Surgeons Use Computer-Generated Models for Jaw Reconstruction
By Bryan Tutt
Recent advances in technology have enabled surgeons to perform facial reconstruction with a degree of precision that was impossible just a few years ago.
Resection of head and neck tumors can leave patients permanently disfigured, especially if sections of bone must be removed along with the tumor. Because cancers of the head and neck often involve the mandible or the maxilla, reconstructive surgeons are constantly seeking new techniques to rebuild patients’ jaws to match the original as precisely as possible.
“Reconstructive surgery has come a long way in our lifetimes,” said Matthew Hanasono, M.D., an associate professor in the Department of Plastic Surgery at The University of Texas MD Anderson Cancer Center, who explained that the current technique for jaw reconstruction using tissue harvested from the patient’s leg was developed in the early 1980s. Since then, surgeons at MD Anderson and other institutions have worked to refine the technique. These efforts have led to an unusual collaboration between surgeons and engineers to create virtual and physical models of patients’ bones using software and tools adapted from the manufacturing industry.
Reconstructing the jaw
When head and neck surgeons have to remove part of a patient’s jaw bone to resect a tumor, the plastic surgeon’s ability to rebuild the jaw to match its former shape affects not only appearance but also functions such as eating and speech. Chronic pain in the temporomandibular joint also can result from an imperfectly aligned jaw.
The standard reconstruction technique involves harvesting a section of the fibula and any necessary skin, muscle, or fat from the patient’s leg. The surgeons cut the harvested section of bone into pieces, which are then formed together along a titanium plate, which the surgeons have bent to match the shape of the original mandible or maxilla as closely as possible. “This is where plastic surgery can become an art,” said Roman Skoracki, M.D., an associate professor in the Department of Plastic Surgery. Autologous tissue transplants, or free flap transfers, are used to rebuild the lining inside the mouth and/or the facial skin. All of this is done immediately following the tumor resection.
To complete the reconstruction, Dr. Skoracki said, “Our dental colleagues anchor osseointegrated implants to the new jaw bone. For all intents and purposes, these act like the patient’s natural teeth.”
Because the tibia is the main weight-bearing bone in the lower leg, the middle portion of the fibula can be removed without causing disability to the patient—Dr. Skoracki described the fibula as “a built-in spare part.” Patients who have jaw reconstruction using a fibula flap typically are able to resume walking within 5 days, eat solid food within 2 weeks, and resume normal activity within 3 months. However, recovery may take longer for patients receiving adjuvant chemotherapy or radiation therapy.
Limitations of reconstructive surgery
One area of concern for surgeons performing jaw reconstruction is the amount of time required for the surgery. When patients undergo resection of a tumor from the mandible or maxilla followed by reconstruction with autologous tissue, they are under general anesthesia for 10–12 hours. Dr. Skoracki said, “Our part of the surgery—harvesting the leg bone, reconstructing the jaw to the shape we want it to be, finding the appropriate donor blood vessels to use, setting the plate and tissue into place, resurfacing the inside of the mouth where it may be necessary, attaching the blood vessels under the microscope, and finally putting the external skin back together—takes 6–8 hours.”
Dr. Hanasono said, “If we can cut that time by a couple of hours, it benefits the patient in many ways, including lowering blood loss and risk of infection.”
In standard autologous tissue reconstruction, the titanium plate must be measured and bent to match the patient’s existing jaw bone. But for some patients, this is not possible. “Some patients have very distorted bones—from the tumor itself, from previous surgery, or from osteonecrosis from radiotherapy,” Dr. Skoracki said. “The challenge in reconstructing a jaw for these patients is that you can’t place the plate on the original bone to bend it—the ‘normal’ is not there.”
The difficulty in estimating the shape of the plate—and the resulting pain and loss of function for patients whose rebuilt jaws did not align perfectly—led surgeons to search for a more precise technique.
“We worked with a software design company to develop a modified version of computer-assisted design software, which is used in drafting and engineering, specifically for the craniofacial skeleton,” Dr. Skoracki said. The software creates a virtual replica of the patient’s anatomy from magnetic resonance imaging (MRI) or computed tomography (CT) images of the patient’s jaw. The software helps surgeons to plan the reconstruction by creating the exact shape of the jaw that will be resected. The surgeons can then cut a virtual fibula to the exact angles that will optimize bone apposition, further helping plan the surgery.
To take this planning aid from the computer screen to the physical world, physicians at MD Anderson, working with another design company, developed plastic cutting guides that can be snapped in place on the fibula so that it can be cut to the exact lengths and angles defined by the virtual plan. These cutting guides are created using a three-dimensional printer—a technology used in the manufacturing industry to make prototypes—which prints the starch or polymer model layer by layer. The printer can also produce a three-dimensional replica of a patient’s jaw.
“It’s wonderful to have these models because we have an exact template of what the ideal would be,” Dr. Skoracki said. “We can bend plates on the model, which allows us to be more exact in our reconstruction. We can actually perform surgery on these acrylic or starch models to rehearse.”
In addition to improving the accuracy of reconstruction, Dr. Hanasono said that the models reduce the time required for surgery because the surgeons can bend the titanium plate to the correct shape before surgery.
Surgeons at MD Anderson outsource the virtual modeling and three-dimensional printing to a private company. The surgeons send the patient’s MRI or CT images to engineers at the company and discuss the case with them in videoconferences. The engineers then create the virtual models, and if needed, physical models and cutting guides are printed and shipped.
Because the private contractor can create these models from imaging studies, the technology is available to surgeons at almost any institution. Dr. Skoracki said the models can be especially beneficial to surgeons who perform only one or two jaw reconstructions per year. “This technology helps the surgeon plan the surgery and execute it more precisely,” he said.
Dr. Hanasono said that surgeons at MD Anderson do more jaw reconstructions using autologous tissues than any hospital in the United States, but the models are used only for the most complicated cases—about 12 per year.
Dr. Skoracki added, “We use the whole gamut of these technologies for those patients who have very large tumors that prevent us from doing the measurements necessary for the usual method of reconstruction.”
Dr. Hanasono pointed out that the full potential of the modeling technology has not yet been realized. “This technology has been in development for 8–10 years, but its current form has only been in use about 3 years,” he said. “The technology has implications not only for cancer but for all types of reconstruction, including reconstruction in trauma patients.”
Other articles in OncoLog, February 2011 issue: