Characteristics of tissue growth into Proplast and porous polyethylene implants in bone

Seminars in Plastic Surgery: Pediatric Ear Anomalies and Reconstruction

Congenital ear anomalies affect 15 to 20% of neonates and can be categorized as either auricular deformations or malformations. Deformations involve a fully developed, albeit abnormally shaped, chondrocutaneous framework, which makes them amenable to correction with ear molding within the first few months of life. Malformations involve hypoplastic or fully absent auricular structures that require augmentation with alloplastic and/or autogenous reconstruction. The goal of this article is to outline the various auricular deformities and malformations, followed by a description of the latest clinical management options, both nonsurgical and surgical, by auricular anomaly.

The Clinical History and Basic Science Origins of Transcutaneous Osseointegration for Amputees

Transcutaneous osseointegration for amputees (TOFA) refers to an intramedullary metal endoprosthesis which passes transcutaneously to connect with a limb exoprosthesis. The first recognizably modern experiments and attempts occurred in the 1940s. Multiple researchers using a plethora of materials and techniques over the following 50 years identified principles and obstacles which informed the first long-term successful surgery in 1990. Unfortunately, the current mainstream TOFA literature presents almost exclusively subsequent developments, generally omitting prior research, leading to some historical mistakes being repeated. Given the increasing interest and surgical volume of TOFA, this literature review was performed to delineate TOFA's basic science and surgical origins and to integrate these early efforts within the contemporary understanding. Studying this research could protect and benefit future patients, surgeons, and implant developers as TOFA is entering a phase of increased attention and innovation. The aim of this article is to provide a focused reference of foundational research, much of which is difficult to identify and retrieve, for clinicians and researchers.

Auricular Reconstruction Using Porous Polyethylene Implant Technique

Alloplast-based ear reconstruction has become more popular over the years because it offers many advantages compared with the traditional staged autologous costal cartilage approach. Advantages include earlier reconstruction in the setting of microtia, fewer procedures, less donor site morbidity, shorter surgeon learning curve, and improved consistency in the final aesthetic result. Although other implantable materials have been used in auricular reconstruction with variable success, porous high-density polyethylene frameworks combined with recent advances in the creation of the soft tissue coverage have significantly improved outcomes with minimal complications and long-term viability. This article describes the authors' technique.

Use of an anionic collagen matrix made from bovine intestinal serosa for in vivo repair of cranial defects

Polymeric biomaterials composed of extracellular matrix components possess osteoconductive capacity that is essential for bone healing. The presence of collagen and the ability to undergo physicochemical modifications render these materials a suitable alternative in bone regenerative therapies. The objective of this study was to evaluate the osteogenic capacity of collagen-based matrices (native and anionic after alkaline hydrolysis) made from bovine intestinal serosa (MBIS). Twenty-five animals underwent surgery to create a cranial defect to be filled with native and anionic collagen matrixes, mmineralized and non mineralized. The animals were killed painlessly 6 weeks after surgery and samples of the wound area were submitted to routine histology and morphometric analysis. In the surgical area there was new bone formation projecting from the margins to the center of the defect. More marked bone neoformation occurred in the anionic matrices groups in such a way that permitted union of the opposite margins of the bone defect. The newly formed bone matrix exhibited good optical density of type I collagen fibers. Immunoexpression of osteocalcin by osteocytes was observed in the newly formed bone. Morphometric analysis showed a greater bone volume in the groups receiving the anionic matrices compared to the native membranes. Mineralization of the biomaterial did not increase its osteoregenerative capacity. In conclusion, the anionic matrix exhibits osteoregenerative capacity and is suitable for bone reconstruction therapies.

Maxillofacial reconstruction with Medpor porous polyethylene implant: a case series study

Objectives

The role of alloplastic materials in maxillofacial reconstruction is still controversial. Determining the utility of porous, high-density, polyethylene implants as a highly stable and flexible, porous alloplast, with properties such as rapid vascularization and tissue ingrowth, is crucial in cases of maxillofacial deformities and aesthetic surgery.

Materials and Methods

Thirty high-density porous polyethylene implants were implanted in 16 patients that had been referred to a private office over a three-year period. These implants were used for correcting congenital deformities, posttraumatic defects and improving the aesthetic in nasal, paranasal, malar, chin, mandibular angle, body and orbital areas.

Results

The outcomes of the cases in this study showed good aesthetic and functional results. The majority of patients had no signs of discomfort, rejection or exposure. Two implants suffered complications: a complicated malar implant was managed by antibiotic therapy, and an infected mandibular angle implant was removed despite antibiotic therapy.

Conclusion

Based on the results, the Medpor implant seems to be an excellent biomaterial for correcting various facial deformities. Advantages include its versatility and relatively ideal pore size that allows for excellent soft tissue ingrowth and coverage. It is strong, flexible and easy to shape.

Clinical Experience with the M4 Ahmed Glaucoma Drainage Implant

Aim

To evaluate the safety and efficacy of the M4 (porous polyethylene plate) Ahmed Glaucoma Valve (AGV) drainage implant in a multicenter retrospective study.

Materials and methods

A retrospective chart review of medical records of patients who had undergone the M4 Ahmed valve was performed from January 2013 to April 2015. The primary outcome measure was surgical failure defined as: Less than a 20% reduction in baseline intraocular pressure (IOP) to last follow-up visit, final IOP less than 5 mm Hg or greater than 18 mm Hg, reoperation for glaucoma, or loss of light perception vision. All eyes not meeting the above criteria were defined as success.

