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  • 1
    Electronic Resource
    Electronic Resource
    Impact near the hip dominates fracture risk in elderly nursing home residents who fall (1993)
    Springer
    Calcified tissue international 52 (1993), S. 192-198 
    Details
    ISSN: 1432-0827
    Keywords: Hip fracture ; Falls ; Osteoporosis ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Hip fractures among the elderly are a significant and rapidly growing public health problem. The prevailing view is that most hip fractures are the consequence of age-related bone loss or osteoporosis. However, because over 90% of hip fractures are the result of falls, we have undertaken a falls surveillance study to determine if factors related to the mechanics of falling are associated with increased risk of hip fracture. Case subjects with hip fracture and control subjects without hip fracture were sampled from falls recorded at the Hebrew Rehabilitation Center for Aged, a chronic care facility. Fall information was obtained by interview of the subject and witnesses if the fall was witnessed. Data were analyzed by multiple logistic regression. Increased risk of hip fracture from a fall was associated with impacting on the hip or side of the leg and potential energy associated with the fall. Quetelet, or body mass index, was inversely related to fracture risk. The adjusted odds ratio of hip fracture for a fall involving impact on the hip region was 21.7 (95% confidence interval, 8.2–58). The potential energy associated with these falls was an order of magnitude greater than the average energy required to fracture elderly, cadaveric, proximal femurs in earlier in vitro experiments. We conclude, therefore, that a fall from standing height should no longer be considered minimal trauma but rather trauma of sufficient magnitude to pose a high risk of hip fracture if impact occurs on the hip and if energy-absorbing processes are inadequate. These new findings suggest that fall mechanics play an important role in the etiology of hip fracture among the elderly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298717
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  • 2
    Electronic Resource
    Electronic Resource
    The formation of propylene fumarate oligomers for use in bioerodible bone cement composites (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 973-985 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(propylene fumarate) (PPF) oligomers were synthesized by step polymerization using bis(2-hydroxypropyl fumarate) or propylene bis(hydrogen maleate) as starting materials. Oligomers possessing identical degrees of polymerization (DP), but varying in their end group character (either hydroxyl or carboxyl) were first prepared and characterized, then used as part of a bone cement preparation consisting of oligomer, tricalcium phosphate, calcium carbonate, and methyl methacrylate. Compressive strength of the resulting composite appeared to be dependent on both the degree of polymerization of the PPF, and the nature of the oligomers' end groups.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280503
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  • 3
    Electronic Resource
    Electronic Resource
    In vitro characterization and biomechanical optimization of a biodegradable particulate composite bone cement (1988)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 1071-1082 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We have developed a biodegradable particulate composite bone cement and used in vitro and in vivo methods for studying its suitability for orthopaedic applications. The composite matrix consists of gelatin, water, and sodium salicylate. The particulate phase is made up of powdered and particulate (355-600 μm diameter) tricalcium phosphate. Paraformaldehyde (0.1% to 0.5% by weight) is used as a matrix cross-linking agent. The effects of incubation time, particulate volume fraction, density of the individual particles, water content, concentration of crosslinking agent, and freeze-drying on the unconfined compressive strength and modulus of the particulate composite were measured. Compressive strengths of 7 MPa and moduli of 65 MPa could be achieved. Mechanical properties depended critically upon the water content of the particulate composite, with values of strength and modulus decreasing rapidly outside a range of 10-14% of specimen dry weight. High-density tri-calcium phosphate particulate produced cement with twice the strength found with porous particulate. In a companion study we document in vivo performance of this particulate composite in an animal model system.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820221110
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  • 4
    Electronic Resource
    Electronic Resource
