Biomechanical Robustness of a Contemporary Cementless Stem to Surgical Variation in Stem Size and Position

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Rami M. A. Al-Dirini ◽  
Dermot O'Rourke ◽  
Daniel Huff ◽  
Saulo Martelli ◽  
Mark Taylor
Keyword(s):  
Fibrous Tissue ◽  
Femoral Stem ◽  
Primary Stability ◽  
Bone Adaptation ◽  
Stair Climbing ◽  
Patient Specific ◽  
Fe Model ◽  
Bone Implant ◽  
Stem Size ◽  
Automated Method

Successful designs of total hip replacement (THR) need to be robust to surgical variation in sizing and positioning of the femoral stem. This study presents an automated method for comprehensive evaluation of the potential impact of surgical variability in sizing and positioning on the primary stability of a contemporary cementless femoral stem (Corail®, DePuy Synthes). A patient-specific finite element (FE) model of a femur was generated from computed tomography (CT) images from a female donor. An automated algorithm was developed to span the plausible surgical envelope of implant positions constrained by the inner cortical boundary. The analysis was performed on four stem sizes: oversized, ideal (nominal) sized, and undersized by up to two stem sizes. For each size, Latin hypercube sampling was used to generate models for 100 unique alignment scenarios. For each scenario, peak hip contact and muscle forces published for stair climbing were scaled to the donor's body weight and applied to the model. The risk of implant loosening was assessed by comparing the bone–implant micromotion/strains to thresholds (150 μm and 7000 με) above which fibrous tissue is expected to prevail and the periprosthetic bone to yield, respectively. The risk of long-term loosening due to adverse bone resorption was assessed using bone adaptation theory. The range of implant positions generated effectively spanned the available intracortical space. The Corail stem was found stable and robust to changes in size and position, with the majority of the bone–implant interface undergoing micromotion and interfacial strains that are well below 150 μm and 7000 με, respectively. Nevertheless, the range of implant positions generated caused an increase of up to 50% in peak micromotion and up to 25% in interfacial strains, particularly for retroverted stems placed in a medial position.

Statistical Analysis of Interfacial Gap in a Cementless Stem FE Model

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Youngbae Park ◽  
DonOk Choi ◽  
Deuk Soo Hwang ◽  
Yong-San Yoon
Keyword(s):  
Mechanical Stability ◽  
Femoral Stem ◽  
Primary Stability ◽  
Stair Climbing ◽  
Fe Model ◽  
Contact Ratio ◽  
Cementless Stem ◽  
Noticeable Effect ◽  
Significant Difference ◽  
Interfacial Gap

In cementless total hip arthroplasty, a fair amount of interfacial gap exists between the femoral stem and the bone. However, the effect of these gaps on the mechanical stability of the stem is poorly understood. In this paper, a finite element model with various interfacial gap definitions is used to quantify the effect of interfacial gaps on the primary stability of a Versys Fiber Metal Taper stem under stair climbing loads. In the first part, 500 random interfacial gap definitions were simulated. The resulting micromotion was approximately inversely proportional to the contact ratio, and the variance of the micromotion was greater with a lower contact ratio. Moreover, when the magnitude of the micromotion was compared between the gap definitions that had contact at a specific site and those that had no contact at that site, it was found that gaps located in the proximal-medial region of the stem surface had the most important effect on the micromotion. In a second trial, 17 gap definitions mimicking a gap pattern that has been observed experimentally were simulated. For a given contact ratio, the micromotion observed in the second trial was lower than the average result of those in the first, where the gaps were placed randomly. In either trial, when the contact ratio was higher than 40%, the micromotion showed no significant difference (first trial) or a gentle slope (−0.24μm∕% in the second trial) in relation to the contact ratio. Considering the reported contact ratios for properly implanted stems, variations in the amount of interfacial gap would not likely cause a drastic difference in micromotion, and this effect could be easily overshadowed by other clinical factors. In conclusion, differences in interfacial gaps are not expected to have a noticeable effect on the clinical micromotion of this cementless stem.