Results

A total of 291 eyes met all study inclusion criteria. The average follow-up in the study was 6 months (±7.6 months) with 112 patients achieving 12-month follow-up (38.5%). 208 eyes (71.5%) met the study success criteria at final follow-up. No statistically significant spikes in postoperative IOP at 1 and 4 months were detected. The average preoperative IOP was 26.0 on an average of 2.8 medications. At 6 months, the average IOP dropped to 16.7 on 0.9 medications and stayed relatively stable at 15.8 on 1.2 medications at 12-month follow-up.

Conclusion

The M4 valve appears to have less of a hypertensive phase compared with the other Ahmed class valves with a similar safety profile. While 71.5% success rate was achieved at final follow-up, the failure rate steadily increased over time.

Clinical significance

While the M4 production has been discontinued, the porous design of the M4 may avoid a pressure spike in the Ahmed valve class and warrants future investigation for valve design.How to cite this article: Sluch I, Gudgel B, Dvorak J, Ahluwalia MA, Ding K, Vold S, Sarkisian S. Clinical Experience with the M4 Ahmed Glaucoma Drainage Implant. J Curr Glaucoma Pract 2017;11(3):92-96.

Ahmed glaucoma valve implant: surgical technique and complications

Implantation of Ahmed glaucoma valve is an effective surgical technique to reduce intraocular pressure in patients affected with glaucoma. While in the past, the use of this device was reserved to glaucoma refractory to multiple filtration surgical procedures, up-to-date mounting experience has encouraged its use also as a primary surgery for selected cases. Implantation of Ahmed glaucoma valve can be challenging for the surgeon, especially in patients who already underwent previous multiple surgeries. Several tips have to be acquired by the surgeon, and a long learning curve is always needed. Although the valve mechanism embedded in the Ahmed glaucoma valve decreases the risk of postoperative hypotony-related complications, it does not avoid the need of a careful follow-up. Complications related to this type of surgery include early and late postoperative hypotony, excessive capsule fibrosis around the plate, erosion of the tube or plate edge, and very rarely infection. The aim of this review is to describe surgical technique for Ahmed glaucoma valve implantation and to report related complications.

Applications of Medpor Porous Polyethylene in Facial Bone Augmentation

We report our experience in facial bone augmentation and nasal dorsal onlays with the Medpor porous polyethylene implant. Medpor is a highly stable, somewhat flexible alloplast which has been sintered to form a network of interconnecting pores. Its surface characteristics and porosity have been shown to promote rapid tissue ingrowth, vascularization, and fixation to the underlying bone. A total of 88 implants were placed in 68 patients during a 5-year period. Implants were used for augmentation in the chin (15), malar area (11), nasal dorsum (20), the orbit (19), and the cranium (23). The patients ranged in age from 10 to 76 years old. The etiologies of deformities were related to trauma (40), burns (17), aesthetic (8), and congenital (3). One malar implant became infected and was removed. There were no other implant-related complications. As a result of rapid soft-tissue ingrowth all implants became firmly fixed in position. No subsequent bone resorption, implant migration, or exposure were observed in our patient group. On the basis of these findings, we recommend the Medpor porous polyethylene implant as a dependable choice in the array of alloplastic materials available for facial reconstruction. Its remarkable stability, conductivity for tissue ingrowth, and ease of use allow for an accurate and reliable establishment of contour and symmetry in the craniofacial skeleton.

In vivo tissue response and durability of five novel synthetic polymers in a rabbit model

Alloplastic materials are frequently used in facial plastic surgeries such as rhinoplasty and nasal reconstruction. Unfortunately, the ideal alloplastic material has not been found. This experimental study evaluates the tissue response and durability of five novel polymers developed as an alloplastic material. In this experimental study involving a tertiary university hospital, six subcuticular pockets were formed at the back of 10 rabbits for the implantation of each polymer and sham group. Each pocket was excised with its adjacent tissue after three months, and collected for histopathological examination. Semi-quantitative examination including neovascularisation, inflammation, fibrosis, abscess formation, multinucleated foreign body giant cells was performed, and integrity of polymer was evaluated. A statistical comparison was performed. No statically significant difference was detected in neovascularisation, inflammation, fibrosis, abscess formation and multinucleated foreign body giant cells when a paired comparison between sham and polymer II, III and IV groups was performed individually. Nevertheless, the degree of fibrosis was less than sham group in polymer I (p = .027) and V (p = .018), although the other variables were almost similar. The integrity of polymers III (9 intact, 1 fragmented) and IV (8 intact, 2 absent) was better than the other polymers. These novel synthetic polymers could be considered as good candidates for clinical applicability. All polymers provided satisfactory results in terms of tissue response; however, fibrovascular integration was higher in polymers II, III and IV. In addition, the durability of polymer III and IV was better than the others.

Comparative study of the safety and efficacy of the Ahmed glaucoma valve model M4 (high density porous polyethylene) and the model S2 (polypropylene) in patients with neovascular glaucoma

OBJECTIVE

To prospectively evaluate the safety and efficacy of the Ahmed glaucoma valve model M4 (High density porous polyethylene plate; Medpor) compared with the model S2 (polypropylene plate).

