Imaging, virtual planning, design, and production of patient-specific implants and clinical validation in craniomaxillofacial surgery

Abstract

The purpose of this article was to describe the workflow from imaging, via virtual design, to manufacturing of patient-specific titanium reconstruction plates, cutting guide and mesh, and its utility in connection with surgical treatment of acquired bone defects in the mandible using additive manufacturing by electron beam melting (EBM). Based on computed tomography scans, polygon skulls were created. Following that virtual treatment plans entailing free microvascular transfer of fibula flaps using patient-specific reconstruction plates, mesh, and cutting guides were designed. The design was based on the specification of a Compact UniLOCK 2.4 Large (Synthes(®), Switzerland). The obtained polygon plates were bent virtually round the reconstructed mandibles. Next, the resections of the mandibles were planned virtually. A cutting guide was outlined to facilitate resection, as well as plates and titanium mesh for insertion of bone or bone substitutes. Polygon plates and meshes were converted to stereolithography format and used in the software Magics for preparation of input files for the successive step, additive manufacturing. EBM was used to manufacture the customized implants in a biocompatible titanium grade, Ti6Al4V ELI. The implants and the cutting guide were cleaned and sterilized, then transferred to the operating theater, and applied during surgery. Commercially available software programs are sufficient in order to virtually plan for production of patient-specific implants. Furthermore, EBM-produced implants are fully usable under clinical conditions in reconstruction of acquired defects in the mandible. A good compliance between the treatment plan and the fit was demonstrated during operation. Within the constraints of this article, the authors describe a workflow for production of patient-specific implants, using EBM manufacturing. Titanium cutting guides, reconstruction plates for fixation of microvascular transfer of osteomyocutaneous bone grafts, and mesh to replace resected bone that can function as a carrier for bone or bone substitutes were designed and tested during reconstructive maxillofacial surgery. A clinically fit, well within the requirements for what is needed and obtained using traditional free hand bending of commercially available devices, or even higher precision, was demonstrated in ablative surgery in four patients.

Keywords: electron beam melting; implant; reconstruction.

Figures

Figure 1

The DICOM files were converted to *.tiff and then imported into Autodesk Maya 2009 (Autodesk). The image was aligned with the polygon mandible to check the resection.

Figure 2

(A) A saw guide was designed. (B) The EBM-produced titanium saw guide shown on a plastic model of the mandible.

Figure 3

The saw guide was checked against the patient mandible.

Figure 4

A four-hole and a six-hole polygon plate was constructed against the treatment plan conducted in SurgiCase (Materialise, Leuven, Belgium).

Figure 5

The EBM-produced titanium reconstruction plates in place.

Figure 6

Difference between the preoperative treatment plan and treatment outcome. Dark blue is the preoperative treatment plan. Red being the postoperative treatment outcome.

Figure 7

Schematic workflow used when designing and producing patient-specific implants.

Figure 8

Porous titanium scaffolds in place with load-bearing plates.