BR202014024100U2 - FEMORAL ISOELASTIC STEM MADE IN POLYMER - Google Patents

Abstract

isoelastic femoral stem made of polymer the present utility model describes a isoelastic femoral stem made of polymer for hip prostheses. the novelty consists in obtaining a differentiated femoral stem design, manufactured in po | i-ether-ether-ketone (peec), which is a biomaterial commercially used with the closest properties of human bone and which supports the fatigue test that simulates the conditions of efforts to which a stem must be submitted in order to be mechanically approved for use. the rod can also be made of polymers with less mechanical resistance than 0 peec, according to tests carried out by testing on nailon polymer

Description

Femoral Isoelastic Rod Made of polymer

Field of the Invention

001, The present utility model describes an isoelastic femoral stem made of polyether-ether-ketone polymer (PEEC) or polymers of adequate mechanical strength, as described in the application, for hip prostheses. The novelty consists in obtaining a differentiated femoral stem design, created entirely in PEEC material (biomaterial commercially used with the closest properties to human bone) or biomedical grade polymer with adequate mechanical resistance as described, which supports the fatigue test that simulates the stress conditions to which a stem must be subjected in order to be mechanically approved for use (ISO 7206-4, 2011). Preliminary tests show that polymers with a lower mechanical resistance value have also been shown to withstand mechanical stress, proving that the proposed femoral stem design allows the use of different polymers in its manufacture, without compromising its resistance to cyclic efforts.

Background of the Invention

002. From the 70s onwards, the chronology of the new prosthetic models that emerged based on the great success of cement fixation and the concept of low friction cannot be specified. This concept, although showing great evolution, showed flaws: wear of polyethylene, nail fractures and frequent infections, difficulties that were somehow being controlled. Trying to provide solutions to problems, then attributed to cement, European biological fixation prostheses also appeared in this decade, with different designs, characteristics and raw materials. They soon became known through models developed by Judet, Lord, Mittelmeyer (Autophor model), Parhoffer, Roy Camille, Freeman, Müller and others, in addition to the well-known American stems of Thompson and Moore (Macedo CAS Development of National Cementless Femoral Stem , Validated by International Standards // Doctoral Thesis - Porto

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Alegre: UFRGS, 2007) and (Anderson J., Neary, F., Pickstone, J. V. Surgeons, Manufacturers and patients - a transatlantic history of Total Hip Replacement [Book], - [s.L]: Palgrave MacMillan, 2007).

003. Later, there were also the rods of Zweissmuller and Spotorno, which consolidated the quadrangular and cuneiform shape as a design and the titanium alloys as raw material, basic concepts that remain accredited until today. In the early 1980s, American surgeons such as Sarmiento and Galante also started using titanium alloys as raw material, while Engh, Hungerford and others continued to use chromocobalt alloy for cementless implants (Macedo CAS Development of National Cementless Femoral Stem, Validated by International Standards // Doctoral Thesis - Porto Alegre: UFRGS, 2007) and (Anderson J., Neary, F., Pickstone, JV Surgeons, Manufacturers and patients - a transatlantic history of Total Hip Replacement [Book], - [ sL]: Palgrave MacMillan, 2007).

004. The first attempts at the systematic use of prostheses were made by Judet (1946), who proposed cephalic prostheses with straight and short nails with an acrylic head. Thompson (1950) and Moore (1952) described cephalic prostheses with intramedullary nails.

005. Moore's nail showed fenestrations, where the cancellous bone should penetrate and, consequently, fix the prosthesis, being one of the first designs with the objective of making the biological principle of osteointegration viable. Thus began the discussion, which continues today, about cementation or osteointegration as a means of fixing the prostheses (Macedo CAS Development of National Cementless Femoral Stem, Validated by International Standards // Doctoral Thesis. - Porto Alegre: UFRGS, 2007 ).

006. Chanrley, London, 1958, introduced the acetabular component in teflon® and the systematic use of cement fixation. In 1962, it introduced the acetabular component in polyethylene. Sir Chanrley's new results greatly clarified fundamental aspects of arthroplasties (Macedo C. A. S. Development of National Cementless Femoral Stem,

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Validated by International Standards // Doctoral Thesis. - Porto Alegre: UFRGS, 2007).

007. The systematic use of Total Hip Prostheses occurred in the second half of the 20th century. Since then, due to the better knowledge of the cementation technique and the factors involved in the osteointegration process, there have been several changes in the design and in the raw material used in the prostheses (Macedo CAS Development of National Cementless Femoral Stem, Validated by International Standards // Thesis PhD - Porto Alegre: UFRGS, 2007).

008. The coating prostheses were defended by a few authors at different times with different appeals and with short-term, debatable results. The knowledge of this evolution, although vague, is important to give an idea of the time, the attempts and the difficulties and the factors involved in the development of the prostheses (Macedo CAS Development of National Cementless Femoral Stem, Validated by International Standards // Doctoral Thesis. - Porto Alegre: UFRGS, 2007) and (Anderson J., Neary, F., Pickstone, JV Surgeons, Manufacturers and patients - a transatlantic history of Total Hip Replacement [Book], - [sL]: Palgrave MacMillan, 2007).

009. Hip implants are the most common joint prostheses in humans (Esslinger JO and Rutkowski EJ Studies on the skeletal attachment of experimental hip prostheses in the pygmy goat and dog [Article] // Journal of Biomedical Materials Research Symposium. - 1973 - Vol. 4. - pp. 187-193).

010. More than one hundred and fifty thousand of these implants are placed in the United States of America (USA) each year (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] // Composites Science and Technology. - [sL]: Elsevier, 2001.- Vol. 61.- pp. 1189-1224).

011. Approximately 800,000 hip implant surgeries are performed worldwide each year and this number is growing (Gross S. and Abel E. W. The finite element analysis of hollow stemmed hip prostheses as a

4/30 means of reducting stress shielding of the femur [Article] // Journal of Biomechanics. - [s.L]: Elsevier, 2001. - Vol. 34. - pp. 995-1003).

012. Most orthopedic surgeries performed in Brazil use prostheses with metal / polymer type head / acetabulum articulation, which has shown high failure rates. This type of joint can last for about ten years, with loosening of the joint being the biggest problem in the long run. Naturally, the duration depends on the way of use. Obesity, heavy work or a lot of activity can hasten loosening, which often requires revision surgery to change the prosthesis. The results of a second operation are not as good as those of the first and there is a greater possibility of complications during surgery (Hippert E. and Azevedo CRF Some cases of failure analysis of surgical implants [Book], - São Paulo: Instituto de Pesquisa Technologies, 2001).