METHOD

Mexican patients with neovascular glaucoma were randomly included for each group (M4 and S2). They were operated on using conventional techniques and creating a sub-episcleral tunnel to place the valve tube in the anterior chamber. After one year of follow-up, the results were evaluated with respect to a post-operative reduction in pressure, changes in visual acuity, the need for drugs, and complications, as well as the demographic characteristics of each group. Each operation using the M4 valve was performed by a single surgeon (FGC). Those operated on using the S2 model had their surgery performed by the staff surgeons at the Glaucoma Department of the Mexican Association to Prevent Blindness (APEC).

RESULTS

Each group (M4 and S2) contained 21 eyes of 21 Mexican patients with a diagnosis of neovascular glaucoma, leading to a total of 42 patients undergoing surgery. The mean preoperative intraocular pressure (IOP) was 43.5 (±11.8), and 42.24 (±12.84) mmHg for the M4 and S2 groups, respectively. After one year of follow-up, the IOP reported was 18.9 (±9.7) mmHg for the final 18 patients in the M4 group, and 16.38 (±9.76) mmHg for the 21 patients in the S2 group.

DISCUSSION

The design of a drainage valve device such as that of Ahmed has characteristics such as moderate control of IOP, thanks to the valve component in the immediate post-operative period, which makes them safer than other non-valve devices. This avoids an excess of flat chambers and the presence of low IOPs, which can lead to bleeding in the early post-operative period due to the weak desmosomal junctions of the newly formed vessels, with the advantage of maintaining suitable control of IOP from the first day after surgery.

CONCLUSION

Further studies with longer follow-up with a larger number of patients are needed to evaluate the effectiveness of this porous coating in the control of neovascular glaucoma.

The effect of sterilization methods on the osteoconductivity of allograft bone in a critical-sized bilateral tibial defect model in rabbits

Clinically, allogeneic bone graft is used extensively because it avoids the donor site morbidity associated with autograft. However, there are concerns over the optimal sterilization method to eliminate immunological risks whilst maintaining the biological efficacy of the graft. This study compared the effect of Supercritical fluid (SCF) treatment and gamma irradiation at 25 kGy on the osteoconductivity of allograft bone in a bilateral critical sized defect rabbit model. Osteoconductivity was evaluated at 2 and 4 weeks using X-ray, CT, histology (qualitative and quantitative) and immunohistochemistry (Alkaline Phosphatase and Cathepsin-K). Both grafts were well tolerated and osteoconductive. At 2 weeks, there was decreased bone volume and density in the gamma irradiated graft compared to the SCF treated graft, corresponding with a greater inflammatory response histologically and increased Cathepsin-K expression. Catabolic activity predominated at 4 weeks, with both grafts undergoing significant resorption and remodeling inside the defect. Alkaline Phosphatase expression was greater in the SCF group at both time points indicative of a more anabolic response. Allograft bone sterilized with either gamma irradiation or SCF treatment was osteoconductive and capable of healing a critical sized tibial defect in a rabbit. Gamma irradiated allografts elicited an acute inflammatory reaction when implanted which may increase the amount of graft resorption compared to the SCF treated bone.

Osteoconductivity of porous polyethylene in human skull

PURPOSE

Recently, biomaterials have been generally used in reconstruction of a bony defect or augmentation of the facial skeleton. Medpor implants in vivo in animal models showed both soft tissue and bony ingrowth into its pores and have been widely accepted to have an osteoconduction activity. However, in an in vivo study in humans, there was no definite evidence of bony ingrowth into the pores of Medpor. This study examined the osteoconductivity of Medpor in human vivo.

METHODS

We gained a total of 24 Medpor blocks when removing a distraction device in 11 patients with craniosynostosis. The Medpor blocks were used for secure placement of the distraction device. The blocks were taken out after distraction and consolidation periods. The surface of Medpor in contact with the bone was histologically examined to confirm the osteogenic activity.

RESULTS

There was no evidence of osteoconduction in all 24 specimens. The mean total duration of implantation was 2.5 months.

CONCLUSIONS

In human vivo, implantation of a porous polyethylene implant is thought to have no osteogenetic effect through osteoconductive activity even in young children.

Enhancing facial esthetics by other modalities

Preprosthetic surgeries are generally dealt with surgical procedures performed to facilitate fabrication of prosthesis or improve the prognosis of prosthodontic care. In general the surgical procedures include various soft and hard tissue procedures which are restricted intraorally. Maxillofacial prosthodontics is not restricted to restorations performed intra-orally. Various extraoral surgical procedures have come into light in the recent past which helps to improve the prosthodontic outcome of craniofacial region. The current paper tries to elaborate various minimally invasive cosmetic reconstructive procedures and materials available in recent times.

Response of Bone Subjected to Optimized High Dose Irradiation

Allograft tissues are used in over one million musculoskeletal procedures per year. Consequently, it is crucial tissue banks use procedures to militate against allograft associated bacterial and viral infections. Recent studies have identified an important pathogen inactivation technology for musculoskeletal allografts that utilizes high-dose gamma irradiation (50 kGy) under controlled conditions. A total dose of 50 kGy assures that the current standard for medical devices for a microbial sterility assurance level of 10— 6 is met. Furthermore, the pathogen inactivation technology results in a greater than four log inactivation of enveloped and nonenveloped viruses. Efficacious clinical outcome from musculoskeletal allografts exposed to this innovative sterilization procedure will require that there is no performance decrement in the allograft’s biological properties. Therefore, to validate this objective, we executed a study focusing on remodeling and osteoconduction of bone allografts treated with a high dose of gamma irradiation (50 kGy), radioprotectants and well-defined operating parameters of temperature and water content. A rabbit calvarial model was used to test the hypothesis that remodeling and osteoconduction of allogeneic bone treated with the new pathogen inactivation technology would be equivalent to nontreated allogeneic bone. Results indicated treated bone allografts were comparable to nontreated allografts. We conclude, therefore, that based on this outcome and other reports, that high doses of gamma irradiation under optimized conditions designed to reduce free radical damage to tissue will provide safer allografts.

