Cranioplasty with the Medpor porous polyethylene flexblock implant. Technical note

High-Density Porous Polyethylene Implant Cranioplasty: A Systematic Review of Outcomes

Porous polyethylene has been widely used in craniofacial reconstruction due to its biomechanical properties and ease of handling. The objective of this study was to perform a systematic review of the literature to summarize outcomes utilizing high-density porous polyethylene (HDPP) implants in cranioplasty. A literature search of PubMed, Cochrane Library, and Scopus databases was conducted to identify original studies with HDPP cranioplasty from inception to March 2023. Non-English articles, commentaries, absent indications or outcomes, and nonclinical studies were excluded. Data on patient demographics, indications, defect size and location, outcomes, and patient satisfaction were extracted. Summary statistics were calculated using weighted averages based on the available reported data. A total of 1089 patients involving 1104 cranioplasty procedures with HDPP were identified. Patients' mean age was 44.0 years (range 2 to 83 y). The mean follow-up duration was 32.0 months (range 2 wk to 8 y). Two studies comprising 17 patients (1.6%) included only pediatric patients. Alloplastic cranioplasty was required after treatment of cerebrovascular diseases (50.9%), tumor excision (32.0%), trauma (11.4%), trigeminal neuralgia/epilepsy (3.4%), and others such as abscesses/cysts (1.4%). The size of the defect ranged from 3 to 340 cm2. An overall postoperative complication rate of 2.3% was identified, especially in patients who had previously undergone surgery at the same site. When data were available, contour improvement and high patient satisfaction were reported in 98.8% and 98.3% of the patients. HDPP implants exhibit favorable outcomes for reconstruction of skull defects. Higher complication rates may be anticipated in secondary cranioplasty cases.

Acceptable durability of split inner table graft for the reconstruction of a bone defect in pterional craniotomies: a case series

Objective

During a pterional craniotomy, the bone defect was reconstructed by a surgical technique using an autogenous bone graft instead of commercially available alloplastic materials. The technical feasibility, durability of the grafted bone, and cosmetic outcome were all evaluated.

Methods

After a pterional craniotomy was performed, the bone defect at the frontobasal burr hole and drilled sphenoid wing was reconstructed using an autogenous split inner table graft (1 cm × 2 cm) harvested from the craniotomy bone flap.

Results

The bone reconstruction technique was successfully performed on nine patients with intracranial aneurysms. After 12-19 months from the surgery, a volumetry study using three-dimensional skull images reconstructed from computed tomography angiography showed a minimal decrease in the area of the split inner table graft due to bone resorption in six patients, which ranged from 5.7% to 14.8%. In the other three patients, the bone resorption was more substantial, ranging from 21.2% to 27.5%. However, in the three latter cases, the resorption was mainly limited to the posterior part of the split inner table graft covered by the temporalis muscle and did not affect the cosmetic outcomes. The resultant cosmetic outcomes for the nine patients were all favorable, with only a slight or no anterior temporal hollow.

Conclusion

The proposed surgical technique using a split inner table graft harvested from the craniotomy bone flap seems viable for reconstructing the bone defect at the frontobasal burr hole and drilled sphenoid wing after a pterional craniotomy.

A Staged Approach for Contouring of Temporal Deformities Using Porous Polyethylene and Lipofilling

ABSTRACT

Many studies evaluated the effectiveness of a single reconstructive material during temporal cranioplasty, or in comparison to the outcome of another material. To our knowledge, no previous study evaluated a staged combination of reconstruction modalities during temporal cranioplasty. In a prospective interventional study, the authors combined high-density porous polyethylene (HDPP) implant insertion (stage I) with a following lipofilling session (stage II) in 8 patients scheduled for temporal cranioplasties. This two-staged approach was evaluated 6 months after each stage independently. The patients' satisfaction as regards the aesthetic outcome was evaluated through a 5-points Likert scale by the patients themselves. For every individual patient, this psychometric analysis was repeated by medical staff from other departments. Statistical analysis of the patients and medical staff satisfaction scores showed a statistically significant increase after the addition of lipofilling session (stage II) if compared to implant insertion only (stage I). Clinically, this outcome was maintained in a long-term follow-up ranged from 1 - 8 years. Nevertheless, 2 patients needed one more lipofilling session to obtain their satisfaction as regards the final aesthetic outcome. No other complications were recorded in this study. In conclusion, combining alloplastic and autogenous reconstruction modalities in a staged approach can suffice the reconstruction requirements for such temporal defects. After a long follow-up period, the insertion of high-density porous polyethylene implant with the addition of a following lipofilling session showed more evaluators' satisfaction in terms of the final aesthetic outcome.

Use of Stock Titanium Mesh Plates in Cranioplasty

Craniofacial surgeons are often confronted with major defects of the calvarium. These most commonly are post-traumatic but could also be consequent upon neurosurgical procedures, infection, or tumor removal. There are several options available to reconstruct these defects including autogenous, heterogeneous, and alloplastic material. The goal is to have a method that is easy, cost-effective, with minimal complications, and long-lasting. In our unit we review 100 cases of the use of stock titanium mesh during a 5-year period. Complications occurred in 5 patients (5%) with 3 exposures, 1 late seroma and 1 case requiring repositioning of the plate following trauma. None of the patients required removal of the plate.

