Biomedical Engineering Reference
In-Depth Information
of HCV transmission by musculoskeletal
allografts from three donors were reported in
the United States between
Studies of bacterial infection or contamina-
tion of musculoskeletal allografts have shown
that most of the allograft contamination is due
to
Staphylococcus
and other mixed skin fl ora
[
].
These donors had negative medical and social
histories and initially tested negative for HCV
when subjected to an anti-HCV immunoassay.
In these cases, previously undetected HCV was
identifi ed from retrospective testing of tissue
and sera with newer anti-HCV immunoassays
and PCR analysis. After the donor tissues had
been identifi ed, a protocol was initiated to
inform and test all recipients of tissues or
organs from these donors. Interestingly, this
study reported that when the high-risk
seroconverted individual was excluded, all
recipients of minimally processed allografts
seroconverted for HCV. However, recipients of
irradiated tissue that had been freeze-dried,
frozen or cryopreserved did not test positive
for HCV infection [
1995
and
2003
[
1
,
12
4
,
8
,
24
,
26
,
33
,
65
]. Kainer et al. [
27
] identifi ed
14
cases of infection by
Clostridium
species
that they traced to nine donors. The time
between death and tissue procurement in two
of the nine donors exceeded industry stan-
dards. The
infected patients had received
nine frozen bone-patellar tendon-bone
allografts, four fresh femoral condyles, and one
meniscus graft. All of the processed allograft
tissues from the
14
identifi ed cases came from
one tissue bank, and the unprocessed donor
tissues originated from seven other tissue
banks. The tissue banks that provided the
allografts to the recipients had procured the
tissues using aseptic techniques that included
decontamination by suspension in a proprie-
tary antibiotic solution, but did they did not
employ terminal sterilization. However, when
terminal sterilization was performed, whether
by gamma-irradiation or by low temperature,
or if chemical sterilization had been employed
at other tissue banks, the resulting allografts
from fi ve of the nine identifi ed donors did not
induce infection. Even though the overall rate
of
Clostridium
infection was less than
14
, the Centers for
Disease Control (CDC) reported four cases of
HCV transmission that resulted from a screened
donor of bone-patellar-bone and tendon
allografts [
12
]. In
2002
]. The CDC investigation was
prompted by the fact that acute hepatitis C was
diagnosed
1
weeks after a recipient received a
bone-patellar-bone allograft. Further testing
with an anti-HCV immunoassay showed that
the donor serum was negative for the HCV
protein, but PCR analysis showed a positive
result for HCV mRNA. Testing of the other
recipients of the infected allografts revealed
no cases of HCV transmission if the bone
allografts had undergone gamma irradiation
[
6
%
among recipients of allografts from the tissue
bank that reported
Clostridium
infection, this
rate was still signifi cantly higher than the rate
among recipients of allografts from the tissue
banks with no
Clostridium
infection [
0
.
5
].
An additional means of reducing the risk of
contamination involves harvesting the tissues
in an operating room with sterile techniques
[
27
]. Gamma-irradiation of musculoskeletal
allografts would therefore appear to reduce
the risk of HCV transmission from infected
tissues.
1
,
12
26
,
65
]. The degree of bacterial contamination
Table 3.2.
Factors influencing allograft performance
Factor
Implication
Graft donor age
Osteoinductive potential is greater from donors aged 42 years and younger. Mechanical
properties of allograft bone are inversely proportional to donor age after the fifth decade.
Presence of osteoporosis
Osteoporotic and osteopenic bone have decreased mechanical properties.
or osteopenia
According to histologic appearance, the incidence of osteoporosis is higher in donors after
the fifth decade of life.
Graft anatomic origin
Fibular strut grafts are stronger than femoral ring or tibial grafts. Iliac crest grafts from the
anterior iliac spine are stronger than those from the posterior iliac spine.
Tissue processing
Gamma-irradiation of
≥
3.0 megarads (virucidal levels) reduces mechanical properties.
Lyophilization can also weaken allografts. Pasteurization may also decrease the
mechanical strength of allograft bone.
