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Numerical modelling of head-neck taper junction in hip prosthesis: contact pressure and micromotions assessment

Sara Di Rico

Numerical modelling of head-neck taper junction in hip prosthesis: contact pressure and micromotions assessment.

Rel. Alberto Audenino, Mara Terzini, Giovanni Putame, Federico Andrea Bologna. Politecnico di Torino, Corso di laurea magistrale in Ingegneria Biomedica, 2022

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Nowadays, total hip replacement represents the most common orthopaedic surgery performed to restore proper functioning of the hip joint in patients affected by chronic hip pain and disability. There are different available prosthesis designs, from those that replace only the proximal femoral bone (endoprosthesis) to those that replace the entire joint (arthroprosthesis) and, by exploiting the modularity of the implant, it is possible to choose the prosthesis that best matches the patient's anatomy, age, weight and level of activity. Modular prostheses present issues related to the establishment of relative micromotions between coupled components, which can lead to the failure of the implant due to wear of contacting surfaces at the junction (i.e., trunnionosis) and, consequently, to the need for revision surgery. It has been proven that micromotions at the junction interface are influenced by different parameters, like head diameter, femoral offset, lever arm, taper angle mismatch and the characteristic of loads the joint undergoes. This thesis aims to investigate the contact pressure and micromotions that occur at the taper junction of a hip prosthesis by varying the taper geometry and loads. Overall, four finite element models of the hip prosthesis’s head and trunnion were developed to analyse different assembly conditions and the influence of the variation of the geometric features. The first model consists of a taper angle of 5.6° and a smaller contact area than the following three models, which were designed to evaluate the influence related to different taper angles (5.2°, 5.6° and 6°, respectively). Finite element analyses were carried out in Abaqus/CAE by simulating the assembly of the head on the trunnion (4 kN applied force). In addition, the first model was used to simulate forces and moments of a walking cycle lasting 1.1 s, investigating the junction behaviour under daily load conditions. Furthermore, an analytical model, derived from the literature, was used to predict contact pressures, and verify the simulation outcomes. Results from simulations regarding contact pressures were successfully verified by the analytical solution. Moreover, findings showed that there are no relevant differences in contact pressure among models with different taper angles. However, comparing geometries with different contact areas, as expected, the model with a smaller area showed higher contact pressure values. The distribution of contact pressure is uniform and symmetrical along the surface of the trunnion during the assembly phase with a maximum value in the range of 20-30 MPa in the central area. However, the pressure distribution changes during the walking cycle, becoming asymmetrical resulting from the establishment of different contact between the surfaces, with a maximum value in the range of 20-40 MPa. The relative micromotion is strictly linked to contact pressure since the greater the pressure value, the greater the micromotion will be. The relative micromotion recorded showed a value of around 2 µm. The proximal edge of the trunnion is the area in which both pressure and micromotion are maximum, and, evaluating the radial displacements, this is the point where there is the highest trunnion compression. In conclusion, a model that simulates the joint behaviour was successfully developed and it will be used in the next future to create boundary conditions deriving from variations in the geometric parameters of the prosthesis, such as head diameter, femoral offset and lever arm.

Relators: Alberto Audenino, Mara Terzini, Giovanni Putame, Federico Andrea Bologna
Academic year: 2022/23
Publication type: Electronic
Number of Pages: 96
Corso di laurea: Corso di laurea magistrale in Ingegneria Biomedica
Classe di laurea: New organization > Master science > LM-21 - BIOMEDICAL ENGINEERING
Aziende collaboratrici: Politecnico di Torino
URI: http://webthesis.biblio.polito.it/id/eprint/25740
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