Cranioplasty of Large Cranial Defects With Porous Polyethylene Implants

BACKGROUND

Reconstruction of cranial defects due to trauma or other causes has been carried out since ages with a wide variety of materials. The aim of reconstruction was mainly to restore cosmesis and protect the brain from further injury. However, recent studies have shown that cranioplasty not only improves the cerebral blood flow but also leads to improvement of cognitive functions. The materials used include autologous bone, allogeneic bone, xenografts, and alloplasts. The search for an ideal material continues. The authors present their experience with cranioplasty using prefabricated porous polyethylene implants.

MATERIALS AND METHODS

Patients requiring cranioplasty for reconstruction of large sized (more than 15 cm in any 1 dimension) cranial defects were selected. Three patients were men and 2 were women. The age group of the patient ranged from 18 to 58 years. Preformed Biopore Hemisphere was used in every patient for cranial reconstruction.

RESULTS

No complications were seen in our patients. One patient who had undergone titanium cranioplasty previously showed remarkable improvement in cognitive functions.

CONCLUSION

Porous polyethylene prefabricated implants are a good restorative material for reconstruction of large cranial defects.

Porous Polyethylene Implant as Aesthetic Complement in Orthognathic Surgery

Porous polyethylene implants have been used as an alternative in the treatment of patients with zygomatic and paranasal projections deficiency. These implants promote a facial rejuvenating effect due to the attenuation of the nasal and chin prominences. The advantages of porous polyethylene include biocompatibility, dimensional stability, easy adaptation and fixation, low complication rate, and its availability in different sizes and shapes. A 27-year-old woman presenting vertical deficiency associated with midface hypoplasia was treated with orthognathic surgery. Clockwise rotation and genioplasty were performed. In order to improve facial aesthetics, porous polyethylene implants were placed in the paranasal area, optimizing the facial contour with the correction of the midface projection.

A Method for Combining Thin and Thick Malleable Titanium Mesh in the Repair of Cranial Defects

Introduction: Cranial defects following the removal of tumor involved bone require repair and reconstruction for brain protection and cosmesis. A variety of autologous bone substrates and synthetic materials can be employed, alone or in combination. In this article, we describe the use of dual thin and thick titanium mesh, connected together using plate hardware, to repair a right frontotemporal sphenoidal bone defect following resection of a hyperostosing sphenoid wing meningioma.

Methods: Reconstruction of the pterion was done with a dual mesh cranioplasty. After replacement of the native orbitozygomatic and frontotemporal bone pieces, a piece of thinner mesh was molded to the pterional defect connecting the two bone pieces and re-creating the concave shape of the pterion below the superior temporal line. The circular area of the bony defect overlying the frontal and temporal lobes was supplemented by cutting and molding an additional piece of thicker mesh which was secured to the thinner mesh with burr hole cover sectors using rescue screws.

Results: A 30-year-old woman presented with painless proptosis and was found to have a hyperostosing right sphenoid wing meningioma. The patient underwent a frontotemporal orbitozygomatic craniotomy for tumor resection and extensive bony osteotomy. Repair and reconstruction of the cranial defect in the region were accomplished at the time of open operation using two thicknesses of mesh connected one to another with titanium plate pieces and rescue screws. The patient underwent gross total resection of the meningioma and near total resection of the soft tissue and bony components (Simpson Grade II). The external cosmetic results following the orbital-cranial reconstruction with the dual mesh technique was deemed “very good” by the surgeon and patient. Postoperative CT imaging demonstrated symmetric re-approximation of the shape of the pterion as compared to the opposite side.

Conclusions: We present a method for connecting two titanium mesh sheets with available hardware to improve the strength in compression while maintaining the ability to mold thinner sheets as necessary for the best cosmetic results. This method is an option for coverage of bony defects in the region of the pterion for young, physically active patients providing them with additional mesh cranioplasty strength.

Sellar Floor Reconstruction with the Medpor Implant Versus Autologous Bone After Transnasal Transsphenoidal Surgery: Outcome in 200 Consecutive Patients

OBJECTIVE

The Medpor porous polyethylene implant provides benefits to perform sellar floor reconstruction when indicated. This material has been used for cranioplasty and reconstruction of skull base defects and facial fractures. We present the most extensive use of this implant for sellar floor reconstruction and document the safety and benefits provided by this unique implant.

METHODS

The medical charts for 200 consecutive patients undergoing endonasal transsphenoidal surgery from April 2008 through December 2011 were reviewed. Material used for sellar floor reconstruction, pathologic diagnosis, immediate inpatient complications, and long-term complications were documented and analyzed. Outpatient follow-up was documented for a minimum of 1-year duration, extending in some patients up to 5 years.

