Biomedical Engineering Reference
In-Depth Information
PROBLEM 7.4
Compared with stainless steels and cobalt-base alloys, pure titanium is
(select the best answer[s])
A. Relatively flexible
B. Wea ker
C. Heavier
D. Easier to machine into complex shapes
E. Nonelastic
ANSWER:
A
(poor term, but refers to modulus). Titanium has a higher σ
u
than cast
stainless steel (not
B
), is less dense than either stainless steel or cobalt-
base alloys (not
C
), is relatively difficult to machine (not
D
), and is obvi-
ously elastic (not
E
).
PROBLEM 7. 5
The most important theoretical advantage of titanium alloy over stain-
less steel internal fracture fixation plates is (select the best answer[s])
A. Titanium alloys are lighter than stainless steel.
B. Fracture healing rates are somewhat improved by the use of tita-
nium alloy plates.
C. Titanium alloy plates are considerably less costly.
D. There is less bone loss under titanium alloy plates during healing
and remodeling.
E. Greater screw torque and therefore better fixation stability can be
achieved with titanium alloy parts.
ANSWER:
It has been reported that less rigid plates, within limits, do produce
less resorption and remodeling in an animal model (Moyen BJ-L,
Lahey PJ Jr, Weinberg EH, Harris WH: Effects on intact femora of
dogs of application and removal of metal plates. A metabolic and
structural study comparing stiffer and more flexible plates.
Bone
Joint Surg
60A:940-947, 1978); thus,
D
is the best answer. Titanium
is lighter than stainless steel, but this apparently does not affect
fracture healing (not
A
). A large comparative clinical study between
stainless steel and titanium alloy plates (Holzach P, Matter P: The
comparison of steel and titanium dynamic compression plates used
for internal fixation of 256 fractures of the tibia.
Injury
10:120-123,
1978) showed no advantage in healing time for titanium (not
B
).
Titanium alloy components are typically two to three times the cost
of stainless steel ones (not
C
). Maximum achievable screw torque
depends on bone strength rather than on the metal used, given an
adequate screw design (not
E
).
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