Mechanical competence of bone-implant systems can accurately be determined by image-based micro-finite element analyses

Wirth, Andreas; Mueller, Timothy I.; Vereecken, Wim; Flaig, Cyril; Arbenz, Peter; Müller, Ralph; Lenthe, G. Harry van

doi:10.1007/s00419-009-0387-x

Cited by 36 publications

(31 citation statements)

References 46 publications

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“…In the cadaver study we found a good linear correlation between predicted and measured force at yield (R 2 ¼ 0.75, p¼0.003) and a weaker correlation for the force at pullout (R 2 ¼0.65, p¼0.009) within a VOI of 3 mm diameter, with an octahedral shear strain level of 0.5% and a highly strained bone volume fraction of 30%. A significant but weaker linear correlation was also found for (Wirth et al, 2010;Stadelmann et al, 2013). One possible explanation for this difference is probably due to our osteoporotic model with a load transfer from the comparatively small screws mainly into the cortices.…”

Section: Discussionmentioning

confidence: 72%

“…This way we eliminated one of the limitations of other microFE studies, which were based on in vivo microCT scans presenting metal artifact biased peri-implant bone structure (Wirth et al, 2010;Stadelmann et al, 2013). At the same time, the comparatively soft polymer screws did not allow us performing pullout tests for a validation of the model.…”

Section: Discussionmentioning

confidence: 99%

“…Bone failure was assumed to occur when a certain bone volume fraction within a predefined VOI exceeded a critical strain level. Instead of using an effective strain criterion as has been done in other studies (Wirth et al, 2010;Stadelmann et al, 2013;Pistoia et al, 2002), we have chosen an octahedral shear strain criterion as it has been shown to be a good predictor for the spatial distribution of microdamage within trabecular bone (Nagaraja et al, 2005). For the determination of the best failure criteria for forces at yield and pullout, we analyzed the microFE predicted reaction force at the points where a certain volume fraction of the bone within our pre-defined ROI (highly strained bone volume fraction) passed a certain level of γ oct .…”

Section: Identification Of the Failure Criteriamentioning

confidence: 99%

“…Simulation of the Pull-out: -Cylindric Constraint of the Sample -Vertical Screw Head Displacement The experimentally measured stiffness from the cadaver study was compared to the microFE predicted stiffness to test for a linear correlation and to determine a scaling factor as microFE is known to significantly overestimate the boneimplant stiffness (Wirth et al, 2010).…”

Section: Processed Microct Scanmentioning

confidence: 99%

“…One very promising approach to monitor implant fixation in vivo is a technique introduced by Wirth et al that combines microCT imaging with a micro-finite element (microFE) analysis for the investigation of the stability of bone-implant constructs (Wirth et al, 2010). This group demonstrated an excellent correlation between microFE predicted pull-out strength and measured pull-out strength in a cadaveric ovine vertebra model.…”

Section: Introductionmentioning

confidence: 99%

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Time course of bone screw fixation following a local delivery of Zoledronate in a rat femoral model – A micro-finite element analysis

Kettenberger

Latypova

Terrier

et al. 2015

Journal of the Mechanical Behavior of Biomedical Materials

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Hydrogel BisphosphonateScrew fixation microCT microFE a b s t r a c t A good fixation of osteosynthesis implants is crucial for a successful bone healing but often difficult to achieve in osteoporotic patients. One possible solution to this issue is the local delivery of bisphosphonates in direct proximity to the implants, A critical aspect of this method, that has not yet been well investigated, is the time course of the implant fixation following the drug release. Usual destructive mechanical tests require large numbers of animals to produce meaningful results. Therefore, a micro-finite element (microFE) approach was chosen to analyze implant fixation. In vivo micro computed tomography (microCT) scans were obtained, first weekly and later bi-weekly, after implantation of polymeric screws in the femoral condyles of ovariectomized rats. In one half of the animals, Zoledronate was released from a hydrogel matrix directly in the peri-implant bone stock, the other animals were implanted only with screws as control. The time course of the implant fixation was investigated with linear elastic microFE models that were created based on in vivo microCT scans. The numerical models were validated against experimental pullout-tests measurements in an additional cadaver study. The microFE analysis revealed a significant increase in force at yield of the Zoledronate treated group compared to the control group. The force of the treated group was 28% higher after 17 days of screw implantation, 42% higher after 31 days. The significant difference persisted until the end of the in vivo study at day 58 (po0.01). The early onset and prolonged duration of the implant anchorage improvement that was found in this study indicates the great potential of Zoledronate-loaded hydrogel for an enhancement of osteosynthesis implant fixation in impaired bone.

