Metallic biomaterials of knee and hip - a review

One of the most significant current discussionsin orthopedic is the total joint replacementsespecially hip and knee and the increasingtrend to replace degraded and destroyedbiological materials by artificial organs. It isestimated that approximately 1 million hipreplacements and 250,000 knee replacementsare carried out per year [1]. This number isexpected to double between 1999 and 2025 asa result of aging populations worldwide andgrowing demand for a higher quality of life [2].Another statistical data estimated that by theend of 2030, the number of total hipreplacements will increase by 174% and totalknee arthoplasties is predicted to grow by 673%from the present rate [3]. An increasing trend ofthe number of knee replacements in differentcountries over the last 10–15 years is shown infig 1.Yet-increasing demand for implants makes itcrucial to accelerate efforts on biomaterials.Unfortunately, the currently used materials havebeen found to have tendencies to fail after long-term usage due to not fulfilling some vitalrequirements such as modulus close to that ofbone, high wear and corrosion resistance andgood biocompatibility. Rimnac et al.[4]investigated the failure of orthopedic implantsin three case studies (hip and knee) andillustrated that both material and designdeficiencies contribute to failure of total jointreplacements. Failure of current biomaterialsimposes pain for patient and after some timerevision surgery should be performed.The purpose of this paper is to review somerecent researches about presently usedmetallic biomaterials and discuss on greatpotential of NiTi and porous NiTi shape memoryalloys (SMA) for orthopedic implant. Meanwhilethis study seeks to address the followingquestions:1) When a material is going to be used in thehuman body, what kinds of requirements shouldbe fulfilled by that material to be considered asa successful biomaterial?2) What kind of problems can occur if theserequirements are not satisfied by the material?3) Which of the requirements present in thecurrently used materials and which cannot befulfilled?4) What solutions are available for improvingthe properties which are not completelysatisfied by the biomaterials?5) Do the NiTi and porous NiTi shape memoryalloys have necessary requirements to beutilized as a metallic biomaterial for orthopedicimplants especially hip and knee?The reminder of this paper is organized asfollows; section 2 describes the requirementsand general issue about biomaterials. So thetwo first research questions will be answeredin this section. Section 3 will address questions3-5. Superior properties of these materials willbe discussed in section 4. Final sectionconcludes and purposes further works.