013. About ten to fifteen percent of implants fail when they are 5 to 7 years old (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] // Composites Science and Technology. - [sL]: Elsevier, 2001. - Vol. 61. - pp. 1189-1224.).

014. The failure of a hip implant is usually associated with osteolysis induced by residues from the wear process in the joint of the metallic head with the PEUAPM acetabulum. This promotes biological reactions of infection of the surrounding living tissue, leading to premature loosening and subsequent failure of the prosthesis (Alves HLR, Bergmann CP and Stainer D. Pro-Rectory of Research [Online]. - Federal University of Rio Grande do Sul (UFRGS), 2003, - 10 of 01 of 2010, - http://www.ufrgs.br/propesq/livro2/artigo_hugo.htm).

015. The premature failure of implants can be associated with numerous other factors such as mechanical loading (overload, impact, fatigue and wear), the corrosive environment (pitting, crevice, metallosis), failure in the selection, design and manufacture of the implantation, poor placement, implant damage during surgery or due to poor bone quality of the

5/30 patient (Ravaglioli A. and Krajewski A. Bioceramics: Materials, Properties, Applications [Book], - New York: Chapman & Hall, 1992).

016. The first acetabular components were manufactured in Co-Cr alloys. An effort to minimize friction and eliminate metallic particulate wear led Charnley, in the early 1960s, to use a stainless steel metal rod with a PTFE acetabulum. However, PTFE exhibited unacceptable high wear and distortion. The debris particles caused tissue reaction and granuloma formation. For this reason, PTFE is no longer used in mechanical loading applications. In sequence, the acetabular component was manufactured in PEUAPM and applied with satisfactory results for many years (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] // Composites Science and Technology. - [sl ]: Elsevier, 2001. - Vol. 61. - pp. 1189-1224).

017. Some researchers have proposed reinforcing PEUAPM with carbon fibers (Rushton N and Rae T. The intra-articular response to particulate carbon fiber reinforced high density polyethylene and its constituents: an experimental study in mice [Article] // Biomaterials. - 1984. - Vol. 5. - pp. 352-356) e (Sclippa E. and Piekarski K. Carbon fiber reinforced polyethylene for possible orthopedic uses [Article] // Journal of Biomedical Materials Research. - 1973. - Vol. 7. - pp. 59-570) or even with PEUAPM fibers with the intention of improving resistance to creep, thickness and mechanical strength (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] / / Composites Science and Technology. - [sl]: Elsevier, 2001. - Vol. 61. - pp. 1189-1224). The literature presents contradictory reports, but Deng et al. found no significant difference between PEUAPM with and without reinforcement (Deng M and Shalaby SM Properties of self-reinforced utra-high-molecular weight polyethylene composites [Article] // Biomaterials. - 1997.- Vol. 18.- pp. 654655) .

018. In recent years some geometries of dense alumina or zirconia spheres and acetabulum of similar materials have been proposed

6/30 mainly due to the potential advantages of ceramic materials over high hardness and resistance to compression, low friction coefficient, low wear rate and good biological acceptability of debris particles (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] // Composites Science and Technology. - [sL]: Elsevier, 2001. - Vol. 61. - pp. 1189-1224).

019. The history of substitutions, to relieve and recover the movements of the hip joint compromised by degenerative processes, had the following evolution:

020. Gluck, in Germany, in 1890, was the first to carve ivory to replace the head of the femur and use a rare type of glue. Delber (1919) and Hey-Groves (1926) used ivory to make implants. In 1925 Marius Smith and Peterson created a glass acetabulum. In 1933 the first polymeric acetabulum made of Viscaloid appeared. In 1938, there was the first attempt at an acetabulum made of bakelite. Philip Wiles, in London, 1938, introduced the idea of total prosthesis with acetabular and femoral components, made of stainless steel and implanted in six patients with Still's disease. In 1940, McKee used screws to fix the acetabular component, launching the Mckee-Farrar prosthesis. In 1951, Haboush used, for the first time, acrylic dental cement to fix the components. McKee and Farrar, in Norwich, introduced cobalt chromium, the most inert material (Macedo CAS Development of National Cementless Femoral Stem, Validated by International Standards // Doctoral Thesis. - Porto Alegre: UFRGS, 2007) and (Anderson J. , Neary, F., Pickstone, JV Surgeons, Manufacturers and patients - a transatlantic history of Total Hip Replacement [Book], - [sL]: Palgrave MacMillan, 2007).

021. The application of metallic materials in hip implants is already consolidated in Brazil and in the world (figure 1), however the use of these has brought some problems to users.

022. The metallic biomaterials used in these types of implants have a much higher modulus of elasticity than that of human bone (figure 2), which

7/30 leads to the concentration of efforts on the implant. Human bone grows only by the action of compressive force, so when the patient walks, he is concentrating efforts on the metal. With the decrease of the compressive force under the bone, it starts to suffer weakening caused by descaling (stress shielding).

023. In many cases, the consequence of this decalcification forces the patient to undergo a new surgical procedure to replace the implant with a larger one, in order to recover its stability. It should be noted that most patients who use this type of implant are elderly; surgery has a higher risk and, in some cases, it is impossible to be performed, resulting in the person's inability to walk again.

024. The use of polymeric materials in hip implants can better distribute the compressive load on the bones because they have a lower elastic modulus and decrease the action of descaling the bones by the human body, bringing the benefit of less surgical interventions during the patient's life. .

025. Still, a typical hip implant has an approximate durability of 15 years. Approximately 11% of patients who received total hip implants are over 40 years old. In 2010 the population of people in their 40s was 40 million. This greatly increases the chances that more people will have to do two or more revisions of prostheses during their lives, hence the need to improve existing ones (Latham B. and Goswami T. Effect of geometric parameters in the design of hip implants paper IV [Article] // Materials and Design. - [sL]: Elsevier, 2004. - Vol. 25. -pp. 715-722).

Interaction between implant and human body

026. Tibia, femur and radius have an elastic modulus of approximately 18 GPa while the metals used for hip implants are in the range of 60 to 250 GPa. The polymers used for hip implants are the ones that come closest of the modulus of elasticity

8/30 of the bones mentioned, highlighting PEEC with 8.3 GPa (Katti KS Biomaterials in total joint replacement [Article] // Colloids and Surfaces B: Biointerfaces. - [sl]: Elsevier, 2004. - Vol. 39 - pp. 133-142) e (Schambron T „Lowe A. and McGregor Η. V. Effects of environmental aging on the static and cyclic bending properties of braided carbon fiber / PEEK bone plates [Article] // Composites: Part B - [sl]: Elsevier, 2008. - Vol. 39. - pp. 1216-1220).