RESULTS

Of the 200 consecutive patients, 136 received sellar floor cranioplasty using the Medpor implant. Postoperative complications included 6 complaints of sinus irritation or drainage, 1 postoperative cerebrospinal fluid leak requiring operative re-exploration, 1 event of tension pneumocephalus requiring operative decompression, 1 case of aseptic meningitis, 1 subdural hematoma, and 1 case of epistaxis. The incidence of these complications did not differ from the autologous nasal bone group in a statistically significant manner.

CONCLUSIONS

Sellar floor reconstruction remains an important part of transsphenoidal surgery to prevent postoperative complications. Various autologous and synthetic options are available to reconstruct the sellar floor, and the Medpor implant is a safe and effective option. The complication rate after surgery is equivalent to or less frequent than other methods of reconstruction and the implant is readily incorporated into host tissue after implantation, minimizing infectious risk.

Reconstruction after retrosigmoid approaches using autologous fat graft-assisted Medpor Titan cranioplasty: assessment of postoperative cerebrospinal fluid leaks and headaches in 60 cases

BACKGROUND

Postoperative cerebrospinal fluid (CSF) leaks and headaches remain potential complications after retrosigmoid approaches for lesions in the posterior fossa and cerebellopontine angle. The authors describe a simple repair technique with an autologous fat graft-assisted Medpor Titan cranioplasty and investigate the incidence of postoperative CSF leaks and headaches using this technique.

METHODS

A retrospective chart review was conducted on all cases (n = 60) of retrosigmoid craniectomy from September 2009 to May 2014 in patients who underwent fat graft-assisted cranioplasty. After obtaining a watertight dural closure and sealing off any visible mastoid air cells with bone wax, an autologous fat graft was placed over the dural suture line and up against the waxed-off air cells. The fat graft filled the retrosigmoid cranial defect and was then bolstered with a Medpor Titan (titanium mesh embedded in porous polyethylene) cranioplasty. A postoperative mastoid pressure dressing was applied for 48 h, and prophylactic lumbar drainage was not used. Factors examined in this study included postoperative CSF leak (incisional, rhinorrhea, otorrhea), pseudomeningocele formation, incidence and severity of postoperative headache, length of hospital stay, and length of follow-up.

RESULTS

No patients developed postoperative CSF leaks (0 %), pseudomeningoceles (0 %), or new-onset postoperative headaches (0 %) with the described repair technique. There were no cases of graft site morbidity such as hematoma or wound infection. Mean duration of postoperative hospital stay was 3.8 days (range 2-10 days). Mean postoperative follow-up was 12.4 months (range 2.0-41.1 months).

CONCLUSIONS

Our multilayer repair technique with a fat graft-assisted Medpor Titan cranioplasty appears effective in preventing postoperative CSF leaks and new-onset postoperative headaches after retrosigmoid approaches. Postoperative lumbar drainage may not be necessary.

Role of a dentist in comprehensive management of a comatose patient with post traumatic head injury and neuropathological chewing

Injury of the head and neck region can result in substantial morbidity. Comprehensive management of such patients requires team work of several specialties, including dentists. A young female patient with extensive loss of cranium and associated pathological chewing was referred to the dental department. The lost cranium was replaced by a custom-made, hand-fabricated cranioplast. Trauma due to pathological mastication was reduced by usage of a custom-made mouthguard. Favorable results were seen in the appearance of the patient and after insertion of the mouthguard as evidenced in good healing response. The intricate role of a dental specialist in the team to manage a patient with post traumatic head injury has been highlighted. The take away message is to make the surgical fraternity aware of the scope of dentistry in the comprehensive management of patients requiring special care.

Cranioplasty with autologous cryopreserved bone after decompressive craniectomy: complications and risk factors for developing surgical site infection

Background

Renewed interest has developed in decompressive craniectomy, and improved survival is shown when this treatment is used after malignant middle cerebral artery infarction. The aim of this study was to investigate the frequency and possible risk factors for developing surgical site infection (SSI) after delayed cranioplasty using autologous, cryopreserved bone.

Methods

This retrospective study included 74 consecutive patients treated with decompressive craniectomy during the time period May 1998 to October 2010 for various non-traumatic conditions causing increased intracranial pressure due to brain swelling. Complications were registered and patient data was analyzed in a search for predictive factors.

Results

Fifty out of the 74 patients (67.6 %) survived and underwent delayed cranioplasty. Of these, 47 were eligible for analysis. Six patients (12.8 %) developed SSI following the replacement of autologous cryopreserved bone, whereas bone resorption occurred in two patients (4.3 %). No factors predicted a statistically significant rate of SSI, however, prolonged procedural time and cardiovascular comorbidity tended to increase the risk of SSI.

Conclusions

SSI and bone flap resorption are the most frequent complications associated with the reimplantation of autologous cryopreserved bone after decompressive craniectomy. Prolonged procedural time and cardiovascular comorbidity tend to increase the risk of SSI.

Dural adhesion to porous cranioplastic implant: A potential safety concern

Background:

Patient-specific implants are used for cranioplastic skull reconstruction when large bone flaps must be replaced or where there are complex or critical contours, especially near the face. These implants have a low complication rate, with poor fit and postoperative infection being the most common complications. We report here a potentially serious hazard that may arise from the use of porous implants.

