Orthopedic implants are artificial devices incorporated into bones and joints to restore normal function. Often, orthopedic implants act as joint replacements in cases where the hip, knee, shoulder or elbow have been damaged by injury or by diseases such as osteoarthritis, where wear and tear on joints leads to pain and stiffness. Orthopedic implants are usually only used when non-surgical treatment methods have failed. They tend to wear out after a number of years and, for this reason, implants given to younger people may need replacing at some point.
A number of different materials are used to make orthopedic implants, including plastic, ceramic and metals such as stainless steel and titanium. Implants may be fixed into place in a variety of ways. Cement or screws may be used to anchor them, or they may be held in position by the pressure of their surroundings. Often, bone growing in from around an orthopedic implant can help secure it. Sometimes one part of an implant is cemented while another part is not, as is the case for a type of hip replacement, referred to as hybrid, where the stem bearing the ball part of the joint may be fixed with cement while the receiving cup is not.
Titanium orthopedic implants have the advantages of being strong yet light, and the body does not usually react to them. A disadvantage is that it is hard for bone cells to stick to the shiny surface of the metal, making it difficult for fusion with bone to occur as part of the healing process. Advances in research are finding new ways to etch microscopic tubes called nanotubes into the surface of titanium, a process which was previously too expensive to be practical. The structure of these nanotubes makes them attractive to water and provides a suitable environment for the growth of cells.
Although orthopedic implants have benefits, such as increasing mobility and reducing the pain associated with injury or degenerative joint disease, there are some disadvantages which occur occasionally. Implants may loosen or break, and rarely the body may react against them. Sometimes infection may set in, which can make it necessary to replace an implant. Bacteria can grow on the surface of an orthopedic implant, forming what is called a biofilm, and to resolve this the implant must be removed and the infection treated before a replacement can be installed. Research into what are known as hydrogels may offer hope for the future, as these water-absorbing substances are unfriendly to bacteria, while still allowing the growth of bone cells, and they can be added to the surface of an implant to minimize the chances of infection taking hold.