Clinical Experience in Cranioplasty With PorousPolyethylene Implant

Porus Polietilen implant ile Kranioplasti Klinik Deneyimi

SERDAR KAHRAMAN, HAKAN KAYALI, SAlT $lRlN, ALi KAFADAR*

MURAT AKBORu*, ERDENER TiMURKAYNAK

Department of Neurosurgery, School of Medicine, CUlhane Military Medical Academy, Etlik, Ankara, Turkey

* Department of Neurourgery, Air Force Hospital, Etimesgut, Ankara, Turkey

Received: 14.11.20020 Accepted: 01.11.2003

Abstract: Objective: Cranial defects and their optimumreconstructions have been a deal in neurosurgicalpractice. In the recent time, we used porous polyethyleneimplants for cranioplasty to provide better cosmetic,surgical and long-term safety results.Material and method: Porous polyethylene implants(Medpor", PorexMedical, Atlanta, CA) were used in 36patients with different localization and size of cranialdefects.

Result: Using porous polyethylene has shortened theoperation time and led no complication except one lateinfection due to skin trauma.

Conclusion: Porous polyethylene has many advantagesin restoring all cranial defects with low morbidity.

Key Words: Alloplastic material, cranioplasty, porouspolyethylene

INTRODUCTION

Desirable properties of alloplastic materialsfor closure of skull defects include rigid fixationand cosmetically acceptable edge-to-edge contactand contour. Many techniques using alloplasticand autogenous materials have been championedfor this purpose, including autogenous bone grafts,

Ozet : AmaF Nbro~iri.irji pratiginde kranial defektlerinen iyi ~ekilde onanml problem olu~turmaya devametmektedir. Son dbnemde kranioplasti i<;in daha iyikozmetik, cerrahi ve uzun sureli gUvenilir sonw;lan olanporous polyethylene kullandlk.Materyal ve Metod: 36 hastada farkh lokalizasyon vegeni~likte olan kranial defektler i<;inporous polyethyleneimplant kullamldl..Sonu(: Porous polyethlene kullamml operasyonzamamm kisaltmaktadlr. Travmatik cilt defektine baghge<; dbnem enfeksiyonu olan bir olgu dl~mdakomplikasyon gbri.ilmerni~tir. Kranial defektlerin porouspolyethylen ile onanml du~uk morbiditeyle beraber pek<;okavantaja sahiptir.

Anahtar Kelimeler: Alloplastik materyal, kranioplasti,porous polyethylene

silicone, porous hydroxyapatite, and variousmetals either alone Or in association with methylmethacrylate (6,11,13,16,18).

An alloplastic material should have someideal properties, which include ease of adaptation,biocompatibility, permitting ingrowth of newtissue, stability of shape, low level of resorption.

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Turkish Neurosurgery 13: 89-93, 2003 Kalmlll1nn: C1i/lienl Experience in Cranioplasty With Porol/s Polyethyle/le Implanl

Polyethylene has been used in the craniofacialskeleton, in some cases with follow-up periods ofmore than 30 years (15), it has long been used astand art reference material for biocompatibilitytesting (8). The porous polyethylene implant is ahighly stable and somewhat flexible porousalloplast that has been shown to exhibit rapidtissue ingrowth into its pores (19) and may be usedto cover any shape of cranial defect (2).

Here, we present our experience with porouspolyethylene for the restoring of cranial defects.

MATERIAL AND METHOD

We used porous polyethylene implant forcranioplasty in 36 patients between 1998 and 2001.All patients were male and their ages werebetween 20-35 years. Cranial defect localizationsand the pathological diagnoses of the patients weresummarized in Table 1. Four cases with frontal

defect had also frontal sinus damage. Cranialdefects were also classified as small, medium and

large in respect of their largest diameter which isconsidered to be a very important parameter,

particularly in stability (Table 2). In five cases,orbital reconstructions have also been performedtogether with cranioplasty. Timing of surgery wasvariable depending on the pathologies of thepatients. In traumatic cases, cranioplasty wasperformed after following infection-free period ofone-year. Simultaneous cranioplasty was done inthe remaining cases. No patient had a radiationtherapy before cranioplasty operation.

Table 2. Classification of the cranial defects

TypeLargest diameter of cranial defectNo

Small

<4cm 9

Medium

4-8 cm22

Large

>8cm 5

Porous polyethylene implants were adaptedto the cranial defects with trimming the edges ofthe implants after softenning in sterile warm saline.Consequently, the implants were fixed on thecranium using titanium or bioabsorbable mini­screws and in some cases titanium or bioabsorbable

mini-plates (Figure 1 a-b and 2 a-b, Figure 3).Follow-up periods ranged from 1 to 4 years.

Table 1. Localizations of the cranial defects and pathological diagnoses of the patients.

Localization / PathologyFibrousLeptomeningealPosttraumaticSecondaryNo

dysplasia

cystcranialdefectto cranial

operationLeft frontal

-- 9110

Right frontal

-- 415

Right fronto-orbital

3- --3

Left fronto-orbital

1- 1-2

Occipital

-- 3-3

Right parietal

-1 326

Right temporal

-- 2-2

Right temporo-parietal

-- 3-3

Right fronto-parietal

-- 112

Total

4126536

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Turkish Neurosurgery 13: 89-93, 2003 Kllhramllll: ClilliclIl Experiellce ill Crallioplllsty With Porous Polyethylelle Implllllt

Figure 1: Preoperative axial (a) and coronal (b) computed tomography scans of the patient with fronto-orbital fibrousdysplasia.

