Technical Information

Literature Review
MEDPOR® Biomaterial and Porex Surgical Products

Basic Science

Martinez, J.M., “Use of Multiple Alloplastic Implants for Cosmetic Enhancement of Structural Maxillofacial Hypoplasia” Aesthetic Surgery Journal, Volume 23, Number 6, pp.433-440 (Nov/Dec 2003)

Background: The anthropometric proportions of the maxillofacial skeleton are the foundation on which facial beauty stands.

Objectives: In this article, a procedure for facial cosmetic enhancement of young patients with varying degrees of structural hypoplasia with the use of multiple facial implants is reported.

Methods: Subjective criteria for beauty, proportion and harmony were used by the author as a basis for modifying the structural architecture of the face. Between 1 (one) and 5 (five) alloplastic facial implants per patient were placed in a single procedure.

Results: Since 1989, a total of 500 implants have been placed in 258 patients, with excellent results and a low incidence of complications.

Conclusions: The use of alloplastic implants enables the surgeon to achieve improvements in facial contour that are safe, stable, long-lasting, and cost-effective.

This abstract is provided for educational purposes only. It contains information about cleared uses of the product. It may contain other potential uses not cleared by the Food and Drug Administration and not advocated by the manufacturer. The uses and opinions expressed within the article are those of the author derived from his or her personal experience with the product. For additional information on cleared product specific indications and to request a copy of the cleared labeling please contact the manufacturer's customer care department.

Wladis, E.J., Wolansky, L.J., Turbin, R.E., Langer, P.D., “Computed Tomographic Characteristics of Porous Polyethylene Orbital Implants” Presented at the 2003 ASOPRS Scientific Symposium, Anaheim, California (November 15, 2003)

Porous polyethylene sheet implants are frequently used in the surgical management of several orbital conditions, including the repair of traumatic orbital fractures and the enhancement of volume in anophthalmic sockets. However, the computed tomographic (CT) appearance of these implants has not been described, likely due to their lack of radiodensity. We studied the CT scan characteristics of implanted orbital porous polyethylene sheets to determine if the location of these implants can be ascertained radiologically.

Nine patients who had undergone insertion of porous polyethylene orbital implants were randomly chosen and had post-operative CT scans obtained and reviewed. Three patients were chosen with implants placed for fractures of the orbital floor, three for fractures of the orbital medial wall, two for anophthalmic socket volume augmentation, and one as a replacement for a resected orbital roof and supraorbital rim. In each case, the implant was easily visualized on CT scan. Since polyethylene implants are porous, they appear as a hypodense, linear strip on computed tomography that is easily contrasted against adjacent soft tissue, bone, or mucosa. The mean density of the implants varied between –30 and –50 Hounsfield units, midway between the mean densities of water and fat.

Though not as easily visualized as radiodense implants such as titanium, porous polyethylene implants can nevertheless be appreciated on CT scans using soft tissue windows. Their radiographic density, which approximates that of fat, creates a linear silhouette that makes them visible against the surrounding tissue. Clinicians should be aware that they can accurately determine the anatomic location of these implants post-operatively by computed tomography.

Uysal, A., Özbek, S., and Özcan, M., “Comparison of the Biological Activities of High-Density Porous Polyethylene Implants and Oxidized Regenerated Cellulose-Wrapped Diced Cartilage Grafts” Plastic and Reconstructive Surgery, Volume 112, Number 2, (August 2003)

