Engineering patient-specific drill templates and bioabsorbable posterior cervical plates: a feasibility study

Technical note

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  • 1 Carver College of Medicine,
  • 2 Department of Neurosurgery, and
  • 3 Departments of Electrical-Computer Engineering and
  • 4 Biomedical Engineering, University of Iowa, Iowa City, Iowa
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Object

The authors describe a method of using computer models to generate customized cervical implants. A promising yet challenging technique in cervical spine surgery involves the use of pedicle screws to assist with posterior instrumentation. Surrounding anatomical structures such as the vertebral arteries and cervical nerve roots present challenges for safe screw placement; however, the use of computer-generated templates seems to be a promising method to assist with placement. In this study, the authors explore the use of computer-generated templates and introduce their methods for creating custom, bioabsorbable posterior cervical implants.

Methods

The cervical spines (C2–T1) from 4 cadavers were scanned with volumetric CT. Using commercially available software, the authors generated volumetric models of a cervical drill template and the mold for a cervical plate spanning a desired number of vertebrae. The computer generated models of the cervical drill template and cervical plate mold were converted into physical models using a rapid prototyping machine. The biopolymer polylactic acid resin was heated to 250°C and resolidified to form thin ~ 5-mm-thick plates. The newly formed plates were reheated to 60°C and cast on the cervical mold.

Results

The resulting translucent plates were found on visual inspection to have a secure lock-and-key fit on the original cadaver spine, and the techniques used were robust and reproducible. The process described in this brief report provides the background to proceed with development and testing of these patient-absorbable templates.

Conclusions

The creation and use of patient-specific bioabsorbable posterior cervical plates in conjunction with multilevel drill templates appear promising. Additional feasibility studies are planned, and in vitro studies are required to determine the safety and efficacy of using patient-specific drill templates and converting them into bioabsorbable implants.

Abbreviations used in this paper: ABS = acrylonitrile butadiene styrene; PLA = polylactic acid; PS = pedicle screw; STL = stereolithography.

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Contributor Notes

Address correspondence to: Timothy C. Ryken, M.D., Department of Neurosurgery, University of Iowa Carver College of Medicine, 1846 JPP 200 Hawkins Drive, Iowa City, Iowa 52242. email: timothy-ryken@uiowa.edu.
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