Case Description:

A 45-year-old woman sustained severe head trauma in a motor vehicle accident that required urgent surgical intervention. Because of progressive resorption of her native bone flap, she underwent replacement of her native flap with a hard tissue replacement/patient-matched implant cranioplasty. Eight years later, she sustained a traumatic laceration over her vertex that necessitated removal of her cranioplastic implant because of persistent local infection. Intraoperatively, the dural flap was ingrowing and firmly adherent to the inside surface of the porous cranioplasty. After several failed attempts to remove the whole implant piecemeal, we attempted to dissect the dural flap from the brain surface to remove it together with the cranioplastic implant but exposure of the extensive cortical adhesions between the brain surface and the dural flap was compromised by the hard overlying cranioplastic implant. Despite our meticulous attempts to cut off these cortical adhesions, a perisylvian blood vessel was avulsed, resulting in intraparenchymal hemorrhage.

Conclusion:

In this case, dural adhesion and ingrowth to the underside of the cranioplasty implant led to disastrous bleeding when the implant needed to be removed years after initial implantation.

Prefabricated patient-matched cranial implants for reconstruction of large skull defects

Cranial defects can be caused by injury, infection, or tumor invasion. Large defects should be reconstructed to protect the brain and normalize the cerebral hemodynamics. The conventional method is to cover the defect with bone cement. Custom-made implants designed for the individual patient are now available. We report our experience with one such product in patients with large cranial defects (>7.6 cm in diameter). A CT scan with 2 mm slices and a three-dimensional reconstruction were obtained from the patient. This information was dispatched to the company and used as a template to form the implant. The cranial implant was received within four weeks. From 2005 to 2010, custom-made cranial implants were used in 13 patients with large cranial defects. In 10 of the 13 patients, secondary deep infection was the cause of the cranial defect. All the implants fitted well or very well to the defect. No infections were seen after implantation; however, one patient was reoperated on for an epidural hematoma. A custom-made cranial implant is considerably more expensive than an implant made of bone cement, but ensures that the defect is optimally covered. The use of custom-made implants is straightforward and timesaving, and they provide an excellent medical and cosmetic result.

A review of reconstructive materials for use in craniofacial surgery bone fixation materials, bone substitutes, and distractors

Over the last 40 years, craniofacial surgery, in general, and surgery for craniosynostosis, in particular, has witnessed the introduction of a number of new materials for use in operations involving the cranial vault. Some of these materials have proven quite useful over time, while others have failed to meet their stated objectives. In this review, the more popular implant materials are analyzed, and their relative merits and drawbacks are discussed. Craniofacial surgery in the pediatric population has its own unique limitations, quite different from the adult population and those issues are reviewed as well.

Calvarial reconstruction using high-density porous polyethylene cranial hemispheres

AIMS

Cranial vault reconstruction can be performed with a variety of autologous or alloplastic materials. We describe our experience using high-density porous polyethylene (HDPE) cranial hemisphere for cosmetic and functional restoration of skull defects. The porous nature of the implant allows soft tissue ingrowth, which decreases the incidence of infection. Hence, it can be used in proximity to paranasal sinuses and where previous alloplastic cranioplasties have failed due to implant infection.

MATERIALS AND METHODS

We used the HDPE implant in seven patients over a three-year period for reconstruction of moderate to large cranial defects. Two patients had composite defects, which required additional soft tissue in the form of free flap and tissue expansion.

RESULTS

In our series, decompressive craniectomy following trauma was the commonest aetiology and all defects were located in the fronto-parieto-temporal region. The defect size was 10 cm on average in the largest diameter. All patients had good post-operative cranial contour and we encountered no infections, implant exposure or implant migration.

CONCLUSIONS

Our results indicate that the biocompatibility and flexibility of the HDPE cranial hemisphere implant make it an excellent alternative to existing methods of calvarial reconstruction.

Reconstruction of the skull base and cranium adjacent to sinuses with porous polyethylene implant: preliminary report

Surgical reconstruction of the skull base and cranium adjacent to open paranasal sinuses with alloplastic materials is problematic secondary to an increased risk of implant infection in these locations. The authors report their initial experience with the use of a porous polyethylene implant for closure of defects in these locations in 20 patients, in 14 of these with the implant placed in direct contact with the mastoid or paranasal simuses. The implant is flexible, which facilitates surgical reconstruction of the cranial base, and porous in nature, which enhances soft tissue and bone ingrowth in decrease the risk of infection. The implant is radiolucent on plain roentgenograms and CT, and produces no imaging artifact on MRI. The implant was utilized for a variety of skull base of cranium adjacent to sinus reconstructive applications with no infectious complications, with a follow-up period ranging from 8 to 50 months. This preliminary experience suggests that the alloplast may be a useful adjunct in skull base reconstruction, and further evaluation of its use in this application is warranted.