027. The material that will replace bone should ideally have the same mechanical, chemical, biological and functional properties as the original (mimicry) (Mano JF [et al.] Bioinert, biodegradable and injectable polymeric matrix composites for hard tissue replacement: state of art and recent developments [Article] // Composites Science and Technology. - [sl]: Elsevier, 2004. - Vol. 64. - pp. 789-817).

028. Biomaterials must resist the internal environment of the human body, which is very aggressive. For example, the pH of fluids in various internal tissues ranges from one to nine. During daily activities, the bones are subjected to stresses of approximately 4 MPa, where tendons and ligaments reach peak tension in the range of 40 to 80 MPa. The average load on the hip joint is greater than three times the weight of a person (3000 N) and the peak during jumps can reach ten times the weight of the body itself. As if that were not enough, these tensions are repetitive and fluctuating, depending on activities such as: standing, sitting, running, stretching and climbing (Black J. Biological Performance of Materials: Fundamentals of Biocompatibility [Book], - New York: Marcel Dekker , 1992).

029. The stress cycles that the finger and hip joints are exposed to each year are estimated to be as high as 1x10 ⁶ and for a standard heart are in the range of 0.5x10 ⁷ to 4x10 ⁷ cycles. This information shows, in a rough way, how critical is the environment to which biomaterials have to resist and also that the conditions of the patient and their activities are important factors to be considered (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] //

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Science and Technology Composites. - [s.l.]: Elsevier, 2001. - Vol. 61. - pp. 1189-1224).

030. In fact, the total hip implant is a clinical service and a technical solution to a problem. Even if the implant is of excellent quality and has a good engineering design, there are other factors that will influence the success of the application, such as: surgical technique, surgical invasion, surgeon's experience, surgical environment and instruments, prophylaxis effects for thrombosis and pulmonary embolism, rehabilitation procedures and patient factors such as bone quality and disease severity (Faulkner A. [et al.] Effectiveness of hip prostheses in primary total hip replacement: a critical review of evidence and an economic model [Journal] / / Health Technology Assessment. - Bristol, UK: HTA, July 1998. - 6: Vol. 2. - p. 146).

031. Titanium has been used extensively for implants because it is inert inside the human body, has high resistance to fatigue and atoxicity. Titanium's ability to promote bone integration depends on its oxide layer as well as on its surface properties such as topography and surface energy (Steinemann S. Titanium - the material of choice? [Article] // Periodontology 2000. - 1998. - Vol. 17. - pp. 7-21).

032. Some in vitro studies have revealed that metal ions, even in non-lethal doses, interfere in the differentiation of osteoblasts and osteoclasts (Thompson GJ and Puleo DA Effects of sublethal metal ion concentrations on osteogenic cells derived from bone marrow stromal cells [Article] / / Journal of Applied Biomaterials. - 1995. - Vol. 6. - pp. 249-258), (Thompson GJ and Puleo DA TÍ-6AI-4V ion solution inhibition of osteogenic cell phenotype as a function of differentiation time-course in vitro [Article] // Biomaterials. - [sl]: Elsevier, 1996. - Vol. 17. - pp. 1949-1954) e (Nichols KG and Puleo DA Effect of metal ions on the formation and function of osteoclastic cells in vitro [ Article] // Journal of Biomedical Materials Research. - 1997.- Vol. 35.- pp. 265-271). It remains to be determined whether these effects on bone cells also occur in vivo (Puleo D. A. and Nanci A. Understanding and controlling the bone-implant

10/30 interface [Article] // Biomaterials. - [s.l.]: Elsevier, 1999. - Vol. 20. - pp. 23112321).

033. The incidence of migration (permanent displacement of a bone implant that occurs after time of use) is an important clinical parameter for predicting the behavior of prostheses over time. This migration factor, the stress field and the material directly influence the design of the total hip prosthesis and are linked to the duration of the proper functioning of the implant until revision (Simões JA and Marques AT Design of a composite hip femoral prosthesis [ Article] // Materials and Design, Porto: Elsevier, 2005. - Vol. 26).

034. The stems of more flexible materials cause less stress on the bone directly connected to the prosthesis, but greater stress on the proximal region and on the cement (when present). In contrast, rigid rods cause greater stress fields, but less stress at the interface. The design challenge is knowing how to minimize the stress field while maintaining the interface tension and micro-movements at acceptable levels (Simões JA and Marques AT Design of a composite hip femoral prosthesis [Article] // Materials and Design. - Porto: Elsevier, 2005. - Vol. 26).

035. There are several methods of fixing hip implants to the human body, but all of them can be grouped into four generic types: mechanical, cemented, growth and adhered means. Most of the time, the prostheses are attached to the bone through growth or a cement. As the name suggests, the type of mechanical means uses pressure placement and various types of clamps, piles and screws. In the last method, fixation is achieved through direct adhesion of the nail to the bone (Ramakrishna S. [et al.] Biomedical applications of polymer-composite materials: a review [Article] // Composites Science and Technology. - [sl]: Elsevier , 2001. - Vol. 61. - pp. 1189-1224).

036. The second type, on the other hand, normally uses a Poly-MethylMet-Acrylate (PMMA) -based cement, mainly in older patients, with the objective of reducing the post-operative rehabilitation time (figure 3a). O

11/30 bone cement is used to fix the prosthesis, but it does not act as an adhesive, but as a filling material. However, for the alternative growth fixation procedure without cement (figure 3b), in young and more active patients, prostheses with a hydroxyapatite (HA) coating or porous surface treatment can be used, which allows bone adhesion, occurring fixation without the possible complications of using cement: erroneous thickness, empty spaces, blood and tissues in contact during surgery, heating of the bone by thermal healing process, healing time that can displace the prosthesis from its original position, breaking of the cement together with parts of the bone, cytotoxic effects, among others (Alves HLR, Bergmann CP and Stainer D. Research Dean [Online], Federal University of Rio Grande do Sul (UFRGS), 2003. - 10 of 01 of 2010. -http: //www.ufrgs.br/propesq/livro2/artigo_hugo.htm) and (Jye WK Stress Analysis of Femur and Femoral Stems for HIP Arthroplasty // Master's Dissertation - Malaysia: [sn], 2006).