The use of alloplastic materials in rhinoplasty surgery: a meta-analysis

BACKGROUND

Conventional wisdom regarding the use of alloplastic materials in rhinoplastic surgery would advise against their use because of safety and aesthetic concerns. However, autogenous tissue harvest is not without associated morbidity and may be inadequate or insufficient in some clinical situations. Prior studies examining this issue have not provided definitive recommendations regarding implant selection, ideal locations in which to use specific implants, and necessary follow-up.

METHODS

First, the authors systematically reviewed the available literature on alloplastic implant use in rhinoplastic surgery by searching the MEDLINE database (from 1966 through September of 2005). Bibliographies from retrieved articles were searched for additional references. All data were independently extracted by two coauthors. Second, the authors performed a meta-analysis of the three most commonly used implant types.

RESULTS

Although a wide variety of alloplastic materials have been used historically and are still currently available, the most commonly used materials are silicone, expanded polytetrafluoroethylene (Gore-Tex), and porous high-density polyethylene (Medpor). In our meta-analysis, the removal rate for both Gore-Tex and Medpor implants was 3.1 percent, whereas the removal rate for silicone implants was significantly higher at 6.5 percent.

CONCLUSIONS

Alloplastic implants in rhinoplastic surgery have acceptable complication rates and can be used when autogenous materials are unavailable or insufficient. Outcomes with Medpor or Gore-Tex implants may be slightly better than those with silicone. Improved reporting of implant failures and follow-up times in future studies are needed to better define specific guidelines for the use of these materials.

Nasal grafts and implants in revision rhinoplasty

Problems associated with primary rhinoplasty are often due to overresection of the nasal skeleton. One of the primary goals in revision rhinoplasty is to restore nasal architecture. To do so, the facial plastic surgeon can choose from numerous grafting materials. A key understanding of the benefits and limitations of each implant or graft and implants commonly used in revision rhinoplasty surgery.

Behavior of the different implant materials in acute infection and efficacy of antibiotherapy: Experimental study in rats

In this study, we propose a comparison of the behaviors of four different implant materials in case of acute infection: expanded polytetrafluoroethylene (e-PTFE), porous high density polyethylene (PHDPE), silicone, and autogenous cartilage tissue. The efficacy of prophylactic and therapeutic antibiotic therapies was also investigated in a rat model as four groups: group A, acute infection and no antibiotic therapy (n = 24); group B, acute infection and prophylactic antibiotic therapy (n = 24); group C, acute infection and therapeutic antibiotic therapy (n = 24); and control, no infection and no antibiotic therapy (n = 24). All materials with dimensions of approximately 1 x 1 cm(2) diameter were implanted separately under the dorsal skin of rats. Staphylococcus aureus was used as the infectious agent and antibiotic therapy was done with seftriaxone (Desefin, I.M., 20 mg/kg/day). Tissue specimens were obtained on postoperative days 14 and 21. Semiquantitative and qualitative alterations existing in the connective tissue neighboring the implant material (reaction zone-capsule tissue), fixation to the host tissue, cellular ingrowth (interstice qualitatively), and infection signs were assessed either macroscopically or microscopically. In group A, all materials were affected negatively that led to continuous regression in the wound healing process. Fixation of the cartilage to the surrounding tissue was weak compared with other groups. Fibrovascular tissue ingrowth in porous implants was delayed, and no regular capsule formation was observed around silicone implants. In group B, outcomes were similar to control groups. Porous materials showed tissue ingrowth into the pores as good as the control group. Regular capsular tissue formed around the silicone implants and cartilage tissues. In group C, where silicone had been used, wound healing was not as good as in group B and the control group. In the e-PTFE group, the granulation tissue forming through the pores did not show a good quality as the control group, and capsule formation around the material was irregular, leading to insufficient fixation. While the wound healing properties of the PHDPE group were not as good as the control group, there was no difference in terms of fixation to the wound bed. On the other hand, wound healing of the cartilage group was as satisfying as the control group.

Immediate autogenous cartilage grafts in rhinoplasty after alloplastic implant rejection

BACKGROUND

It is accepted in rhinoplasty that complications are more common with alloplastic implants than with autografts. There is little guidance in the literature on how to deal with the cosmetic and/or functional problems that follow alloplastic implant rejection. The conventional advice has been to remove the allograft and not place any graft at the same time. The present article presents our experience treating allograft rejection and immediately repairing any structural defect with autografts.

OBJECTIVE

To demonstrate that immediate nasal reconstruction using autogenous cartilage is a good technique when an alloplastic material has to be removed because of rejection, inflammation, or infection.

DESIGN

A retrospective analysis of outcome for a case series.