    Ex vivo degradation of a poly(propylene glycol-fumarate) biodegradable particulate composite bone cement (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 35 (1997), S. 383-389 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We have developed a biodegradable particulate composite bone cement consisting of a poly(propylene glycolfumarate)-(methylmethacrylate) matrix mixed with calcium carbonate and tricalcium phosphate particulates. Previous ex vivo studies suggest that this system provides sufficient strength for a number of potential clinical applications including structural reinforcement of osseous defects, internal fixation devices for age-related fractures, and delivery of antibiotics to treat osteomyelitis. As a first step toward investigating in vivo responses to this material, we studied the influence of varied concentrations of crosslinker, accelerator, and free radical on the mechanical properties of the cement. We then developed an ex vivo degradation assay and correlated the mechanical properties of degrading cement with the temporal changes in chemical properties of both the cement and the bathing medium. The optimal cement formulation was composed of one-third poly(propylene glycol-fumarate)-(methylmethacrylate), one-third calcium carbonate, and one-third tricalcium phosphate, and provided initial compressive strengths of up to 30 MPa and compressive moduli of up to 300 MPa. Degradation rates, measured by a decline in mechanical properties, dissolution of calcium from the cement, and change in pH of the bathing medium, could be controlled by changing the concentration of reactants in the matrix. Specifically, an increase in methylmethacrylate or increase in both methylmethacrylate and benzoyl peroxide was inversely proportional to the rate of degradation and directly proportional to the initial mechanical properties. The degradation products and environmental changes appear to be compatible with physiologic remodeling and therefore justify examination of the in vivo response to implantation of this material. © 1997 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    In vivo histologic and biomechanical characterization of a biodegradable particulate composite bone cement (1989)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 23 (1989), S. 1-16 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A biodegradable particulate composite bone cement consisting of a crosslinked gelatin matrix and tricalcium phosphate particles was implanted intraosseously in rabbits for up to 12 weeks. Cured cylindrical implants were inserted in holes drilled in the proximal tibial metaphysis. Sequential fluorochrome labeling and radiographs were done, and specimens were processed for decalcified and nondecalcified histology. At 4 weeks, the cross-sectional diameter of the implant was slightly greater than at implantation. There was considerable dissolution of the matrix and some new bone ingrowth. At 12 weeks, the diameter was reduced to half the original diameter and bone had grown throughout the matrix. In the distal femur, freshly mixed cement was used to stabilize an osteochondral fracture. Mechanical testing of the cement-stabilized fracture revealed a decrease in compressive strength and modulus at 4 weeks followed by an increase to greater than initial values at 12 weeks. Over time, the osteochondral fragment subsided into the underlying cement, but the subsidence did not correlate with mechanical strength. This osteochondral fracture model permits measurement of the overall material properties of a cement simultaneously weakened by resorption and reinforced by ingrowing bone.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820230102
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  • 6
    Electronic Resource
    Electronic Resource
    Biomechanical optimization of a model particulate composite for orthopaedic applications (1986)
    Hoboken, NJ [u.a.] : Wiley-Blackwell
    Journal of Orthopaedic Research 4 (1986), S. 76-85 
    Details
    ISSN: 0736-0266
    Keywords: Particulate composites ; Bone augmentation ; Biocompatibility ; Biomaterials ; Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Particulate composites are a potential solution to the need for an injectable, biocompatible, resorbable material that could be used to reinforce fractures and defects in bone and temporarily to stabilize porous ingrowth prostheses. We have developed a model system for producing and testing particulate composites to determine if mechanical properties suitable for orthopaedic applications can be achieved. The experiments used bovine cortical bone and various forms of hydroxyapatite for the particulate phase and a collagen and particulate reinforced gelatin-resorcinol-formaldehyde (G-R-F) adhesive for the matrix phase. Using unconfined compression testing, we measured the effects of variation in particulate type, size, shape, and volume fraction on the material properties of the particulate composites. We found that compressive strengths greater than 10 MPa and compressive moduli greater than 100 MPa could be achieved in this model system. Rough and irregular particulates exhibited higher compressive strengths and moduli than smooth and spherical particulates. Mechanical properties were largely independent of particulate size in the range of 125-850 μm diameter. This model system suggests that, with the development of new biocompatible matrix materials, particulate composites with mechanical properties suitable for orthopaedic applications can be achieved.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jor.1100040109
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