Biomedical Engineering Reference
In-Depth Information
2
Titanium and cobalt±chromium alloys for
hips and knees
C . Y A O , Nanovis LLC, USA and J . L U and
T . J . WE B S T E R , Brown University, USA
Abstract: As dominant materials used in today's joint prostheses, titanium
and cobalt±chromium alloys frequently suffer from failure due to wear
particles, mismatch of modulus, lack of sufficient osseointegration for
cementless implants, etc. From this point of view, this chapter will first
review material science fundamentals of titanium and cobalt±chromium
alloys currently used in hip and knee replacement as well as pointing out
their shortcomings in some specific areas. Then, advances in this field will
be discussed. Lastly, this chapter will focus on discussing one of the
promising metal surface modification methods, called anodization, which has
increased implant osseointegration. Some additional surface treatments to
increase wear resistance and biocompatibility of titanium and cobalt±
chromium alloys surfaces will also be discussed at the end of the chapter.
Key words: titanium, cobalt±chromium, hip replacement, knee replacement,
surface modification, osseointegration.
2.1 Hip and knee joint replacement
The use of modern hip replacements can be traced back to the 1960s when
Charnley (1961) performed the first modern total hip replacement with low
friction arthroplasty (shown in Fig. 2.1). Following Charnley's success, numerous
attempts have been made to design knee replacements. Since then, continued
innovations in hip and knee replacements have been made and they have become
one of the most successful and revolutionized surgeries in the orthopedic field.
Total hip replacements as well as knee replacements enable hundreds of thousands
of elderly patients to fight against arthritis and restore their quality of life. Today,
younger patients can even expect physically demanding activities after
implantation of highly functional and long-lasting joint prostheses.
2.1.1 Hip implant design and construction
Physiologically, the hip joint is called a ball-and-socket structure because the
spherical head of the thighbone (femur) moves inside the cup-shaped hollow
