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Porous Polyethylene Spheres
Clinical evaluation Five animals (27.8%) with porous polyethylene spheres presented implant extrusion after 30 days of surgery. Conjunctival dehiscence occurred in two animals (11.1%) and one of them was excluded due to systemic infection not related to the surgical procedure.
Ultrasound evaluation Spheres vascularization was observed though neovessels filling theirs porous, indicating spherehosted integration. Porous polyethylene showed medium reflectivity (40%60%) until 90 days after surgery, although the image was more echodense at the time. An irregular internal structure indicating heterogeneous architecture was also present, despite of the sound attenuation observed during the examination (Figure 2).
DISCUSSION
This study compared the porous polyethylene, already commercially available, and the polyethylene sphere in the gel form.
Both spheres were made by the same professional and consisted basically of the same chemical substance. However, the porous polyethylene sphere presented a rough external surface and the gel polyethylene, a smooth surface because of its membranelike wrapper material, employed to contain the gel or semiliquid polyethylene.
The main cause of gel implant extrusion seemed to be the sphere volume increase after implantation. The spheres showed an increase in size which caused suture dehiscence due to mechanical forces and elicited their extrusion. The extrusion was probably a combination of factors: the increase of the spheres size which hydrated and became bigger than the orbital volume and the lack of implants integration to the host tissues,observed by the high early expulsion rate after surgeries.
The integration rate of a biomaterial is measured by the pattern of vascularization between the implant and the host tissues. Many studies described the vascularization pattern using histological methods[79]. Others used the computerized tomography and/or the magnetic resonance imaging[35].
Figure 1 B scan ultrasound of a gel polyethylene sphere 90 days after surgery（略）
Figure 2 B scan ultrasound of a porous polyethylene sphere 90 days after surgery（略）
However, there are only few studies using conventional ultrasound scan to evaluate the vascularization pattern inside the sphere implants[10].
A previous reports showed that the porous polyethylene implant vascularization occurred during the first month after surgeries[9,11], we decided to start the B ultrasound evaluation around this time. This method provided useful information for further studies in vivo. The vascularized porous polyethylene implants showed low reflective peaks similar to blood pattern[12]. So, the B ultrasound evaluation showed us that the Polietigel implants did not vascularize, in contrast to the Polipore implants which presented increased neovessels colonization inside.
The polyethylene spheres in the gel form hydrated and increased in volume after orbital implantation procedure. More studies need to be performed to determine the ideal biomaterial size necessary to replace the orbital volume deficiency in the anophthalmic cavity reconstruction.
The B scan ultrasound technique is an alternative method to substitute the more expensive methods employed to evaluate the spheres vascularization pattern.
Acknowledgements: The authors thank Romualdo Rossa, MD (in memorian) for providing the polyethylene spheres.
【参考文献】
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