037. Some of the problems that also occur in the use of cements (with the exception of surgical problems, formation of cracks and rupture of the lining during use) are often described in association with osteolysis and formation of spongy tissue (Jacobs JJ [et al.] Clinicai implications of osteolysis [Book Section] // Total Hip Revision Surgery / A. from the book Galante JO and Rosenberg AG Callaghan, JJ. - New York: Raven Press Ltd., 1995), (Kawate K. [et al.] Thin cement mantle and osteolysis with a precoated stem [Article] // Clinical Orthopaedics. - 1999. - Vol. 365. - pp. 124129) e (Topoleski LD and Ducheyne P. Cuckler, JM A fractographic analysis of in vivo poly (methyl methacrylate) bone cement failure mechanisms [Article] // Journal of Biomedical Materials Research. - 1990.- Vol. 24.- pp. 135-154). Although cracks have already been revealed through autopsy, damage accumulation through continuous growth and crack growth has not yet been demonstrated in vivo (Cristofolini L. [et al.] Comparative in vitro study on the long term performance of cemented hip stems: validation of a protocol to

12/30 discriminate between good and bad designs [Article] // Journal of Biomechanics. - [s.L]: Elsevier, 2003. - Vol. 36. - pp. 1603-1615).

038. Some authors defend the thesis that the failure starts by detaching from the cement interface with the prosthesis and, afterwards, continues to develop small fractures in the layer of the adhesive component. Some studies using the Finite Element Method (FEM) support this thesis (Harrigan TP [et al.] A finite element study of the initiation of failure of fixation in cemented femoral total hip components [Article] // Journal of Orthopedic Research. 1992. - Vol. 10. - pp. 134-144).

039. The procedures for placing prostheses without cement also have disadvantages such as: very forced (tight) placement where parts of the bone may penetrate the bloodstream and interrupt the flow, the femur may rupture by excessive force during placement and, finally, Surface treatment particles can come off the prosthesis and cause frictional wear between the bone and the bone. For these reasons there is no unanimity on which procedure is better: with or without cement, which refers to the analysis of the case in question and the surgeon's preference (Jye WK Stress Analysis of Femur and Femoral Stems for HIP Arthroplasty // Master's Dissertation. Malaysia: [sn], 2006).

040. The stress analysis in figure 4 shows why the stress fields are normally not the same between the femur bone without and with implant (Jye WK Stress Analysis of Femur and Femoral Stems for HIP Arthroplasty // Master's Dissertation - Malaysia: [ sn], 2006).

041. Hunter's study on cell adhesion (osteoblasts and fibroblasts) shows that PEEC (PEEK450G) showed similar or slightly better results compared to traditional titanium or PEUAPM in orthopedic applications (Hunter A. [et al.] Attachment and proliferation of osteoblasts and fibroblasts on biomaterials for orthopaedic use [Article] // Biomaterials - Great Britain: Elsevier, 1995. - Vol. 16. - pp. 287-295).

042. Polymer hip implants (manufactured with the same dimensions as current metal materials) can minimize the effect of

13/30 stress field through the distribution of charges in a more similar to physiological way. In this way, bone formation around the implant is stimulated and osteolysis is reduced. On the other hand, any material that replaces titanium must have good cytocompatibility in the case of orthopedic applications, which will support the formation of minerals through osteoblasts that help in the initial integration (Sagomonyants KB [et al.] The in vitro response of human osteoblasts to polyetheretherketone (PEEK) substrates compared to comercially pure titanium [Article] // Biomaterials. - [sL]: Elsevier, 2008. - Vol. 29. - pp. 1563-1572).

Poly-Ether-Ether-Ketone Polymer (PEEC)

043. The attempt to use the PEEC in cementless femoral stems (fixed to the bone without the use of adhesives) and isoelastic (that avoid stress shielding) was already carried out in the 1970s and 1980s with unsuccessful results. In the 1990s, it was tried to use composite rods using polysulfones and other combinations of composites also without success. The first composite isoelastic rod successfully created by engineers at Zimmer Inc. (Warsaw, IN) was the model called Epoch I. The rod is composed of three parts: a forged CoCr core, an intermediate PEEC layer and a layer of commercially pure Ti (Kurtz SM PEEK Biomaterials Handbook [Book], - Oxford: Elsevier, 2012. - p. 298).

044. The Epoch I prosthesis has PEEC, but it is not only manufactured with this material. The production process of this rod is extremely complicated and expensive. In addition, it is believed that isoelasticity (reduction of the stress shielding effect) is not so effective since the stem core is metallic and should concentrate a large part of the compressive load that should be passed on to human bone.

045. In addition to Epoch I, other rods have been presented so far, but all with a metallic core (Kurtz S. M. PEEK Biomaterials Handbook [Book], Oxford: Elsevier, 2012. - p. 298).

046. Poly-Ether-Ether-Ketone (PEEC) is a thermoplastic polymer from the Poly-Aryl-Ether-Ketone (PAEC) polymer family that maintains its stability in

14/30 temperatures exceeding 300 ° C, resists chemical and radiation damage, exhibiting greater strength per unit mass than metallic materials, in addition to its biocompatibility and affinity with many different types of reinforcing agents. Other characteristics are: it presents good sterilization (Godara A., Raabe D. and Green S. The influence of sterilization process on the micromechanical properties of carbon fiber-reinforced PEEK composite for bone implant applications [Article] // Acta Biomaterials. - 2007. - Vol. 2. - pp. 209-220) through an autoclave (Morrison C. [et al.] Biomaterials [Article], - Great Britain: Elsevier, 1995.- Vol. 16.- pp. 987-992) , minimal systemic, intracutaneous and intramuscular toxicity (Kurtz SM and Devine JN PEEK biomaterials in trauma, orthopedic, and spinal implants [Article] // Biomaterials. - [sL]: Elsevier, 2007. - Vol. 28. - pp. 4845- 4869), (Vadapalli S. [et al.] Biomechanical rationale for using polyetheretherketone (PEEK) spacers for lumbar interbody fusion-a finite element study [Article] // Spine. - 2006. - Vol. 31. - pp. E992- 888p) and (Toth JM [et aL] Polyetheretherketone as a biomaterial for spinal applications [Article] // Biomaterials. - [sL]: Elsevier, 2006. - Vol. 27 - pp. 324-34).

047. This is a semicrystalline polymer, that is, it has a crystalline and amorphous phase. The percentage of crystallinity is defined by its thermal production process. The crystallinity for PEEC produced by injection is typically 30-35%. The PEEC crystals are spherulitic (approximately 25 to 40 pm in diameter) and formed from thin lamellae (50 to 60A). To obtain changes in crystallinity you can choose between the manufacturing process by machining and injection, but also to control parameters such as the processing temperature, mold time, cooling rate of the part and subsequent annealing. The injection process can form a peripheral layer that can differentiate from the center of the material (Sagomonyants KB [et al.] The in vitro response of human osteoblasts to polyetheretherketone (PEEK) substrates compared to comercially pure titanium [Article] // Biomaterials. - [sL]: Elsevier, 2008. - Vol. 29. - pp. 1563-1572).