The use of alloplastic materials in plastic surgery has become more extensive with advancement of autogenous-tissue reconstruction technique for the repair of defects, tissue augmentation, and the stabilization of bones. An ideal alloplastic material should be non-allergenic, non-carcinogenic, sterilizable, and easy to shape, and should not cause rejection. Alloplastic material used for tissue augmentation should have a low rate of resorption and distortion. High-density porous polyethylene implants (MEDPOR®) have been used widely and successfully for tissue augmentation. The Turkish Delight is a material composed of diced cartilage grafts wrapped in oxidized regenerated cellulose (Surgicel). Its indications are similar to those of the MEDPOR Implant, and an additional donor site is usually not needed. Both materials are used in the same anatomical locations, especially for augmentation. Therefore, the authors evaluated the long-term stability of and suitable anatomical sites for these materials. MEDPOR Implants or Turkish Delights were placed subperiosteally or subfacially in 10 young rabbits, and resultant changes were evaluated 16 weeks after the operation by macroscopy and histopathology. Changes in projections were measured with an ocular micrometer. MEDPOR Implants were neither resorbed nor distorted when placed subperiosteally or subfacially, and were highly stabilized by the surrounding tissues. Turkish Delights also enabled tissue augmentation, but had a significantly higher rate of resorption compared with the MEDPOR Implant and was loosely bound to the surrounding tissue. The Turkish Delight was less resorbed and better fixed to adjacent tissue when placed subperiosteally than when placed subfascially.

Yaremchuk, M. J., “Facial Skeletal Reconstruction Using Porous Polyethylene Implants,” Plastic Reconstruction Surgery, 111: 1818, 2003

A retrospective review of clinical outcomes was performed to determine the clinical utility and morbidity associated with the use of porous polyethylene facial implants. Three hundred seventy (370) implants were placed in 162 consecutive patients, in 178 operations performed in 11 years. The number of patients, the number of implants used, and the average follow-up period were categorized according to the cause of the deformity. The resultant distribution was as follows: acquired (tumor-related), 17 patients, 39 implants, and 30 months; congenital, eight patients, 31 implants, and 92 months; aesthetic, 39 patients, 97 implants, and 24 months; secondary post-traumatic, 48 patients, 139 implants, and 37 months; and acute trauma (internal orbit reconstruction), 50 patients, 64 implants, and 9 months. The distribution of implants according to location was as follows: frontal, 21; temporal, 30; internal orbit, 145; infraorbital rim, 28; malar, 58; paranasal, 29; nasal 13; mandible, 24; and chin, 22. The combined average follow-up period per patient was 27 months (range, immediate postoperative period to11 years). All implants were placed in the subperiosteal plane, and the majority were fixed with titanium screws. Antibiotics were administered perioperatively. No implants were extruded or migrated, formed clinically apparent capsules, or caused symptoms attributable to bio-incompatibility. The overall re-operation rate was10 percent (n = 16), which included operations to remove implants because of acute infections (2 percent, n = 3), or a late infection (1 percent, n = 1), to remove implants causing displeasing contours (2 percent, n = 3), and to improve contours (6 percent, n = 9). Porous polyethylene implants have biomaterial properties favorable for facial skeletal augmentation. Screw application of the implants to the skeleton allows precise predictable contouring, thus limiting the need for revisional surgical procedures.

Rubin, P.J., Yaremchuk, M.J. "Morbidity And Facial Implants", The Art of Alloplastic Facial Contouring, Authors, Terino and Flowers, Published by Mosby, Chapter 19, pp 273-286 (2000)

The use of implantable biomaterials for bone or soft tissue substitution has become an integral part of aesthetic and reconstructive surgery of the face. This review of the scientific literature examines the risks and complications of these materials. First, we present an overview of commonly used materials. Second, we address general considerations of toxicity relevant to all biomaterials. Third, we present data from a large number of clinical series on the incidence of complications for individual materials used in specific applications.

Sclafani, A.P., Romo, T. III "Biology and Chemistry of Facial Implants", Facial Plastic Surgery, Volume16, Number 1, pp 4-6 (2000)

Facial implants have become increasingly more sophisticated in the past 10 to 15 years. The concept of "the ideal implant" has progressed from an inert material that interacts minimally with the host tissue to one that participates in the normal function of the tissues. A thorough understanding of their chemical properties is essential to understand the biologic events that occur around these materials after implantation. This article outlines the salient features of common materials encountered in facial implants used in plastic surgery.

