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Design of Customized Cemented Stems for Hip Joint Arthroplasty Surgery in Patients with Severe Femoral Deformity

Ebadi, Yashar | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56278 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farahmand, Farzam
  7. Abstract:
  8. Hip replacement surgery is performed with the aim of relieving pain and restoring the normal function of the joint for patients who are in the final stages of arthritis. Standard prostheses offered by implant manufacturers come in a wide variety of models and sizes to meet the needs of patients. However, these commercial prostheses may not be suitable for patients with significant bony abnormalities, leading to implant instability and loosening. In such cases, a suitable solution is to use customized implants that are specifically designed to match the patient's unique anatomy. The purpose of this research was to design a customized cement stem for hip joint replacement surgery in patients with severe femoral bone deformity, especially juvenile arthritis. To achieve this goal, first, a parametric study was conducted to investigate the effect of different geometric parameters of the stem on biomechanical results, including the strength of the implant and the range of motion of the artificial joint, in order to gain a deeper understanding of the effect of the design parameters on the biomechanical efficiency of the stem. Then, an algorithm was developed to select the appropriate dimensions for the implant, taking into account anatomical, biomechanical, and clinical considerations specific to each patient. This algorithm, through the design of the geometry of the neck of the stem, enables the reproduction of the necessary vertical and horizontal angles and distances, and also by designing the geometry of the stem shaft, in accordance with the size of the femur bone canal, it provides reliable stabilization with the bone. It should be designed to have sufficient mechanical strength to prevent fatigue failure. In the parametric study phase, two distinct problems of finite element analysis and collision analysis were addressed using the response surface method. The results showed that the geometrical parameters such as the medial cone angle, shaft end diameter, lateral curve radius, and lateral curve distance from the center line have a significant effect on the maximum stress applied to the stem shaft. Similarly, the diameter of the shaft end, the lateral angle of the cone, the radius of the lateral curve, and the distance of the lateral curve from the centerline significantly affect the maximum stress in the cement. Finally, using the results of the parametric study, an optimal model was developed, which had a lower maximum stress in the stem (11%) and cement (66%) than the standard model of Exeter brand Zimmer. The algorithm introduced in this research included four steps and was evaluated by designing a customized stem for a patient with juvenile arthritis. According to the results of the finite element analysis, the designed stem and the cement layer around it, despite their small size, had reliability coefficients against fatigue of 4.76 and 1.62, respectively, and the amount of subsidence of the stem inside the cement layer during 50 hours of loading was equal to 1.6 micrometers. Also, the collision analysis showed that the designed artificial joint has a range of motion of 18 degrees of adduction, 69 degrees of abduction, 84 degrees of flexion, and 45 degrees of extension, and it successfully replaces the natural range of motion of the hip joint, recovers, and enables the patient to perform daily activities without restrictions. Finally, this small custom-made stem is now ready to be implanted in the patient's body
  9. Keywords:
  10. Hip Implant ; Parametric Study ; Finite Element Analysis ; Subsidence Phenomenon ; Fatigue ; Hip Prosthesis ; Bone Implant ; Bone Cement ; Customized Implants

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