Medpor Craniotomy Gap Wedge Designed to Fill Small Bone Defects along Cranial Bone Flap

OBJECTIVE

Medpor porous polyethylene was used to reconstruct small bone defects (gaps and burr holes) along a craniotomy bone flap. The feasibility and cosmetic results were evaluated.

METHODS

Medpor Craniotomy Gap Wedges, V and T, were designed. The V implant is a 10 cm-long wedge strip, the cross section of which is an isosceles triangle with a 4 mm-long base, making it suitable for gaps less than 4 mm after trimming. Meanwhile, the Medpor T wedge includes a 10 mm-wide thin plate on the top surface of the Medpor V Wedge, making it suitable for gaps wider than 4 mm and burr holes. Sixty-eight pterional craniotomies and 39 superciliary approaches were performed using the implants, and the operative results were evaluated with respect to the cosmetic results and pain or tenderness related to the cranial flap.

RESULTS

The small bone defects were eliminated with less than 10 minutes additional operative time. In a physical examination, there were no considerable cosmetic problems regarding to the cranial bone defects, such as a linear depression or dimple in the forehead, anterior temporal hollow, preauricular depression, and parietal burr hole defect. Plus, no patient suffered from any infectious complications.

CONCLUSION

The Medpor Craniotomy Gap Wedge is technically easy to work with for reconstructing small bone defects, such as the bone gaps and burr holes created by a craniotomy, and produces excellent cosmetic results.

LONG-TERM OUTCOME OF SUBCUTANEOUSLY PRESERVED AUTOLOGOUS CRANIOPLASTY

OBJECTIVE

Decompressive craniectomy for intracranial hypertension mandates later cranioplasty. Autologous cranioplasties can be preserved either by freezing or placement in a subcutaneous pocket. There are few data on the long-term follow-up of patients treated in such a fashion.

METHODS

A retrospective study was conducted on 100 consecutive patients who underwent decompressive craniectomy and placement of the bone flap in a subcutaneous pocket in the abdominal wall between 2000 and 2005. Initial diagnosis, Glasgow Coma Scale score on admission, complications, and Glasgow Outcome Score were recorded.

RESULTS

Of the 100 patients who underwent autocranioplasty, the primary diagnosis was traumatic brain injury (76%), subarachnoid hemorrhage (17%), primary intracerebral hemorrhage (3%), and tumor (4%). The mean age of the sample was 39 years (age range, 10–72 years). The mean follow-up duration was 25 months. The average Glasgow Coma Scale score on admission was 7. Eight patients died before replacement of the bone flap. The average time between craniectomy and replacement of bone flap was 42 days. The mean Glasgow Outcome Score was 4 at the time of the 1-year follow-up evaluation. Seven of the 79 patients (9%) for whom 1-year review data were available had a cosmetic result that was unacceptable and required removal of the flap (bone flap infections in 5 patients, unacceptable bone flap resorption in 2 patients)

CONCLUSION

Our study indicates that storage of a cranioplasty flap in a subcutaneous pouch in the abdominal wall has a favorable long-term outcome.

In situcranioplasty with methylmethacrylate and wire lattice

Most techniques of cranioplasty are expensive and require advance preparation if a custom-moulded prosthesis is to be used. Technical problems with cranioplasties using synthetic materials include sinking, elevation and rotation, while those with hydroxyapatite or bone graft cranioplasties include resorption and harvest site disfigurement. We report our technique of in situ cranioplasty using methylmethacrylate and a wire lattice that is fast, inexpensive and avoids these technical problems.

Imaging of porous polyethylene implant by using multidetector spiral computed tomography

The porous polyethylene implant (Medpor; Porex Surgical, Inc., Newnan, GA) is one of the most usable implants in clinical practice. Because it is radiolucent on both direct radiography and conventional computed tomography, visualization of the implant becomes an important issue. In this clinical study, availability of multidetector spiral computed tomography for visualization of the implant was evaluated. The technique was used in 15 patients who had Medpor reconstructions on their faces, including frontal (seven), malar (five), and mandibular (five) regions. A 16-channel multislice computed tomography scanner was used in spiral scanning mode. Sagittal, coronal, and transverse multiplanar reformation and volume-rendered images were reformatted using a PC-based three-dimensional reconstruction program (Extended Brilliance Workspace, Release 1.0.1.1, Philips Medical Systems, Amsterdam, The Netherlands). The three-dimensional images along the course of the implant were additionally reformatted. Window width and level were adjusted for viewing the bone as respective values of 1100 HU and 450 HU in contrast to the values of 800 HU and 200 HU, respectively, for the implant. The detailed contour of the implants could be easily traced on the multidetector computed tomographic images, including either the concave or convex areas. The calcifications and cystic formations around the implants and the spatial relationship between the defects and the implants were also shown. We believe that the present multidetector computed tomographic technique offers direct visualization of the Medpor implant in the body. It has many advantages over the current magnetic resonance imaging techniques that need tissue in growth for visualization.