048. The insertion of hydroxy groups on the PEEC surface, through reduction carried out heterogeneously with NaBH ₄ in Dimethylsulfoxide

15/30 (DMSO) at 120 ° C, increases the biocompatibility of this polymer moderately. Another way to activate hydroxyls is by reacting with p-nitrophenyl chloroformate. Compounds containing an amine group (lysine) are attached to activate the surface through carbamate bonding, as (Jagur-Grodzinski J. Biomedical application of functional polymers [Article] // Reactive & Functional Polymers. - 1999. - Vol. 39 - pp. 99-138).

049. The PAEC family of polymers has been increasingly used since 1980 as a biomaterial in trauma, orthopedics and spine implant applications (Ponnappan RK [et al.] Biomechanical evaluation and comparison of polietheretherketone rod system to traditional titanium rod fixation [Article] / / The Spine Journal. - [sl]: Elsevier, 2009. - Vol. 9. - p. In press). In the middle of the same decade, PEEC was recognized as a possible candidate for new designs of isoelastic hip stems (which have mechanical properties close to the bone) (Skinner Η. B. Composite technology for total hip arthroplasty [Article] // Clin Orthop Relat Res. - 1988. - Vol. 235. - pp. 224-236).

050. These polymers have a great radiographic facility in relation to titanium, which means a significant advantage in large-scale application (Ponnappan RK [et al.] Biomechanical evaluation and comparison of polietheretherketone rod system to traditional titanium rod fixation [Article] // The Spine Journal. - [sl]: Elsevier, 2009. - Vol. 9. - p. In press). In 1988, Skinner wrote that there was a clear need for femur stems with less thickness and modulus of elasticity (Skinner B.. B. Composite technology for total hip arthroplasty [Article] // Clin Orthop Relat Res. - 1988. - Vol. 235 - pp. 224-236).

051. Another important fact is that this polymer is considered relatively biologically inert, with no reports of an inflammatory reaction caused by the formation of debris particles (particles generated by wear) (Rivard CH, Rhalmi S. and Coillard C. In vivo biocompatibility testing of peek polymer for a spinal implant system: a study in rabbits [Article] // Journal of Biomedical Materials Research. - 2002. - Vol. 62. - pp. 488-498).

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052. Around 1990 PEEC emerged as a leading candidate among high performance thermoplastics to replace metallic implant components, especially in orthopedics and trauma (Liao K. Performance characterization and modeling of a composite hip prosthesis [Article] / / Exp Tech. - 1994.- pp. 33-38) e (Maharaj GR and Jamison RD Intraoperative impact: characterization and laboratory simulation on composite hip prostheses // Jamison, RD; Gilbertson, LN; STP 1178: composite materials for implant applications in the human body: characterization and testing. - Philadelphia: ASTM, 1993. - pp. 98-108).

053. Regarding the need for mechanical loading for these implants, in 1993 surgeons Arthur Steffee and John Brantigan initially envisioned a titanium device that would allow the growth of the bone around them; that's when the two realized that design was the first step. Within this, the biggest challenge was the great thickness of the titanium device that could promote the support of the mechanical load, preventing bone growth. Carl McMillin, a polymer engineer at AcroMed, was familiar with high-performance thermoplastics and recommended the PAEC family to address these limitations. The clinical and commercial success of this lumbar device was a milestone in the current increase in the use of PEEC in spine implants (McMillin C. Evaluation of PEKEKK composites for spine implants [Conference] // 38th international SAMPE symposium. - 1993.- pp. 591 -598).

054. PEEC is still in a period of careful consideration and adoption in orthopedics. The clinical need for the orthopedic community has been focused on extending the longevity of existing implants for the older population, as well as on expanding the clinical success of total joint repair for the youngest and sportsmen. Consequently, recent orthopedic implant technologies need to demonstrate long-term performance over traditional alternatives (NIH Consensus Statement Total Knee Replacement [Online] // National Institutes of Health Technology Assessment Conference, 1994) and (NIH Consensus

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Statement Total Knee Replacement [Online] // National Institutes of Health Technology Assessment Conference. - 2003. - July 30, 2009. - http://consensus.nih.gov/).

055. According to Kurtz, the application of PEEC in hip implants may be feasible through the study of new designs, such as isoelastic nails and modification on the surface of these devices. However, it will take many years, perhaps a decade, before these new devices can be judged to be superior to those currently used (Kurtz SM and Devine JN PEEK biomaterials in trauma, orthopedic, and spinal implants [Article] // Biomaterials. - [sL ]: Elsevier, 2007. - Vol. 28. - pp. 4845-4869).

056. A recent study mentions that so far the objective of osseointegration has not yet been achieved through the selection of the polymeric material, the optimization of the design and the surface finish of the hip prostheses. For this reason, radiographic and histological analysis of PEEC hip stems reinforced by carbon fiber implanted without bone cement in adult sheep and with a control group using titanium rods was proposed. The conclusions show that 50% of the cases of PEEC reached bone anchorage against 100% of the cases of titanium nails. In contrast, 100% of implanted PEEC cases did not show bone resorption in a 12-month period, while 60% of the titanium rods presented osteopenia (precursor to osteoporosis) (Nakahara I. [et al.] Novel Surface Modifications of Carbon Fiber -Reinforced Polyetheretherketone Hip Stem in an Ovine Model [Article] // Artificial Organs. [SL]: Wiley Periodicals, Inc, 2011. - In press).

057. Fatigue tests (see figure 5) showed that the majority of the load was elastic and was dedicated to opening the crack, with the propagation of the crack and consequent rupture being given at the end of the tests. This Sobieraj study was aimed at analyzing PEEC in orthopedic applications and concludes that the stress vs. fatigue displacement showed insignificant hysteresis (material with elastic behavior) indicating the material's resistance range. Finally, the study shows that PEEC is a good option

18/30 for making hip prostheses (Sobieraj M. C. [et al.] Notched fatigue behavior of PEEK [Article] // Biomaterials. - [s.l.]: Elsevier, 2010. - 9156-9162p: Vol. 31).

058. In the patent scope, the following documents were found:

059. Patent US2013282134 (A1), 2013/10/24, “Multi-layered prosthetic constructions, kits, and methods”, this patent reports an invention of a constructive form of prostheses using overlapping layers of ceramic material. In the proposed PEEC invention the material is polymeric and isoelastic, that is, totally solid and formed by a single material that was obtained by extrusion and later machined until its final shape.

