Biomechanical Evaluation of Patient-Specific Polymethylmethacrylate Cranial Implants for Virtual Surgical Planning: An In-Vitro Study.

Bilal Msallem,Florian S Halbeisen,Michaela Maintz,Guido R Sigron,Shuaishuai Cao,Simon Meyer,Florian M Thieringer,Neha Sharma

doi:10.3390/ma15051970

Bilal Msallem, Florian S Halbeisen + Show 6 more

Open Access

https://doi.org/10.3390/ma15051970

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Abstract

Cranioplasty with freehand-molded polymethylmethacrylate implants is based on decades of experience and is still frequently used in clinical practice. However, data confirming the fracture toughness and standard biomechanical tests are rare. This study aimed to determine the amount of force that could be applied to virtually planned, template-molded, patient-specific implants (n = 10) with an implant thickness of 3 mm, used in the treatment of a temporoparietal skull defect (91.87 cm2), until the implant cracks and finally breaks. Furthermore, the influence of the weight and porosity of the implant on its force resistance was investigated. The primary outcome showed that a high force was required to break the implant (mean and standard deviation 1484.6 ± 167.7 N), and this was very strongly correlated with implant weight (Pearson’s correlation coefficient 0.97; p < 0.001). Secondary outcomes were force application at the implant’s first, second, and third crack. Only a moderate correlation could be found between fracture force and the volume of porosities (Pearson’s correlation coefficient 0.59; p = 0.073). The present study demonstrates that an implant thickness of 3 mm for a temporoparietal skull defect can withstand sufficient force to protect the brain. Greater implant weight and, thus, higher material content increases thickness, resulting in more resistance. Porosities that occur during the described workflow do not seem to reduce resistance. Therefore, precise knowledge of the fracture force of polymethylmethacrylate cranial implants provides insight into brain injury prevention and serves as a reference for the virtual design process.

Highlights

Reconstruction of the craniofacial skeleton’s highly complex shape is routinely achieved using various autogenous or alloplastic materials [1,2]
A systematic review comparing titanium mesh, PMMA, polyetheretherketone (PEEK), and Norian implants states that PMMA implants are associated with a significantly higher infection rate [7]
Cranial implants that are thinner than the average parietal bone thickness while still providing equal protection for the brain can be fabricated

Summary

Introduction

Reconstruction of the craniofacial skeleton’s highly complex shape is routinely achieved using various autogenous or alloplastic materials [1,2]. Alloplastic reconstructions using freehand-molded polymethylmethacrylate (PMMA) have been a gold standard in cranioplasty since World War II [1,3,4]. The use of PMMA in cranioplasty resulted from the need to improve cranioplasty techniques during World War II, and it is believed that. The use of PMMA has been extensively studied and reports of long-term experience with this material are accumulating, making it well established in clinical practice [6]. Despite conflicting data in the literature regarding infection rates, it has remained a commonly used material to date. A systematic review comparing titanium mesh, PMMA, polyetheretherketone (PEEK), and Norian implants states that PMMA implants are associated with a significantly higher infection rate [7]. PMMA and autologous bone have been reported to have significantly higher infection rates than titanium mesh [8].

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