Biomedical Engineering Reference
In-Depth Information
of a musculoskeletal allograft is a direct func-
tion of the time that elapses between death and
refrigeration [
evaluated for their effects on osteoinductive
potential and structural support of the
allografts (Table
]. Tissues obtained from
living donors have lower rates of bacterial
contamination than tissues harvested from
cadavers at autopsy [
38
,
65
).
Increased donor age may be inversely related
to the osteoinductive potential of bone
allografts. Using an in vivo nude murine model,
Schwartz et al. [
3
.
2
]. Musculoskeletal
allografts from donors who suffered multiple
trauma, with or without resuscitation, had
higher rates of bacterial contamination than
allografts from organ donors [
26
,
65
] reported that an increase in
donor age decreased the osteoinductivity of the
demineralized, freeze-dried bone allograft
(DFDBA). Areas of new bone formation, new
cortical bone function, and new bone-marrow
production were smaller in allografts obtained
from older donors (
50
]. These obser-
vations are best explained by the fact that as
postmortem time increases, the risk of infec-
tion by intestinal fl ora such as
Clostridium
and
Escherichia
species also increases [
65
years) than in allografts
obtained from younger donors (
>
50
]. This is
particularly true for spore-forming bacteria
such as
Clostridium
that are capable of long
dormancy. As with surgical infection rates, the
rate of allograft contamination is directly pro-
portional to the number of persons present in
the operating room during procurement [
27
years).
Osteoconductivity was not affected by donor
gender. Lohman et al. [
<
29
] confi rmed the age-
dependent effect by noting that allograft osteo-
inductive potential was signifi cantly greater for
donors under
37
42
than for donors over
70
years
].
The order in which tissues are harvested also
affects the rate of bacterial contamination; the
rate is higher in specimens from the hemipelvis
than in specimens from the femur or tibia [
65
of age.
Several studies have shown that the mechan-
ical properties of bone decline with age. Burn-
stein et al., using cadaveric human specimens,
observed a highly signifi cant negative correla-
tion between age and femoral yield stress, ulti-
mate stress, elastic modulus, and ultimate
strain [
],
probably because the hemipelvis is typically
the last large structural bone to be harvested.
Prolonged handling of the skin also increases
the risk of contamination [
26
] observed a negative
correlation between the tensile stress of bone
and age in vivo. McCalden et al. demonstrated
that there is an inverse relationship between
the mechanical properties of cortical bone and
age, and theorized that the decrease in bone
strength is the result of an age-dependent
increase in bone porosity [
11
]. Smith et al. [
55
]. The risk of
contamination can be reduced by antiseptic
soaking, irrigation, and terminal sterilization
[
26
24
].
3.4 Donor Selection Factors
Affecting Musculoskeletal
Allograft Performance
].
Allografts from donors with osteoporosis
or osteopenia, conditions that are not contra-
indicated for bone transplant donation, may
have less strength and stiffness [
39
17
]. Dickenson
et al. [
] reported a signifi cant decrease in
the modulus of elasticity, the ultimate tensile
strength, and the amount of plastic and elastic
energy absorbed in osteoporotic bone in com-
parison with nonosteoporotic bone in vitro.
They also theorized that the decrease in
strength and stiffness in osteoporotic bone
grafts was due to greater porosity. In vivo, Lill
et al. observed a signifi cant reduction in the
bending stiffness of intact osteoporotic tibiae
in comparison with normal tibiae, as well as
delayed fracture healing in osteoporotic bone
[
15
All potential allograft transplant donors are
screened for a variety of factors, including but
not limited to sex, age, cause of death, and past
medical and social history; the results of sero-
logical tests for medical diseases; and, most
importantly, the presence of bacterial and viral
pathogens. The most commonly reported
exclusion factors for tissue donors include a
medical history of infection at the excision
sites, benign or malignant tumors at the exci-
sion sites, autoimmune diseases, severe endo-
crine/metabolic diseases, collagen diseases,
and infection by HIV, HCV, and/or HBV. Age,
sex, medical history, and the type of bone har-
vested from screened tissue donors have been
].
Histologic evaluation of bone allografts has
shown that osteoporosis and osteopenia affect
bone allograft performance [
34
43
,
51
,
58
]. Histo-