060. Patent US8506642 (B1), 2013/08/2013, “Hip implant with porous body”, the document describes a metal rod proposed in two parts to be assembled (split). The material proposed in US8506642 for making the stem is metallic and differs from the present invention which uses polymeric material, PEEC.

061. Patent KR20130069567 (A), 06/26/2013, “Hip implant”, this document describes a rod shape with a design very different from the proposal of the present invention and is specific to the Asian public.

062. Patent US20130131824 (A1), 2013/05/23, “Porous coating for orthopedic implants”, the document makes reference to a process of superficial treatment through the metallic coating of the femur rods aiming at the best adhesion, but it does not deal with its own creation of a stem model.

063. Patent US2013218288 (A1), 2013/03/15, “Dynamic porous coating for orthopedic implant”, the patent refers to a super artificial treatment of nails to improve the fixation at the interface between human bone and nail, and not the proposition of a new design of femoral stem in PEEC polymer as is the case of the invention proposed here.

064. WO2013028735 (A1), 2013/02/28, “Medical device for bone implant and method for producing such a device”, the document describes

19/30 a way to improve the interface between human bone and femoral stems of titanium and zirconia (non-polymeric) through a surface treatment that creates small holes along the stem. In this case, there is no invention of a stem model as proposed in this document.

065. Patent US2013018482 (A1), 2013/01/17, “Implant sleeve for cement hip stems”, the patent describes an accessory called a glove to be attached to nails to assist in the interface / fixation between the human bone and the prosthesis. In this case, there is no proposal for a new fully polymeric design in PEEC as the invention proposed here.

066. Patent US2012265319 (A1), 2012/10/18, “Total hip arthroplasty”, the patent describes the invention of a new model of femoral stem and acetabulum, however the femoral stem is metallic and non-polymeric as proposed in this invention. Furthermore, the design of the rod is very different from the proposed invention.

067. US2012221116 (A1), 2012/08/30, “Hip stem prosthesis”, this document deals with a femoral stem invention using metallic and non-polymeric material (in this case PEEC) proposed in this invention.

068. Patent US20120136455 (A1), 2012/05/31, "Prosthetic hip implants", the patent deals with an invention of a composite stem of a different design from the one proposed here, that is, which has polymer and metal. The invention proposed here shows an isoelastic rod, that is, made entirely of only one polymeric material, in this case PEEC.

069. Patent WO2012065068 (A1), 2012/05/18, “Orthopedic implant with porous polymer bone contacting surface”, the document deals with an invention of a totally polymeric stem, but not isoelastic since it proposes two different polymers (one internal and another external), contrary to the invention proposed here as a massive PEEC rod.

Summary of the Invention

070. It is an object of the present utility model to produce an isoelastic femoral stem made of polymer for hip prostheses.

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071. In a preferred embodiment, the polymeric material used is polyether-ether-ketone (PEEC).

072. In a preferred embodiment, the rod manufacturing process takes place by machining.

073. The novelty lies in the fact that it is possible to obtain a femoral stem design made from commercially used polymers with properties closer to human bone, which support the fatigue test that simulates the stress conditions to which a stem must be subjected in order to be mechanically approved for use.

074. There are no records in scientific articles or patents that demonstrate that this has been achieved. There are only successful cases in composite prostheses using PEEC and other polymers, but always with a metallic core. It is believed that this does not achieve the objective of bringing the properties of the femur closer to the substitute material, since the metal has very different properties from human bone.

075. The industrial application of this invention is potentially integral, as the stem was developed with medical grade polymeric material commercially known as PEEK OPTIMA LT1 donated by Invibio Ltd. (Thornton Cleveleys, United Kingdom) and which is already used commercially in medical applications in humans such as: bone intramedullary fixators, intervertebral cages (cages), screws and plates.

076. The use of PEEC or other polymers in hip implants better distributes the compressive load on bones, as it has a lower density and mainly a lower elastic modulus that reduces the action of descaling bones by the human body, bringing the benefit of less surgical interventions during the patient's life.

077. The advantages of using PEEC or other polymers in hip implants are:

a) non-occurrence of metallosis (inflammatory reaction of tissues to metal);

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b) ease of manufacturing by machining at lower costs than metal;

c) possibility of even greater cost savings through plastic injection;

d) possibility of increasing the duration of the implanted nail, reducing the number of nail replacement surgeries throughout the patient's life (reduction of the sfress shielding effect).

Description of the Figures

Figure 1 - Components of a typical total hip implant (Alves, et al., 2003), as described below:

a) Acetabulum - acetabular component

b) Femoral head

c) Femoral stem

Figure 2 - Example of a hip implant placed on a patient's two legs (Machado, 2008)

Figure 3a - Sectional view of a hip implant with cement in older patients, comprising:

a) metal

b) cement

c) bone

Figure 3b - Sectional view of a hip implant without cement and with superficial porosity treatment in young and active patients, composed of:

a) metal

b) porous treatment

c) bone

Figure 4a - Load transfer in the intact femur

Figure 4b - Load transfer in the femur with hip prosthesis

Figure 5 - Experimental data and regression curves based on Basquin relationships of fatigue

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Figure 6 - Prosthesis stem proposed for manufacture in polyetheretherketone polymer (PEEC)

Figure 7 - Bottom photo of the standard alumina sphere used in conjunction with the proposed stem model the ten proposed stem models

Figure 8 - Three-dimensional model of the alumina sphere used

Figure 9 - Fatigue curve for TECAST-L manufactured by injection.

Figure 10a - Stem meshing results with frontal view of the acetabulum, sphere and stem

Figure 10b - Stem meshing results with side view

Figure 10c - Stem meshing results alone

Figure 11 - Von Mises stress results in the static test of stem 01 in TECAST-L

Figure 12 - Results of deformations in the static nail test in TECAST-L.

Figure 13 - Displacement results in the static stem test in TECAST-L.

Figure 14 - Von Mises stress results in the TECAST-L stem fatigue test.

Figure 15 - Tractive fatigue curve for PEEK Optima® LT1 at 23 ° C and 0.5Hz Figure 16 - Von Mises stress results in the static test of stem 01 in PEEC.

Figure 17 - Results of deformations in the static test of the stem in PEEC. Figure 18 - Displacement results in static PEEC stem test.

Figure 19 - Von Mises stress results in the PEEC stem fatigue test.

