BIOMATERIAL APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 529

(a)
Metal acetabular
shell
UHMWPE liner
Femoral head
Porous coating
Femoral stem
(b)
Figure 15.2. Typical components found in an assembled total hip replacement (THR) implant.
It should be noted that this is one of many artifi cial joint designs used in THR arthroplasty.
For example, implants secured by bone cements would not be porous coated. Similarly, the
ultrahigh molecular weight polyethylene (UHMWPE) acetabular cup is sometimes not capped
by a metal (cobalt- or titanium-base alloys or unalloyed tantalum) shell (a). Acetabular cup
components, which are fi tted over the femoral head, featuring plasma-sprayed shell with
anatomic screw hole placement (b). Adopted from chapter 1. overview of biomaterials and
their use in medical devices, In: Handbook of materials for medical devices. Ed. J. R. Davis, ASM
International (USA), 2003 pp. 1 - 11.
are not fully known, metals in general do not form an interfacial bond with bone.
The implant is typically connected to bone via a micro-mechanical interlock using
a variety of surface designs and textures that are used to promote bony in-growth
and improve the interfacial attachment. There are many implants available, each
designed for a specifi c function. Most are made of titanium, an inert metal that
has been proven to be effective at fusing with living bone, a process known as
“ osseointegration. ” The cylindrical or screw type implant, called “ root form, ” is
similar in shape to the root of a tooth with a surface area designed to promote
good attachment to the bone. It is the most widely-used design and generally
placed where there is plentiful width and depth of jawbone. Where the jawbone is
too narrow or short for immediate placement of root form implants, the area may
be enhanced with bone grafting to allow for their placement. When the jawbone
is too narrow and not a good candidate for bone grafting, a special narrow implant,
called “plate form,” can be placed into the bone. In cases of advanced bone loss,
the “subperiosteal” implant may be prescribed. It rests on top of the bone but
under the gums. The actual implant procedure involves the surgical placement of