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  • 1
    Language: English
    In: Journal of Biomechanics, 15 March 2013, Vol.46(5), pp.949-955
    Description: Stem–cement and cement–bone interfacial failures as well as cement fractures have been noted in cemented total hip arthroplasty (THA) as the cause of aseptic loosening. Attempts to reduce the risk of femoral component loosening include improving the stem–cement interface by various coatings, using a textured or porous coated stem surfaces or by using a tapered stem having a highly-polished surface. The latter approach, often referred to as “force-closed” femoral stem design, would theoretically result in stem stabilization subsequent to debonding and ‘taper-lock’. Previous work using three-dimensional finite element analysis has shown a state of stress at the stem–cement interface indicative of ‘taper-lock’ for the debonded stem and indicated that stem–cement interface friction and bone cement creep played a significant role in the magnitudes of stresses and subsidence of the stem. However, the previous analysis did not include the viscoelastic properties of bone, which has been hypothesized to permit additional expansion of the bone canal and allow additional stem subsidence ( ). The goal of this study was to investigate the effect of bone viscoelastic behavior on stem subsidence using a 3D finite element analysis. It was hypothesized that the viscoelastic behavior of bone in the hoop direction would allow expansion of the bone reducing the constraint on bone over time and permit additional stem subsidence, which may account for the discrepancies between predicted and clinical subsidence measurements. Analyses were conducted using physiological loads, ‘average peak loads’ and ‘high peak loads’ for ‘normal patient’ and ‘active patient’ ( ) from which short and long term subsidence was predicted. Results indicated that bone creep does contribute to higher stem subsidence initially and after 10 years of simulated loading. However, it was concluded that the “constraint” upon the cement mantle is not mitigated enough to result in stem subsidence equivalent to that observed clinically.
    Keywords: Cemented Total Hip Arthroplasty ; Cortical Bone Creep ; Bone Cement Creep ; Stem Subsidence ; Stem–Cement Interface Failure ; Medicine ; Engineering ; Anatomy & Physiology
    ISSN: 0021-9290
    E-ISSN: 1873-2380
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  • 2
    Language: English
    In: Osteoarthritis and Cartilage, April 2018, Vol.26, pp.S291-S291
    Keywords: Medicine
    ISSN: 1063-4584
    E-ISSN: 1522-9653
    Source: ScienceDirect Journals (Elsevier)
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  • 3
    Language: English
    In: Journal of Biomechanics, 2001, Vol.34(10), pp.1325-1333
    Description: The clinical success of polished tapered stems has been widely reported in numerous long term studies. The mechanical environment that exists for polished tapered stems, however, is not fully understood. In this investigation, a collarless, tapered femoral total hip stem with an unsupported distal tip was evaluated using a ‘physiological’ three-dimensional (3D) finite element analysis. It was hypothesized that stem–cement interface friction, which alters the magnitude and orientation of the cement mantle stress, would subsequently influence stem ‘taper-lock’ and viscoelastic relaxation of bone cement stresses. The hypothesis that creep-induced subsidence would result in increases to stem–cement normal (radial) interface stresses was also examined. Utilizing a viscoelastic material model for the bone cement in the analysis, three different stem–cement interface conditions were considered: debonded stem with zero friction coefficient ( μ =0) (frictionless), debonded stem with stem–cement interface friction ( μ =0.22) (‘smooth’ or polished) and a completely bonded stem (‘rough’). Stem roughness had a profound influence on cement mantle stress, stem subsidence and cement mantle stress relaxation over the 24-h test period. The frictionless and smooth tapered stems generated compressive normal stress at the stem–cement interface creating a mechanical environment indicative of ‘taper-lock’. The normal stress increased with decreasing stem–cement interface friction but decreased proximally with time and stem subsidence. Stem subsidence also increased with decreasing stem–cement interface friction. We conclude that polished stems have a greater potential to develop ‘taper-lock’ fixation than do rough stems. However, subsidence is not an important determinant of the maintenance of ‘taper-lock’. Rather subsidence is a function of stem–cement interface friction and bone cement creep.
