Orthopaedic implant technology is heavily based on the development and use of biomaterials. These are non-living materials (e.g. metals, polymers and ceramics) that are introduced into the human body as constituents of implants that fulfil or replace some important function. Examples would be prosthetic joint replacements and fracture fixation implants. For orthopaedic biomaterials to succeed in their desired functions and outcomes in the body, a number of factors need to be considered. The most obvious mechanical properties of the implants are that they need to suit their intended function, and various classes and types of biomaterials have been developed and characterised for use in different implant components depending on their demands. Less well understood but no less important are the interactions that occur between the constituent biomaterials and the living cells and tissues, both of the human host as well as pathogens such as bacteria. Biomaterials used for orthopaedic applications are generally considered to be biocompatible. However, adverse effects arising from interactions at the implant interface can result in various modes of implant failure, such as aseptic loosening and implant infection. This review paper uses the illustrative example of total hip replacement (which has been called the operation of the century) to highlight key points in the evolution of orthopaedic biomaterials. It will also examine research strategies that seek to address some of the major problems that orthopaedic implant surgery are facing today.
The orthopaedic implant sector forms a significant portion of the worldwide biomedical industry. In the US alone, the orthopaedic implant market was estimated at over US$14 billion in 2008, and this is projected to rise to US$23 billion by the year 2012. Within this large and diverse field of orthopaedic surgical practice, there are 4 major implant applications: (i) reconstructive joint replacements, (ii) spinal implants, (iii) orthobiologics and (iv) trauma implants. The clinical need in all of these areas is anticipated to continue to grow for the foreseeable future, boosted by local and worldwide ageing populations, as well as increasing prevalence of physically active lifestyles and higher expectations of quality of life in older age groups.
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