Peer-Review Short Reports

Traumatic Fracture of a Polymethyl Methacrylate Patient-Specific Cranioplasty Implant

Andrew L. Ko, John D. Nerva, Jason J. J. Chang, Randall M. Chesnut

-OBJECTIVE: To present a case of a traumatic fracture of a polymethyl meth-acrylate (PMMA) patient-specific implant (PSI) for cranioplasty.

-METHODS: A 14-year-old boy with a history of right decompressive hemi-craniectomy and reconstructive cranioplasty with a PMMA PSI presented afteran unhelmeted bicycle accident with somnolence, confusion, seizures, lefthemiparesis, and an obviously deformed cranium.

-RESULTS: Computed tomography scan showed a comminuted, depressedfracture of the implant and cerebral contusions. The implant was seen to beshattered, resulting in displaced, overriding fragments and significant damage tounderlying brain. The patient remained neurologically stable. To minimize thenumber of operations, intervention was delayed while a polyetheretherketonePSI was fabricated. During surgery, it was noted that the fractured pieces of theimplant had caused dural lacerations, and some pieces were embedded in brainparenchyma. The fractured PMMA was removed, and the new implant wasplaced. The patient remained hemiparetic and was later transferred to aninpatient rehabilitation facility.

-CONCLUSIONS: PMMA PSIs are commonly used for large defects andgenerally have good outcomes with low rates of revision. The case reportdescribed involves a shattered PMMA PSI after a traumatic impact, whichresulted in hemiparesis. The question arises if this type of complication can beeasily avoided with the addition of titanium onlay to restrict displacement in theevent of fracture. This onlay represents a minor change of technique that couldprevent migration of fracture fragments.

Key words- Cranioplasty fracture- Patient-specific implants- Pediatric neurosurgery- Synthetic cranioplasty- Traumatic brain injury

Abbreviations and AcronymsPMMA: Polymethyl methacrylatePSI: Patient-specific implant

Department of Neurological Surgery, Universityof Washington, Seattle, Washington, USA

To whom correspondence should be addressed:John D. Nerva, M.D.[E-mail: jdnerva@uw.edu]

Citation: World Neurosurg. (2014).http://dx.doi.org/10.1016/j.wneu.2013.09.025

Journal homepage: www.WORLDNEUROSURGERY.org

Available online: www.sciencedirect.com

1878-8750/$ - see front matter ª 2014 Elsevier Inc.

INTRODUCTION

Various synthetic materials have been usedfor reconstructive cranioplasty with compa-rable results, including polymethyl methac-rylate (PMMA), titanium, hydroxyapatite,polyetheretherketone, and bioceramic. Pre-formed, patient-specific implants (PSIs)using these materials are available, a devel-opment that allows for a good cosmeticresult andminimal operative time dedicatedto reshaping of the implant.Traumatic fracturing of PSIs appears

to be rare. Hydroxyapatite constructionshave been noted to fracture at relatively lowforces roughly equivalent to ground-levelfalls, but preformed constructs augmentedwith titanium mesh have been shown inbiomechanical studies to be resistant atsuch forces (3). PMMA appears to haveimpact resistance at least equivalent to thatof native bone (1), and although fractures ofself-curing PMMA are documented (6), nosuch cases to our knowledge have been re-ported when using preformed PSIs. Theliterature contains 1 report of a traumaticfracture of a bioceramic patient-specificcranioplasty (5). This case is significantinsofar as the fracture fragments weresignificantly displaced, requiring operative

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intervention to remove overriding frag-ments. We present a case of a traumaticfracture of a PMMA PSI. The implant wasshattered, resulting in massively displaced,overriding fragments with significant dam-age to underlying brain and persistentneurologic deficit.

CASE REPORT

A 14-year-old boy had a prior history ofsevere traumatic brain injury and rightdecompressive hemicraniectomy in 2006.The patient underwent reconstructive cra-nioplasty with a PMMA PSI (Stryker,Kalamazoo, Michigan, USA) in a delayedfashion and recovered function to a greatdegree. He was admitted to a referringfacility 5 years later after involvement in anunhelmeted bicycle accident. He wasnoted to be somnolent and confused with

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a laceration over his forehead and anobviously deformed cranium. He vomitedseveral times and was intubated after aseizure. A computed tomography scanshowed traumatic subarachnoid hemor-rhage underlying a comminuted, dep-ressed fracture of his previous implant,with several fragments stacking onebeneath the other (Figure 1A).On admission to our institution, the pa-

tient was intubated, followed commands,and had left hemiparesis. A repeat com-puted tomography scan showed intervaldevelopment of a small cerebral contusionunder the displaced fragments (Figure 1B).The patient remained neurologically stableand was extubated without event. Nofurther evolution was seen on subsequentimaging. To minimize the number ofoperative procedures for this patient, wedelayed intervention over the week

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Figure 1. Traumatic fracture of synthetic cranioplasty. (A) Computedtomography (CT) reconstruction shows stellate fracture pattern andretropulsion of multiple implant fragments. (B) CT scan of the head showsstacking of fragments up to 3 in depth and underlying contusions of brainparenchyma. (C) Photograph taken during revision cranioplasty shows

overriding fragments. (D) Intraoperative photograph shows fragments havebeen significantly displaced, with some driven into the brain. Durallacerations are apparent, and contusions underlying this fragment arecausing a left hemiparesis.

