You are in: eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > RECONSTRUCTIVE SURGERY Implants, Soft Tissue, High-Density Porous Polyethylene (Medpor)Article Last Updated: Dec 1, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Daniel J Verret, MD, Innovations Facial Plastic Surgery and Wellness Center Daniel J Verret is a member of the following medical societies: Alpha Omega Alpha, American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Medical Association, Texas Medical Association, and Triological Society Coauthor(s): Yadro Ducic, MD, FRCS(C), FACS, Director, Department of Surgery, Division of Otolaryngology and Facial Plastic and Reconstruction Surgery, John Peter Smith Hospital; Assistant Professor, Department of Otolaryngology, University of Texas Southwestern Editors: Mark K Wax, MD, Professor and Program Director, Department of Otolaryngology-Head and Neck Surgery, Oregon Health Sciences University; Service Chief, Department of Surgery, Section of Otolaryngology, Veterans Affairs Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Karen Hall Calhoun, MD, Chair, Professor, Department of Otolaryngology-Head and Neck Surgery, University of Missouri; Christopher L Slack, MD, Otolaryngology-Facial Plastic Surgery, Private Practice, Associated Coastal ENT; Medical Director, Treasure Coast Sleep Disorders; Arlen D Meyers, MD, MBA, Professor, Department of Otolaryngology-Head and Neck Surgery, University of Colorado School of Medicine Author and Editor Disclosure Synonyms and related keywords: Medpor, Medpor implants, facial augmentation, facial reconstruction, implants, porous high-density polyethylene, fibrovascular ingrowth, craniofacial implants, orbital implants, orbital reconstruction, nasal implants, full-thickness skin grafts, skin grafts, auricular reconstruction, ear reconstruction, tracheal reconstruction, thyroid cartilage reconstruction, chin augmentation, mandibular reconstruction BACKGROUNDSection 2 of 11
  Porous high-density polyethylene (PHDPE) is currently marketed in the United States under the trade name Medpor (Porex Surgical, Inc, College Park, Ga). It is formed by sintering small particles of high-density polyethylene to create a strong firm material that can be molded using hot water (Lee, 2005). Pore sizes range from 100-250 µm, with 50% being larger than 150 µm. This is important because previous animal studies have shown that pore sizes greater than 100 µm encourage tissue ingrowth (Klawitter, 1976; Spector, 1975). Medpor comes in prefashioned models or can be tailored to a specific patient's needs based on stereolithographic reconstruction from a 3-dimensional CT scan. Medpor is radiolucent on CT scans and MRI images, causing no interference with postoperative imaging, although a new version with titanium mesh embedded in the Medpor is radiopaque with minimal scatter and is MRI safe (Liu, 2004). BIOCOMPATIBILITYSection 3 of 11
The basic structure of Medpor is a simple carbon chain that makes it the reference standard for an inert substance in assays of tissue reaction (Rubin, 1997). Early studies of Medpor implants demonstrated fibroblast ingrowth that prevents capsule formation and promotes stabilization of the implant (Menderes, 2004; Spector, 1979). De Potter and colleagues demonstrated fibrovascular ingrowth in vivo in patients who underwent orbital Medpor implantation (De Potter, 2000). They showed, through serial MRI examinations, enhancement as early as 1.5 months postoperatively. Over long periods, bone eventually incorporates at the implant-bone interface, providing additional stability (Liu, 2004; Spector, 1976). The fibrovascular ingrowth has also been suggested to aid in preventing infection (Merritt, 1979). This was first demonstrated in a rabbit model of implants being placed adjacent to the maxillary sinus in orbital fractures. Numerous human studies have since borne out low rates of infections with these implants (Liu, 2004; Romano, 1993). Medpor implants carry low overall complication rates; the most common reported complications include persistent pain, paresthesias, implant exposure, infection, and subsequent implant removal. Certain areas of implant placement have also been shown to carry higher rates of complications. In an evaluation of their extrusion rates, Sevin and colleagues showed 3 extrusions in 52 implant placements over 4 years (Sevin, 2000). These implants were placed in the nasal dorsum and in the zygomatic area and were used as a construct for microtia repair. Of note, none of their orbital, chin, or mandibular implants required removal. In a retrospective analysis of 285 implants, Cenzi and colleagues looked at several variables to illustrate failure trends (Cenzi, 2005). They analyzed age, sex, underlying disease states, site of implant, type of insertion, primary stability fixation method, and outcome. They demonstrated, in their experience, that implants of the nose, maxilla, and ear are at an increased risk of failure. In addition, the risk of implant failure in patients with various syndromes was statistically significantly increased. Of note, screws and sutures were found to carry the same risk of complications. As with all implants, Medpor should be used carefully in areas of irradiation. In a dog study, Kim showed that dogs with Medpor implants needed more time to heal after radiation than nonradiated controls (Kim, 2001). In addition, they irradiated dogs 4 weeks after Medpor implantation; this group showed delayed osteoblastic activity compared with the controls, although this group showed increased activity over the presurgical radiation group. Many different sizes and shapes of Medpor are available. Although a complete discussion of all possible uses is beyond the scope of this article, some of the more common areas are covered in detail, with mention made of less common areas. CRANIOFACIAL IMPLANTSSection 4 of 11
