Even a thin layer of soft tissue may compromise the primary stability of cementless hip stems

Viceconti, Marco; Monti, Luisa; Muccini, Roberto; Bernakiewicz, Marek; Toni, Aldo

doi:10.1016/s0268-0033(01)00052-3

Cited by 65 publications

(40 citation statements)

References 30 publications

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“…Compared with the solution obtained by imposing displacement congruency at the nodes shared by implant and bone meshes, the difference in micromotion was less than 2 gm. The fibrous condition was modelled with the contact stiffness relaxation technique (CSR), a method described and validated in a previous study (VICECONTI et al, 2001). in particular, a contact 1 stiffness of 15 N mm-was foundto produce the structural effects of a 500 gm gap filled with soft tissue (VICECONTI et al, 2001).…”

Section: Methodsmentioning

confidence: 99%

“…From the observations made in vivo or ex vivo, low micromotion favours bonding (KIENAPFEL et al, 1999;VICECONTI et al, 2001). At the same time, however, such interface bonding can be disrupted if the interface stresses are excessive (debonding) (KIENAPFEL et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

“…At the same time, however, such interface bonding can be disrupted if the interface stresses are excessive (debonding) (KIENAPFEL et al, 1999). in addition, where the micromotion is higher than a threshold, or the bone-implant gap becomes too high, the bone tissue near the implant differentiates into a fibrous tissue (fibrous differentiation) (KIENAPFEL et al, 1999), which is too weak to provide mechanical support to the implant (VICECONTI et al, 2001). These last two processes, suspected to be fundamental in the clinical failure of total hip replacements, are neglected in all the models proposed so far.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of the initial implant fitting on the predicted secondary stability of a cementless stem

Viceconti

Pancanti

Dotti

et al. 2004

Med. Biol. Eng. Comput.

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A numerical model able to investigate the influence of biomechanical factors on the long-term secondary stability of implants would be extremely useful for the design of new cementless prosthetic devices. A purely biomechanical model of osseo-integration has been developed, formulated as a rule-based adaptation scheme. Due to its complexity, the problem was divided into three steps: preliminary implementation of the model (proof of concept); implementation of the complete model and investigation of the model solution; and model validation. The paper describes the first of these three steps. The model was implemented as a discrete-states machine, and the few parameters required were derived from the literature. It was then applied to a real clinical case. The study was conducted using the frictional contact finite element model of a human femur implanted with a cementless anatomical stem. A stable solution was achieved after between three and 15 iterations for all initial positions considered. Similar initial conditions yielded similar final configurations. The model predicted all initial configurations, with the exception of a partial osseo-integration, ranging between 62% (distal fit) and 78% (proximal fit) of the viable interface. This is in good agreement with the values reported in the literature that never exceed 75%, even in the best conditions, and report better clinical results for proximal fit. For the varus configuration, which lacks cortical support, the algorithm predicted a completed loosening.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of the initial implant fitting on the predicted secondary stability of a cementless stem

Viceconti

Pancanti

Dotti

et al. 2004

Med. Biol. Eng. Comput.

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“…in a previous study, we found that the value of 0.32 minimised the deviation from experimental measurements of bone-implant micromotion (VICECONTI et al, 2000). From a biomechanical point of view, the presence of a layer of soft tissue between the bone and the metal is equivalent to the presence of an empty gap (VICECONTI et al, 2000) between bone and implant (VICECONTI et al, 2001). Thus we can assume that the coefficient of friction for the fibrous condition is nearly zero.…”

Section: Identification Of the Parametersmentioning

confidence: 81%

Numerical model to predict the longterm mechanical stability of cementless orthopaedic implants

Viceconti

Ricci

Pancanti

et al. 2004

Med. Biol. Eng. Comput.

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The objective of this research was to develop a purely biomechanical model, intended to predict the long-term secondary stability of the implant starting from the biomechanical stability immediately after the operation. A continuous rule-based adaptation scheme was formulated as a dynamic system, and the work verified if such a model produced unique and clinically meaningful solutions. It also investigated whether this continuous model provided results comparable with those of a simpler, discrete-states model used in a previous study. The proposed model showed stable convergence behaviour with all investigated initial conditions, with oscillatory behaviour limited to the first steps of the simulation. The results obtained with the wide range of initial conditions support the hypothesis of the existence and uniqueness of the solution for all initial conditions. The differences between the continuous model and the simpler and more efficient finite-states model were found to be extremely modest (less than 4% over the predicted bonded area). Because of these minimal differences, the use of the much faster finite-states model is recommended to investigate asymptotic conditions, and the continuous model described should be used to investigate the evolution over time of the adaptive process.

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“…Finally, more detailed models on bone resorption (Boyle and Kim, 2011a, b;Weinans et al, 1992a;Weinans et al, 1992b) and implant stability (Abdul-Kadir et al, 2008;Viceconti et al, 2006;Viceconti et al, 2001;Viceconti et al, 2000) could be used to assess both the short and long term performance of the implant.…”

mentioning

confidence: 99%

Fatigue design of a mechanically biocompatible lattice for a proof-of-concept femoral stem

Khanoki

Pasini

2013

Journal of the Mechanical Behavior of Biomedical Materials

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A methodology is proposed to design a spatially periodic microarchitectured material for a twodimensional femoral implant under walking gait conditions. The material is composed of a graded lattice with controlled property distribution that minimizes concurrently bone resorption and interface failure. The periodic microstructure of the material is designed for fatigue fracture caused by cyclic loadings on the hip joint as a result of walking. The bulk material of the lattice is Ti6AL4V and its microstructure is assumed free of defects. The Soderberg diagram is used for the fatigue design under multiaxial loadings. Two cell topologies, square and Kagome, are chosen to obtain optimized property gradients for a two-dimensional implant. Asymptotic homogenization (AH) theory is used to address the multiscale mechanics of the implant as well as to capture the stress and strain distribution at both the macro and the microscale. The microstress distribution found with AH is also compared with that obtained from a detailed finite element analysis. For the maximum value of the von Mises stress, we observe a deviation of 18.6 % in unit cells close to the implant boundary, where the AH assumption of spatial periodicity of the fluctuating fields ceases to hold. In the second part of the paper, the metrics of bone resorption and interface shear stress are used to benchmark the graded cellular implant with existing prostheses made of fully dense titanium implant.The results show that the amount of initial postoperative bone loss for square and kagome lattice implants decreases, respectively, by 53.8% and 58%. In addition, the maximum shear interface failure at the distal end is significantly reduced by about 79%.A set of proof-of-concepts of planar implants have been fabricated via Electron Beam Melting (EBM) to demonstrate the manufacturability of Ti6AL4V into graded lattices with alternative cell size. Optical microscopy has been used to measure the morphological parameters of the cellular microstructure, including cell wall thickness and pore size, and compared them with the nominal values. No sign of fracture or incomplete cell walls was observed, an assessment that shows the satisfactory metallurgical bond of cell walls and the structural integrity of the implants.

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Even a thin layer of soft tissue may compromise the primary stability of cementless hip stems

Cited by 65 publications

References 30 publications

Effect of the initial implant fitting on the predicted secondary stability of a cementless stem

Effect of the initial implant fitting on the predicted secondary stability of a cementless stem

Numerical model to predict the longterm mechanical stability of cementless orthopaedic implants

Fatigue design of a mechanically biocompatible lattice for a proof-of-concept femoral stem

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