Polymers - Orthopaedic Biomaterials in Research and Practice - page 158

composed of these materials do not provide enough fracture stability
to be safely used in the load-bearing regions of most adult patients.
Because the materials have low strength, resorbable bone plates tend
to be bulky and cumbersome. The materials may also associated with
a significant amount of redness and swelling, discharge, local pain,
and osteolysis. These are symptoms of a transient mild microscopic
foreign body reaction associated with the macrophage digestion of the
polymers. Inflammation has been linked to a local acidosis secondary
to an imbalance between rapid material degradation and slow mate-
rial resorption. Osteolytic changes around self-reinforced polylactide
screws have been demonstrated to occur in approximately a quarter of
cases in some studies. Large plates have been associated with swelling
recorded up to 3 years after the surgery. Resorbable materials can be
self-reinforced (SR) to improve on some of the drawbacks to the mate-
rial performance. But despite recent advances, absorbable plating has
not seen widespread use because of the stated concerns.
Other resorbable polymeric materials, including processed collag-
enous allografts and xenografts, natural and synthetic suture mate-
rials, and bone void fillers, have also been used to varying degrees.
Absorbable sutures and bone void fillers are currently widely available,
while resorbable orthopaedic grafting materials are still on the market
fringe.
Other polymers
The profusion of polymers and the growing ability to fashion them to
yield specific properties have led to the experimental use of many new
polymers in biomedical devices. In orthopaedic implants, this has been
relatively limited. However, for completeness, several of these materials,
their trade names, and their potential applications are listed in Table 6.4.
Medical grades of the vast majority of these materials do not exist nor
have they been approved for routine clinical use. However, some have
been previously qualified for and used in food-packaging applications;
these “food contact” grades are suitable for early experimental aspects
of new biomaterials and implant development.
additional problems
PROBLEM 6.4
Polymers are (select the best answer[s])
A. Brittle, strong
B. Ductile, weak
C. Ductile, strong
D. Brittle, weak
E. None of above