Wellisz, T., Wallace, R.D. "Porous Polyethylene And Its Biocompatibility", The Art Of Alloplastic Facial Contouring, Authors, Terino and Flowers Published by Mosby, Chapter 18, pp 261-272 (2000)

Interest in porous implant materials for use in the facial skeleton is increasing. Porous polyethylene has become an important facial reconstructive material that serves both as a bone and cartilage substitute and as an alternative to silicone. Porous polyethylene is marketed as MEDPOR® Biomaterial* for use in non-load-bearing regions of the craniofacial skeleton. The implant is easy to shape, strong yet somewhat flexible, and highly stable, and most importantly, it allows ingrowth into its pores. The tissue ingrowth results in collagen deposition within the pores that forms a highly stable complex resistant to infection, exposure, and deformation by contractile forces. 6,28,40 Porous polyethylene is now widely used for mandible and malar augmentation, nasal surgery, orbital reconstruction, ear reconstruction, and a variety of craniofacial applications.

Bigham, W.J., Stanley, P., Cahill, J.M., Curran, R.W., Perry A.C. "Fibrovascular Ingrowth In Porous Ocular Implants: the Effect Of Material Composition, Porosity, Growth Factors, And Coatings", Ophthalmic Plastic and Reconstructive Surgery, Vol., No. 5, pp 317-325 (September 1999)

Purpose: Fibrovascular ingrowth into various porous ocular implants as a function of implant material composition, porosity, growth factors, and coatings was investigated in a pilot study in an animal model.

Methods: Eighty-one New Zealand white rabbits underwent unilateral enucleation and implantation with ocular implants composed of the following materials: coralline hydroxyapatite (HA) with 200-mm pores (HA200) or 500-mm pores (HA500), synthetic HA (synHA), and high-density porous polyethylene (PP). The HA200, HA500, and PP implants were implanted untreated or after treatment with recombinant human basic fibroblast growth factor (Rh-bFGF). Nine HA500 implants were implanted after coating with calcium sulfate (plaster of Paris) to provide a smooth outer surface. Implants were harvested at 1-, 2-, 4-, or 8-week intervals and were examined histologically.

Results: A significant difference was found between untreated HA500 and PP, with PP showing better ingrowth. There was no significant difference between untreated HA and PP, nor between untreated HA500 and synHA. Significant increases in ingrowth were found in HA200 compared with HA500, and in Rh-bFGF-treated implants compared with untreated controls. The calcium sulfate-coated implants showed less vascularization compared with the uncoated implants, although the difference was not significant.

Conclusions: Fibrovascular ingrowth occurred earlier in HA200 implants than in HA500 implants, and was enhanced when implants were treated with Rh-bFGF.

Choi J.C., Iwamoto, M.A., Bstandig, S., Rubin, P.A.D., Shore, J.W. "MEDPOR® Motility Coupling Post: A Rabbit Model", Ophthalmic Plastic and Reconstructive Surgery, Vol. 15, No. 3, pp 190-200 (March 1999)

Purpose: To verify if a MEDPOR® porous polyethylene orbital implant (PPOI, Porex Surgical Inc.), once vascularized, will tolerate a partially exposed titanium screw on its anterior surface.

Methods: Ten New Zealand white rabbits were enucleated and given MEDPOR PPOIs. Eight weeks postoperatively, MEDPOR Motility Coupling Posts (MCP, Porex Surgical Inc.) were placed into the orbital implants. Clinical tissue tolerance and histologic response to the new device were noted.

Results: The titanium screws were well tolerated by the animals. No case of postoperative infection, conjunctival inflammation, conjunctival erosion, MCP dislocation, or PPOI fragmentation was noted. A fibrous tissue growth over the titanium head was noted in all screws with a head height of 2.5 mm. The fibrous tissue overgrowth was not observed in screws with a head height of 4 mm or more.

Conclusion: During the 6-month observation period, all implanted MEDPOR MCPs demonstrated favorable tissue tolerance and stable interfaces between the MCP and the conjunctiva and between the MCP and the PPOI.