METHODS

A retrospective review of the management of 8 patients who presented to 2 tertiary referral centers with alloplastic implant rejection following rhinoplasty. In 7 cases, the alloplastic implant had to be removed because it had migrated and caused a foreign body reaction; in 1 case, the implant had caused a bacterial infection.

RESULTS

In all 8 cases, the nasal deformity that followed the removal of the allograft was so marked that the nose was immediately reconstructed with autogenous cartilage. The patients all made a good recovery after immediate reconstruction, although skin changes associated with the alloplastic implant remained after a mean follow-up of 3 years 3 months.

CONCLUSION

The use of autogenous cartilage is a good option for nasal augmentation immediately after the removal of an alloplastic implant.

Craniofacial Reconstruction With High-Density Porous Polyethylene Implants

Deformities of the facial skeleton may be reconstructed using autogenic or allogenic materials. Porous polyethylene is one of the few alloplastic materials currently in use having a well-documented history of reconstruction or augmentation in the maxillofacial region. High-density porous polyethylene, which is shown to be effective as a biomaterial, has additional advantages like tissue ingrowth, no capsule formation around it, and easy fixation. In this study, 83 implants in 71 patients were evaluated. Seven patients were in need of a second intervention. Three of the seven secondary interventions were for contour alignment, and four interventions were for extraction of the implants because of extrusion or infection. Placement of porous polyethylene implants directly under the skin without coverage of periosteum or another fascial envelope has an increased risk of early and especially late exposure. In cases like nasal dorsum or microtia reconstruction, we prefer autogenic grafts instead of allogenic materials.

Comparing the Osteogenic Capacities of Bone Substitutes: Hydroxyapatite, High-Density Porous Polyethylene, and Bone Collagen: A Biochemical and Histological Analysis

Several inorganic materials have been shown previously to hold some osteogenic capacity. The purpose of this study is to compare the bone-forming abilities of hydroxyapatite ceramic, high-density porous polyethylene, and bone collagen within the periosteal island flap of rabbit tibia using histological and biochemical analysis. With this goal, four discrete experimental groups were formed, each comprising 22 New Zealand male rabbits. A sac was created on each rabbit tibial periosteum flap in each of the groups, and each of the previously mentioned materials was placed within this sac separately. One of these groups was thought as a control group without any material being placed inside the periosteal sac. Biopsies were taken at weeks 1, 2, 4, and 8 for biochemical analysis and at weeks 2 and 8 for histological evaluation. Neo-osteogenesis was evaluated quantitatively by determination of alkaline phosphatase and osteocalcin levels biochemically as well as by the percentage of new bone formation inside the periosteal sac histologically. Results show statistically that the osteogenic effect of high-density porous polyethylene is greater than that of the other materials used in this study (P < 0.05).

Facial skeletal reconstruction using porous polyethylene implants

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 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 posttraumatic, 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 to 11 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 bioincompatibility. The overall reoperation rate was 10 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.

An unusual complication of a Medpor implant in nasal reconstruction: a case report

There are few implant materials which have been successfully used for nasal reconstruction. Of these, the medpor implant is the most accepted alloplastic material for reconstruction of the nasal framework. Here, an unusual complication of a medpor implant in nasal reconstruction is presented. A 24-year-old medical student suffering from a saddle nose deformity after a primary rhino plasty was admitted to our department. The medpor nasal implant was used to restore the nasal dorsum. The surgical result was appreciated by the patient. No problem was encountered during two years after surgery. Recently, the patient suffered from an asymmetry of the nasal dorsum. The physical examination revealed a step on the nasal dorsum with caudal mobility of the implant. The nasal implant was suspected to be broken. Multislice CT scan and ultrasonographic imaging of the implant were obtained. The radiologic evaluation of the region confirmed the fracture of the medpor nasal implant. Nasal reconstruction with a medpor implant is a good choice with low complication rates. This is the first case in the literature reporting a broken medpor nasal implant. Moreover, in this study a new method is described for imaging the medpor implant material.

Exposure of high-density porous polyethylene (Medpor) used for contour restoration and treatment

Porous high-density polyethylene (Medpor) is a biocompatible large-pore, high-density polyethylene implant. It is well tolerated by surrounding tissue, and its porous structure is rapidly infiltrated by host tissue. It is a highly stable and somewhat flexible porous alloplast that has rapid tissue ingrowth into its pores. However, when the implant is placed under a thin cover of skin, there is a risk of exposure. A total of 52 Medpor implants were placed in 31 patients over a four-year period. The implants were used for the chin, malar area, nasal reconstruction, ear reconstruction, orbital reconstruction, and the correction of mandibular contour deformities. Many of these implants were placed in areas considered problematic, such as those with thin or atrophic soft-tissue coverage and extensive scarring. There were nine complications, including three patients in whom the implant was exposed; these are presented here.

Alloplastic implantation

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Define an alloplastic material and know the differences between an alloplast and other types of implants available for surgical use. 2. Determine the biologic response to alloplastic implantation and the material and host characteristics that contribute to long-term reconstruction success with their use. 3. Review the criteria for choosing a specific alloplastic material for a reconstruction site and the principles of surgical technique for its proper placement. 4. Evaluate the various alloplastic material types that are currently available for surgical use and be able to discuss several physical properties of each as they relate to handling and clinical implantation. 5. Discuss the complication of alloplastic infection, its pathogenesis, preoperative and intraoperative measures for its avoidance, and the postoperative management of its occurrence.

