Compositional and mechanical properties of growing cortical bone tissue: a study of the human fibula.

Human cortical bone contains two types of tissue: osteonal and interstitial tissue. Growing bone is not well-known in terms of its intrinsic material properties. To date, distinctions between the mechanical properties of osteonal and interstitial regions have not been investigated in juvenile bone and compared to adult bone in a combined dataset. In this work, cortical bone samples obtained from fibulae of 13 juveniles patients (4 to 18 years old) during corrective surgery and from 17 adult donors (50 to 95 years old) were analyzed. Microindentation was used to assess the mechanical properties of the extracellular matrix, quantitative microradiography was used to measure the degree of bone mineralization (DMB), and Fourier transform infrared microspectroscopy was used to evaluate the physicochemical modifications of bone composition (organic versus mineral matrix). Juvenile and adult osteonal and interstitial regions were analyzed for DMB, crystallinity, mineral to organic matrix ratio, mineral maturity, collagen maturity, carbonation, indentation modulus, indicators of yield strain and tissue ductility using a mixed model. We found that the intrinsic properties of the juvenile bone were not all inferior to those of the adult bone. Mechanical properties were also differently explained in juvenile and adult groups. The study shows that different intrinsic properties should be used in case of juvenile bone investigation.

Paxillin localisation in osteocytes--is it determined by the direction of loading?

External mechanical loading of cells aligns cytoskeletal stress fibres in the direction of principle strains and localises paxillin to the mechanosensing region. If the osteocyte cell body can indeed directly sense matrix strains, then cytoskeletal alignment and distribution of paxillin in osteocytes in situ will bear alignment to the different mechanical loading patterns in fibulae and calvariae. We used confocal microscopy to visualise the immunofluorescence-labelled actin cytoskeleton in viable osteocytes and paxillin distribution in fixated osteocytes in situ. In fibular osteocyte cell bodies, actin cytoskeleton and nuclei were elongated and aligned parallel to the principal (longitudinal) mechanical loading direction. Paxillin was localised to the 'poles' of elongated osteocyte cell bodies. In calvarial osteocyte cell bodies, actin cytoskeleton and nuclei were relatively more round. Paxillin was distributed evenly in the osteocyte cell bodies. Thus in osteocyte cell bodies in situ, the external mechanical loading pattern likely determines the orientation of the actin cytoskeleton, and focal adhesions mediate direct mechanosensation of matrix strains.

Light microscopic, immunohistochemical, and ultrastructural findings in congenital fibular aplasia or hypoplasia (FAH).

Congenital aplasia or hypoplasia of the fibula (FAH) is a rare malformation that is defined by a partial or complete absence of the fibular bone. Etiology and pathogenesis are unknown and the precise morphology of the tissue cord replacing the malformed fibula has not been well described. Therefore, tissue cord was examined in 8 patients with FAH. Light microscopic, immunohistochemical, and electron microscopic investigations showed a core of embryonic cartilage with collagen II and VI expressions surrounded by connective tissue. Although collagen II expression is typical for chondroid differentiation, collagen VI reactivity is normally seen in articular cartilage and tendon-like fibrocartilaginous tissue but is absent in hyaline cartilage. Further ultrastructural analyses by electron microscopy supported these findings. The histomorphologic changes correspond to the histologic findings of Papenbrock et al. (2000, Mech Dev 92:113-123) who produced a congenital malformation in transgenic mice that resembled FAH by overexpression of Hox c11.

Pathogenesis of retinoic acid-induced abnormal pad patterns on mouse volar skin.