Cicciarelli, N., Murray, T.G., Croft, B.H., Voigt, M., Garonzik, S., Hernandez, E. "Magnetically Integrated Microporous Implant: Evaluation Of Feasibility And Efficacy", Investigative Ophthalmology and Visual Science, Vol. 40, No. 4 (March 1999)

Purpose: To determine the orbital tolerance of a microporous implant fitted with an integrated stainless steel post and the enhanced motility associated with magnetic coupling of the prosthetic.

Methods: Six New Zealand White Rabbits underwent enucleation surgery under sterile conditions. Each animal was implanted with a 12 mm microporous polyethylene implant with a 2 x 3 mm stainless steel post embedded flush within the anterior surface. At one month, the rabbits were fitted with an external prosthesis containing two 1mm circular rare earth dental magnets embedded into the porcelain implant at 0.5 mm off midline (right and left of center at the horizon). Ophthalmologic and photographic documentation of post enucleation socket appearance was recorded biweekly. Two animals were euthanized at each of three time points: 1, 2 and 6 months. The implant and orbital contents were removed for histopathological examination.

Results: No evidence of toxicity was observed in association with this integrated ocular implant. There was no evidence of either conjunctival dehiscence or localized rejection. Clinical grading of motility documented a significant enhancement in lateral excursion when compared to nonintegrated controls.

Conclusions: Magnetically integrated microporous implants achieve excellent enhancement of motility. No evidence of complications associated with the surgical placement of this prosthetic coupling implant was found.

CR: None. Support: American Cancer Society, Fight for Sight/Prevent Blindness America and Knights Templar Eye Foundation.

Schellini, S.A., Marques, M.E.A., Taga, E.M., Roca, R., Padovani, C.R. "Comparison Between Synthetic Hydroxyapatite And Porous Polyethylene In Rabbits Eviscerated Cavities, Investigative Ophthalmology and Visual Science, Vol. 40, No. 4 (March 1999)

Purpose: To compare the tecidual reaction produced with the spheres use of synthetic hydroxyapatite and porous polyethylene in eviscerated cavities of rabbits.

Methods: They were used 56 New Zealand white rabbits underwent a unilateral evisceration with placement of spheres of synthetic hydroxyapatite (G1- 28 animals) or porous polyethylene (G2-28 animals). Four animals of each group were sacrificed in 7 experimental moments: 7, 15, 30, 60, 90, 120 and 180 days after the evisceration. After the sacrifice, the orbital content was removed and fastened in formol. Then, the wrapped up sphere was cross-sectional in it largest axis and prepared for histopatologic exam.

Results: Slack tecidual reaction was observed with both materials, reaching until the sphere center after 7 to 15 days after the surgery. The tecidual reaction became denser about 60 to 90 days, period in that bony metaplasia began in G1. In every observation moment, G1 had more inflammation than G2. There was a fibrous layer around the implants that was denser in G1 than in G2 animals. The scleral cavity area (measured by image analyser) is better maintained in G2 than in G1 rabbits.

Conclusion: The synthetic hydroxyapatite sphere provoked more inflammation than the porous polyethylene and it was less efficient in the maintenance of the cavity volume, what takes us to consider the porous polyethylene superior to the synthetic hydroxyapatite in the anophthalmiccavity reconstruction.

Özgür, F., Aksoy, H.M., Kayikçioglu, A., Ariyürek, M. "The Effect Of Onlay MEDPOR® Implants On Mandibular Growth In Young Rabbits: An Experimental Study", Annals of Plastic Surgery, Vol. 42, No. 2 (February 1999)

MEDPOR® implants were placed on the periosteum of the mandible in infant rabbits to study their effects on growth. Three months later radiological and histopathological studies were performed in situ and after removal of the mandible. The authors demonstrate that implants did not affect normal development of the mandible; however, there was a decrease in bone thickness and a mononuclear cell reaction was caused where the implant came in contact with the bone.

