Biomedical Engineering Reference
In-Depth Information
7.2.1 Problems With the Current Orthopedic Implants
With the rapid development of orthopedic implant technology, various bone
implant surgeries and procedures (such as for healing bone fractures, repairing
defects, and inserting hip and knee replacements) are routinely performed.
The fi rst hip replacement was conducted in 1923. However, the most signifi cant
breakthrough happened in the 1960s with the introduction of the ultra-low
friction cemented arthroplasty by John Charnley [2,3]. Since then, as one of the
most important surgery advances of last century, this orthopedic implant technol-
ogy has rescued a myriad of people suffering intense pain and limited mobility
from arthritis. The American Academy of Orthopedic Surgeons reported that in
the United States alone, in just a four-year period, there was a 19.7% increase in
hip replacements performed from nearly 274,000 procedures in 1999 (including
168,000 total hip replacements and 106,000 partial hip replacements) to 328,000
procedures in 2003 (including 220,000 total hip replacements and 108,000 partial
hip replacements) [4]. The total number of hip replacements is projected to
almost double by 2030 to 272,000 procedures [4], a staggering number as well as
a trend unavoidably accompanied by increasing hospitalization costs.
Although orthopedic implants have become more successful over the recent
decades, it is important to note that current orthopedic implant technology has
not been perfected. While 90% of hip and knee replacements can last ten to
fi fteen years on average, and implant joints for some patients have endured for
more than 20 years with no problems, occasionally hip or knee replacement
implants may fail immediately after surgery [5]. Considering the endurance of
current orthopedic implants, younger and more active patients (men under
60-years-old and women under 55-years-old) will inevitably need more than one
revision surgery in their lives. For example, in the United States, nearly 11% of
hip replacements (36,000 revisions for 328,000 replacements) and 8% of knee
replacements (33,000 revisions for 418,000 replacements) were revision proce-
dures of previously failed hip and knee replacements in 2003 [5]. A similar trend
occurs in other industrialized countries as well. Due to the strikingly increasing
number of patients who need various medical implants and the relatively high
percentage of revision procedures performed around the world, it is urgent to
develop a new generation of orthopedic implant technology and a set of materials
that can signifi cantly lengthen the service lifetime of orthopedic implants and,
thus, dramatically reduce patient pain and health insurance costs.
7.2.2 Reasons for Implant Failures
Many reasons can lead to implant failures. For example, in the early stage of im-
plant surgery, many acute complications, severe host responses (such as infection
and infl ammation), prosthesis dislocations, and surgery failures (such as improp-
er placement and cement extrusion) may lead to implant failure [6]. After several
years, various additional reasons including implant loosening, osteolysis (soften-
ing of the bone tissue), wear of articulating surfaces and biomaterial fracture
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