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  • 1
    Electronic Resource
    Electronic Resource
    New means in spinal pedicle hook fixation (1995)
    Springer
    European spine journal 4 (1995), S. 114-122 
    Details
    ISSN: 1432-0932
    Keywords: Thoracic spine ; Biomechanics ; Pedicle screw ; Pedicle hook ; Pull-out test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Pedicle hooks which are used as an anchorage for posterior spinal instrumentation may be subjected to considerable three-dimensional forces. In order to achieve stronger attachment to the implantation site, hooks using screws for additional fixation have been developed. The failure loads and mechanisms of three such devices have been experimentally determined on human thoracic vertebrae: the Universal Spine System (USS) pedicle hook with one screw, a prototype pedicle hook with two screws and the Cotrel-Dubousset (CD) pedicle hook with screw. The USS hooks use 3.2-mm self-tapping fixation screws which pass into the pedicle, whereas the CD hook is stabilised with a 3-mm set screw pressing against the superior part of the facet joint. A clinically established 5-mm pedicle screw was tested for comparison. A matched pair experimental design was implemented to evauluate these implants in constrained (series I) and rotationally unconstrained (series II) posterior pull-out tests. In the constrained tests the pedicle screw was the strongest implant, with an average pull-out force of 1650 N (SD 623 N). The prototype hook was comparable, with an average failure load of 1530 N (SD 414 N). The average pull-out force of the USS hook with one screw was 910 N (SD 243 N), not significantly different to the CD hook's average failure load of 740 N (SD 189 N). The result of the unconstrained tests were similar, with the prototype hook being the strongest device (average 1617 N, SD 652 N). However, in this series the difference in failure load between the USS hook with one screw and the CD hook was significant. Average failure loads of 792 N (SD 184 N) for the USS hook and 464 N (SD 279 N) for the CD hook were measured. A pedicular fracture in the plane of the fixation screw was the most common failure mode for USS hooks. The hooks usually did not move from their site of implantation, suggesting that they may be well-suited for the socalled segmental spinal correction technique as used in scoliosis surgery. In contrast, the CD hook disengaged by translating caudally from its site of implantation in all cases, suggesting a mechanical instability. The differences in observed hook failure modes may be a function of the type and number of additional fixation screws used. These results suggest that additional screw fixation allows stable attachment of pedicle hooks to their implantation site. Hooks using additional fixation screws passing obliquely into the pedicle apparently provide the most rigid attachment. The second fixation screw of the prototype hook almost doubles the fixation strength. Thus, the prototype hook might be considered as an alternative to the pepdicle screw, especially in the upper thoracic region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00278923
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  • 2
    Electronic Resource
    Electronic Resource
    Compressive strength of interbody cages in the lumbar spine: the effect of cage shape, posterior instrumentation and bone density (1998)
    Springer
    European spine journal 7 (1998), S. 132-141 
    Details
    ISSN: 1432-0932
    Keywords: Key words Spine ; Interbody ; Fusion ; Compression ; Biomechanics ; Implant ; Posterior ; lumbar intervertebral fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract One goal of interbody fusion is to increase the height of the degenerated disc space. Interbody cages in particular have been promoted with the claim that they can maintain the disc space better than other methods. There are many factors that can affect the disc height maintenance, including graft or cage design, the quality of the surrounding bone and the presence of supplementary posterior fixation. The present study is an in vitro biomechanical investigation of the compressive behaviour of three different interbody cage designs in a human cadaveric model. The effect of bone density and posterior instrumentation were assessed. Thirty-six lumbar functional spinal units were instrumented with one of three interbody cages: (1) a porous titanium implant with endplate fit (Stratec), (2) a porous, rectangular carbon-fibre implant (Brantigan) and (3) a porous, cylindrical threaded implant (Ray). Posterior instrumentation (USS) was applied to half of the specimens. All specimens were subjected to axial compression displacement until failure. Correlations between both the failure load and the load at 3 mm displacement with the bone density measurements were observed. Neither the cage design nor the presence of posterior instrumentation had a significant effect on the failure load. The loads at 3 mm were slightly less for the Stratec cage, implying lower axial stiffness, but were not different with posterior instrumentation. The large range of observed failure loads overlaps the potential in vivo compressive loads, implying that failure of the bone-implant interface may occur clinically. Preoperative measurements of bone density may be an effective tool to predict settling around interbody cages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005860050043
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of animal species and age on plate-induced vascular damage in cortical bone (1992)
    Springer
    Archives of orthopaedic and trauma surgery 111 (1992), S. 78-84 
    Details
