Biomedical Engineering Reference
In-Depth Information
Figure 15.5
V-Lox PEEK anchor marketed by Parcus
Medical. The image is reprinted here with the permis-
sion of the manufacturer.
century
[46]
, where gold, silver, and plant materials
were used for the implant materials
[49]
. Today, the
most frequently used materials are autogenous bone
fragments and hydroxyapatite (HA) materials
[47]
.
None of these techniques are without complications.
Autogenous bone reconstruction, most frequently
from the iliac crest, rib, and split calvarium, is the
ideal option
[46,49]
. Native bone is favored due to its
biocompatibility, infection resistance, stiffness, and
strength characteristics that are similar to cranial
bone. Disadvantages are primarily the donor-site
morbidity, the extra time required to harvest, limited
availability, risk of graft resorption, and a lack of
shaping options
[49]
. A lack of blood supply may
cause the material to lose its three-dimensional
structure and vitality due to being sequestered from
the blood supply for any extended period of time
[50]
. The body will inevitably treat the nonperfused
bone as a foreign implant and remodel the material as
part of the natural resorptive process. Furthermore,
any autogenous bone has inherent donor-site
morbidity and is highly irregular compared to
a designed implant. This irregularity can be espe-
cially problematic when fitting to the complex
supraorbital bar and lateral orbital regions, as well as
between the frontal cranium and temporal fossa
[48]
.
Due to these limitations, alloplastic cranial defect
materials have been used extensively. Major advan-
tages to any alloplastic material are that they require
no donor site and thus reduce operative time signif-
icantly. Further, they are more easily contoured to the
defect, again reducing operating time and providing
better scaffolding for immediate functional stability.
Another advantage is that they are typically available
in unlimited quantities
[48]
. Long-term alloplastic
stability is dependent on the shape of the implant and
the hardware used to secure it in place.
The principal alloplast in use is polymethyl
methacrylate (PMMA), with or without metal
Figure 15.6
Different sizes for the Healix-threaded
PEEK anchors marketed by Depuy Mitek. The anchor
is available with a thread diameter of 4.5, 5.5, and
6.5 mm. The image is reprinted here with the permis-
sion of the manufacturer.
support. PMMA is supplied in powder and liquid
constituents that are mixed in the operating room into
a dough-like cement that will gradually harden.
PMMA is extremely contourable in situ
[48]
. When
used properly and in the correct locations, this has
produced excellent results. Unfortunately, PMMA is
brittle and requires significant time for preparation,
contouring, and setting
[49]
. Also, PMMA undergoes
an exothermic reaction during the curing process,
