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12 t m c » p u l s e | n o v e m b e r 2 0 1 9 Patient-specific design In September 2018, LeTourneau met with Clyburn to discuss her X-rays and total hip replacement surgery for both hips. The hip prosthesis consists of a stem that is inserted into the thigh bone, a head joint (ball) that fits into the stem and a cup that is inserted into the socket of the hip joint. Typically, during hip replacement surgery, surgeons select parts for the thigh bone and the socket from a list of five to seven available sizes from medical device manufacturers. "You take a wild guess at what might fit," Clyburn explained. "[The computer system] brings you the template for that and you put it onto the X-ray and look at it. If it's too big or too small, you just pick a size up or down, and you keep doing that by trial and error until you get the size that fits most appropriately." It's not the most perfect fit, but the most appropriate fit. "It's like going to the shoe store," Clyburn said. "If you have big feet, or wide feet, or short wide feet, or feet that are a little bit different left to right, which most people do, you're never, ever going to find a pair of shoes that fits you perfectly." Custom-made hip replacement parts, on the other hand, provide a perfect fit. Clyburn starts with a detailed CAT scan of the patient's pelvis and femur to capture every dimension of the hip anatomy. Conformis then creates a 3D virtual model of the patient's hip, which doctors use to make adjustments and corrections—whether it be widening or narrowing the hip, known as the "offset." "If we don't widen the hip the appropriate amount, it causes weakness of certain muscles and can cause the patient to have a limp," Clyburn said. "If we make it too wide, it can cause pain over the side of the hip because it's pushing out against some of the structures on the outer part." The new patient-specific design is sent to Conformis engineers, who then create the implant parts out of titanium alloy, along with customized 3D-printed tools and guides for the surgical procedure. On the day of surgery, the socket can be placed in a variety of positions relative to the patient's anat- omy, but there are certain positions that are more likely to create complications, including dislocation of the hip. Surgeons strive for the "safe zone"—the optimal position of the socket that minimizes the risk of problems. "When we're templating the hip using a traditional technique, we visualize in our head how we want to put the cup in," Clyburn said. "Then when we go in during surgery and we put the cup in, we do our best using the computer … to put the cup in the position that we think is optimal." However, studies have shown that even the most skilled surgeons reach the "safe zone" only 60 per- cent of the time during a traditional hip replacement. The Conformis Hip System, though, takes the guesswork out of surgical planning and targets the pre- cise position for the parts, minimizing the need for the patient to go under the knife again so the implants can be readjusted. "The more form-fitting the device is to the individual's bone, the better the success rate of bone grow- ing into it and stabilizing the implants," said Clyburn, who has performed more than 15 hip replacement surgeries using the Conformis system in the last year. On Oct. 24, 2018, LeTourneau underwent surgery on her right hip. "Later that day I told Dr. Clyburn, 'Okay, I'm ready to do the other one,' … because the surgery just went so well," LeTourneau recalled. Nearly a year later, on Sept, 4, 2019, she returned to Houston for surgery on her left hip. As a grandmother of two, LeTourneau was more than happy to travel four hours to Houston from her Longview home for an operation that would relieve her pain and improve her mobility. "Four hours seems like nothing to get to where I am today," she said. "I remember one time after the surgery, my granddaughter said, 'Grandma, can you skip?' I thought, 'Skip? That has been years and years,' but I said, 'Well, let's try it.' And I was able to do it after my surgery. It seems simple, but it's just simple things that I couldn't do I could do again." Terry Clyburn, M.D., is an orthopedic surgeon at Houston Methodist Hospital.