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Section: Discussionmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

Section: Identification Of the Failure Criteriamentioning

confidence: 99%

Section: Processed Microct Scanmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Time course of bone screw fixation following a local delivery of Zoledronate in a rat femoral model – A micro-finite element analysis

Kettenberger

Latypova

Terrier

et al. 2015

Journal of the Mechanical Behavior of Biomedical Materials

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Augmentation of peri‐implant bone improves implant stability: Quantification using simulated bone loss

Wirth

Müller

Lenthe

2011

Journal Orthopaedic Research

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Low bone quality, such as induced by osteoporosis, is considered a main factor leading to failure of fracture fixations. Periimplant bone augmentation has been proposed as a means of reducing failure rates in osteoporotic bone by improving implant stability. The beneficial effects of pharmacological augmentation of bone in the immediate vicinity of the implant have been demonstrated. Yet, a quantitative understanding of the role of peri-implant bone in implant stability is lacking. Therefore, the aim of our study was to quantify the effects of bone loss and peri-implant bone augmentation on implant stability using image-based finite element analyses. Using a validated model, we simulated how osteoporotic bone loss would affect implant stability in human humeral heads. We also quantified how augmentation of peri-implant bone can enhance implant stability. Our simulations revealed that a 30% reduction in bone mass led to a 50% decrease in implant stability. We also found that peri-implant bone augmentation increased implant stability and that the efficiency of bone augmentation decreased with increasing peri-implant distance. These findings highlight the strong effect that bone loss has on implant fixation and the potential of peri-implant bone augmentation for improving implant anchorage in low quality bone. Keywords: bone loss; peri-implant bone quality; bone augmentation; micro-finite element (micro-FE) analysis A large variety of implants and implant systems allows the successful treatment of even severe and complex fractures. These tools are becoming more important as the number of fractures grows due to the aging population, leading to higher numbers of elderly people with reduced bone quality, such as induced by osteoporosis.1 Experimental evidence shows that some of the most common implants used for internal fracture fixation have a markedly decreased performance when used in low quality bone.2 The mechanisms behind this phenomenon are still not fully understood and therefore a subject for current research.The proximal humerus is an anatomical site prone to osteoporotic fractures, and high complication rates caused by low bone quality have been reported with internal fracture fixation.3,4 Different approaches have been suggested to improve implant stability in such bone. Changes in the thread design of cancellous screws cause moderate enhancements in implant anchorage.5 Increasing implant diameter and length strongly improves implant stability. 6 Unfortunately, the maximum implant dimensions are to a large extent determined by bone size, which limits the feasibility of this approach for screws in the humeral head. The use of locking screws, which has led to a significant improvement in implant stability at other anatomical sites, has not fully solved the clinical problems for the humerus. 7,8 Therefore, as a complementary approach to changing implant design, the possibilities and merits of improving the bone's potential for implant anchorage has received attention. The benefits of bone augmentati...

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A novel in silico method to quantify primary stability of screws in trabecular bone

Steiner

Christen

Affentranger

et al. 2017

Journal Orthopaedic Research

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Insufficient primary stability of screws in bone leads to screw loosening and failure. Unlike conventional continuum finite-element models, micro-CT based finite-element analysis (micro-FE) is capable of capturing the patient-specific bone micro-architecture, providing accurate estimates of bone stiffness. However, such in silico models for screws in bone highly overestimate the apparent stiffness. We hypothesized that a more accurate prediction of primary implant stability of screws in bone is possible by considering insertion-related bone damage. We assessed two different screw types and loading scenarios in 20 trabecular bone specimens extracted from 12 cadaveric human femoral heads (N = 5 for each case). In the micro-FE model, we predicted specimen-specific Young's moduli of the peri-implant bone damage region based on morphometric parameters such that the apparent stiffness of each in silico model matched the experimentally measured stiffness of the corresponding in vitro specimen as closely as possible. The standard micro-FE models assuming perfectly intact peri-implant bone overestimated the stiffness by over 330%. The consideration of insertion related damaged peri-implant bone corrected the mean absolute percentage error down to 11.4% for both loading scenarios and screw types. Cross-validation revealed a mean absolute percentage error of 14.2%. We present the validation of a novel micro-FE modeling technique to quantify the apparent stiffness of screws in trabecular bone. While the standard micro-FE model overestimated the bone-implant stiffness, the consideration of insertion-related bone damage was crucial for an accurate stiffness prediction. This approach provides an important step toward more accurate specimen-specific micro-FE models. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2415-2424, 2017.

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Mechanical competence of bone-implant systems can accurately be determined by image-based micro-finite element analyses

Cited by 36 publications

References 46 publications

Time course of bone screw fixation following a local delivery of Zoledronate in a rat femoral model – A micro-finite element analysis

Time course of bone screw fixation following a local delivery of Zoledronate in a rat femoral model – A micro-finite element analysis

Augmentation of peri‐implant bone improves implant stability: Quantification using simulated bone loss

A novel in silico method to quantify primary stability of screws in trabecular bone

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