Reconstruction of contour and anterior wall defects of frontal bone with a porous polyethylene implant

Frontal bone contour defects cause marked facial deformity, which is instantly obvious to the observer. The aetiology is usually post-traumatic either following a traffic accident or a gunshot injury. The contour deformity of the frontal bone was reconstructed using Medpor porous polyethylene in 12 consecutive patients during a period of 2 years. In four of the patients, we used a coronal approach, whilst using the old incision scar and laceration for access in the remainder. In two of the patients it was not necessary to fix the implant at all, but the remainder were fixed with lag screws because of implant mobility. The aetiology, the technique used, and the results obtained are presented.

Polyethylene terephthalate and polyurethane coatings for endovascular stents: preliminary results in canine experimental arteriovenous fistulas

PURPOSE

To evaluate polyethylene terephthalate and polyurethane as coatings of vascular endoprostheses in the treatment of experimental arteriovenous fistulas (AVFs).

MATERIALS AND METHODS

Nineteen bilateral carotid artery-to-external jugular vein AVFs were created in 10 adult dogs. Fourteen polyethylene terephthalate-coated and five polyurethane-coated self-expandable nitinol stents were placed with a transfemoral approach. Angiography was performed immediately after placement, after 1 and 3 weeks, and at months 3, 6, 9, and 12. All grafts were examined histopathologically.

RESULTS

The AVF was successfully occluded with all but one of the polyethylene terephthalate-coated stents. Graft patency was seen with 12 polyethylene terephthalate-coated stents, while acute vessel occlusion was evident with two polyethylene terephthalate-coated stents following percutaneous transluminal angioplasty immediately after implantation. In the group with polyurethane-coated stents, three graft dislocations and two delayed vessel occlusions were observed. In both groups, histologic examination disclosed a mild foreign body reaction with a few macro-phages. No inflammatory reactions were seen. An unorganized fibrin layer was found adjacent to the polyurethane coating.

CONCLUSION

Polyethylene terephthalate-coated nitinol stents showed good biocompatibility and a high rate of occlusion of experimental AVFs. The mechanical properties of the polyethylene terephthalate coating were similar to those of the nitinol stents, which facilitated handling. Polyurethane-coated stents showed frequent dislocation.

Implant fixation by bone ingrowth

The term osseointegration referred originally to an intimate contact of bone tissue with the surface of a titanium implant; the term bone ingrowth refers to bone formation within an irregular (beads, wire mesh, casting voids, cut grooves) surface of an implant. The section dealing with the historical background describes the development of macroporous, microporous, and textured surfaces with an emphasis on the evolution of porous and textured metal surfaces. The principal requirements for osseointegration and bone ingrowth are systematically reviewed as follows: i) the physiology of osseointegration and bone ingrowth, including biomaterial biocompatibility with respect to cellular and matrix response at the interface; ii) the implant surface geometry characteristics; iii) implant micromotion and fixation modes; and iv) the implant-bone interface distances. Based on current methods of bone ingrowth assessment, this article comparatively reviews and discusses the results of experimental studies with the objective of determining local and systemic factors that enhance bone ingrowth fixation.

Simultaneous malaroplasty with porous polyethylene implants and orthognathic surgery for correction of malar deficiency

PURPOSE

Patients with skeletal malrelationships caused by maxillary anteroposterior defect and midface hypoplasia may present with an alteration of cheekbone contour. High osteotomies, segmental osteotomies of the zygomatic complex, and malar expansion with alloplastic materials can be performed to improve facial aesthetics. This article describes the restoration of cheekbone-nasal base-lip contour by performing a malaroplasty using an alloplastic implant in addition to orthognathic surgery.

PATIENTS AND METHODS

From 1995 to 1996, 17 patients with maxillomandibular malrelationships and deficient cheekbone contour were tested by malar augmentation with porous high-density polyethylene in association with maxillary advancement and mandibular setback. The diagnosis of cheekbone contour alteration was made after observing the patient from a lateral, frontal, and oblique point of view. The position of the implant was determined by using Mladick's point, with lateral or medial extension in relation to the depressed area.

RESULTS

By the restoration of normal cheekbone-nasal base-upper lip contour produced excellent aesthetic results in all patients.

CONCLUSIONS

Malaroplasty in association with bimaxillary orthognathic surgery seems to be an effective procedure for treating midface skeletal deficiencies.

Clinical and histologic behavior of exposed porous high-density polyethylene implants

Reconstruction in the head and neck is difficult and often requires complex solutions to restore functional and aesthetic form. While autogenous tissue is preferred, many alloplasts have been investigated. These materials, however, are foreign bodies, and most alloplasts tolerate exposure and infection poorly. An alloplast's in vivo behavior is a function not only of its composition but also of its form and macrostructure, as well as the interaction at the host-implant interface. Porous high-density polyethylene is well tolerated by surrounding tissue, and its porous core is rapidly infiltrated by host tissue. In order to further investigate the response of porous high-density polyethylene under adverse conditions, we implanted three porous high-density polyethylene disks and one silicone disk underneath the dorsal skin in each of 12 rats. The implants were exposed at differing times after implantation. After 7 days, the exposed areas were either skin grafted or allowed to close by secondary intention. Silicone implants all tolerated exposure poorly. Porous high-density polyethylene implants exposed soon after implantation also tolerated exposure poorly; however, none of these extruded. Porous high-density polyethylene implants exposed after the host tissue had invaded the pores tolerated exposure well, healing either by secondary intention or by skin grafting. Porous high-density polyethylene is a safe and reliable material for use in aesthetic and functional reconstruction of the head and neck. Porous high-density polyethylene and possibly other porous alloplasts tolerate exposure well once host fibrovascular tissue has invaded the implant pores. Further investigation of differing clinical settings and implant behavior is currently in progress.

