Abstract
Introduction
At present, all available cervical fusion cages have standardized sizes and mimic the anatomy of the intervertebral disc space more or less. Usually, the patient's anatomy is adapted during the surgery to the cage. Our idea was to respect the individual patient's anatomical situation and manufacture an individual cage with a perfect fitting accuracy. The production of individualized cages might be the next step for further improvement of spinal implants due to their perfect fit and improved load bearing surface.
Material and Methods
The computer-assisted planning, manufacturing, and implantation of the individualized cervical cage was performed in close co-operation with 3D-Systems Corporation, Rock Hill, SC 29730, USA and EIT Emerging Implant Technologies GmbH, Tuttlingen, Germany. A 3D model of the patient's cervical spine obtained from CT data was rendered. This model is the basis for the exact simulation of the operation. The newly developed 3D planning algorithms and special reconstruction software implemented in a high-end image-processing computer allow a virtual surgical procedure. The correction of degenerative deformities by repositioning of vertebrae and also the virtual resection of osteophytes is possible. The cage implantation can be simulated to check the accuracy of fit. These data are the basis for the production of the cage. This custom-made cage is manufactured of trabecular titanium by selective laser melting (3D printing procedure).
Results
The pilot project of the first implantation of an individualized cervical cage ever resulted in a high accuracy of fit of the implant. During surgery the cage ‘found’ its correct position after suspending disctraction due to its unique endplate design. Furthermore, it was impossible to move the cage in any direction. Thus, it can be assumed that the individualized cervical implant provides excellent primary fitting accuracy and stability.
Conclusion
Preconditions for the manufacturing of individualized cervical fusion cages using specific patient data are given. The implantation is uncomplicated. The improved load-bearing surface will lower the rate of implant dislocation and subsidence. The next essential steps will be to improve the workflow of the surgical simulation and shorten the time of the overall production process. The manufacturing of individualized cages at a reasonable price has to be figured out by spine surgeons and the industry.