Surgeons Bone Up -- in Stereo -- Before Cutting
By Douglas J. Gillert
American Forces Press Service
SAN ANTONIO, Texas, June 4, 1998 The patient awaiting surgery at the Air Force's Wilford Hall Medical Center had been shot through the head with an AK-47 assault rifle. The bullet had entered through his right ear and exited through his right eye socket, blowing the eyeball out.
The bullet also fragmented his jaw, but didn't break the skin. Surgeons assigned to repair the damage couldn't see where the bone fragments were, only the patient's severely swollen face.
Thanks to a special computer originally used to model automobile and aircraft parts, the Wilford Hall surgical team soon had a life-size model of the patient's skull, complete with damaged ear and eye socket and shattered jaw. Each of the bone fragments appeared as embedded in the patient's mangled face. The tool helped the sugeons save the patient's life.
Three-D computer wizardry? Much better, actually. Inside DoD's only in-hospital stereo lithography laboratory, maxillofacial prosthodontists and dental technicians will use manufacturing technology to build an epoxy replica of the skull.
The process begins with computed temography -- basically a digital 3-D photograph of the patient's head. Technicians feed their computer with information from the CT scan and magnetic resonance imaging. This produces 3-D computer imagery of the skull they then download to a stereo lithography machine.
Inside a box that resembles an incubator or greenhouse, epoxy polymer bars go to work building the skull.
"The stereo lithography machine builds the bone structure in layers about one millimeter thick," said Air Force Dr. (Lt. Col.) Doug Erickson. "A skull requires 900 to 1,000 layers and takes up to 48 hours to build." By comparison, an entire hip takes two to three days to build, a jaw four to six hours. Dye is added to the model to show abnormalities, teeth and other internal structures that otherwise would be hidden, Erickson explained.
In 1994, two Air Force prosthodontists visiting an auto show in Detroit saw immediately how stereo lithography could enhance medical care, Erickson said. Through their efforts, Wilford Hall became the only hospital in the country with the setup. The medical center routinely receives referrals from other military and civilian hospitals from as far away as Tripler Army Medical Center in Hawaii and as nearby as the University of Texas Health Sciences Center in San Antonio.
Surgical teams use the epoxy models in ways that help them and their patients, Erickson said. "The surgeons can handle a model that is exactly the size and shape of the patient's part they will operate on," he said. "So when they begin operating, they already know what to look for." For the true-life gunshot victim, for instance, doctors could see beforehand exactly where in his cheek the bone fragments from his shattered jaw were.
"The ability to see and touch accurate models of damaged bone structures saves time in the operating room and usually results in less blood loss and fewer post-operative complications for the patient," Erickson said.
After building 76 models, Erickson's department surveyed physicians to see how well they like the technique. Of the 38 surgeons who completed the survey:
- 92 percent said they used models in patient care;
- 62 percent said it improved diagnoses;
- 73 percent used the model to visualize the patient during surgery; and
- 73 percent used the model to help educate the patient.
But Erickson said the most telling response was perhaps this: "Sixty-five percent said it changed the way they approached the patient. The model gave them more information about the patient's unique anatomy and helped them achieve ideal results in the operating room."
Stereo lithography also could enhance the treatment of soldiers wounded in combat, Erickson said. Medical teams in the field could scan wounded patients, transmit the information to Wilford Hall, and a model could be made. Then, when the patient is aeromedically evacuated to San Antonio, physicians will have had time and a model to prepare their surgical plan.
Wilford Hall's commander is a strong advocate of the technique. "Stereo lithography has allowed us to do some amazing things," said Air Force Dr. (Maj. Gen.) Paul Carlton. "Two years ago, surgeons used models to plan a successful separation of conjoined twins. Today, the girls are living normal, healthy lives." In another case, doctors used a hip model to repair a teen-age accident victim's shattered pelvis. "This machine helps us perform better medicine," Carlton said.
The better medicine stereo lithography facilitates benefits everyone, Erickson said -- commanders who need healthy troops, physicians, and most of all, the patients.