BACKGROUND: Abnormal dermatoglyphs on human volar skin have been reported in many syndromes, but little is known about the pathogenesis. Patterns of pads on rodent limb volar skin are homologous to human dermatoglyphs. METHODS: In previous studies, we showed that transplacental exposure to teratogens induced abnormal pads in mouse fetuses. Moreover, teratogens caused abnormal pad patterns at levels below those that caused skeletal malformations. In this study, we examined morphology and cytokinetics in developing abnormal pads. Pregnant mice were treated with all-trans-retinoic acid at 20 mg/kg orally at embryonal day (E) 12.5 (vaginal plug = E0). The hindlimbs of the embryos were harvested and observed under a light microscope and by scanning electron microscopy. Cell proliferation and cell death were estimated by 5-bromo-2'-deoxyuridine (BrdU) labeling, Nile blue A vital staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). RESULTS: Retinoic acid induced aplasia of the fibular tarsal pad and supernumerary interdigital pads on hindlimbs. Cell proliferation was observed in the area of developing pad, but cell death was very rarely seen in either normal or abnormal pads. CONCLUSIONS: Retinoic acid disturbed pad patterning as a whole rather than individual pad formation.

Epithelioid hemangioendothelioma of bone. A clinicopathologic, ultrastructural, and immunohistochemical study.

In a review of 29 cases of solitary and multicentric hemangioendothelial sarcomas of bone, 14 were found to have histologic features of epithelioid hemangioendotheliomas. These were characterized by the presence of epithelioid or "histiocytoid" endothelial cells that were either round or spindle-shaped. Intracytoplasmic vacuolization was noted, and some showed nesting of cells, mimicking metastatic adenocarcinoma. The presence of a myxoid matrix suggested the diagnosis of chondrosarcoma in some cases. Some of the tumors strongly resembled the lesions formerly designated as intravascular bronchioloalveolar tumor, angioglomoid tumor of bone, or malignant myxoid angioblastoma of bone. Factor VIII-related antigen was detected in five of the six cases examined, and ultrastructural study in five cases confirmed the endothelial nature of the tumor cells; Weibel-Palade bodies were present in three cases. There were 11 men and three women, and the tumors were seen predominantly in patients who were under 30 years of age (10 cases). Four cases involved solitary tumors, and nine were multicentric in bone. The multicentric tumors had a predilection for the bones of one lower extremity (five cases). The total series had a protracted clinical course, and the multicentric tumors appeared to follow a less aggressive course.

[Micromorphology of torsional bone fractures]. / Udaje k mikromorfológii torzných zlomenín kostí.

Characteristic microlesions can be found along the torsion fractures of long bones related to special anatomy of compact tissue: Torsion severs singular lamellae of broken osteons along the longitudinal fracture lines. Exposed bone bridges are partially broken and haversian canaliculi longitudinally opened among severed lamellae. Torsion mechanism of the bone injury can be estimated and reconstructed by SEM with sufficient certainty. An expert can be more conclusive about the body fall or flight in the moment of injury or collision. Evidence of rotation movement can be helpful in explaining secondary injuries. A more perfect medical opinion can help to more satisfactory elucidation and evaluation of accident conditions by the court.

[Tendinous fibers in the periosteum and bone]. / O sukhozhil'nykh voloknakh v nadkostnitse i v kodti.

The relation of muscles and bony skeleton studied in the work demonstrates a rather complex mechanism of connections existing between tendinous elements and periosteum and bone. Investigation on fixation of muscular tendons to the skeleton has demonstrated that in some cases tendinous filaments plait into the periosteum and terminate in it, while in other cases not all the tendinous filaments terminate at the level of the periosteum, but some of them penetrate into the bone. Thus, it has been demonstrated for the first time that tendinous filaments penetrate into the compact substance of the bone.

[Structure of the osteon lamella]. / Struktura plastinok osteona

The structure of osseous laminas of osteons was studied by methods of translucent and rastral electron microscopy. All laminas were shown to consist of collagenous fibrils and crystals of hydroxyapatite. The collagenous fibrils in the lamina are united into interwining bundles. The adjacent osseous laminas are different in orientation of fibrils and bundles in relation to the axis of the Haversian canal. The laminas are bound by bundles and solitary fibrils passing from one lamina into the other. In decalcificated sections of laminas of osteons have different relief. The laminas with longitudinally disposed fibrils project over the laminas with transversely disposed fibrils.