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

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 degrees C and resolidified to form thin approximately 5-mm-thick plates. The newly formed plates were reheated to 60 degrees 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.

[1]  T. Albert,et al.  Transpedicle screw fixation of the cervical spine. , 1999, Clinical orthopaedics and related research.

[2]  R. Adhikari,et al.  Biodegradable synthetic polymers for tissue engineering. , 2003, European cells & materials.

[3]  N. Crawford,et al.  Biomechanical analysis of a newly designed bioabsorbable anterior cervical plate. Invited submission from the joint section meeting on disorders of the spine and peripheral nerves, March 2005. , 2005, Journal of neurosurgery. Spine.

[4]  Marcel Rooze,et al.  Evaluation of a transpedicular drill guide for pedicle screw placement in the thoracic spine , 2003, European Spine Journal.

[5]  K. Radermacher,et al.  Computer assisted orthopaedic surgery with image based individual templates. , 1998, Clinical orthopaedics and related research.

[6]  D. Silcox,et al.  Cervical Pedicle Screws Versus Lateral Mass Screws: Anatomic Feasibility and Biomechanical Comparison , 1997, Spine.

[7]  L. Claes,et al.  New bioresorbable pin for the reduction of small bony fragments: design, mechanical properties and in vitro degradation. , 1996, Biomaterials.

[8]  H. Richter,et al.  Complications of transpedicular screw fixation in the cervical spine , 2006, European Spine Journal.

[9]  D E Cutright,et al.  Evaluation and comparisons of biodegradable substances as osteogenic agents. , 1977, Oral surgery, oral medicine, and oral pathology.

[10]  J O Hollinger,et al.  Preliminary report on the osteogenic potential of a biodegradable copolymer of polyactide (PLA) and polyglycolide (PGA). , 1983, Journal of biomedical materials research.

[11]  M. Neo,et al.  Spinous process plate fixation as a salvage operation for failed anterior cervical fusion. Technical note. , 2006, Journal of neurosurgery. Spine.

[12]  J Vander Sloten,et al.  Three-Dimensional Computed Tomography-Based, Personalized Drill Guide for Posterior Cervical Stabilization at C1–C2 , 2001, Spine.

[13]  Shigenobu Sato,et al.  Spinal Reconstruction Using a Cervical Pedicle Screw System , 2005, Clinical orthopaedics and related research.

[14]  H N Herkowitz,et al.  Spinal pedicle fixation. Confirmation of an image-based technique for screw placement. , 1993, Spine.

[15]  B B Seedhom,et al.  Personalised image-based templates for intra-operative guidance , 2005, Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine.