the reattachment of tendons and ligaments to bone.     

The bone and the kidney

Renal tubular diseases may present with osteopenia, osteoporosis or osteomalacia, as a result of significant derangements in body electrolytes. In case of insufficient synthesis of calcitriol, as in renal failure, the more complex picture of renal osteodystrophy may develop. Hypothetically, also disturbed renal production of BMP-7 and Klotho could cause bone disease. However, the acknowledgment that osteocytes are capable of producing FGF23, a phosphaturic hormone at the same time modulating renal synthesis of calcitriol, indicates that it is also bone that can influence renal function. Importantly, a feed-back mechanism exists between FGF23 and calcitriol synthesis, while Klotho, produced by the kidney, determines activity and selectivity of FGF23. Identification of human diseases linked to disturbed production of FGF23 and Klotho underlines the importance of this new bone-kidney axis. Kidney and bone communicate reciprocally to regulate the sophisticated machinery responsible for divalent ions homeostasis and for osseous or extraosseous mineralisation processes.     

Predicting the structural integrity of bone defects repaired using bone graft materials

Bone defects create stress concentrations which can cause fracture under impact or cyclic loading. Defects are often repaired by filling them with a bone graft material; this will reduce the stress concentration, but not completely, because these materials have lower stiffness than bone. The fracture risk decreases over time as the graft material is replaced by living bone. Many new bone graft materials are being developed, using tissue engineering and other techniques, but currently there is no rational way to compare these materials and predict their effectiveness in repairing a given defect. This paper describes, for the first time, a theoretical model which can be used to predict failure by brittle fracture or fatigue, initiating at the defect. Preliminary results are presented, concentrating on the prediction of stress fracture during the crucial post-operative period. It is shown that the likelihood of fracture is strongly influenced by the shape of the defect as well as its size, and also by the level of post-operative exercise. The most important finding is that bone graft materials can be successful in preventing fracture even when their mechanical properties are greatly inferior to those of bone. Future uses of this technique include pre-clinical assessment of bone replacement materials and pre-operative planning in orthopaedic surgery.     

Paradoxical bilateral asymmetry in bone size and bone mass in the hand

Among 227 chronic renal disease patients, micrometer caliper radiogrammetric measurements of the second metacarpal at midshaft showed the right metacarpal to be larger (with greater bone area) and with a greater cortical area than the left second metacarpal, both in 208 right-handed individuals and in 19 left-handed individuals. This direction of asymmetry was individually characteristic of the majority of individuals, whether right-handed, left-handed or ambidextrous.     

Adipocytes and reticular cells of the bone marrow stroma in the human iliac bone

The results of the histological and electron microscopic investigation of adipose and reticular cells and their interconnections with blood cells are presented in the material of trephine biopsies of the iliac bone. A possibility for development of adipocytes from the adventitial reticular cells is demonstrated. Close contacts are revealed between pre-adipocytes and young hemopoietic cells. Two types of the reticular cells are characterized, they differ in their position, structural organization and interconnection with the young hemopoietic elements. The peculiarities revealed in the morphofunctional state of the microenvironmental structures demonstrate functional variegation of the stromal elements, and also attest an essential importance of intercellular contacts of the hemopoietic predecessors and the stromal cells in maintaining the hemopoietic function of the bone marrow.     

How the osteoclast degrades bone

Osteoclasts are multinucleated monocyte-macrophage derivatives that degrade bone. Their specialized role is central to a process that continuously removes and replaces segments of the skeleton in the higher vertebrates. Osteoclasts allow skeletal mineral to be used to manage extracellular calcium activity, which is an important adaptation for life on land, and solid skeletal structure to be replaced by hollow architecture that has a superior strength-to-weight ratio. Degrading bone also allows periodic repair and remodeling for ordered growth and efficient response to mechanical loads. A fairly comprehensive view of osteoclastic ontogeny and function is emerging from recent studies. Osteoclasts dissolve bone mineral by massive acid secretion and secrete specialized proteinases that degrade the organic matrix, mainly type I collagen, in this acidic milieu. The site of bone dissolution is a high-calcium environment; removal of degradation products by transcytosis of membrane vesicles allows the osteoclast to maintain a normal intracellular calcium. Osteoclastic differentiation is normally balanced with bone formation, although bone formation is the function of unrelated stromal cell-derived osteoblasts. Interactions between osteoclast precursors and bone-forming cells are believed to control osteoclast differentiation under most circumstances, preserving bone architecture over many cycles of bone replacement. BioEssays 20 :837–846, 1998. © 1998 John Wiley & Sons, Inc.     

Mathematical modelling of bone adaptation of the metacarpal subchondral bone in racehorses

In Thoroughbred racehorses, fractures of the distal limb are commonly catastrophic. Most of these fractures occur due to the accumulation of fatigue damage from repetitive loading, as evidenced by microdamage at the predilection sites for fracture. Adaptation of the bone in response to training loads is important for fatigue resistance. In order to better understand the mechanism of subchondral bone adaptation to its loading environment, we utilised a square root function defining the relationship between bone volume fraction \((f_{BM} )\) and specific surface \((S_v )\) of the subchondral bone of the lateral condyles of the third metacarpal bone (MCIII) of the racehorse, and using this equation, developed a mathematical model of subchondral bone that adapts to loading conditions observed in vivo. The model is expressed as an ordinary differential equation incorporating a formation rate that is dependent on strain energy density. The loading conditions applied to a selected subchondral region, i.e. volume of interest, were estimated based on joint contact forces sustained by racehorses in training. For each of the initial conditions of \(f_{BM} \) we found no difference between subsequent homoeostatic \(f_{BM} \) at any given loading condition, but the time to reach equilibrium differed by initial \(f_{BM} \) and loading condition. We found that the observed values for \(f_{BM} \) from the mathematical model output were a good approximation to the existing data for racehorses in training or at rest. This model provides the basis for understanding the effect of changes to training strategies that may reduce the risk of racehorse injury.