1,720,981 research outputs found
A critical damping approach for assessing the role of marrow fat on the mechanical strength of trabecular bone
No full textSeveral clinical findings revealed that post-menopausal osteoporosis and age-related osteopenia are
accompanied by trabecular bone marrow fat (BMF) increase. To help understand this phenomenon, a vibrating string
model is proposed, based on the hypothesis that, when bone marrow properties change, the trabecular bone structure
remodels itself to preserve its critical damping state. It is found that an inverse relationship holds between trabecular
average length and marrow damping coefficient. Such a result leads us to hypothesize the following bone-weakening
mechanism. Since fat-rich bone marrow is a worse damper, a BMF increment causes an increase of trabecular average
length, which is accomplished by the absorption of horizontal trabeculae (structurally less important than vertical
trabeculae). The resulting bone patterns are in excellent agreement with clinical observations of osteoporotic bone. A
definitive confirmation of the proposed mechanism will support a therapeutical approach to widespread osteopenic
diseases aimed at avoiding, or limiting, BMF increase
"Rottura traumatica della testa protesica in ceramica in artroprotesi d'anca"
No full textThe authors describe breakage of the 32 mm alumina AL2 O3 ceramic head in 3 cases of total hip replacement using two different models of prosthesis (Charnley-Müller and Mittelmeier). All three patients were of average height, weight, and activity (Brown et al., 1985; Callaghan et al., 1988), and the breakage had been caused by an accidental fall. The same mechanism of injury, in people the same age as our subjects, can cause femoral neck fractures. Reoperation was necessary in order to replace the component. The implants all appeared to be positioned correctly, and the patients had reported no symptoms. Before the trauma that caused breakage, there had been no other injuries worth noting. All patients were satisfied with their hip replacements
Scanning electron microscopy of human cortical bone failure surfaces
No full textUndecalcified samples extracted from human femoral shafts are fractured by bending and the fracture surfaces are examined with a scanning electron microscope (SEM). The investigation is performed on both dry and wet (hydrated with a saline solution) specimens. SEM micrographs show patterns in many respects similar to those observed in fractography studies of laminated fiber reinforced synthetic composites. In particular, dry and wet samples behave like brittle and ductile matrix laminates, respec¬tively. An analysis carried out on the basis of the mechanisms that dominate the frac¬ture process of laminates shows that a reasonable cortical bone model is that of a lami¬nated composite material whose matrix is composed of extracellular noncollage¬nous calcified proteins, and the reinforcement is constituted by the calcified collagen fiber system
Tensile experiments and SEM fractography on bovine subchondral bone
No full textSubchondral bone undecalcified samples, extracted from bovine femoral heads, are subjected to a direct tensile load. The Young's modulus of each sample is determined from repeated tests within the elastic limit. In a last test, the tensile load is increased up to the specimen failure, determining the ultimate tensile strength. The investigation is performed on both dry and wet specimens. The measured Young's modulus for dry samples is 10.3 +/- 2.5 GPa, while that of wet samples is 3.5 +/- 1.2 GPa. The ultimate tensile strengths are 36 +/- 10 and 30 +/- 7.5 MPa for dry and wet specimens, respectively. SEM micrographs of failure surfaces show characteristic lamellar bone structures, with lamellae composed of calcified collagen fibers. Rudimentary osteon-like structures are also observed, Failure surfaces of wet samples show a marked fiber pull-out, while delamination predominates in dry samples. The obtained results are interpreted on the basis of the deformation mechanisms typical of fiber-reinforced laminated composite materials. (C) 2000 Elsevier Science Ltd. All rights reserved
Traumatic sacral fractures: navigation technique in instrumented stabilization.
No full textBackground: Sacral fractures are a challenge regarding treatment and classification. Surgical techniques using spinal navigation systems can improve treatment, especially if used in collaboration among different specialists. Methods: Between 2015 and 2017, we treated 25 consecutive cases of sacral fracture. Twelve patients (48%) underwent mechanical ventilation due to hypovolemic shock for severe thoracoabdominal trauma; bleeding was blocked with pelvic packing in 9 cases (36%) and transcatheter embolization in 2 cases (8%). External fixation was used in 7 cases (28%). In 20 cases (80%) spinal fractures were associated. All patients were operated on using spinal navigation by a team of neurosurgeons and orthopedic surgeons. Results: The mean time from first observation to surgery was 18 days (range 8–31). Surgical treatment consisted of iliosacral fixation in 19 cases (76%) and spinopelvic fixation in 6 cases (24%). The mean number of screws for spinopelvic fixation was 9.67 (range 6–17) with a mean operation time of 323.67 minutes (range 247–471); in iliosacral osteosynthesis the mean screw number was 1.37 (range 1–3) and mean surgical time was 78.93 minutes (range 61–130). Postoperative computed tomography showed the correct screw placement. Wound infection occurred in 2 cases (8%), managed with vacuum-assisted closure therapy; in 1 case (4%) a sacral screw was removed for decubitus. Conclusions: Navigation systems in instrumented spinopelvic and sacropelvic reconstruction provide greater safety, reducing learning times and malpositioning. Multidisciplinary management allows us to achieve optimal results, especially when the sacral fracture is combined with spinal and pelvic lesions. The use of navigation systems could represent an important advancement
An elastic compound tube model for a single osteon.
No full textA model is developed whereby the secondary osteon - the dominant microstruc¬tural com¬ponent of the cortical bone tissue - is consid¬ered as an n layered cylinder with internal stresses in linear isotropic elasticity. An exact solution is obtained for a loading condition represented by a tensile/compressive force. The length¬en¬ing, the side deforma¬tion, and the strain energy of the system are explicitly calculated. The behavior of the main elastic quan¬tities is illus¬trated by graphs. In particular, the impor¬tant role played by the parity of the number of lamellae is revealed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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