Figure 20 - Machining of the first shank performed in PEEC OPTIMA® LT1 in (a) roughing of the upper part; (b) finishing the upper part; (c) finishing the sides of the upper part; (d) finishing the bottom; (e) and (f) finishing the sides of the bottom

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Figure 21 - Finishing of the rod made in PEEC OPTIMA® LT1 after sanding and polishing the four faces

Figure 22 - Fixation of the rod in TECAST-L (a) positioning of the rod before placing it in the device together with the placement of a thermocouple to control the curing temperature, (b) internal view of the fixation device, (c) view of top of the stem insertion into the fixation device respecting the lateral and frontal angles of the standard (ISO 7206-4, 2011) and (d) device with the resin inserted together with the stem and in the curing process soaked in water at room temperature

Figure 23 - Configuration of fatigue test on stem 01 in TECAST-L with coupled thermographic camera

Figure 24 - Graph of the fatigue test performed on stem 01 in TECAST-L showing the recorded values of minimum and maximum load until the end of the 5x10 ⁶ cycles.

Figure 25 - Graph of the fatigue test performed on stem 01 in PEEC showing the recorded values of minimum and maximum load until the end of the 1x10 ⁷ cycles.

Detailed Description of the Invention

078. The examples shown here are intended only to exemplify one of the numerous ways of carrying out the invention, however without limiting the scope of it.

Hip stem and ball used

079. The rod proposed in this utility model (figure 6) and sphere were modeled using the three-dimensional Computer Assisted Design (DAC) software, SolidWorks 2010 and have the following characteristics:

a) the commercial sphere (figure 7) used is made of alumina and has a 32 mm external diameter;

b) according to the fatigue norm ISO 7206-4: 2011 the proposed stem length (CT) was within the average size range (120 mm <CT <250 mm);

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c) the project provides for application without using cement to fix the femur (cementless prostheses).

080. The three-dimensional model of the commercial sphere used (figure 8) was obtained through a Coordinate Measuring Machine (MMC) with resolution (0.0001 mm) and dimensional capacity of 750 (x) x 500 (y) x 500 ( z).

Finite element analysis

081. The model of the presented femoral stem was analyzed by the Finite Element Method (MEF) through the computer simulation software SolidWorks Simulation 2012.

082. The results presented were produced using the criteria described below:

• the form of contact between the acetabulum-sphere and the sphere-rod was of the contact type without penetration and without friction (the most severe condition possible);

• the sphere and the acetabulum were considered completely homogeneous and made of material called alumina (AI ₂ O ₃ );

• the stem was considered totally homogeneous and with the mechanical properties (tensile and compressive yield stress, elastic modulus, flexion, etc.) of the medical grade commercial PEEC Optima® LT1 from Invibio Ltd. (Thornton Cleveleys, United Kingdom) for the simulation, as we have traction, compression and flexion occurring at different points during compression and the fatigue curve and properties in the same way were also used for the simulation with TECAST-L;

• shank of the stem 80 mm apart from the lower end of the stem (ISO 7206-4, 2011);

• fixed rod with frontal tilt angle, a, 10 ° and lateral, β, 9 ^o (ISO 7206-4, 2011);

• static test with a maximum compressive force of 2300 N applied orthogonally in the acetabulum and always passing through the center of the sphere;

• after the static test the rod was submitted to the fatigue test with a minimum cyclic load of 200 N and a maximum of 2300 N for a minimum of 5x10 ⁶ cycles (ISO 7206-4, 2011).

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083. Firstly, a simulation was performed using TECAST-L material (properties shown in table 2) and figure 9 shows the fatigue performance of this material.

084. Figure 10 shows the images of the solid rod mesh with an element size of 1.5 mm. This mesh was of the type Jacobian 4 points with 0.075 mm tolerance, total knots of 277,273 and total elements of 190,863 with 99.5% of the elements with aspect ratio less than 3.

085. The results regarding the static stress field (Von Mises) of the stem are shown in figure 11. Note that the maximum stresses reached approximately 60 MPa in the region of the setting. It is important to note that the compressive yield stress of TECAST-L is close to 70 MPa.

086. The deformations suffered by the stem are shown in figure 12 where it is seen that the maximum is in the range of 2.9% in the region of the bezel and neck.

087. In addition to the deformations, the stem also suffered displacements from its original position and these are shown in figure 13, where it is noted that the greatest displacement occurred in the acetabulum, which moved about 2.8 mm, however the stem had its displacement maximum of approximately 2.3mm.

088. The stem was considered approved in the static test simulation, therefore, it was subjected to the simulated fatigue test and the results are shown in figure 14 which shows that the stem, in numerical simulation, perfectly supported the 5x10 ⁶ cycles required by the ISO standard 7206-4: 2011 reaching up to 1x10 ⁷ cycles.

089. The mechanical properties of the PEEC material of the stem were the same as the commercial PEEK Optima® LT1 of Invibio Ltd. (Thornton Cleveleys, United Kingdom) and are shown in table 1.

Optima® Unit Method Property

Voltage of

ISO 527

MPa

100

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flow Elongation ISO 527 % 20 Flexion Module ISO 178 GPa 4 Bending Stress ISO 178 GPa 170 Izod Impact ISO 180 kj / m ² 7.6 (notch) Density ISO 1183 g / cm ³ 1.3 Module of «Βίββ iSiSS # GPa 3.5 Elasticity

Table 1 - Mechanical Properties of PEEC Optima® LT1. Source: adapted from (Kurtz, 2012).

090. Figure 15 shows the fatigue performance of the commercial PEEC PEEK Optima® LT1, which was used for fatigue simulation of the acetabulum, sphere and stem set according to ISO 7206-4: 2011. Although this curve was obtained in traction and the fatigue performance is simulated in compression, it is believed that the real compressive performance must be equal to or greater than the tractive one.

091. Figure 10 shows the images of the solid rod mesh with an element size of 1.5 mm. This mesh was of the type Jacobian 4 points with 0.075 mm tolerance, total knots of 277,273 and total elements of 190,863 with 99.5% of the elements with aspect ratio less than 3.

092. The results regarding the static stress field (Von Mises) of the stem are shown in figure 16. Note that the maximum stresses reached 80.9 MPa in the neck and bezel region. It is important to note that the compressive yield stress of PEEC is close to 118 MPa (Calvary Spine, 2012) and the tensile strength is 100 MPa (see table 1).

093. The deformations suffered by the stem are shown in figure 17 where it can be seen that the maximum is in the range of 3.5% in the region of setting and neck.

094. In addition to the deformations, the stem also suffered displacements from its original position and these are shown in figure 18, where it is noted that the largest

27/30 displacement occurred in the acetabulum, which moved about 3.7 mm, but the stem had its maximum displacement of approximately 3.3 mm.

095. The stem was considered approved in the static test simulation, therefore, it was subjected to the simulated fatigue test and the results are shown in figure 19 which shows that the stem, in numerical simulation, perfectly supported the 5x10 ⁶ cycles required by the ISO standard 7206-4: 2011.