Among the alloplastic materials, Silicone, Biocoral, Biofax, Proplast, Teflon, Plasti-pore, Seramic, Polyamide-mesh and hydroxyapatite have been used both experimentally and clinically. Silicone, methyl methacrylate, porous hydroxyapatite and porous polyethylene have been shown to have the necessary biomechanical properties for use in treatment of complex facial bone defects.

MEDPOR is a white, ultrahigh-density porous polyethylene material. The biocompatibility of this alloplastic material is well established.

Results: Considerable histological changes are seen on the contact surface of the bone.

Discussion: During the growth of the animal, MEDPOR caused thinning of the bony cortex, a periosteal reaction, a mononuclear cell inflammatory reaction on the surface of the bone and spur formation at the edge of the implant. Medpor is reported to result in thinning of bone with low incidence and thickness of the implant does not alter this effect. There was only one sample that showed thinning of bone histologically.

In conclusion, the adverse effects of MEDPOR implants on the mandibles were neither shown to retard bone growth nor caused gross asymmetry. MEDPOR implants have good stability on bone with acceptable adverse effects.

Wellisz, T., Lawrence, M., Jazayeri, M., Golshani, S. and Zhou, Z. "The Deformation Of The Mandible Beneath Alloplastic Implants", Plastic and Reconstructive Surgery (September 1995)

To determine the effects of three alloplastic implant materials on bone, silicone, methlymethacrylate and porous polyethylene, 96 implants were placed on the mandibles of 16 rabbits. Both thin (1.5 mm) and thick (6.0 mm) onlays were used to determine the relative importance of pressure on bone deformation. Fluorescent markers were administered at different time intervals to evaluate the patterns of new bone growth. After 12 and 24 weeks, each of the implants was examined grossly, histologically and under fluorescent microscopy.

The frequency and degree of thinning of the bone were related to the type of alloplast, as well as to the implant's thickness. Solid silicone implants were associated with the greatest amount of bone resorption (p < 0.05). Thicker silicone implants were associated with a greater degree of thinning (p < 0.05). Bone resorption beneath the implants was documented by the presence of osteoclasts actively eroding bone and by changes in the normal patterns of the fluorescent markers. Both the thin solid methylmethacrylate and the thin porous polyethylene implants had a low incidence of bone thinning. Significantly more thinning of the bone was observed with the thick methylmethacrylate, although this was less than the silicone groups. The thick porous polyethylene implants did not increase the incidence of bone thinning.

Dougherty, W. and Wellisz, T. "The Natural History Of Alloplastic Implants In Orbital Floor Reconstruction: An Animal Model", The Journal of Craniofacial Surgery, Vol. 5, No. 1, pp 26-32 (February 1994)

A new animal model was developed in which the condition of an open fracture in communication with the maxillary sinus was recreated to evaluate the behavior of alloplastic implants in human orbital floor reconstruction. Full thickness defects through the maxillary sinuses (including bone and mucosa) were made in 21 New Zealand White rabbits. MEDPOR® and silicone implants were placed to obturate the defects, exposing one surface of the implant to the open sinus and were examined at 1, 2, 3 and 4 weeks and 2, 4 and 5 weeks after placement. Complete regeneration of sinus wall structures with closure of the defect occurred more rapidly with the MEDPOR implant (p < 0.004 at week 4). MEDPOR showed clearing of debris from within the implant with concomitant vascular soft-tissue ingrowth at week 1 and bony ingrowth at week 3, resulting in bone and soft-tissue fixation with overlying mature mucosa. Silicone implants never became fixated to bone or soft tissue.

This study supports the clinical observation that MEDPOR can be used successfully in the orbital floor, even when exposed to an open facial sinus.

Rubin, P.A.D., Popham, J.K., Bilyk, J.R. and Shore, J.W. "Comparison Of Fibrovascular Ingrowth Into Hydroxyapatite And Porous Polyethylene Orbital Implants", Ophthalmic Plastic and Reconstructive Surgery, Vol. 10, pp 96-103 (1994)

A study using 32 enucleated New Zealand White rabbits was performed to determine the rate and extent of fibrovascular ingrowth into 14 mm MEDPOR® and hydroxyapatite orbital implants. Wrapped either in autologous sclera with and without anterior fenestrations or as unwrapped spheres, the implants were harvested at 6 and 12 weeks. It was determined that MEDPOR and hydroxyapatite are both capable of complete vascularization in this animal model.

