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Loading configuration of hip joint creates resultant bending effect on femoral implants. So, the lateral side of femoral implant which is under tension retracts from peri‑implant bone due to positive Poisson's ratio. This retraction of implant leads to load shielding and gap opening in proximal-lateral region, thereby allowing entry of wear particle to implant-bone interface. Retraction of femoral implant can be avoided by introducing auxetic metamaterial to the retracting side. This allows the implant to push peri‑implant bone under tensile condition by virtue of their auxetic (negative Poisson's ratio) nature. To develop such implants, a patient-specific conventional solid implant was first designed based on computed-tomography scan of a patient's femur. Two types of metamaterials (2D: type-1) and (3D: type-2) were employed to design femoral meta-implants. Type-1 and type-2 meta-implants were fabricated using metallic 3D printing method and mechanical compression testing was conducted. Three finite element (FE) models of the femur implanted with solid implant, type-1 meta-implant and type-2 meta-implant were developed and analysed under compression loading. Significant correlation (R 2  = 0.9821 and R 2  = 0.9977) was found between the experimental and FE predicted strains of the two meta-implants. In proximal-lateral region of the femur, an increase of 7.1% and 44.1% von-Mises strain was observed when implanted with type-1 and type-2 meta-implant over the solid implant. In this region, bone remodelling analysis revealed 2.5% bone resorption in case of solid implant. While bone apposition of 0.5% and 7.7% was observed in case of type-1 and type-2 meta-implants, respectively. The results of this study indicates that concept of introduction of metamaterial to the lateral side of femoral implant can prove to provide higher osseointegration-friendly environment in the proximal-lateral region of femur., Competing Interests: Declaration of Competing Interest None declared, (Copyright © 2023. Published by Elsevier Ltd.)

Stress shielding due to difference in stiffness of bone and implant material is one among the foremost causes of loosening and failure of load-bearing implants. Thus far, femoral geometry has been given priority for the customization of total hip joint replacement (THR) implant design. This study, for the first time, demonstrates the key role of bone condition and subject-weight on the customization of stiffness and design of the femoral stem. In particular, internal hollowness was incorporated to reduce the implant stiffness and such designed structure has been customized based on subject parameters, including bone condition and bodyweight. The primary aim was to tailor these parameters to achieve close to natural strain distribution at periprosthetic bone and to reduce interfacial bone loss over time. The maintenance of interfacial bone density over time has been studied here through analysis of bone remodeling (BR). For normal bodyweight, the highest hollowness exhibited clinically relevant biomechanical response, for all bone conditions. However, for heavier subjects, consideration of bone quality was found to be essential as higher hollowness induced bone failure in weaker bones and implant failure in stronger bones. Moreover, for stronger bone, thinner medial wall was found to reduce bone resorption over time on the proximo-lateral zone of stress shielding, while lateral thinning was found advantageous for weaker bones. The findings of this study are likely to facilitate designing of femoral stems for achieving better physiological outcomes and enhancement of the quality of life of patients undergoing THR surgery., (Copyright © 2020 by ASME.)

The objective is to make the strain deviation before and after implantation adjacent to the femoral implant as close as possible to zero. Genetic algorithm is applied for this optimization of strain deviation, measured in eight separate positions. The concept of composite desirability is introduced in such a way that if the microstrain deviation values for all eight cases are 0, then the composite desirability is 1. Artificial neural network (ANN) models are developed to capture the correlation of the microstrain in femur implants using the data generated through finite element simulation. Then, the ANN model is used as the surrogate model, which in combination with the desirability function serves as the objective function for optimization. The optimum achievable deviation was found to vary with the bone condition. The optimum implant geometry varied for different bone condition, and the findings act as guideline for designing patient-specific implant., (© 2019 John Wiley & Sons, Ltd.)

Background: Hip fracture depends on various anthropometric parameters such as trochanteric soft tissue thickness, body height and body weight. The objective was to evaluate the responses to the variations in anthropometric parameters during sideways fall, and to identify the most dominant parameter among them., Method: Seven finite element models were developed having anthropometric variations in trochanteric soft tissue thickness (5-26 mm), body height (1.70-1.88 m), and body weight (63-93.37 kg). These were simulated for sideways fall with ANSYS-LS-DYNA® code., Findings: Significant effect of trochanteric soft tissue thickness variation was found on 'normalized peak impact force with respect to the body weight' (p=0.004, r²=0.808) and strain ratio (p=0.083, r²=0.829). But, variation in body height was found to be less significant on normalized peak impact force (p=0.478, r²=0.105) and strain ratio (p=0.292, r²=0.217). Same was true for the variation in body weight on normalized peak impact force (p=0.075, r²=0.456) and strain ratio (p=0.857, r²=0.007). The risk factor for fracture was also well correlated to the strain ratio for the inter-trochanteric zone (p<0.0007, r²=0.917) where the most fractures are clinically observed to happen., Interpretations: Trochanteric soft tissue thickness was found likely to be the most dominant parameter over body height and body weight, signifying that a slimmer elderly person, taller or shorter, with less trochanteric soft tissue thickness should be advised to take preventive measures against hip fracture under sideways fall., (© 2013.)

Hip fractures due to sideways falls are a worldwide health problem, especially among the elderly population. The objective of this study was to simulate a real life sideways fall leading to hip fracture. To achieve this a computed tomography (CT) scan based three-dimensional (3D) finite element (FE) model of the pelvis-femur complex was developed using a wide range of mechanical properties in the bone of the complex. For impact absorption through large deformation, surrounding soft tissue was also included in the FE model from CT scan data. To incorporate the inertia effect, the whole body was represented by a spring-mass-dashpot system. For trochanteric soft tissue thickness of 14 mm, body weight of 77.47 kg and average hip impact velocity of 3.17 m/s, this detailed FE model could approximately simulate a sideways fall configuration and examine femoral fracture situation. At the contact surface, the peak impact load was 8331 N. In spite of the presence of 14 mm thick trochanteric soft tissue, within the trochanteric zone the most compressive peak principal strain was 3.5% which exceeds ultimate compressive strain. The modeled trochanteric fracture was consistent with clinical findings and with the findings of previous studies. Further, this detailed FE model may be used to find the effect of trochanteric soft tissue thickness variations on peak impact force, peak strain in sideways fall, and to simulate automobile side impact and backward fall situations.

Pelvic injuries and fractures (abbreviated injury scale > 2) are caused by intrusion of car door structure during motor vehicle side impacts. The objective was to simulate automotive side impact situation for the occupant. This was performed with a computed tomography scan-based three-dimensional finite element (FE) model of human pelvis-femur-soft tissue complex with spring-dashpot-mass representation of whole body, using wide range of mechanical property variations. It was impacted with a 12-kg rigid impactor at 13.54 m s-1 to impart impact energy of 1100 J. The pelvic fracture condition was well-examined by the peak impact force (16.98 kN), peak strain (23.4%) and peak stress (189 MPa). It was concluded that this FE model could reconstruct clinically observed pelvic injury. Moreover, this FE model could reduce the need for modelling the complex whole body with a huge number of elements and nodes when pelvic fracture is the area of focus. Furthermore, this detailed FE model may be used for finding out different response corridors for automobile side impact, and the detailed responses may be used for developing occupant protective systems, better vehicle door structures and side impact dummies. [ABSTRACT FROM AUTHOR]