Orbital floor implant and drilling guide

Based on the high-resolution CT scan of the patient (0.5mm slice thickness), we reconstructed the anatomy in 3D. This first step is called segmentation and is performed by selecting the Hounsfield units (level of grey) corresponding to bone on the CT scan. Extra efforts were made to segment the sinus cavity and the contralateral orbital floor, in order to create some references for the design of the implant.

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The design requirements, such as thickness and size of the implant, were determined by the surgeon, Mr Komath. Surgical approach and clinical obstacles were taken into account for the design of the implant.

Using some mirroring tools and CAD software, 3D LifePrints’ biomedical engineer designed a patient-specific orbital floor implant which would sit on the defect to recreate a healthy orbital floor. The implant was designed with a 0.8mm thickness and the screws positioned on the orbital rim so that the implant could not be felt through the skin by the patient.

Mirror (in red) superimposed to the anatomy.

CMF Case Study 1 2

CMF Case Study 1 3

To improve the accuracy of the implant positioning, the engineer designed a patient-specific drilling guide. This guide allows to pre-drill the position of the screws which will stabilise the implant.

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The devices were then printed by Renishaw and delivered to the hospital, where they were sterilised.

The 3D printing technique used is SLS (Selective Laser Melting). The process is digitally driven, direct from sliced 3D CAD data. For each slice of CAD data a thin even layer of fine metal powder is deposited across the build plate, then the selected areas of the powder are precisely melted by the laser. This process is repeated building up, layer by layer, until the build is complete.

Some post-processing, such as cleaning, heat treatment and polishing are performed. The surgical guide, as it is used temporarily, was delivered clean (“as built”). The implant was polished in order to have a smooth surface, eliminating risks of tissue attachment.

 

The outcome of this surgery was excellent: there was no diplopia (double vision) and the eyelid was in great position. No post-operative scan was made as it was judged unnecessary due to patient’s excellent recovery.