Carvable calcium phosphate bone substitute material

This study investigated the use of partially set hydroxyapatite forming calcium phosphate cement as a carvable and mechanically stable bone substitute material. Hydroxyapatite-forming cements were made of either mechanically activated alpha-tricalcium phosphate or a mixture of tetracalcium phosphate and dicalcium phosphate anhydrous and setting was arrested up to 4 h post setting. The study showed that these partially set rigid samples of defined geometry could be carved into a desired shape when the degree of reaction was 30-40% and the relative porosity between 40 and 50%; samples are then expected to set completely after implantation in the presence of water or serum, having the same compressive strength as a continuously set calcium phosphate cement (up to 36 MPa). The development of compressive strength, phase composition, and crystallinity when varying production parameters of these partially "preset" bone substitute materials are presented for both cement systems.

Evaluation and Management of Exposed High-density Porous Polyethylene Implants

Numerous autogenous and alloplastic materials have been used for restoration of contour deformities of the face. Alloplastic materials have come into use to replace autogeneous bone grafts because bone grafts are associated with donor site morbidity, resorption and difficulty in shaping. Porous high-density polyethylene (HDPPE) is a commercial product which is nonallergenic, nonantigenic, noncarcinogenic and nonresorbable, highly stable and somewhat flexible. It has pores of 125-250 mum which enable tissue ingrowth resulting in firm attachment and integration of the implant to the surrounding tissues. In this study we aimed to evaluate the fate of the exposed implants and proposed a method to manage the exposed medpor implants. Twenty rats were used for this experimental study. Three phases involving the implantation, exposition, and the closure of the implants were held respectively. Closure was performed in two groups: 1) After perforating the exposed implants; 2) Without perforating the exposed implants. No serious complications were seen. Perforated exposed implants when covered with flaps rather than grafts could be covered. Exposed implants were not covered easily as indicated by the previous studies. This study demonstrates that early closure of perforated implants with flaps can give the best clinical results when exposed implants are covered in a short period after exposition so that the ingrown fibrous tissues are still intact. We believe that grafting of the exposed medpor implants cannot be effective either in early or late period. Perforating the exposed implants yield successful results as ingrowth of the tissues are enabled.

Genetic Effects of Medpor® on Osteoblast-like Cells

Porous polyethylene (PP or Medpor) is an alloplastic material used worldwide for craniofacial reconstruction. Although several clinical studies are available, there is a lack as regard the genetic effects. Because PP is always fixed on bone and the mechanism by which PP acts on osteoblasts is unknown, we therefore attempted to address this question by using microarray techniques to identify genes that are differently regulated in osteoblasts exposed to PP. By using DNA microarrays containing 19,200 genes, we identified in osteoblast-like cell lines (i.e. MG-63) cultured on PP several genes where expression was differentially regulated. The differentially expressed genes cover a broad range of functional activities: 1) signal transduction, 2) transcription, 3) translation, 4) cell cycle regulation, 5) vesicular transport, and 6) production of cytoskeletal elements, cell-adhesion molecules and extracellular matrix components. The data reported are, to our knowledge, the first genetic portrait of osteoblast-like cells cultured on PP. They are relevant to better understanding of the molecular mechanism of bone-PP interaction and as a model for comparing other materials used for bone reconstruction.

Analyses of the factors influencing bone graft infection after delayed cranioplasty

BACKGROUND

Several factors influencing bone graft infection after delayed cranioplasty are analyzed in order to reduce the occurrence of infection.

METHODS

For about 10 years, from March 1995 to February 2005, delayed cranioplasty was performed for 206 cases. The cases comprised 124 males and 82 females. Age distribution of the patients ranged from 6 months to 79 years old. The mean postoperative follow-up period was 1834 days. Autogenous bone, which was preserved in 100% ethanol at -20 degrees C and autoclaved before operation, was used in 54 patients. Polymethylmethacrylate (PMMA) was used in 55 patients. Custom-made PMMA was used in 3 patients. Custom-made titanium mesh was used in 77 patients. Custom-made ceramics (Alumina-ceramics 10 cases and hydroxyapatite 7 cases) was used in 17 patients.

FINDINGS

Autoclaved and autogenous bone graft and PMMA have a significantly high rate of graft infection. Titanium mesh has the significantly lowest rate of graft infection. Alumina-ceramic has a merit that it has sufficient strength, however the number of cases using custom-made ceramics including alumina-ceramic was relatively small, and thus we cannot find significant differences in infection rate compared with that of other materials. There was no statistically significant difference in the bone graft infection rate among four categories of preceding diseases; cerebrovascular diseases, head trauma, infectious diseases, and brain tumour.

CONCLUSION

Autoclaved and autogenous bone grafts and PMMA have a significantly higher rate of graft infection. Titanium mesh has the significantly lowest rate of graft infection.

