Cementless Fixation of Total Hip Replacements Essay

Cementless Fixation of Total Hip Replacements - Essay Example Literature supporting or refuting both philosophies is available. Cemented fixation - Cemented stems have a variety of smooth, textured, and coated surfaces that bond to a layer of cement. These stems occupy 80% of the medullary canal to allow for a mantle (ie, cement-occupied space). A centralizer is added to many cemented stems to keep the stem in the center of the canal, which provides a uniform space for the cement around the implant. (Canale, 1998, 314). Differing philosophies guide surgeons in selecting cemented femoral implants for patients. There was a trend in the 1980s to use more cementless implants; in the 1990s, cemented implants regained popularity. Currently, surgeons are favoring cementless techniques again as a result of proven extended service life in long-term outcome studies on porous implants. Cement is indicated when a patient's bone quality cannot be stabilized satisfactorily with a cement-less implant (Wheeless', 2003). The basic principle of uncemented fixation is that the initial stability of an implant is achieved by mechanical interlock and initial apposition of implant surfaces to host bone is converted to long-term stability by the ingrowth/ongrowth of a stable biological interface (Bloebaum etal, 1997) Cementless or pressfit fixation - with use of cemented impant systems, problems related to cement fixation, including loosening, bone loss, and signs of fragmented cement, were identified. Research efforts led to fixation without cement by using femoral stems tightly fit into the canal. This technique often is referred to as pressfit. Pressfit femoral stems have a porous surface that allows bone ingrowth into the stem, referred to as biological fixation (Hoffmann, 2000). One of the coating systems for implants is calcium phosphate-based material called calcium hydroxyapatite. Hydroxyapatite is the inorganic phase of bone, is inherently compatible with the body, and has been shown to promote bone growth and enhance implant fixation (Geesink etal, 1987). It is used as an additional way to bond bone biologically to a stem and cup. These stems provide immediate implant stability and fit tightly to the endosteal cavity of the proximal femur. There are four basic shapes for press-fit femoral stems-anatomical (ie, bowed), modular, straight, and tapered (Canale, 1998, 315, Hoffmann etal, 2000). The anatomical stem has experienced increased popularity and market growth as a result of excellent long-term results documented in the literature (Hoffmann etal, 2000). The porous coated stem previously was indicated for use in active, young patients and for revision of cemented hips, but now surgeons are using pressfit stems in patients of all ages who have good bone stock (S Rapp, 2003, 14). Physiology of the cementless system Micromotion of 20 m or less at the bone-implant interface will create an environment in which stable bone ingrowth can occur, that motions of 40 m lead to less stable interfaces, and that motions of 150 mm will prevent this