A three-dimensional finite element model from computed tomography data: A semi-automated method

2001 ◽  
Vol 215 (2) ◽  
pp. 203-212 ◽  
Author(s):  
P M Cattaneo ◽  
M Dalstra ◽  
L H Frich
Keyword(s):  
Computed Tomography ◽  
Finite Element ◽  
Three Dimensional ◽  
Patient Specific ◽  
Fe Model ◽  
Element Analysis ◽  
Automated Method ◽  
Bone Properties ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Three-dimensional finite element analysis is one of the best ways to assess stress and strain distributions in complex bone structures. However, accuracy in the results may be achieved only when accurate input information is given. A semi-automated method to generate a finite element (FE) model using data retrieved from computed tomography (CT) was developed. Due to its complex and irregular shape, the glenoid part of a left embalmed scapula bone was chosen as working material. CT data were retrieved using a standard clinical CT scanner (Siemens Somatom Plus 2, Siemens AG, Germany). This was done to produce a method that could later be utilized to generate a patient-specific FE model. Different methods of converting Hounsfield unit (HU) values to apparent densities and subsequently to Young's moduli were tested. All the models obtained were loaded using three-dimensional loading conditions taken from literature, corresponding to an arm abduction of 90°. Additional models with different amounts of elements were generated to verify convergence. Direct comparison between the models showed that the best method to convert HU values directly to apparent densities was to use different equations for cancellous and cortical bone. In this study, a reliable method of determining both geometrical data and bone properties from patient CT scans for the semi-automated generation of an FE model is presented.

Patient-specific design process and evaluation of a hip prosthesis femoral stem

2018 ◽  
Vol 42 (6) ◽  
pp. 271-290 ◽  
Author(s):  
Osama Abdelaal ◽  
Saied Darwish ◽  
Hassan El-Hofy ◽  
Yoshio Saito
Keyword(s):  
Load Transfer ◽  
Hip Prosthesis ◽  
Femoral Stem ◽  
Primary Stability ◽  
Patient Specific ◽  
Medical Implants ◽  
Element Analysis ◽  
Cross Sectional ◽  
Custom Implant ◽  
Metaphyseal Region

Introduction: There are several commercially available hip implant systems. However, for some cases, custom implant designed based on patient-specific anatomy can offer the patient the best available implant solution. Currently, there is a growing trend toward personalization of medical implants involving additive manufacturing into orthopedic medical implants’ manufacturing. Methods: This article introduces a systematic design methodology of femoral stem prosthesis based on patient’s computer tomography data. Finite element analysis is used to evaluate and compare the micromotion and stress distribution of the customized femoral component and a conventional stem. Results: The proposed customized femoral stem achieved close geometrical fit and fill between femoral canal and stem surfaces. The customized stem demonstrated lower micromotion (peak: 21 μm) than conventional stem (peak: 34 μm). Stress results indicate up to 89% increase in load transfer by conventional stem than custom stem because the higher stiffness of patient-specific femoral stem proximally increases the custom stem shielding in Gruen’s zone 7. Moreover, patient-specific femoral stem transfers the load widely in metaphyseal region. Conclusion: The customized femoral stem presented satisfactory results related to primary stability, but compromising proximo-medial load transfer due to increased stem cross-sectional area increased stem stiffness.

Load transfer in the proximal femur and primary stability of a cemented and uncemented femoral stem: An experimental study on cadaver femurs

2017 ◽  
Vol 231 (12) ◽  
pp. 1195-1203 ◽  
Author(s):  
Cathrine H Enoksen ◽  
Tina S Wik ◽  
Jomar Klaksvik ◽  
Astvaldur J Arthursson ◽  
Otto S Husby ◽  
...  
Keyword(s):  
Proximal Femur ◽  
Load Transfer ◽  
Femoral Stem ◽  
Primary Stability ◽  
The Elderly ◽  
Stair Climbing ◽  
Physiological Strain ◽  
Fixation Methods ◽  
Cemented Stem ◽  
Total Point

There are principally two fixation methods in total hip arthroplasty, cemented and uncemented. Both methods have in general good long-time survival. Studies comparing cemented and uncemented femoral stems indicate that the cemented stems perform somewhat better, at least in the elderly population. The aim of this study was to compare load transfer and the initial micromotion pattern for an uncemented and a cemented stem. A total of 12 human cadavers were tested in a hip simulator during single leg and stair climbing. Strain was measured on the proximal femur before and after implantation of the prostheses, and the values were presented as percentage of physiological strain. The micromovements between the stem and bone were measured and a total point motion was calculated. The results showed small statistically significant differences between the fixation methods, the largest difference being 8.1 percentage points. The uncemented stem had somewhat higher micromotion than the cemented stem, but less than 10 µm. Both stems thus had acceptable primary stability. The main finding of this study is the strain and micromotion pattern of a cemented and an uncemented stem of similar geometry is overall equal. There were small statistical significant differences between the two fixation methods regarding strain and micromotion levels. The differences are considered too small to be clinically relevant.