Bone regeneration with resorbable polymeric membranes. III. Effect of poly(L-lactide) membrane pore size on the bone healing process in large defects

Poly(L-lactide) membranes of various pore sizes: microporous, medium pore size (10-20 microns), and large pore size (20-200 microns) were implanted in 15 mature New Zealand female rabbits to cover a 10-mm diaphyseal defect created in the radius. Five rabbits were implanted with each membrane. No internal fixation was used, as it was assumed that the intact ulna splints the radius adequately. Postoperative radiographs revealed the formation of hematoma within the bone defect. At the 2nd week after surgery, the hematoma was resorbed and the formation of new bone was noted radiologically either at the ends of the bone fragments or as osteophytes on the proximal and distal edges of the membrane. At 4 weeks, the newly formed bone was growing centripetally from the fragment ends. The bone regeneration took place in the majority of the cases under investigation, regardless of the pore size of the polymeric membranes used. There were, however, some differences in the intensity of the bone regeneration process. Although at 2 weeks after surgery bone formation was seen radiographically in all animals, at 6 months five rabbits of five, four rabbits of five, and three rabbits of five implanted respectively with microporous membrane, medium pore-size membrane, and large pore-size membrane showed complete regeneration of bone within the defects. It is suggested that the primary function of the membrane used to cover bone defects is to preserve the osteogenic components present in the space under the membrane from escaping and support the growth of cells within the "medullary cavity" formed by the tubular implant.

Poly(alpha-hydroxy acids): carriers for bone morphogenetic proteins

A broad spectrum of cells and cell products is associated with bone homeostasis and the renewal of bone following injury. The coupled interactions among cells provide the power behind sculpting of bone, sustaining form, and ensuring functionality. Local and systemic regulatory molecules (e.g. growth factors, hormones) direct cellular interactions through autocrine, paracrine, and hormonal pathways. Recently, genes for a class of osteogenic regulatory molecules have been cloned, and gene product expression has enabled investigators to assess safety and efficacy in animal studies. The molecules are known as bone morphogenetic proteins (BMPs). Therapeutic applications of BMPs depend on a carrier system. A carrier could spatially and temporally localize BMP for regional needs and be custom-tailored for acute craniofacial applications or for recalcitrant extremity non-unions. The poly(alpha-hydroxy acids) (PHAs) may be suitable for these applications. Therefore, the purposes of this paper are (i) to mention, briefly, basic concepts of the bone wound continuum and the possible therapeutic roles of BMPs; (ii) to outline several properties of selected PHAs relevant to bone regeneration dynamics; and (iii) to review selected preclinical studies with PHAs.

Augmentation of the anterior temporal fossa after temporalis muscle transfer

Pedicled transfer of the temporalis muscle has proven to be a reliable and versatile procedure in reconstructive craniomaxillofacial surgery. Excluding those complications related to the coronal incision, little specific attention has been given in the literature to the prevention or treatment of the esthetic defect that remains after muscle transfer. This article describes a case in which block porous high-density polyethylene was used to eliminate the residual defect of the anterior temporal fossa after transmaxillary pedicled transfer for closure of a large oral-antral communication. The implant provided an esthetically pleasing augmentation of the defect. A discussion and analysis of the implant materials available for reconstruction of this region is also presented.

Long-term retrospective analysis of twenty-three Proplast-Teflon temporomandibular joint interpositional implants

This retrospective analysis reviews 15 patients with a total of 23 Proplast-Teflon interpositional implants. Most of the implants have been removed because of implant fragmentation and giant-cell inflammatory reaction. Recommendations for continued long-term care of patients with such implants are offered.

Clinical experience with the Medpor porous polyethylene implant

The Medpor porous polyethylene implant is a highly stable and somewhat flexible porous alloplast that has been shown to exhibit rapid tissue ingrowth into its pores. A total of 116 Medpor implants were placed in 70 patients over a four-year period. Implants were used for the chin, malar area, nasal reconstruction, ear reconstruction, orbital reconstruction, and the correction of craniofacial contour deformities. Many of these implants were placed in areas long considered problematic such as areas of thin soft tissue coverage, extensive scarring, and severe facial burns. Nine complications occurred including seven exposures, all of which occurred in areas of minimal soft tissue coverage. Because of the rapid vascularization of the implants, only two implants were removed, both from the columella. On the basis of our results, it is felt that the Medpor implant is an excellent alternative to existing implant materials. The implant is easy to shape; it is strong yet somewhat flexible; it is remarkably stable; and it exhibits tissue ingrowth into its pores.