    Keywords: Total Hip Replacement ; Finite Element Analysis ; Bone Cement ; Debonding ; Creep ; Medicine ; Engineering ; Anatomy & Physiology
    ISSN: 0021-9290
    E-ISSN: 1873-2380
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  • 4
    Language: English
    In: Journal of Biomechanical Engineering, Feb, 2006, Vol.128(1), p.13(5)
    Description: Cementless total hip femoral components rely on press-fit for initial stability and bone healing and remodeling for secondary fixation. However, the determinants of satisfactory press-fit are not well understood. In previous studies, human cortical bone loaded circumferentially to simulate press-fit exhibited viscoelastic, or time dependent, behavior. The effect of bone viscoelastic behavior on the initial stability of press-fit stems is not known. Therefore, in the current study, push-out loads of cylindrical stems press-fit into reamed cadaver diaphyseal femoral specimens were measured immediately after assembly and 24 h with stem-bone diametral interference and stem surface treatment as independent variables. It was hypothesized that stem-bone interference would result in a viscoelastic response of bone that would decrease push-out load thereby impairing initial press-fit stability. Results showed that push-out load significantly decreased over a 24 h period due to bone viscoelasticity. It was also found that high and low push-out loads occurred at relatively small amounts of stem-bone interference, but a relationship between stem-bone interference and push-out load could not be determined due to variability among specimens. On the basis of this model, it was concluded that press-fit fixation can occur at relatively low levels of diametral interference and that stem-bone interference elicits viscoelastic response that reduces stem stability over time. From a clinical perspective, these results suggest that there could be large variations in initial press-fit fixation among patients. [DOI: 10.1115/1.2133766]
    Keywords: Compact Bone -- Physiological Aspects ; Compact Bone -- Analysis ; Internal Fixation -- Analysis ; Viscoelasticity -- Observations
    ISSN: 0148-0731
    E-ISSN: 15288951
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  • 5
    Language: English
    In: Journal of Biomechanics, 1988, Vol.21(10), pp.856-856
    Keywords: Medicine ; Engineering ; Anatomy & Physiology
    ISSN: 0021-9290
    E-ISSN: 1873-2380
    Source: ScienceDirect Journals (Elsevier)
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  • 6
    In: Journal of Biomechanical Engineering, August, 1996, Vol.118(3), p.399(6)
    Description: A tapered femoral total hip stem with a debonded stem-cement interface and an unsupported distal tip subjected to constant axial load was evaluated using two-dimensional (2D) axisymmetric finite element analysis. The analysis was performed to test if the mechanical condition suggest that a "taper-lock" with a debonded viscoelastic bone cement might be an alternative approach to cement fixation of stem type cemented hip prosthesis. Effect of stem-cement interface conditions (bonded, debonded with and without friction) and viscoelastic response (creep and relaxation) of acrylic bone cement on cement mantle stresses and axial displacement of the stem was also investigated. Stem debonding with friction increased maximum cement von Mises stress by approximately 50 percent when compared to the bonded stem. Of the stress components in the cement mantle, radial stresses were compressive and hoop stresses were tensile and were indicative of mechanical taper-lock. Cement mantle stress, creep and stress relaxation and stem displacement increased with increasing load level and with decreasing stem-cement interface friction. Stress relaxation occur predominately in tensile hoop stress and decreased from 1 to 46 percent over the conditions considered. Stem displacement due to cement mantle creep ranged from 614 [[micro]meter] to 1.3 [[micro]meter] in 24 hours depending upon interface conditions and load level.
    Keywords: Finite Element Method -- Usage ; Hip -- Models
    ISSN: 0148-0731
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  • 7
    Language: English
    In: Journal of Biomechanics, 1979, Vol.12(8), pp.628-628
    Keywords: Medicine ; Engineering ; Anatomy & Physiology
    ISSN: 0021-9290
    E-ISSN: 1873-2380
    Source: ScienceDirect Journals (Elsevier)
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  • 8
    Language: English
    In: The Journal of Arthroplasty, October 2000, Vol.15(7), pp.921-927
    Description: Sixteen paired human cadaver femora were prepared using conventional broaches. Cancellous bone was irrigated with 1 L pulsed lavage in one femur and 1 L syringe lavage in the contralateral femur. The specimens were embedded in specially designed pots, and vacuum-mixed bone-cements were applied in a retrograde manner. After application of a standard pressure to the pots, the femora were removed and radiographed, and horizontal sections were obtained and analyzed to assess cement penetration into cancellous bone and the ratio of the area of supported to unsupported cancellous bone (Rcb). Our results show that in equal quality bone, the use of jet lavage yields significantly ( 〈.0001) improved cement penetration and Rcb compared with syringe lavage specimens. Jet lavage should be considered routine to achieve interdigitation with cancellous bone in cemented total hip arthroplasty.
    Keywords: Total Hip Arthroplasty ; Bone-Cementing Technique ; Cement Mantle ; Lavage ; Broach Design
    ISSN: 0883-5403
    E-ISSN: 1532-8406
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  • 9
    Language: English
    In: Bone, 1989, Vol.10(3), pp.223-233
    Description: Studies demonstrate that geometric changes in bone architecture in response to altered mechanical strain occur through the formation of woven bone. The goal of this study was to test the hypothesis that these changes are partly the result of surgical manipulation rather than a true adaptive response to altered strain. Beagle dogs were subjected to either an ulnar osteotomy, an osteotomy with plate fixation, or sham operation. Strains on the radius were measured just prior to sacrifice 1, 3 or 6 months after surgery. Our results support the idea that woven bone can be a normal response to an abnormal strain environment if the mechanical challenge is intense enough; that elevated mechanical strains can cause the endocortical bone envelope to revert to a state of net formation; and that "adaptive remodeling" in adults in response to a change in mechanical strain may be a special case of modeling in which resorption is not required prior to formation at a particular skeletal site.
    Keywords: Strain ; Woven Bone ; Bone Remodeling ; Dogs ; Medicine ; Anatomy & Physiology
    ISSN: 8756-3282
    E-ISSN: 1873-2763
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  • 10
    Language: English
    In: Bone, 1989, Vol.10(3), pp.215-221
    Description: This study defines the alteration in bone tissue kinetics responsible for the "adaptive remodeling" response to altered strain environments. Adult beagle dogs were separated into three experimental groups: ulnar osteotomy, ulnar osteotomy with fracture fixation plate spanning the gap and sham surgery. Four sets of double fluorochrome labels were administered. Prior to sacrifice at 1, 3, and 6 months, strains were measured through rosette strain gages on the cranial and caudal surfaces of the intact radius. Histomorphometric analysis indicated that the increased bone mass in response to elevated strain results from increased activation frequency of modeling with more sites undergoing formation processes than resorption processes on periosteal and endocortical surfaces. Increased remodeling activation did not lead to increased bone mass. There was no evidence that elevated strain changes the individual vigor of osteoclasts or osteoblasts, or that the sigma period was altered by elevated strain.
    Keywords: Strain ; Bone Kinetics ; Remodeling ; Dogs ; Medicine ; Anatomy & Physiology
    ISSN: 8756-3282
    E-ISSN: 1873-2763
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