    ISSN: 1434-3916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Plates used for fracture fixation produce vascular injury to the underlying cortical bone. During the recovery of the blood supply, temporary osteoporosis is observed as a result of Haversian remodeling of the necrotic bone. This process temporarily reduces the strength of the bone. We tackled the postulate that quantitative differences exist between animal species, and in different bones within the same species, due to variations in the relative importance of the endosteal and periosteal blood supplies. Using implants scaled to the size of the bone, we found comparable cortical vascular damage in the sheep and in the dog, and in the tibia and femur of each animal. We observed a significant reduction in cortical vascular damage using plates that had a smaller contact area with the underlying bone. No significant difference in cortical vascular damage was noted in animals of different ages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00443472
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  • 4
    Electronic Resource
    Electronic Resource
    Incidence and Direct Medical Costs of Hospitalizations due to Osteoporotic Fractures in Switzerland (1997)
    Springer
    Osteoporosis international 7 (1997), S. 414-425 
    Details
    ISSN: 1433-2965
    Keywords: Key words: Epidemiology; Fractures; Hospital costs; Incidence; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract: The objective of this study was to estimate the annual direct medical costs of hospitalizations due to osteoporotic fractures in Switzerland. Days of hospital stay in 1992 were quantified using the casuistic of the medical statistics department of VESKA (Vereinigung Schweizerischer Krankenhäuser, the Swiss Hospital Association), which covers 43% of all hospital beds of that country. Number and incidence of total hospitalizations due to fractures were calculated by extrapolating to 100% the 43% VESKA-selected sample. To estimate number and incidence of hospitalizations due to osteoporotic fractures, internationally accepted age-specific osteoporosis attribution rates were applied. According to the latter the probability of a fracture being causes by osteoporosis increases with age. Mean length of stay for all fractures was calculated (= total hospital days divided by number of cases). By multiplying these mean lengths of stay by the number of osteoporosis-related fracture cases, the number of bed-days due to osteoporotic fractures was calculated. To compare the direct medical costs of hospitalization due to osteoporosis with those due to other frequent diseases, days of hospital stay caused by chronic obstructive pulmonary disease (COPD), stroke, acute myocardial infarction and breast cancer were estimated using the same methodology. A total estimate of 63 170 (f: 33 596, m: 29 574) hospitalizations due to fractures (and other osteoporosis-related diagnoses) was calculated, thus leading to overall annual incidence rates of hospitalizations for fractures of 950/100 000 women and 877/100 000 men. In women, 548 615 hospital days were found to be caused by osteoporosis, 353 654 days by COPD, 352 062 days by stroke, 200 669 days by breast carcinoma and 131 331 days by myocardial infarction. In men, COPD caused more hospitalization days (537 164) than myocardial infarction (196 793), stroke (180 524) or osteoporosis (152 857). Taking a mean price for a hospital day in Switzerland of 845 Swiss francs, the annual costs of acute hospitalizations due to osteoporosis and its complications were approximately 600 million Swiss francs (f: 464, m: 130 million Swiss francs) in 1992. We conclude that there is enough economic evidence to justify wide-scale interventions against osteoporosis in Switzerland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00004149
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  • 5
    Electronic Resource
    Electronic Resource
    Bone mineral density in young women with long-standing amenorrhea: Limited effect of hormone replacement therapy with ethinylestradiol and desogestrel (1994)
    Springer
    Osteoporosis international 4 (1994), S. 99-103 
    Details
    ISSN: 1433-2965
    Keywords: Amenorrhea ; Bone mineral density ; Densitometry ; Desogestrel ; Ethinylestradiol ; Hormone replacement therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To assess bone mineral density (BMD) at different skeletal sites in women with hypothalamic or ovarian amenorrhea and the effect of estrogen-gestagen substitution on BMD we compared BMD of 21 amenorrheic patients with hypothalamic or ovarian amenorrhea with that of a control population of 123 healthy women. All amenorrheic patients were recruited from the outpatient clinic of the Division of Gynecological Endocrinology at the University of Berne, a public University Hospital. One hundred and twenty-three healthy, regularly menstruating women recruited in the Berne area served as a control group. BMD was measured using dual-energy X-ray absorptiometry (DXA). At each site where it was measured, mean BMD was lower in the amenorrheic group than in the control group. Compared with the control group, average BMD in the amenorrheic group was 85% at lumbar spine (p〈0.0001), 92% at femoral neck (p〈0.02), 90% at Ward's triangle (p〈0.03), 92% at tibial diaphysis (p〈0.0001) and 92% at tibial epiphysis (p〈0.03). Fifteen amenorrheic women received estrogen-gestagen replacement therapy (0.03 mg ethinylestradiol and 0.15 mg desogestrel daily for 21 days per month), bone densitometry being repeated within 12–24 months. An annual increase in BMD of 0.2% to 2.9% was noted at all measured sites, the level of significance being reached at the lumbar spine (p〈0.0012) and Ward's triangle (p〈0.033). In conclusion BMD is lower in amenorrheic young women than in a population of normally menstruating, age-matched women in both mainly trabecular (lumbar spine, Ward's triangle, tibial epiphysis) and mainly cortical bone (femoral neck, tibial diaphysis). In these patients, hormone replacement therapy resulted in a limited recovery of BMD. Therefore, early hormone replacement therapy is mandatory for young amenorrheic women to minimize bone loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01623232
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    Paper (German National Licenses)
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