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Planning Surgeries, Virtually

Wed, 10/27/2010 - 5:50am
Dr. David Chen, Chief Technology Officer, SensAble Technologies
Surgery is like playing the violin – it requires intensive finger-learning to achieve technique and mastery, yet a virtuoso performance worthy of a “Bravo!” requires something more. Many procedures can be learned, then basically repeated – while others are so complex that intensive surgical planning is required for success. Craniomaxillofacial (CMF) surgery is one such domain. 

MedCAD used FreeForm to create 3D models based on the patient’s CT scan. This model shows how surgical incisions would create two bony sections, one on either side of the face, to be realigned.

Surgery is like playing the violin – it requires intensive finger-learning to achieve technique and mastery, yet a virtuoso performance worthy of a “Bravo!” requires something more.  Many procedures can be learned, then basically repeated – while others are so complex that intensive surgical planning is required for success.  Craniomaxillofacial (CMF) surgery is one such domain. 

Realigning the bones of the face, while removing bone sections and inserting custom implants, can impact a host of adjacent bones, muscles, ligaments, the eyes and the brain – with the potential for inducing pain or even paralysis in patients if not performed correctly. To prepare for such complex and risky procedures, surgeons must think through surgical incision locations and depth, and explore various “What if?” scenarios ahead of time to assure operative success. 

Traditionally the methods for surgical planning have been rather low-tech, inefficient, and flawed.   Surgeons manually view serial 2D images such as X-rays or computed tomography (CT) scans and use a caliper or ruler next to the image to measure approximate anatomic locations and gauge their incisions. 

However, they are left to make the conceptual leap between the flat 2D cross-sectional images, and the actual 3D anatomy encountered during surgery – which does not always look the same.

Sometimes, though not often, surgeons commission the creation of a 3D study model made from wax or clay by hospital modeling departments or outside service bureaus.  Models are tremendously helpful in allowing surgeons to view adjacent structures at actual size, and then mark up the model with a pen and explore “what if I made this cut here?” or “inserted a custom bone section there” and so forth.

But hand-made models take weeks to create and are approximations of the actual anatomy – and therefore subject to inaccuracies.  What’s more, surgical teams in multiple locations often are involved with complex CMF surgeries, resulting in more time needed to review and annotate the model.  

A LEAP with Faith
Enter virtual surgical planning – a concept that’s not new, but is now sweeping through many surgical specialties as a new generation of surgeons emerge with greater computer savvy, and specialized 3D digital modeling solutions that can better accommodate the difficult task of modeling patient-specific human anatomy while producing 3D study models and specialized tools such as cutting and drilling guides.

In virtual surgical planning, 2D patient image files such as CT scans are converted into a 3D model that can then be used by computer-based modeling applications to experiment with the possible ways facial or cranial defects can be corrected. A QuickTime animation of the digital model showing the proposed surgical plan can then be created and shared via email with physicians anywhere in the world, for viewing on common laptop computers.

Teams of surgeons are not only becoming increasingly sophisticated before they enter the operating room – asking “What if?” more quickly, comprehensively, and collaboratively so they can plan surgeries with greater precision—they are also saving time for themselves and their patients by shortening the actual procedure time.
What’s more, if custom surgical guides are needed, they can be quickly designed digitally and inexpensively, 3D printed by service bureaus in resins that can be sterilized – aiding the surgeon in faster and more precise instrument placement and reducing the operation’s complexity.

The work of Dr. Craig Hobar, co-founder and chief surgeon of the LEAP Foundation of Dallas, highlights the advantages of virtual surgical planning in helping doctors digitally rehearse a complex facial reconstruction surgery on a common laptop. By viewing 3D models of numerous surgical options and then obtaining digitally designed custom surgical guides made on a 3D printer, Dr. Hobar was able to plan the complicated 7-hour surgery with heightened speed, efficiency, and precision. 

FreeForm then allowed surgeons to see how all the bones in the face that would be affected by the surgery.

The LEAP Foundation (Life Enhancement Association for People) is a non-profit, 501(c)(3) medical missionary organization comprised of volunteer plastic surgeons, urologists, eye surgeons, anesthesiologists, orthodontists, nurses, and support staff.  To date, LEAP has provided life-giving surgeries for over 6,000 individuals worldwide, usually in their own countries.