Clinical Outcome of 285 Medpor Grafts used for Craniofacial Reconstruction

Porous polyethylene (Medpor) is an alloplastic material worldwide used for craniofacial reconstruction. To evaluate complications and risk factors associated with this synthetic graft, a retrospective study was performed. A series of 285 Medpor grafts were placed in 187 patients. Age, sex, diagnosis at admission, site, type of surgical insertion, type of fixation, and outcome (no complications, anesthesia, exposure, infection, and implant remodeling and removal) are considered. By means of univariate and multivariate analyses, we detect variables most associated with poor outcome. Univariate analysis showed that graft "survival" curves stratified according to (1) diagnosis at admission and (2) site are statistically significant. Subsequently, a Cox analysis was performed: both variables are also predictors of graft outcome. Porous polyethylene is a reliable alloplastic material that can be satisfactory used for craniofacial reconstruction. However, some sites (i.e., nose, maxilla, and ear) and diagnosis at admission (i.e., syndromic patients previously operated) are related to an higher risk of implant failure.

Porous polyethylene implant for cranioplasty and skull base reconstruction

OBJECT

Cranial reconstruction after skull base surgery is important for restoration of function and cosmesis. The authors describe their experience with the Medpor porous polyethylene implant for cosmetic cranioplasty and reconstruction after skull base surgery.

METHODS

Medpor, a biocompatible implant, is flexible and can be contoured to facilitate surgical reconstruction of small to medium (< 8 cm) convexity or cranial base defects resulting from a variety of skull base approaches. This method provides similar cosmetic results to standard alloplast cranioplasty while decreasing operating time. The porous nature of the material allows ingrowth of soft tissue and bone to increase implant strength and decrease the risk of infection. This material can also be used safely in reconstruction of the cranium and skull base adjacent to the paranasal sinuses.

CONCLUSIONS

The authors have used the Medpor porous polyethylene implant in 611 standard cranial and skull base procedures and have achieved excellent cosmetic results and no implant-related complications.

Comparison of the biological activities of high-density porous polyethylene implants and oxidized regenerated cellulose-wrapped diced cartilage grafts

The use of alloplastic materials in plastic surgery has become more extensive with advancement of autogenous-tissue reconstruction techniques for the repair of defects, tissue augmentation, and the stabilization of bones. An ideal alloplastic material should be nonallergenic, noncarcinogenic, 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 subfascially in 10 young rabbits, and the 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 subfascially, and were highly stabilized by the surrounding tissues. Turkish Delight 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 tissues when placed subperiosteally than when placed subfascially.

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.

The use of frozen autogenous bone flaps in delayed cranioplasty revisited

OBJECTIVE

To reevaluate the use of frozen autogenous bone flaps for patients undergoing delayed cranioplasty.

METHODS

In the past 12 years, 49 patients have undergone delayed cranioplasty using frozen autogenous bone flaps. Bone flaps removed during the initial operation were sealed in three sterilized vinyl bags and stored at -35 degrees C (n = 37) or -84 degrees C (n = 12) for 4 to 168 days (mean, 50.6 d). The bone flaps were thawed at room temperature and replaced in their original positions. After cranioplasty, we monitored resorption of the bone flaps with computed tomography and evaluated the clinical and aesthetic results. Follow-up periods ranged from 14 to 147 months (mean, 59.2 mo).

RESULTS

For 47 patients (95.9%), there were no complications during the follow-up period; there was slight thinning of the bone flap in some cases, but clinical and aesthetic results were highly satisfactory. Resorption was observed for a 12-year-old boy who had undergone cranioplasty, using two pieces of bone flap, 66 days after the initial operation. A 14-year-old boy with a cerebral contusion experienced a bone flap infection. Both patients underwent a second cranioplasty procedure, with ceramic plates.

CONCLUSION

The clinical and aesthetic results of delayed cranioplasty using frozen autogenous bone flaps were satisfactory. The most important factor for success was excellent contiguity between the flap and the bone edge.

Method to improve cosmetic outcome following craniotomy

This technical note describes a simple method for reducing the dead space created by craniotome due to the loss of bone dust and improving the cosmetic outcome following a craniotomy. After drilling the burr holes for the craniotomy, the bone between the holes is drilled away in a standard fashion except that multiple regions of about 1 cm in length are left intact. These intact regions are broken using a periosteal elevator and fixed like a bridge when the bone is replaced. The resulting bone flap is readily returned to its original position without making the dead space created by regular craniotomy. The amount of the dead space caused by losing the bone dust is reduced and a good cosmetic recovery is obtained. This technique is useful for both craniotomy and facial bone surgery, which requires cosmetic results.

Osteochondral reconstruction of a non-weight-bearing joint using a high-density porous polyethylene implant