Manufacturing of the rod by mill

096. The manufacture of the rod by machining was performed in extruded billet of 80mm in diameter by 1m in length of PEEC OPTIMA® LT1 donated by the company Invibio Ltd. (Thornton Cleveleys, United Kingdom).

097. Machining tests were performed on TECAST-L polymer in a billet format with a diameter of 100mm and a length of 1m and which has machining properties close to PEEC, but at a much more affordable cost (see table 2). The TECAST-L used has no medical degree, being used only for preliminary tests and comparison.

properties Value (dry / wet) unity Reference norm MEC / \ NICAS Tensile strength (flow) 70 MPa DIN EN ISO 527 Elongation (flow) % DIN EN ISO 527 Elongation (break) 50 % DIN EN ISO 527 Modulus of elasticity (traction) 3200 MPa DIN EN ISO 527 Modulus of elasticity (flexion) MPa ASTM D 790A Toughness DIN EN 53 456 Deformation resistance after 1000h with static load MPa Strain strain to 1% elongation after 1000h MPa Impact resistance (Charpy - 23 ° C) n.b. KJ / m ² DIN EN ISO 179 Friction coefficient (in ground steel - p = 0.05 N / mm ^2. V = 0.6 m / s) THERMAL Glass transition temperature 40 5 ° C DIN 53 765 Heat distortion temperature (HDT) - ° C ISO R 75 / DIN

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method A 53 461 Heat distortion temperature (HDT) method B ° C ISO R 75 / DIN 53 461 Maximum service temperature - short duration 170 ° C Maximum service temperature - long life 100 ° C Coefficient of thermal conductivity (23 ° C) W / (K.m) Specific heat (23 ° C) J / g.K Thermal expansion coefficient (23 ° C-55 ° C) 9 10 ' ⁵ 1 / K DIN 53 752 ELECTRICAL Dielectric Constant (10 ⁶ Hz) DIN 53 483, IEC-250 Dielectric loss factor (10 ⁶ Hz) DIN 53 483, IEC-250 Specific volume of resistance D * cm DIN IEC 60093 Surface resistance Ω DIN IEC 60093 Dielectric strength KV / mm DIN 53 481, IEC-243, VDE 0303 Leakage current resistance MISCELLANEOUS DATA Density 1.15 g / cm ³ DIN EN 53 479 Water absorption content (23 ° C / 50%) % DIN EN ISO 62 Water absorption content until saturation 6 % DIN 53 495 Flammability HB UL Standard 94 Hot water resistance, baking soda Weathering resistance Crystals Melting Point 220 ° C DIN 53 765

Table 2 - Properties of TECAST-L used as a polymer for machining test.

098. After machining tests in TECAST-L to improve the manufacturing process, the first part of the stem model in PEEC OPTIMA® LT1 was machined in medical grade using only air as the refrigerant (figure 20).

099. After machining, sanding and manual polishing, the final finish of the nail is shown in figure 21. Only the cone and collar of the nail were finished with machining (there was no sanding and polishing process).

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Fatigue test

100. To perform the fatigue test, initially a fixation test was carried out with self-polymerizing acrylic JET brand composed of liquid part (methyl methacrylate monomer) and powder (methyl ethyl methacrylate polymer) on the stem in TECAST-L material, as shown in the figure 22. The inclusion of a T-type thermocouple during curing of the stem was performed to monitor the evolution of temperature. This initial test was not carried out directly on the PEEC stem as there were doubts as to whether the properties of the stem would change due to the temperature reached during the polymerization process and whether the fixation of the same to the resin during the fatigue test would occur.

101. The fixation of the test rod in TECAST-L on the fatigue tester reached a maximum temperature during curing of 95.6 ° C, which is below the glass transition temperature of PEEC OPTIMA LT1 which is 150 ° C ( Kurtz, 2012).

102. After fixing the TECAST-L rod to the device, the fatigue test was performed on a servo-hydraulic machine of the MTS brand (Eden Prairie, Minnesota, United States of America), model 810 and 100kN capacity, initially testing the frequency of 10Hz for 6191 cycles when the test was stopped and resumed with 20Hz for another 16336 cycles, reaching a total of 22527 cycles. According to ISO 7206-4: 2011, the maximum allowed frequency is 30Hz, which was used constantly until the end of the test, which reached 5x10 ⁶ cycles. The minimum compressive load was 300N and the maximum 2300N. To observe the behavior of the stem in relation to temperature (figure 23), a thermographic camera was used.

103. The test rod fatigue test in TECAST-L was carried out and withstood the 5x10 ⁶ cycles without any apparent plastic damage and deformation. During the tests with the frequencies of 10, 20 and 30Hz they also did not show significant heating since the ambient temperature was at 17 ° C and the rod reached 18 ° C during the 6191 cycles

30/30 performed at the frequency of 10Hz, 19 ° C for the next 16336 cycles and 20 ° C until the end of the test (5x10 ⁶ cycles), as shown in figure 24.

104. The fixation of the final PEEC stem in the fatigue tester reached a maximum temperature during curing of 105 ° C, which is below the glass transition temperature of PEEC OPTIMA LT1 which is 150 ° C.

105. The PEEC rod fatigue test was carried out and withstood the 5x10 ⁶ cycles being maintained until reaching 1x10 ⁷ without any apparent plastic damage and deformation (figure 25). During the entire test with the frequency of 30 Hz, there was also no significant heating as the prosthesis reached, at most, 2 ° C higher than the ambient temperature, which was maintained on average at 20 ° C because it was in an air-conditioned room.

Claims (5)

Claims 1. Femoral Isoelastic Rod Made of polymer characterized by comprising the following elements a) a commercial sphere (figure 8) made of alumina with a 32 mm external diameter, but not restricted to this measure b) a rod of length within the medium size range (120 mm <CT <250 mm), but not restricted to this measure. 2. Femoral Isoelastic Rod Made of Polymer, according to claim 1, characterized by being made of polyether-ether-ketone (PEEC) or other biomedical grade polymer. 3. Femoral Isoelastic Rod Made of Polymer, according to the item a) of claim 1, characterized by the sphere and acetabulum being considered totally homogeneous and made of material called alumina (Al2o3), but not being restricted to these materials. 4. Femoral Isoelastic Rod Made of Polymer, according to the item b) of claim 1, characterized in that the stem is considered totally homogeneous and with the mechanical properties of the commercial medical grade PEEC optima®, or other medical grade polymer. 5. Femoral Isoelastic Rod Made of Polymer, according to item b) of claim 1, characterized by containing the provisions shown in figures 1,6, 16,17,18, 19, 21 AND 25.