scholarly journals Evaluation of Bone–Implant Interface Stress and Strain Using Heterogeneous Mandibular Bone Properties Based on Different Empirical Correlations

2021 ◽  
Author(s):  
Mostafa Omran Hussein ◽  
Mohammed Suliman Alruthea
Keyword(s):  
Finite Element ◽  
Group Iv ◽  
Von Mises Stress ◽  
Patient Specific ◽  
Dental Arch ◽  
Stress And Strain ◽  
Bone Implant ◽  
Bone Properties ◽  
Group I ◽  
Von Mises

Abstract Objective The purpose of this study was to compare methods used for calculating heterogeneous patient-specific bone properties used in finite element analysis (FEA), in the field of implant dentistry, with the method based on homogenous bone properties. Materials and Methods In this study, three-dimensional (3D) computed tomography data of an edentulous patient were processed to create a finite element model, and five identical 3D implant models were created and distributed throughout the dental arch. Based on the calculation methods used for bone material assignment, four groups—groups I to IV—were defined. Groups I to III relied on heterogeneous bone property assignment based on different equations, whereas group IV relied on homogenous bone properties. Finally, 150 N vertical and 60-degree-inclined forces were applied at the top of the implant abutments to calculate the von Mises stress and strain. Results Groups I and II presented the highest stress and strain values, respectively. Based on the implant location, differences were observed between the stress values of group I, II, and III compared with group IV; however, no clear order was noted. Accordingly, variable von Mises stress and strain reactions at the bone–implant interface were observed among the heterogeneous bone property groups when compared with the homogenous property group results at the same implant positions. Conclusion Although the use of heterogeneous bone properties as material assignments in FEA studies seem promising for patient-specific analysis, the variations between their results raise doubts about their reliability. The results were influenced by implants’ locations leading to misleading clinical simulations.

Bone Ingrowth Around an Uncemented Femoral Implant Using Mechanoregulatory Algorithm: A Multiscale Finite Element Analysis

2021 ◽  
Author(s):  
Basil Mathai ◽  
Sanjay Gupta
Keyword(s):  
Finite Element ◽  
Bone Tissue ◽  
Bone Ingrowth ◽  
Progressive Increase ◽  
Stair Climbing ◽  
Porous Coating ◽  
Fe Model ◽  
Implant Surface ◽  
Element Analysis ◽  
Medial Side

Abstract The primary fixation and long-term stability of a cementless femoral implant depend on bone ingrowth within the porous coating. Although attempts were made to quantify the peri-implant bone ingrowth using the finite element (FE) analysis and mechanoregulatory principles, the tissue differentiation patterns on a porous-coated hip stem have scarcely been investigated. The objective of this study is to predict the spatial distribution of evolutionary bone ingrowth around an uncemented hip stem, using a 3D multiscale mechanobiology based numerical framework. Multiple load cases representing a variety of daily living activities, including walking, stair climbing, sitting down and standing up from a chair, were used as applied loading conditions. The study accounted for the local variations in host bone material properties and implant-bone relative displacements of the macroscale implanted FE model, in order to predict bone ingrowth in microscale representative volume elements (RVEs) of twelve interfacial regions. In majority RVEs, 20-70% bone tissue (immature and mature) was predicted after two months, contributing towards a progressive increase in average Young's modulus (1200-3000 MPa) of the inter-bead tissue layer. Higher bone ingrowth (mostly greater than 60%) was predicted in the antero-lateral regions of the implant, as compared to the postero-medial side (20-50%). New bone tissue was formed deeper inside the inter-bead spacing, adhering to the implant surface. The study helps to gain an insight into the degree of osseointegration of a porous-coated femoral implant.