Figure 2: Axial (a) and coronal (b) computed tomography scans of the patient after cranioplasty with porous polyethylene

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Turkish Neurosurgery 13: 89-93, 2003

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Kahralllan: Clinical Experience ill Cranioplasty With Porous Polyethylene IlIlplant

methyl methacrylate alone or in combination withtitanium or wire mesh (11,13).

However, the use of methyl methacrylate maybe associated with potential complicationsincluding exothermic reaction produced during thecuring process which may result in local tissuedamage, release of a toxic monomer that has beenimplicated in local and systemic reactions, fractureof the brittle implant, and a significant rate ofinfection (6,12,13,16) .

Since previous alloplastic materials had somedisadvantages, the necessity of new alloplasticmaterials appeared in neurosurgical practice. Porouspolyethylene implants were successfuly used byCouldwell in 25 cases with cranial defects (2 ).

Figure 3: Surgical technique of porous polyethyleneimplant (An original figure from Could well WT et a1.)

RESULTS

After exposing the cranial defect, the avaragetime for implantation of the alloplast was 25minutes. There are different shapes of porouspolyethylene implants which are suitable fordifferent sites and shapes of cranial defects.Excellent surgical and cosmetic results wereobtained in all cases except in one case with leftfronto-orbital defect. In this case, infection was

observed in implant site ue to traumatic skindefect in the second year of cranioplasty. Afterremoval of the infected implant with leavingorbital reconstruction, we followed up the patientfor one-year infection-free time for secondarycranioplasty with porous polyethylene again.Follow-up the patient for one year showed nofurther complication. .

DISCUSSION

A variety of cranioplasty materials andimplantation techniques have been reported in theliterature (6,11,13,16,18). While autogenousmaterials for skull and craniofacial reconstruction

possess optimum biocompatibility characteristics,complications arising from the donor site andincreased operation time limit their widespreaduse. For these reasons alloplastic materialscontinue to be popular, the most widely used being

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Polyethylene is a highly inert material thatexhibits a consistently benign clinical response andhas been proven stable over many years of use inhumans. Porous polyethylene is a form of high­density polyethylene that contains a system ofinterconnecting pores of approximately 150 mm. indiameter (18). This porous architecture enables theingrowth of vascularity and soft tissue within aperiod of 3 to 4 weeks to form a stable interface thatanchors the implant (3,5,9). Over longer periods, itpermits the incorporation of bone at the implant­bone interface (3,9,17). Porous polyethylene wasdetermined to be well tolerated histologically withonly mild chronic inflammation, thin capsuleformation, and partial fibrovascular ingrowth (7).

Maas et a1. compared various porousmaterials ( proplast, silas tic, supramid and porouspolyethylene) for facial bone augmentation in dogsand found the greatest implant stability withporous polyethylene (10). Proplast has poor tissueingrowth ability because of its sponge like frame.The pores do not interconnect and are not strongenough to resist collapse. Berghaus et a1. alsoshowed the fragmentation of proplast implant dueto tissue ingrowth (1). Moreover, Merritt et a1.demonstrated that after healing dense ceramicimplants were more susceptible to infection thanporous polyethylene, they suggested that thevascular ingrowth may protect the implant frominfection (12).

A multi-center experience using porouspolyethylene implants in 140 patients with facial

Turkish Neurosurgery 13: 89-93, 2003 Kahramall: Clillicnl Experiellce ill Cranioplasty With Porous Polyethylene Implmlt

fractures was presented by Romano et al. in 1993(14). In patients with acute injuries, the implantwas placed in the orbit, exposed to open facialsinuses. Despite the use of this implant for acutetrauma reconstruction, there was only one instanceof implant infection requring removal, and noimplant migration or exposure. Similiarly Dumanet al. reported that no implant migration,resorption or infection in their 12 consequtivepatients (4).

In our 36 cases, infection was observed only inone case (2.7%) due to traumatic skin defect whichcould not be contributed to the porouspolyethylene implant itself. In addition to thisresult, no implant fragmentation, resorption ormigration occured in our cases.

In cranioplasty surgery using alloplastreleasing of dural adhesions for preperation offixation holes on cranium may lead tocomplications such as epidural hematoma orcerebrospinal fluid leakage. We experienced thatcranioplasty with porous polyethylene does notrequire dural seperation for the fixation ofalloplastic material. Thus, the operation time andcomplication rate are possibly decreased.

CONCLUSION

Others and our experiences suggest that theporous polyethylene implant offers a safer,cosmetically equivalent alternative to stand artmethyl methacrylate cranioplasty while ease ofimplantation shortens operation time. Porouspolyethylene implant is easy to use, readily curved,time saving and does not lead to any donor sitemorbidity. This material described was found to bea simple and effective method for restoring cranialdefects with low further 'complication . The resultsobtained in our series were excellent.

Corresponding: Serdar Kahraman, M.D.Assistant Professor,Department of Neurosurgery,School of Medicine,Gulhane Military Medical Academy,06018 Etlik, Ankara-TurkeyPhone: +90 312 304 5302Fax: +90 312 304 5300

Running Title: Cranioplasty with Porous Polyethylene

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