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Assessing Vascularization
Good vascularization of the Bio-eye HA orbital implant is necessary for
the implant to provide maximum stability in the orbit and to ensure full
epithelialization of the motility peg hole. The hydroxyapatite orbital
implant must be well vascularized before drilling the peg hole, and vascular
ingrowth must be assessed prior to drilling. This ability to vascularize
is the key element in the success of the Bio-eye HA orbital implant Shields
1992. If vascularization is not assessed by some means prior to drilling,
the risk of infection is greatly, and unnecessarily, increased. If the
implant is well vascularized, the implant surfaces that have been exposed
inside the drill hole will re-epithelialize around the peg, completely
lining the exposed surfaces inside the hole. This capability of the Bio-eye
HA orbital implant allows it to become a direct motility implant while
still remaining a buried implant, since no implant surfaces must remain
exposed to achieve coupling between the artificial eye and the implant.
It should be noted that excellent motility is often possible without the
need of a motility/support peg Shields
1992. The degree of motility achieved by the undrilled hydroxyapatite
implant should be evaluated before drilling is considered. If evaluation
indicates that greater motility is desired, then a motility/support peg
is recommended and a peg hole should be drilled. The preferred method
of assessing vascular ingrowth is by means of a technetium-99m bone scan,
performed approximately 6 months post-implantation Perry
1987, Ferrone 1992, however,
an MRI scan with contrast agent may also give some indication of blood
vessel ingrowth Shields 1991,
Soll 1987, Shields
1992.
Grading Bone Scans
Grading of the technetium 99m bone scan has been established as follows and is most
accurate when done by reference to a graph showing the uptake of the technetium 99m
through the orbits and mid-face. If the orbital implant shows uptake greater darker than
the uptake of the mid-facial bones, it is graded 4+. If the uptake of technetium 99m in
the implant is equal to that of the mid-facial bones, it is graded 3+. If the uptake of
the implant is greater than one-half the distance between the uptake of the normal orbit
and the uptake of the mid-facial bones, it is graded 2+. Uptake greater than the normal
orbit, but less than 2+, is graded 1+. If the technetium 99m bone scan shows an uptake of
2+ or better, the implant is sufficiently vascularized and the hole may be drilled Perry 1991. The time required for the implant to
become vascularized is variable because the fate of the implant wrapping material is
variable Soll 1987a and because of individual
variation DePotter 1992. Porous hydroxyapatite
will vascularize more quickly when it is not wrapped in any collagen material, such as
sclera or fascia lata. Likewise, any openings that are cut into the wrapping material will
increase the rate of vascularization Ferrone 1992,
DePotter 1992 . Most hydroxyapatite orbital
implants, including wrapped implants, will be vascularized within 6 months of
implantation.Perry 1991a, Soll 1987a, Ferrone
1992, DePotter 1992 |
