Can 3D Templating And Simulation Enhance Surgical Planning?

David G. Armstrong DPM MD PhD

We at the Southern Arizona Limb Salvage Alliance (SALSA) have long embraced the benefits of interconnectivity and open source solutions. Surgical planning and collaboration are no exception. The concept of 3D surgical “printing” (templating and simulation) in lower extremity reconstruction is not entirely commonplace. This is likely for a number of reasons. With the continual maturation of free and open source software applications as well as the ever increasing capabilities of “RepRap” technology (see http://reprap.org/wiki/Main_Page ), we can overcome these limitations.

Charcot foot reconstruction is a challenging endeavor with significant intraoperative demands and uncertainties. Even experienced surgeons benefit from preoperative preparation in order to reduce operative time and potential complications. Classic 2D templating techniques may fall short when surgeons face the multiplane and complex nature of neuroarthropathic architecture. For this, members of the Dekalb Medical Residency, SALSA researchers and Freeside Atlanta (a hacker space collective) co-designed a scenario to improve surgical delivery. S. Patrick Dunn, DPM, performed the surgery.

This process started with a high resolution computed tomography (CT) scan. These standard DICOM images were processed with axial data in (freeware) OsiriX Image Viewer. These files were part of 3D surface rendering. This offers physicians an improved sense of spatial pathology. This constructed model is then something that one can import into a 3D application of choice. For our purposes, we were able to use a combination of MeshLab and Blender software for this study.

We started by importing the stereo lithography (STL) data into Blender and templating out a multiplane wedge/chevron across our anatomic reconstruction. We then “practiced” this as a boolean resection in the object’s geometry. This simulation technique afforded real-time viewing and assessment of osseous apposition. The surgeon could undo the process and reattempt it for optimal outcome as many times as one desires. After achieving a satisfactory simulation, one could determine measurements and axis orientation to scale (one must first calibrate Blender units to match the CT scale).

Furthermore, we utilized this STL formatted data for making three-dimensional “prints” of the patient's anatomy. One may manufacture these physical prints on the technology and method of choosing. For our purposes, we chose the selective deposition/binding methods offered by the Zcorp printing technology for printing sawbone replicas.

These printing machines are often expensive at market value. RepRap enthusiast and non-institutional “Printistas” have adopted these devices and have made several modifications of the proprietary hardware as well as printing recipes to serve a number of desired outcomes. We printed our models on the Z400/402 machine technology, which was modified by Nullset with its technique for DIY printer cartridge making.

Before printing these models, one must further optimize the geometry and surface information. Our member, Patch, performed this in MeshLab in order to optimize the geometry prior to ZPrint importation. These printed models were to attempt "freehand" osteotomies, matching the measured landmarks from the simulated ones, which we used to size and fit an Ilizarov frame construct. We subsequently sterilized this construct and used it for the procedure itself.

Surgeons at two locations (Tucson, Ariz. and Decatur, Ga.) discussed telemedical preoperative planning via live video link, exchanging info on alternative fixation options, instrumentation, additional hardware and closure techniques.

Surgeons utilized percutaneous K-wires to match the orientation of the multiplane wedge resection that we simulated. Once this was in place, surgeons performed the sequential resection and achieved reduction. Surgeons applied additional internal fixation occurred and the external Ilizarov construct with minimal modification.

These techniques can be evolutionary advances to current surgical planning and preparation. The integration of open source software solutions with DIY hardware hacking and RepRap technology will continue to demonstrate feasible improvements to quality of care and reduction of cost in the postmodern medical era. Is there more to come? The second phase is printing biocompatible “parts” just as recent advances in solid organ “printing” have shown.

Nicholas Giovinco, DPM, co-authored this blog.

This blog has been adapted with permission from a previous blog that originally appeared at www.diabeticfootonline.blogspot.com .

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