Currently, there is no reliable reconstructive modality allowing anatomic resurfacing of traumatic digital osteochondral articular defects. The purpose of the present study is to demonstrate the utility of Medpor, a high-density porous polyethylene (HDPP) scaffold biomaterial that can (1) be readily contoured to fit any joint defect, (2) permit stable internal fixation, and (3) permit osteocyte and chondrocyte ingrowth and subsequent articular cartilage resurfacing necessary to restore joint congruity. HDPP has gained wide acceptance for use in craniofacial and skeletal reconstruction and augmentation. An avian non-weight-bearing joint model was designed to study the role of the HDPP implant in small joint reconstruction. An osteochondral defect was created with a 5-mm circular punch in the humeral articular surface of both glenohumeral joints of 32 adult White Leghorn chickens. In each animal, one defect was press-fitted with a correspondingly sized HDPP implant (HDPP implant group); the contralateral defect was filled with the original osteochondral plug (isograft group) or left unrepaired (control group). At 2 weeks, and 1, 3, and 6 months,joints from each group were harvested and evaluated. Over the 6-month study period, joints in the control group demonstrated healing with dense collagenous scar tissue leaving residual defects at the articular surfaces and significant degenerative disease of the glenohumeral joints radiographically. Joints in the isograft group demonstrated near-complete resorption with some preservation of the cartilaginous cap but overall depression of the articular surface and significant degenerative joint disease. Joints in the HDPP implant group demonstrated stable fixation by highly mineralized bony trabecular ingrowth, preservation of the articular contour of the humeral head, and no evidence of significant degenerative joint disease. These findings indicate a potential role for this high-density porous polyethylene implant in the reconstruction of small joint articular and osseous defects.

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.

A new technique for cranioplasty with L-shaped titanium plates and combination ceramic implants composed of hydroxyapatite and tricalcium phosphate (Ceratite)

OBJECTIVE

The use of hydroxyapatite-based ceramics for cranioplasties has recently increased in Japan, because of the good cosmetic outcomes, biocompatibility, strength, osteoconductive properties, and lack of risk of disease transmission associated with these materials. However, miniplate fixation has not been possible for ceramic implants. We describe a new technique for miniplate fixation of ceramic implants.

METHODS

Combination ceramic implants composed of hydroxyapatite and tricalcium phosphate (Ceratite; NGK Spark Plug Co., Aichi, Japan) were used for cranioplasties. A slot and a pair of holes were cut in each Ceratite implant, for use as a fixation unit. We have also developed a new L-shaped titanium plate (HOMS Engineering Inc., Nagano, Japan) that fits into the fixation unit. We first insert an L-shaped titanium plate through the slot from the back surface of the Ceratite implant. We then bend the plate outward at the front surface of the Ceratite implant and fix it to the cranium of the patient with titanium screws. The Ceratite implant is usually firmly fixed to the cranium of the patient with three L-shaped titanium plates.

RESULTS

Using L-shaped titanium plates and Ceratite implants, we successfully performed cranioplasties for seven patients with cranial defects resulting from external decompression craniotomies. The Ceratite implant exactly fit the bone window for each patient. Surgical maneuvers were simple and easy for all patients, permitting shorter operating times. All Ceratite implants were firmly fixed, and no postoperative infections have occurred.

CONCLUSION

Our new technique for cranioplasty is simple and allows rigid fixation of Ceratite implants.

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.

A technique for rigid fixation of methyl methacrylate cranioplasty: the vault-locking method

BACKGROUND

Current treatment of difficult to reach lesions of the central nervous system favors extensive bone removal for improved visualization and access with minimal brain retraction. Particularly in the posterior fossa, bone is often removed piecemeal, and a standard craniotomy flap is not always available for simple reattachment. Cranioplasty with methyl methacrylate is used to provide cosmesis and neural protection. A method for the fixation of methyl methacrylate cranioplasty is described, and the results of technique application in 30 patients during a 14-month period are reported.

METHODS

A series of notches are burred in the cancellous margin of the surrounding cranium, preserving the inner and outer tables. Methyl methacrylate is applied to the defect. Overflow of methyl methacrylate into the notches assures solid fixation. The resultant construct resembles the locking mechanism of a bank vault. No mesh, wire, or miniplates are required. Prolene buttresses may be placed through the outer table of the notches to identify their location, should removal of the plasty be required. Removal of the outer table over the notches facilitates rapid removal.

RESULTS

Solid plasty and good cosmesis occurred in all patients. There were no infections or complications related to this technique.

CONCLUSIONS

Firm fixation, molding and hardening in situ, and technical ease are potential advantages over established methods of cranioplasty.

Repairing holes in the head: a history of cranioplasty

Cranioplasty is almost as ancient as trephination, yet its fascinating history has been neglected. There is strong evidence that Incan surgeons were performing cranioplasty using precious metals and gourds. Interestingly, early surgical authors, such as Hippocrates and Galen, do not discuss cranioplasty and it was not until the 16th century that cranioplasty in the form of a gold plate was mentioned by Fallopius. The first bone graft was recorded by Meekeren, who in 1668 noted that canine bone was used to repair a cranial defect in a Russian man. The next advance in cranioplasty was the experimental groundwork in bone grafting, performed in the late 19th century. The use of autografts for cranioplasty became popular in the early 20th century. The destructive nature of 20th century warfare provided an impetus to search for alternative metals and plastics to cover large cranial defects. The metallic bone substitutes have largely been replaced by modern plastics. Methyl methacrylate was introduced in 1940 and is currently the most common material used. Research in cranioplasty is now directed at improving the ability of the host to regenerate bone. As modern day trephiners, neurosurgeons should be cognizant of how the technique of repairing a hole in the head has evolved.