Goldberg, R.A., Dresner, S.C., Braslow, R.A. "Animal Model Of Porous Polyethylene Orbital Implants", Ophthalmic Plastic and Reconstructive Surgery, Vol. 10, pp 104-109 (1994)

The clinical performance of porous polyethylene implants is evaluated in 16 enucleated albino New Zealand rabbits implanted with MEDPOR® and porous coralline hydroxyapatite. In 12 rabbits, MEDPOR implants were unilaterally inserted and exenterated at 4, 8, 12, 24 and 48 weeks and in four rabbits, hydroxyapatite implants were placed and exenterated at 6 and 12 weeks. Early postoperative extrusions occurred in two rabbits with MEDPOR and two rabbits with hydroxyapatite. There were no extrusions and minimal inflammation occurred in the remaining 12 implants (inflammation scores with HA reflected a higher degree of chronic and acute inflammation). MEDPOR was determined to be well tolerated histologically with only mild chronic inflammation, thin capsule formation and partial fibrovascular ingrowth. Easily implanted with minimal "tissue drag" and no brittleness, it is relatively inexpensive. The authors conclude that porous polyethylene may have utility as an orbital evisceration and enucleation implant and that their findings encourage further exploration and refinement of the material.

Wellisz, T., Kanel, G. and Anooshian, R.V. "Characteristics Of The Tissue Response To MEDPOR® Porous Polyethylene Implants In The Human Facial Skeleton - The Long-Term Effects Of Biomedical Implants", The Journal of Long Term Implants, Vol. 3, No. 3, pp 223-235 (1993)

The histological findings of MEDPOR® implant specimens taken from humans are characterized. Thirty-two (32) implants were biopsied from 24 patients. All specimens, including those biopsied because of implant exposure, showed soft tissue ingrowth, vascularization with mature blood vessels and lamellar collagen deposition within the pores of the implant. Ingrowth was demonstrated in all implants including those that became exposed, both early and late after implantation.

Maas, C.S., Merwin, G.E., Wilson, J., Frey, M.D. and Maves, M.D. "Comparison Of Biomaterials For Facial Bone Augmentation", Archives of Otolaryngology - Head and Neck Surgery, Vol. 116, pp 551-556 (1990)

A comparision of biomaterials for facial bone augmentation was performed in various sites in 12 dogs. MEDPOR® implants demonstrated good stability and tissue ingrowth into its pores. When autogenous rib grafts were used in areas with overlying tissue mobility such as the malar region and the chin, resorption of the rib grafts occurred. Proplast implants were found to be mobile with a reported break-up and migration of the Proplast implants. Furthermore, distant fragments of the Proplast implants were found to be surrounded by a large number of imflammatory cells including phagocytes and multinucleated giant cells, implying a continued stimulus for an active cellular response. Bone erosion was noted under two of the Proplast chin implants.

Rubin, L.R. "Polyethylene As A Bone And Cartilage Substitute: A 32-year Retrospective", L. R. Rubin, Editor, Biomaterials In Plastic Surgery, St. Louis: C. V. Mosby, pp 477-493 (1983)

The author presents a 32-year personal retrospective, describing his use of low weight polyetheylene granules in facial areas with different overlaying tissue covers. Surgical techniques are offered, including steps for preparation and implantation. In chin and malar implants, holes were made for fibrous tissue ingrowth to affix implants to underlying bone. He reports an 89.4% success rate (the greatest area of failure being the nose) with no sarcomas or tumors and minimal complication. The author concludes that polyethylene, properly embedded in the orbital floor and malar, mandible and skull regions, could survive the test of time and be considered a good replacement for bone or cartilage.

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Literature Review MEDPOR® Biomaterial and Porex Surgical Products