Improving cervical spine surgery with additive manufacturing
Using customized surgical guides for screws insertion is emerging as a simple and effective method to improve operations success rates and minimise medical complications [6, 7].
High spiral (helical) computed tomography scanners generate conventional or slice-by-slice scans where the patients move slowly through the gantry while the x-ray tube and detectors rotate/spiral around the patient. This technique allows fast and continuous acquisition of the data from a complete volume.
Design for AM of precision positioning guides for spinal surgery
Step 1: Capturing requirements
(1) the contact surface should completely fit the patient’s bone surface;
(2) the strength of the template should be the same or better than the traditionally-made template;
(3) the key positions, such as the guider hole and the locating hole, should be accurate.
Step 2: Extraction and processing of the target spine model [2,3]
Once this 3D file is acquired, it is necessary to numerically ‘clean’ the 3D image. In other words, signal noise is eliminated; the 3D surface is then extracted from the data set of 2D scans. The separate vertebrae files are formed into an assembly that replicate the spine of the patient.
Step 3: Design of the contact surface between the positioning guide and the vertebrae
Step 4: Choice of the locations of the guider hole and locating hole
Step 4: Design of the handle
Dimensional parameters of the surgical guide
Build file preparation
Additive manufacturing a positioning guide for spinal surgery using selective laser melting
Feedback from customers
(1) the length of the template hole is increased so that a dedicated surgical can be used to facilitate the insertion of screws. The length of the guider hole was set to 10 mm to avoid instability caused by the gap during surgery;
(2) several locating holes are added in the template and small screws are provided so that the guide can be fixed closely to the surface of the bone. A locating hole with a diameter of 1 mm is set at the left and right sides of the template respectively to further improve the drilling accuracy.
General visual observation shows that downskin template surfaces are rougher than that of the upper surface. As a result, the critical contact face between guide and cervical vertebra should preferably face upwards to guarantee surface quality.
Clinical test of the customized guide
A 2h30 surgical operation used the SLMed positioning guide to insert the high-precision screws. The results are observed through the CT and screws are seen precisely placed in the desired location after the surgical operation.
Compared with current resin devices, the metal guide can be positioned very accurately, can easily be subjected to autoclaving, and sustains damage and deformations occurring during the operation.
This study shows the potential of metal SLM not only in the field of surgical implants but also its ancillaries.
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8. Design and Fabrication of a Precision template for Spine Surgery Using Selective Laser Melting – D. Wang, Y. Wang, J. Wang, C. Song, Y. Yang, Z. Zhang, H. Lin, Y. Zhen, S. Liao, Materials 2016, 9, 608; doi:10.3390/ma9070608 - www.mdpi.com/journal/materials