Liu and colleagues performed 611 Medpor implants for craniofacial defects in 598 patients (Liu, 2004). Medpor was used most often after frontotemporal approaches, followed by retrosigmoid, subtemporal, and craniofacial approaches. Liu et al reported no infections and no wound breakdowns, although some of the implants were in contact with the frontal sinus. Park and Guthikonda used Medpor to reconstruct the sellar floor after transsphenoidal hypophysectomy in cases of intraoperative cerebrospinal fluid leak (Park, 2004). They noted excellent results with good compatibility based on postoperative MRI scans. Rapidis and Day reported results of using Medpor for filling in temporal defects after temporalis flap reconstruction of various head and neck defects (Rapidis, 2006) (see Image 1). The implants were used in various patients, including those who received both preoperative and postoperative radiation. Rapidis and Day reported no extrusions and a return of normal temporal height in more than 90% of their patients. ORBITAL IMPLANTSSection 5 of 11
Medpor has been used in the orbit for orbital reconstruction after enucleations, correction of lower eyelid retraction, and orbital fracture repair (see Images 2-3). Medpor has been safely used to repair lower eyelid retractions in patients in whom more conventional attempts at surgical correction have failed after animal models demonstrated its safety (Morton, 2000; Tan, 2004; Wong, 2001). Although, in one study, one exposure through the anterior eyelid was found, the same study reported the ability to apply full-thickness skin grafts directly over the implants with good success (Wong, 2001). Medpor has also been used extensively for repair of both orbital floor and medial orbital wall fractures (Chang, 2005; Chen, 2001; Hwang, 2002; Jin, 2000; Lee, 2005; Nam, 2006; Ozturk, 2005; Rinna, 2005; Villarreal, 2002). Approaches include endoscopic, subciliary, transconjunctival, and subtarsal. In repair of orbital floor fractures, the implants have been fixated with sutures, screws, or even suturing of the periosteum over the implant, with good results. Medpor has been shown in experimental studies to support the load of the orbital contents, even in the event of additional orbital contents, and bend, not break, with excess force (Haug, 1999; Jordan, 2005). Estimations based on CT scans of orbital volume after repair of unilateral orbital fractures with Medpor showed that orbital volume between the fractured and nonfractured sides did not significantly differ (Ye, 2006). NASAL IMPLANTSSection 6 of 11
Reports in the literature also show Medpor used in nasal septorhinoplasty. Medpor has been used as an extended spreader graft for correction of middle third deformities and airway narrowing (Gurlek, 2005; Gurlek, 2006; Mendelsohn, 2005). No extrusions or infections were reported in these studies. Other reports have described the use of Medpor as dorsal augmentation or for further correction of dorsal or tip irregularities. In one study by Karnes and colleagues, 2 implant extrusions were reported in a 12-year follow-up (Karnes, 2000). GRAFTINGSection 7 of 11
Full-thickness skin grafts have been directly grafted over Medpor. In a 2-part article by Ozdemir and colleagues, grafting was shown to have good results (Ozdemir, 2005). In the first part of the article, a rabbit model was used to demonstrate tissue ingrowth into the implants and full-thickness skin graft viability. The best results were obtained when grafting was undertaken 6 weeks postimplantation, after neovascular ingrowth was seen in almost all of the pores. In the second part of the study, delayed skin grafting was performed on Medpor implants as part of a 3-stage reconstruction procedure in 7 patients, with excellent results reported. AURICULAR RECONSTRUCTIONSection 8 of 11
Medpor implants have also been used for a core auricular reconstruction. Early reports date back to 1993, when Wellisz reported the reconstruction of a helix after a burn injury (Wellisz, 1993). Since then, Medpor implants have been used for microtia repair and helical reconstruction after trauma (see Image 4). Reports have described a precontoured Medpor auricular construct that is then covered with a pedicled temporalis fascia flap with full-thickness skin graft. Romo and colleagues reported a 4% complication rate in 250 cases of microtia repair over 11 years (Romo, 2006). The most common complication was skin necrosis, although they reported no cases of total loss of the construct. OTHER LOCATIONS FOR RECONSTRUCTIONSection 9 of 11
Animal experiments have been performed with Medpor in tracheal and thyroid cartilage reconstruction (Hashem, 2001; Iseri, 2006). In the laryngeal implant in rabbits, histologic examination revealed a lack of acute inflammatory reaction with the material. Incorporation of the Medpor was seen in as little as 2 weeks. Medpor implants have also been used in the dental field for mandibular reconstructions and by reconstructive and cosmetic surgeons for chin augmentation (see Images 5-6). MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Implants, Soft Tissue, High-Density Porous Polyethylene (Medpor) excerpt Article Last Updated: Dec 1, 2006 | |||||||||||||||||||||||||||||||||||||||||||||||