A computer-based biomechanical analysis of the three-dimensional motion of cementless hip prostheses

A computer-based mathematical technique was developed to measure and completely describe the migration and micromotion of a femoral hip prosthesis relative to the femur. This technique utilized the mechanics of rigid-body motion analysis and apparatus of seven linear displacement transducers to measure and describe the complete three-dimensional motion of the prosthesis during cyclic loading. Computer acquisition of the data and custom analysis software allowed one to calculate the magnitude and direction of the motion of any point of interest on the prostheses from information about the motion of two points on the device. The data were also used to replay the tests using a computer animation technique, which allowed a magnified view of the three-dimensional motion of the prosthesis. This paper describes the mathematical development of the rigid-body motion analysis, the experimental method and apparatus for data collection, the technique used to animate the motion, the sources of error and the effect of the assumptions (rigid bodies) on the results. Selected results of individual test runs of uncemented and cemented prostheses are presented to demonstrate the efficacy of the method. The combined effect of the vibration and electrical noise resulted in a resolution of the system of about 3-5 microns motion for each transducer. Deformation effects appear to contribute about 3-15 microns to the measurement error. This measurement and analysis technique is a very sensitive and powerful means of assessing the effects of different design parameters on the migration and micromotion of total joint prostheses and can be applied to any other case (knee, dental implant) where three-dimensional relative motion between two bodies is important.

Tissue ingrowth into titanium and hydroxyapatite-coated implants during stable and unstable mechanical conditions

Lack of initial mechanical stability of cementless prostheses may be responsible for fibrous tissue fixation of prosthetic components to bone. To study the influence of micromovements on bony ingrowth into titanium alloy (Ti) and hydroxyapatite (HA)-coated implants, a loaded unstable device producing movements of 500 microns during each gait cycle was developed. Mechanically stable implants served as controls. The implants were inserted into the weight-bearing regions of all four femoral condyles in each of seven mature dogs. Histological analysis after 4 weeks of implantation showed a fibrous tissue membrane surrounding both Ti and HA-coated implants subjected to micromovements, whereas variable amounts of bony ingrowth were obtained in mechanically stable implants. The pushout test showed that the shear strength of unstable Ti and HA implants was significantly reduced as compared with the corresponding mechanically stable implants (p less than 0.01). However, shear strength values of unstable HA-coated implants were significantly greater than those of unstable Ti implants (p less than 0.01) and comparable to those of stable Ti implants. The greatest shear strength was obtained with stable HA-coated implants, which was threefold stronger as compared with the stable Ti implants (p less than 0.001). Quantitative determination of bony ingrowth agreed with the mechanical test except for the stronger anchorage of unstable HA implants as compared with unstable Ti implants, where no difference in bony ingrowth was found. Unstable HA-coated implants were surrounded by a fibrous membrane containing islands of fibrocartilage with higher collagen concentration, whereas fibrous connective tissue with lower collagen concentration was predominant around unstable Ti implants. In conclusion, micromovements between bone and implant inhibited bony ingrowth and led to the development of a fibrous membrane. The presence of fibrocartilage and a higher collagen concentration in the fibrous membrane may be responsible for the increased shear strength of unstable HA implants. Mechanically stable implants with HA coating had the strongest anchorage and the greatest amount of bony ingrowth.

Alveolar ridge augmentation in Macaca fascicularis using polysulfone with and without demineralized bone powder

The purpose of this study was to test the soft tissue and bone response to the implantation of porous polysulfone (PPSF) with and without demineralized bone powder (DBP) for ridge augmentation in Macaca fascicularis. The mandibular molar teeth were extracted in five adult female monkeys, followed by massive alveolectomy. Five to eight months later, PPSF + DBP was inserted subperiosteally on the left side, while PPSF alone was inserted on the right side. The animals were killed 42, 60, and 90 days following implantation. Specimens were processed for light microscopy, scanning electron microscopy, tetracycline labeling, and histomorphometric measurement of new bone. The 42-day specimens of the PPSF + DBP and PPSF revealed penetration of fibrous tissue rich in fibroblasts and blood vessels into the pores of the PPSF. At 60 and 90 days, the PPSF side showed organized fibrous tissue, but bone grew only for a short distance into the implant. In contrast, the PPSF + DBP side showed large amounts of bone formation, and bone almost covered the implant. The qualitative results were confirmed by histomorphometric examination.

Zygomatic and mandibular augmentation with proplast and porous hydroxyapatite in rhesus monkeys

Using an extraoral approach, subperiosteal pockets were created bilaterally over the zygomatic and mandibular regions in six Rhesus monkeys. One side of each animal received a Proplast I (Vitek Inc, Houston) implant and the contralateral side received an equivalent sized block of porous hydroxyapatite (HA). The animals were followed clinically and radiographically. Two animals were killed postoperatively at 3, 6, and 12 months, respectively. The implants were retrieved en bloc and halved. Half of each specimen was decalcified, embedded in paraffin, and stained. The other half was embedded in plastic, and sections were stained or carbon-coated for histometry scanning under electron microscopy. Clinical evaluation revealed that porous HA implants were more stable than Proplast implants. The Proplast implants showed complete encapsulation by infiltration with fibrovascular connective tissue, and progressive fragmentation with giant cell reactions. The porous HA implants were united to the underlying cortex by bony ingrowth. The volume of implants sampled within 2.5 mm of the underlying cortex contained 42.5% HA matrix and 23.8% bony ingrowth, and the surface area of the HA matrix (9.7 mm2/mm3) was 47.8% covered by bony ingrowth. No giant cell response, fragmentation, or biodegradation was observed or measured in the porous HA implants. The data from this primate model further substantiate previous canine studies and permit more reliable estimation of clinical performance. These results provide comparative data that can contribute to the decision-making process in selecting clinical implants.