The aim of the study was to clearly determine whether selected modern medical materials and three dimensional printing allow for satisfactory viability of human osteoblasts, which is important from the point of view of the subsequent osseointegration process. Moreover, as implants are produced with various topography, the influence of surface roughness on viability of bone cells was evaluated. To conduct the research, primary human osteoblasts (PromoCell) were used. Cells were seeded on samples of glass-reinforced polyetheretherketone (30% of the filling), Ti6Al4V manufactured with the use of selective laser melting technology and forged Ti6Al4V with appropriately prepared variable surface roughness. To assess the viability of the tested cells the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was used. Results showed that all evaluated materials do not exhibit cytotoxic properties. Moreover, on their basis it can be concluded that there is a certain surface topography (designated i.a. as roughness equal to approx. Ra = 0.30 µm), which ensures the highest possible viability of human osteoblasts. On the basis of the received data, it can also be concluded that modern glass-reinforced polyetheretherketone or Ti6Al4V produced by rapid prototyping method allow to manufacture implants that should be effectively used in clinical conditions.

Nowadays, numerous internal bone remodelling concepts are under development, in order to estimate long-term functionality of implants by evaluating the intensity of stress-shielding effect. This effect is also analysed for the implants for direct skeletal attachment, considered as a better exoprosthesis fixation method than prosthetic sockets. Most of bone remodelling approaches are based on basic concepts, differing with certain assumptions, which may affect the accuracy of the results. This article compares commonly used internal bone remodelling concepts and evaluates the functionality of the proposed Limb Prosthesis Osseointegrated Fixation System for direct skeletal attachment of limb prosthesis in comparison with two currently available implants: the Intraosseous Transcutaneous Amputation Prosthesis and the Osseointegrated Prostheses for the Rehabilitation of Amputees. Three concepts were chosen: without and with lazy zone and with the use of quadratic formula which considers bone overloading. Therefore, three finite element models were created with identical femur implanted with each of analysed implants. The implants were loaded with loads that refer to two stages of gait cycle (heel strike and toe-off). The analysed concepts have given similar results, allowing to assume that each of them can be successfully used to estimate internal bone remodelling around analysed implants for direct skeletal attachment of limb prosthesis. The results also present higher functionality of the proposed implant for direct skeletal attachment of limb prosthesis due to a significant reduction in stress-shielding in the analysed areas around implant in comparison with the Intraosseous Transcutaneous Amputation Prosthesis and the Osseointegrated Prostheses for the Rehabilitation of Amputees. It suggests that the proposed design is a better alternative to the currently used solutions.

The purpose of the research was to evaluate the influence of selected parameters of the implants for bone anchored prostheses on possibility of conducting static load bearing exercises and stress-shielding intensity. A press-fit implant, a threaded implant, and the proposed design were compared using the finite element method. For the analyses two features were examined: diameter (19.0 – 21.0 mm) and length (75.0 – 130.0 mm). To define the possibility of conducting rehabilitation exercises the micromotion of implants while axial loading with a force up to 1000 N was examined to evaluate the changes at implant-bone interface. The stress-shielding intensity was estimated by bone mass loss over 60 months. The results suggest that, in terms of micromotion generated during rehabilitation exercises, the threaded (max. micromotion of 16.00 μm) and the proposed (max. micromotion of 45.43 μm) implants ensure low and appropriate micromotion. In the case of the press-fit solution the load values should be selected with care, as there is a risk of losing primary stabilisation. The allowed forces (that do not stimulate the organism to generate fibrous tissue) were approx. 140 N in the case of the length of 75 mm, increasing up to 560 N, while using the length of 130 mm. Moreover, obtained stress-shielding intensities suggest that the proposed implant should provide appropriate secondary stability, similar to the threaded solution, due to the low bone mass loss during long-term use (improving at the same time more bone remodelling in distal Gruen zones, by providing lower bone mass loss by approx. 13% to 20% in dependency of the length and diameter used). On this basis it can be concluded that the proposed design can be an appropriate alternative to commercially used implants.

Purpose: This study attempted to establish the link between design of implants for bone-anchored prostheses and stress-shielding, affecting the stability of the bone-implant coupling using numerical approach. The objectives were to share a numerical model capable to evaluate the long-term stability of implants and to use this model to extract data sets showing how shape and material stiffness of threaded, press-fit and modular press-fit implants affect stress-shielding intensity. Methods: Three designs were considered: threaded, press-fit and modular press-fit. The effect of shape and material stiffness of each design on stress-shielding intensity was assessed using Young’s modulus (10 to 210 GPa). Furthermore, the impact of the diameter of percutaneous part (10 to 18 mm) and thickness of medullar part (5 to 1 mm) was investigated for the modular press-fit implant. Results: The threaded design generated 4% more bone mass loss at the distal femur but an overall loss of bone mass was by 5% lower to press-fit design. The influence of Young’s modulus on bone mass changes was noticeable for modular press-fit implant, depending on diameter of percutaneous or medullary part. A 20 GPa change of stiffness caused a bone mass change from 0.65% up to 2.45% and from 0.07% up to 0.32% for percutaneous parts with 18 mm and 10 mm diameter, respectively. Conclusions: Results suggested that threaded implant provides greater stability despite an increased bone loss at the distal femur. Altogether, this work provided an initial model that could be applied in subsequent studies on the long-term stability of current and upcoming implants.

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