Variation in femoral anteversion in patients requiring total hip replacement

2019 ◽  
Vol 30 (3) ◽  
pp. 281-287
Author(s):  
Jim W Pierrepont ◽  
Ed Marel ◽  
Jonathan V Baré ◽  
Leonard R Walter ◽  
Catherine Z Stambouzou ◽  
...  
Keyword(s):  
Total Hip Replacement ◽  
Hip Replacement ◽  
Femoral Stem ◽  
Femoral Anteversion ◽  
Patient Specific ◽  
3 Dimensional ◽  
Total Hip ◽  
Age Related ◽  
Gender And Age ◽  
Implant Alignment

Background: Optimal implant alignment is important for total hip replacement (THR) longevity. Femoral stem anteversion is influenced by the native femoral anteversion. Knowing a patient’s femoral morphology is therefore important when planning optimal THR alignment. We investigated variation in femoral anteversion across a patient population requiring THR. Methods: Preoperatively, native femoral neck anteversion was measured from 3-dimensional CT reconstructions in 1215 patients. Results: The median femoral anteversion was 14.4° (−27.1–54.5°, IQR 7.4–20.9°). There were significant gender differences (males 12.7°, females 16.0°; p < 0.0001). Femoral anteversion in males decreased significantly with increasing age. 14% of patients had extreme anteversion (<0° or >30°). Conclusions: This is the largest series investigating native femoral anteversion in a THR population. Patient variation was large and was similar to published findings of a non-THR population. Gender and age-related differences were observed. Native femoral anteversion is patient-specific and should be considered when planning THR.

BIOMECHANICAL RATIONALE FOR CHOICE OF CEMENT MANTLE THICKNESS AROUND A FEMORAL STEM

2018 ◽  
Vol 18 (06) ◽  
pp. 1850064
Author(s):  
IEVGEN LEVADNYI ◽  
JAN AWREJCEWICZ ◽  
OLGA SZYMANOWSKA ◽  
DARIUSZ GRZELCZYK ◽  
JOSÉ EDUARDO GUBAUA ◽  
...  
Keyword(s):  
Bone Density ◽  
Femoral Stem ◽  
Peak Stress ◽  
Proximal Part ◽  
Cement Mantle ◽  
Bone Adaptation ◽  
Replacement Surgery ◽  
Hip Replacement Surgery ◽  
High Reduction ◽  
Hip Arthroplasties

The change in mechanical properties of the femoral bone tissue surrounding hip endoprosthesis stems during the post-operative period is one of the causes of implant instability, and the mathematical description of this phenomenon is the subject of much research. In the present study, a model of bone adaptation, based on isotropic Stanford theory, is created for further computer investigation. The results of implementation of such a mathematical model are presented regarding the choice of cement mantle rational thickness in cemented hip arthroplasties. The results show that for cement mantle thicknesses ranging from 1–1.5[Formula: see text]mm, a peak stress value in the proximal part of the mantle exceeds the limit of durability of bone cement. Moreover, results show that high reduction in the bone density of distal and proximal regions was observed in cases of cement mantle thicknesses varying from 1–3[Formula: see text]mm. No significant changes in bone density of the abovementioned regions were obtained for 4[Formula: see text]mm and 5[Formula: see text]mm. The outcome of numerical investigations can be treated as valuable and will lead to the improvement of cemented hip replacement surgery results.

scholarly journals Biomechanics in dental implants

2021 ◽  
Vol 7 (3) ◽  
pp. 131-136
Author(s):  
Poonam Prakash ◽  
Ambika Narayanan
Keyword(s):  
Dental Implants ◽  
Fibrous Tissue ◽  
Primary Stability ◽  
Biological Tissues ◽  
Implant Design ◽  
Implant Fixation ◽  
Implant Surface ◽  
Bone Apposition ◽  
Functional Connection ◽  
Secondary Stage

Achieving primary stability in dental implants is crucial factor for accomplishing successful osteointegration with bone. Micro-motions higher than the threshold of 50 to 100 μm can lead to formation of fibrous tissue at the bone-to-implant interface. Therefore, osteointegration may be vitiated due to insufficient primary stability. Osseointegration is defined as a direct and functional connection between the implant biomaterial and the surrounding bone tissue. Osseointegration development requires an initial rigid implant fixation into the bone at the time of surgery and a secondary stage of new bone apposition directly onto the implant surface. Dental implants function to transfer the load to the surrounding biological tissues. Due to the absence of a periodontal ligament, its firm anchorage to bone, various forces acting on it and the presence of prosthetic components, they share a complex biomechanical relationship. The longevity of these osseointegrated implants depend on optimizing these complex interactions. Hence, the knowledge of forces acting on implant, design considerations of implant and bone mechanics is essential to fabricate an optimized implant supported prosthesis.

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