Microstructure and Defect-Based Fatigue Mechanism Evaluation of Brazed Coaxial Ti/Al2O3 Joints for Enhanced Endoprosthesis Design

Alumina-based ceramic hip endoprosthesis heads have excellent tribological properties, such as low wear rates. However, stress peaks can occur at the point of contact with the prosthesis stem, increasing the probability of fracture. This risk should be minimized, especially for younger and active patients. Metal elevations at the stem taper after revision surgery without removal of a well-fixed stem are also known to increase the risk of fracture. A solution that also eliminates the need for an adapter sleeve could be a fixed titanium insert in the ceramic ball head, which would be suitable as a damping element to reduce the occurrence of stress peaks. A viable method for producing such a permanent titanium–ceramic joint is brazing. Therefore, a brazing method was developed for coaxial samples, and two modifications were made to the ceramic surface to braze a joint that could withstand high cyclic loading. This cyclic loading was applied in multiple amplitude tests in a self-developed test setup, followed by fractographic studies. Computed tomography and microstructural analyses—such as energy dispersive X-ray spectroscopy—were also used to characterize the process–structure–property relationships. It was found that the cyclic loading capacity can be significantly increased by modification of the surface structure of the ceramic.

Investigation of the effect of porous titanium cups on stress distribution in bone tissue (mathematical modeling)

Introduction. During arthroplasty in patients with altered anatomy and osteoporosis of the acetabulum, stable fixation of the acetabular component of the endoprosthesis is a very difficult task. There are studies on the bone tissue bonding to titanium, tantalum and ceramic coatings of endoprostheses. However, there are insufficient data on the influence of the strength characteristics of modern surfaces of the cups for hip endoprostheses on the distribution of mechanical stresses in the bone tissue around the implanted components. The purpose was to study on a mathematical model the changes in the stress-strain state of the endoprosthesis-bone system as a result of using porous tantalum cup. Materials and methods. A mathematical modeling has been carried out of the stress-strain state of the human hip joint in arthroplasty with porous cup. Du-ring the study, a defect in the acetabular roof filled with a bone implant fixed with two screws was simulated, as well as a defect in the acetabular floor filled with bone “chips”. Endoprosthesis cups were modeled in two versions: from solid titanium with a spray coating of porous titanium, and those entirely made of porous titanium. A distributed load of 540 N was applied to the sacrum. A load was applied between the iliac wing and the greater trochanter of the femur simulating the action of the gluteus medius — 1150 N and the gluteus minimus — 50 N. Results. The use of a cup with a coating of porous titanium in the normal state of the acetabulum leads to the occurrence of maximum stresses (15.9 MPa) in its posterior-upper part. Minimum stresses of 4.6 MPa are observed in the center of the acetabulum. The use of an endoprosthesis with porous titanium cup allows reducing the level of stresses in the bone tissue around the cup. If there is a defect in the acetabular roof, a hip endoprosthesis with porous titanium cup causes less stress than a solid titanium cup with coating of porous titanium. But on the graft, the stress level remains practically unchanged, regardless of the type of cup. The use of porous tantalum cup in the presence of a defect in the acetabular floor causes significantly less stress in the bone tissue around it, compared to an all-metal cup with coating. Conclusions. The cup of the hip endoprosthesis made of porous titanium causes significantly less stress in all control points of the model, compared to a cup made of solid titanium with coating of porous titanium, both with defects in the acetabular roof and floor, and without bone defects.

Monitoring the reduction and maintenance of periprosthetic bone tissue in cementless primary hip endoprosthesis with alendronate therapy

Loss of periprosthetic bone tissue in primary hip endoprostheses is common in clinical practice. This loss can be progressive and in extreme conditions can jeopardize the longevity of the prosthesis. In order to monitor the function of Alendronate therapy for bone maintenance, the study included 50 patients with implanted total cement-free hip endoprosthesis (TPH). The first group of 25 patients received Alendronate, calcium and vitamin D3 orally postoperatively. The second group of 25 patients were examined postoperatively without therapy. Patients were followed by radiographic and dual-energy X-ray absorptiometry (DXA) at 6 and 12 months. The study showed that in patients with TPH there was a difference in the X-ray findings as well as occurrence of osteolysis in certain Gruen zones, which was confirmed by changes in the state of bone mineral density (BMD) and bone mineral content (BMC) in the interval between 6 and 12 months using the DXA method. Alendronate therapy after TPH implantation allows reduction of periprosthetic bone mass loss, maintenance of bone mineralization and implant hardening.

Influence of alendronate therapy on the results of densitometric examination after implantation of total hip endoprosthesis

The development of aloarthroplasty of the hip is continuously rising. After implantation of a total cement-free hip endoprosthesis, often there is a periprosthetic femoral bone loss. Alendronate has been shown to be a potent inhibitor of bone resorption activity; it inhibits osteoclastic bone resorption, increases bone mass, and plays a significant role in post-implantation stabilization of the femur. The aim of this study was to determine the effect of alendronate on osteointegration of hip endoprosthesis.Material and methods: The study analyzed 10 patients operated on with implantation of a total cement-free hip endoprosthesis (THP). The included patients were examined by a radiographic method at 6 and 12 months and DXA method at 6 and 12 months. Results: The study showed differences in the values of bone mineral density and bone mineral content in the interval between 6 and 12 months in patients undergoing THP, and hence we can conclude that alendronate therapy after THP implantation reduced periprosthetic loss of bone mass and implant stiffening. Alendronate is a proven inhibitor of periprosthetic bone loss that occurs after prirmary impantation of a total cement-free hip endoprosthesis.