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Einfluss der Schaftgeometrie einer zementfreien Primärprothese auf Beanspruchungen am proximalen Femur während der Implantation – Eine numerische Analyse
Citation Link: https://doi.org/10.15480/882.15773
Publikationstyp
Master Thesis
Date Issued
2025-08
Sprache
German
Author(s)
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2025-05-27
Institute
TORE-DOI
Citation
Technische Universität Hamburg (2025)
The incidence of coxarthrosis and thus the number of cementless total hip arthroplasties (THA) is increasing as a result of demographic change and the rising prevalence of obesity. However, cementless treatment is associated with an increased risk of intraoperative and postoperative periprosthetic femoral fractures (PPF), which account for 15.8 % of follow-up surgeries in Germany. The main cause of intraoperative PPF is seen in increased tangential strains on the proximal femur during stem insertion. In this research work, the displacement-controlled implantation up to the in vitro determined fracture point was simulated with the implicit time integration method in order to investigate the femoral strains in silico. Based on a quantitative computed tomography image (QCT image) of a human femur, two patient-specific, close-to-reality, linear-elastic femur models with cavities of different sizes were created (mean deviation: 0.13 mm). The comparison and validation of the simulations with two implant designs (with and without medial collar; CORAIL, Total Hip Systems, Johnson & Johnson Medical Limited, UK) against the in vitro study was based on the strains of the proximal femur and the implantation force.
In silico, collared stems resulted in increased load transfer with axial compression in the calcar-collar contact areas compared to the collarless equivalent. However, the axial compression at the proximal medial femoral surface in silico remained below the compression of -0.49 % measured in vitro. The compression of -0.21 % during stem insertion into the femur with a smaller cavity was closest to the in vitro situation. Both in vitro and in silico the proximal medial femur was initially compressed along the hoop axis during implantation. In the medial region close to the calcar, tensile hoop strains occurred only in vitro shortly before the fracture (0.69 % at the time of fracture), where they are generally considered to be the cause of the fracture. This increase was not seen in the simulations. The tangential compression in silico and in vitro is attributed to the anterior-posterior expansion of the cavity.
The simulations show that the implantation force required to reach the intended positioning of the implant and the force at the subsequent fracture position are highly dependent on the geometries used. Due to the lateral widening of the femoral cavity by up to 1.3 mm, the implantation force at the time of fracture was reduced by 55 % when collarless stems were used and by 34 % when collared stems were used. For collared stems, the implantation force prior to the calcar-collar contact was similar to the in vitro situation based on the changed geometry. As soon as calcar-collar contact was achieved, the in silico implantation force increased considerably more for collared stems than for collarless stems, and also compared to the in vitro situation.
The simulation results demonstrate that the use of a femoral geometry closer to reality with a smaller cavity is necessary in order to more realistically reproduce the axial and tangential strain distribution of an in vitro implantation in silico. By defining failure mechanisms in further studies, an implantation force closer to the in vitro situation is expected.
In silico, collared stems resulted in increased load transfer with axial compression in the calcar-collar contact areas compared to the collarless equivalent. However, the axial compression at the proximal medial femoral surface in silico remained below the compression of -0.49 % measured in vitro. The compression of -0.21 % during stem insertion into the femur with a smaller cavity was closest to the in vitro situation. Both in vitro and in silico the proximal medial femur was initially compressed along the hoop axis during implantation. In the medial region close to the calcar, tensile hoop strains occurred only in vitro shortly before the fracture (0.69 % at the time of fracture), where they are generally considered to be the cause of the fracture. This increase was not seen in the simulations. The tangential compression in silico and in vitro is attributed to the anterior-posterior expansion of the cavity.
The simulations show that the implantation force required to reach the intended positioning of the implant and the force at the subsequent fracture position are highly dependent on the geometries used. Due to the lateral widening of the femoral cavity by up to 1.3 mm, the implantation force at the time of fracture was reduced by 55 % when collarless stems were used and by 34 % when collared stems were used. For collared stems, the implantation force prior to the calcar-collar contact was similar to the in vitro situation based on the changed geometry. As soon as calcar-collar contact was achieved, the in silico implantation force increased considerably more for collared stems than for collarless stems, and also compared to the in vitro situation.
The simulation results demonstrate that the use of a femoral geometry closer to reality with a smaller cavity is necessary in order to more realistically reproduce the axial and tangential strain distribution of an in vitro implantation in silico. By defining failure mechanisms in further studies, an implantation force closer to the in vitro situation is expected.
Subjects
finite element analysis
patient-specific model
total hip replacement
cementless
collared
collarless
DDC Class
617: Surgery, Regional Medicine, Dentistry, Ophthalmology, Otology, Audiology
620: Engineering
Publication version
publishedVersion
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2025_05_12 Masterarbeit Theresa Harpeng - Einfluss der Schaftgeometrie einer zementfreien Primärprothese - numerische Analyse.pdf
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