The effect of bone growth onto massive prostheses collars in protecting the implant from fracture

Fromme, Paul; Blunn, Gordon; Aston, William; Abdoola, Tasneem; Koris, Jacob; Coathup, Melanie

doi:10.1016/j.medengphy.2016.12.007

Cited by 23 publications

(28 citation statements)

References 34 publications

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“…An FEA study to understand the effects of extracortical bone formation on stresses in the intramedullary stem found an 80% decrease in stress concentration due to bone growth, protecting the implant from failure at the stem-collar interface. 12 Recent advancements in additive manufacturing enable implant scaffold designs with extensive interface connectivity to enhance bone growth into porous structures, improving stability and fixation. 18,30,33 An in vivo study compared the outcomes of selective laser sintered (SLS) porous and machined grooved collars in segmental prostheses and found that porous designs had higher osseointegration.…”

Section: Introductionmentioning

confidence: 99%

Partial Bone Formation in Additive Manufactured Porous Implants Reduces Predicted Stress and Danger of Fatigue Failure

et al. 2019

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New porous implant designs made possible by additive manufacturing allow for increased osseointegration, potentially improving implant performance and longevity for patients that require massive bone implants. The aim of this study was to evaluate how implantation and the strain distribution in the implant affect the pattern of bone ingrowth and how changes in tissue density within the pores alter the stresses in implants. The hypothesis was that porous metal implants are susceptible to fatigue failure, and that this reduces as osteointegration occurs. A phenomenological, finite element analysis (FEA) bone remodelling model was used to predict partial bone formation for two porous (pore sizes of 700 μm and 1500 μm), laser sintered Ti6Al4V implants in an ovine condylar defect model, and was compared and verified against in vivo, histology results. The FEA models predicted partial bone formation within the porous implants, but over-estimated the amount of bone-surface area compared to histology results. The stress and strain in the implant and adjacent tissues were assessed before, during bone remodelling, and at equilibrium. Results showed that partial bone formation improves the stress distribution locally by reducing stress concentrations for both pore sizes, by at least 20%. This improves the long-term fatigue resistance for the larger pore implant, as excessively high stress is reduced to safer levels (86% of fatigue strength) as bone forms. The stress distribution only changed slightly in regions without bone growth. As the extent of bone formation into extensively porous bone implants depends on the level of stress shielding, the design of the implant and stiffness have significant influence on bone integration and need to be considered carefully to ensure the safety of implants with substantial porous regions. To our knowledge this is the first time that the effect of bone formation on stress distribution within a porous implant has been described and characterised.

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Section: Introductionmentioning

confidence: 99%

Partial Bone Formation in Additive Manufactured Porous Implants Reduces Predicted Stress and Danger of Fatigue Failure

et al. 2019

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“…Finite element analysis (FEA) showed that this improved bone ingrowth results in a reduction in fracture risk of the implant stem, and a more natural stress distribution to the bone [2,4].…”

Section: Introductionmentioning

confidence: 99%

Novel adaptive finite element algorithms to predict bone ingrowth in additive manufactured porous implants