In the past when planning surgeries, Dr. Hobar relied on his nearly 20 years of expertise and traditional planning methods. In the fall of 2009, LEAP identified a 5-year old boy in China with hypertelorism, a congenital misalignment of the face involving a deeply cleft nose, skull and palate. Because of the complexity of his case, the foundation arranged to bring the child to Dallas for surgery.

Shortly before the child’s arrival, Dr. Hobar happened to overhear a conversation about virtual surgical planning in a waiting room. He was intrigued, and introduced himself to Nancy Hairston, president of MedCAD, a digital medical modeling service bureau in Dallas, Texas, which assists numerous surgeons nationwide with medical modeling and surgical planning. Dr. Hobar described the young man’s case, MedCAD agreed to help, and Dr. Hobar arranged to provide the patient’s CT scans the next day.

FreeForm Explorations of Surgical Options
MedCAD began by converting the child’s CT scans into STL files and then imported the STL file into FreeForm, a 3D modeling solution designed to handle complex, organic shapes such as structures of the human body.

A Young Man from China from LEAP Foundation on Vimeo.

MedCAD used FreeForm to design 3D computer models that allowed surgeons to see all the bones in the face that would be affected by this surgery. The models showed the location of incisions that would create two bony sections, one on either side of the face, that the surgical team would realign closer together around the nose and palate to provide a more normal appearance.

As a sculptural CAD solution, FreeForm is aptly named – it allows users to rapidly create intricate, asymmetric and free-form shapes that are not easy for most CAD software programs to define. Rather than require the software user to follow strict procedural design steps for a specific craniofacial procedure, FreeForm gave MedCAD the design freedom to quickly model numerous scenarios for the doctor’s review.

For example, using FreeForm, MedCAD wanted to show Dr. Hobar the impact of rotating one of the bony sections in a particular direction, and how it might then interfere with another anatomical structure elsewhere in the back and side of the head. To do this using the software, MedCAD’s designers created several cutting curve options in multiple orientations for the cranium – options that allowed Dr. Hobar to explore different strategies.

Because the curve tools in FreeForm are so quick and non-procedural the designer needed just 20 minutes to define specific incision measurements, angles and to design a cutting guide to support the chosen plan.  Traditional CAD software would either not be able to define the intricate, organic shapes or would take so long that they would not be a viable solution.

Additionally, FreeForm’s selection/cutting and pasting functions are also non-procedural, so multiple versions of the anatomy could be rapidly created– allowing surgeons to examine all the possible “what ifs” of considered approaches. With computer models designed this way, Dr. Hobar could virtually adjust the amount of downward movement of a particular section of bone, or explore other surgical options such as relocating the incisions – instead of marking up a physical model with a pen.

Although not utilized in this way in this case, 3D models for virtual surgical planning can also be used to educate the patient about the planned procedure.

After Dr. Hobar was satisfied with the proposed model and planned surgical approach, MedCAD created a QuickTime animation of the model, which was then emailed back and forth among colleagues for their input and approval.

Adding Precision, Saving Time
Dr. Hobar characterized the speed of the virtual planning with the FreeForm software as “amazing.”  It allowed him to explore all surgical options on the computer, and iterate on them over and over until he found one that was just right.  The overall workflow was faster and more convenient, while the results preserved accuracy with the right level of sophistication.

Once the team finalized a surgical approach, MedCAD also used FreeForm to digitally design and then create custom surgical cutting guides out of sterilizable resins. Creating custom guides actually requires modeling software that can ‘deform’ a typically straight guide to match the patient’s actual anatomy – allowing a more specific placement of surgical instruments in the right locations, based on the patient’s own measurements – instead of manually creating guides to approximate the fit.  

The surgery, performed in December 2009, was successful and the resulting bone structure provided an ample foundation for a later reconstruction. The child now has a new, more natural appearance that provided a wonderful start to his new life in an adoptive home in the United States.

Dr. Hobar’s opinion is that for complex cases, virtual surgical planning such as he employed in this case is an extremely valuable technique.   It puts a world of “what ifs” and “how tos” in the hands of medical professionals – and sets the stage for brilliant surgical performances.

David Chen, Ph.D. is chief technology officer of SensAble Technologies Inc. He has led the development of software for transforming medical data into formats for visualization, surgical simulation, and biometric qualification. Dr. Chen can be reached at 781-937-8315 or info@sensable.com.

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