PEER-REVIEW SHORT REPORTS

ANDREW L. KO ET AL. TRAUMATIC FRACTURE OF PMMA CRANIOPLASTY IMPLANT

necessary to have a polyetheretherketonePSI fabricated.During surgery, the fractured pieces

of the previous implant were noted tohave traveled significant distances fromtheir original sites, causing dural lacera-tions (Figure 1C). Pieces of PMMA wereembedded in brainparenchyma (Figure 1D).After the fractured PMMA was removed,the new implant was secured in placewith no need for intraoperative reshaping.The patient remained hemiparetic afterthe procedure and was transferred to aninpatient rehabilitation facility with nocomplications.

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DISCUSSION

PMMA PSIs have become increasinglycommon as cranioplasty implants; this islikely in response to convenience of use,and the complication rates associated withother materials, including native bone.Resorption of primary autologous bonecranioplasty is common, especially inchildren and adolescents in cases withdefects >75 cm2, with rates of 66% re-ported (2). Delayed inflammatory re-sponses to hydroxyapatite implants, whichcan lead to scalp dehiscence and exposureof cranioplasty material, can have devas-tating consequences; rates of infection

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and extrusion of 23% have been reported(4). Large studies of PMMA implants showas good or even better outcomes thannative bone using measures such as pa-tient satisfaction and need for revision(4, 6). As a result, materials such as PMMAseem appropriate to use for large defectsbecause they avoid the risk of boneresorption without increasing the rate ofother complications.We describe the case of a shattered

PMMA implant after a traumatic impact.This appears to be a very rare occurrence;however, the implications of such an eventcan be significant. In this case, the patient

dx.doi.org/10.1016/j.wneu.2013.09.025

PEER-REVIEW SHORT REPORTS

ANDREW L. KO ET AL. TRAUMATIC FRACTURE OF PMMA CRANIOPLASTY IMPLANT

at discharge remained with significantneurologic deficit believed to be due tofracture comminution and submarining atthe time of impact. There has been 1previous report of a similar traumaticfracture of a PSI, albeit of a different ma-terial (5). Of particular note is the patternof fracture: stellate fracture lines withpropulsion of fragments a significant dis-tance and depth, resulting in up to 3fragments overriding one another. Bio-mechanical analysis of PMMA PSIs hasshown the tendency of certain formula-tions to fragment into a stellate pattern(1). The question arises if this type ofcomplication can be easily avoided. Thepattern reported here is very similar to thepattern described in the other reported PSIfracture case, wherein the bioceramicimplant also fragmented and submarined.Fractures of hydroxyapatite implants

secondary to relatively minor trauma havebeen noted; the addition of titanium meshas a scaffold tended to improve implantstrength (3). Whether similar scaffolding in

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PMMA would have a comparable effect isunknown. However, incorporating meshinto a PMMA PSI could prevent the forcefulmigration of fracture fragments into brainparenchyma and the submarining effect.Alternatively, long titanium plates currentlyused for craniofacial fixation might be usedas an onlay with the same effect, restrictingthe displacement of fragments in the caseof a traumatic fracture; thiswould representa minor change of technique that couldprevent migration of fracture fragments.With PSI use having become so common,optimizing the safety of such implants un-der traumatic conditions seems warranted.

REFERENCES

1. Eppley BL: Biomechanical testing of alloplasticPMMA cranioplasty materials. J Craniofac Surg 16:140-143, 2005.

2. Grant G, Jolley M, Ellenbogen RG, Roberts TS,Gruss JR, Loeser JD: Failure of autologous bone-assisted cranioplasty following decompressive cra-niectomy in children and adolescents. J NeurosurgPediatr 100:163-168, 2004.

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3. Matic DB, Manson PN: Biomechanical analysis ofhydroxyapatite cement cranioplasty. J CraniofacSurg 15:415-422 [discussion 422-423], 2004.

4. Moreira-Gonzalez A, Jackson IT, Miyawaki T,Barakat K, DiNick V: Clinical outcome in cranio-plasty: critical review in long-term follow-up.J Craniofac Surg 14:144-153, 2003.

5. Petridis AK, Barth H, Doukas A, Mehdorn HM:Broken bioceramic used in a computer-assistedreconstruction of the frontal skull bone. J ClinNeurosci 16:1089-1090, 2009.

6. van Goo AV: Preformed polymethylmethacrylatecranioplasties: report of 45 cases. J Maxillofac Surg13:2-8, 1985.

Conflict of interest statement: The authors declare that thearticle content was composed in the absence of anycommercial or financial relationships that could be construedas a potential conflict of interest.

Received 17 July 2013; accepted 13 September 2013

Citation: World Neurosurg. (2014).http://dx.doi.org/10.1016/j.wneu.2013.09.025

Journal homepage: www.WORLDNEUROSURGERY.org

Available online: www.sciencedirect.com

1878-8750/$ - see front matter ª 2014 Elsevier Inc.All rights reserved.

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