Cheong

Fromme

Mumith

et al. 2018

Journal of the Mechanical Behavior of Biomedical Materials

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Bone loss caused by stress shielding of metallic implants is a concern, as it can potentially lead to long-term implant failure. Surface coating and reducing structural stiffness of implants are two ways to improve bone ingrowth and osteointegration. Additive manufacturing, through selective laser sintering (SLS) or electron beam melting (EBM) of metallic alloys, can produce porous implants with bone ingrowth regions that enhance osteointegration and improve clinical outcomes. Histology of porous Ti6Al4V plugs of two pore sizes with and without electrochemically deposited hydroxyapatite coating, implanted in ovine condyles, showed that bone formation did not penetrate deep into the porous structure, whilst significantly increased bone growth along coated pore surfaces (osteointegration) was observed. Finite Element simulations, combining new algorithms to model bone ingrowth and the effect of surface modification on osteoconduction, were verified with the histology results. The results showed stress shielding of porous implants made from conventional titanium alloy due to material stiffness and implant geometry, limiting ingrowth and osteointegration. Simulations for reduced implant material stiffness predicted increased bone ingrowth. For low modulus Titanium-tantalum alloy (Ti-70%Ta), reduced stress shielding and enhanced bone ingrowth into the porous implant was found, leading to improved mechanical interlock. Algorithms predicted osteoconductive coating to promote both osteointegration and bone ingrowth into the inner pores when they were coated. These new Finite Element algorithms show that using implant materials with lower elastic modulus, osteoconductive coatings or improved implant design could lead to increased bone remodelling that optimises tissue regeneration, fulfilling the potential of enhanced porosity and complex implant designs made possible by additive layer manufacturing techniques.

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“…A cylindrical model was used to illustrate the development of the enhanced computational algorithm, and determine the effects initial density, choice of averaging, and time steps have on the distribution, stability and accuracy of the result. The model was applied to predict extracortical bone growth around a full sized segmental prosthesis, and compared against radiographs of an implanted segmental prosthesis in a 2 years follow-up (Fromme et al 2017). This is the first work to develop an adaptive model for extracortical bone growth around implants in 3D, accounting for the process of growth observed clinically.…”

Section: Near Here]mentioning

confidence: 99%

“…A 1x1x1 mm grooved, 18mm tall collar was modelled as one piece with the stem. A 1mm gap separates the bone/cement and the distal end of the collar as observed in radiographical images (Fromme et al 2017). The soft tissue envelope was modelled as 40mm tall, with a diameter of 42mm and 45⁰ and 59⁰…”

Section: Application To Segmental Prosthesismentioning

confidence: 99%

“…Young patients who receive segmental prostheses after the surgical removal of bone cancer require implants that last through their growth phase and into adult life, but aseptic loosening is the primary mode of implant failure (Unwin et al 1996). Using finite element (FE) method to analyse the effects of implant on bone remodelling, the common approaches are to conduct static stress analysis at different stages of follow-up (Galloway et al 2013, Fromme et al 2017, model changes in the density of existing bone adjacent to an implant (Tomaszewski et al 2012), the healing of the defect (gap) around the implant stem, or ingrowth of bone onto the surface of the implant stem, (Dickinson et al 2012, Tarala et al 2011. To verify results, clinical radiographs are often compared qualitatively with FE predictions, due to difficulties in validating the density of the bone (Tomaszewski et al 2012, Dickinson et al 2012.…”

Section: Introductionmentioning

confidence: 99%

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A novel adaptive algorithm for 3D finite element analysis to model extracortical bone growth

Cheong

Blunn

Coathup

et al. 2018

Computer Methods in Biomechanics and Biomedical Engineering

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Extracortical bone growth with osseointegration of bone onto the shaft of massive bone tumour implants is an important clinical outcome for long-term implant survival. A new computational algorithm combining geometrical shape changes and bone adaptation in 3D Finite Element simulations has been developed, using a soft tissue envelope mesh, a novel concept of osteoconnectivity, and bone remodelling theory. The effects of varying the initial tissue density, spatial influence function and time step were investigated. The methodology demonstrated good correspondence to radiological results for a segmental prosthesis.

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The effect of bone growth onto massive prostheses collars in protecting the implant from fracture

Cited by 23 publications

References 34 publications

Partial Bone Formation in Additive Manufactured Porous Implants Reduces Predicted Stress and Danger of Fatigue Failure

Partial Bone Formation in Additive Manufactured Porous Implants Reduces Predicted Stress and Danger of Fatigue Failure

Novel adaptive finite element algorithms to predict bone ingrowth in additive manufactured porous implants

A novel adaptive algorithm for 3D finite element analysis to model extracortical bone growth

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