Biomedical Engineering Reference
In-Depth Information
either by cracking or adhesion failure. in summary, the analysis of the failed
components pointed towards two materials-related causes of the clinical
failures, one being improper sterilization process parameters, the other
being a design that led to generation of hard particles that could enter the
articulating surfaces, where they acted as an abrasive agent.
15.5.2 Bone anchored amputation prosthesis
An example of another application of osseointegration where retrieval analysis
has been performed is the bone anchored amputation prosthesis. the treatment
of amputees with this technology was introduced in the early 1990s, when
the first surgery was performed on a bilateral trans-femoral amputee. The
surgery is performed in two stages where first a titanium fixture is placed
in the remaining bone and, after about 6 months of healing, a percutanous
abutment is installed.
38
implant installations have been performed on both
upper and lower limb (Fig. 15.4) amputations.
39
in clinical studies it has
been demonstrated that the treatment increases the quality of life
40, 41
of the
patients as well as increases the perception of the environment through a
phenomenon called osseoperception.
42
A forearm bone anchored amputation prosthesis which had suffered a
fatigue fracture after 11 years of use was removed with a threphine together
with the surrounding bone tissue (Fig. 15.5), a removal method which allows
installation of a new implant.
43
The removed implant-tissue block was immersed in buffered formalin prior
to dehydration in a graded series of ethanol baths. A stepwise infiltration of
plastic resin was performed in order to fill out all voids in the bone tissue
prior to curing with an accelerator (lR White, london Resin Company). the
cured embedded block was divided along the long axis by band saw (eXAkt
Apparatebau Gmbh&Co, norderstedt, Germany). A ground section was
prepared according to Fig. 15.6 and subsequently contrasted with toluidine
blue.
The final section thickness was 50 µm containing the whole cross-section
of the implant and the surrounding bone tissue (Fig. 15.7). the counterpart
was gently cut with a slow rotating diamond saw and gently polished prior
to gold sputtering for electron conductivity. the specimen was then mounted
in the vacuum chamber of the FiB system (Fei strata 235 DB FiB/sem)
and a 100 nm thick sample in cross-section was prepared containing both
bone tissue and implant (Figu. 15.7). tem analysis was performed using
different analytical tools such as electron energy loss spectroscopy (eels),
high resolution and energy filtered and transmission electron microscopy
(hRtem and eFtem).
the results of the histomorphometrical evaluation showed a large amount
of mineralized bone in direct contact with the implant (85%) and large
