In the realm of orthopedic surgery, the development of biological hip joint prostheses has been a game-changer, particularly for patients suffering from pertrochanteric fractures. The integration of biofidel Finite Element Models (FEM) with advanced imaging techniques like Computer Tomography (CT) has revolutionized the way we understand the biomechanical behavior of the femur post-implantation. This article delves into the intricacies of these models, their role in assessing stress distribution changes in prosthesized femurs, and the implications for designing biomimetic hybrid biological hip prostheses.
A multidisciplinary team of researchers has been exploring the dynamic nature of bone as a living material, aiming to replicate its unique characteristics and response to physiological loads. This research has led to significant advancements in the biomechanics and biomimetics of implanted bones, paving the way for personalized healthcare solutions and the creation of innovative prosthetic designs.
The human femur, with its specialized internal structure, is adept at managing external stresses while maintaining an optimized mass distribution and morphology. However, as we age, bone mass loss can compromise this ability, leading to fractures, particularly in the elderly. Modeling this behavior has been crucial in understanding the need for hip joint prostheses in such cases.
Despite the success of total hip replacements, there's a growing need for prostheses that can last longer than 15 years, especially for patients under 65. With advancements in healthcare technology and improved prognosis for physical trauma, the demand for more durable and biomechanically compatible prostheses is on the rise.
Current orthopedic prostheses are made from metal alloys, plastics, and ceramics, each with specific properties. Titanium and Cobalt Chrome alloys are favored for their biocompatibility and mechanical strength, ensuring good osteo-integration with bone. However, implant failures often stem from biomechanical incompatibility, where the stiffness of the implant materials disrupts the natural stress distribution in the bone, leading to bone reabsorption and increased risk of implant loosening.
To predict structural alterations in the bone, researchers have developed accurate femur models. These models have been instrumental in predicting physiological stress and strain distribution in various bone structures, including the mandible and dental prostheses.
The process begins with CT image segmentation using software like Mimics (Materialise, Belgium), which creates a precise 3D model of the patient's pelvis and femur anatomy. This model is then used in conjunction with solid modeling and Finite Element analysis to simulate the structural morphology of the femur.
Recent studies have highlighted the importance of FEM analysis in clinical applications and the development of new prosthetic systems. The methodological procedure involves remodeling the external geometry of the femur and pelvis, creating a 3D volume from CT scans, and optimizing the meshing for Finite Element model preparation.
The mechanical properties of the bone are evaluated using the Hounsfield (HU) scale, which measures the X-rays linear attenuation coefficients in tissues. The trabecular bone ranges from 100-300 HU, while cortical bone values range from 200 to about 2000 HU, corresponding to elastic moduli from 0.87 to 15.0 GPa. The mechanical properties of the Titanium alloy used in prostheses are also considered, with an elastic modulus of 124 GPa and a Poisson ratio of 0.3.
The study defines a biofidel model to investigate the femur's structural behavior, using the Von Mises strain criterion to compare stress distributions in sound and prosthesized femurs. The analysis reveals significant alterations in stress distribution due to the "stress shielding effect" caused by the high rigidity of metal prostheses. This effect can lead to bone reabsorption over time, as the bone remodeling process is driven by mechanical strain and micro-damage.
The biofidel modeling of sound and prosthesized bones clarifies the complexity required in FEA when predicting bone remodeling processes. Accurate bone models allow for precise identification of femur locations where isotropic or orthotropic conditions apply. These models can predict undesired bone remodeling and are also applicable in designing new prostheses for orthopedic oncology, supporting bone regeneration after significant losses due to tumor removal.
The biomimetic characteristics of these systems have a positive impact on the quality of life for patients, offering better functional recovery and promoting bone growth while ensuring load-bearing capacity.
For a comprehensive list of references and to view the figures associated with this study, please visit The Science Publications.
Interesting stats and data about the topic that are not commonly discussed include the increasing prevalence of hip fractures and the need for hip replacement surgeries. According to the International Osteoporosis Foundation, an estimated 1.6 million hip fractures occur worldwide each year, and this number could reach between 4.5 to 6.3 million by 2050 (IOF). Additionally, a study published in The Lancet predicts that by 2030, the demand for primary total hip replacements in the US will grow by 174% to 572,000 procedures annually (The Lancet). These statistics underscore the importance of continued research and development in the field of hip prostheses.
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