Bone is a remarkable organ, says orthopedic surgeon and engineering mechanics graduate James McCarthy (BSEM ’86). It grows and heals itself, and not many organs can do that. It can be cut and gradually lengthened. The bone fills itself in. If done at the right rhythm, a bone can grow to be just about as long as you want it to be.
Bone protects internal organs, including the heart, lungs and brain. It transduces sound so that we can hear. It provides the scaffold upon which to hang all our other parts, and works with muscles, tendons, ligaments and joints to generate and transfer forces so that our bodies can move in three-dimensional space. In general, bone is a sort of dream material for the engineering mechanics major. But it wasn’t a fascination with bone that motivated McCarthy to become director of pediatric orthopedic surgery at Cincinnati Children’s Hospital. “After graduating, I applied for and got two jobs,” he says. “One was with Saturn, which was a new, innovative company, and the other was with Hewlett Packard making sonograph equipment. I also had the opportunity to go to medical school. My theory at that time was that if I took a job, I’d never go back to school because I’d be comfortable. So I thought I’d just try medical school for a year, and if I hated it, I hated it. I became more and more intrigued in medical school. Really, it was with the idea that I would be doing biomedical engineering for a company.”
Partway through his medical training, he did some cardiology research in North Carolina and spent some time in pediatrics. All of a sudden, the pieces came together. It all made sense. His engineering physics training was math-heavy and very theoretical. It allowed him to go many different directions, but his medical training forced him to do things he was not comfortable with. “What I was good at was figuring things out. I could sit in a room and work forever and get to the right answer. That came relatively easily, but what I wasn’t good at was memorizing long lists,” McCarthy says. “I was not comfortable with interfacing with patients on a very personal basis. So in some ways, medicine forced me to round out skills that I didn’t think I had. And I don’t know why, but that intrigued me to some degree.”
McCarthy’s specific clinical interests have an engineering focus. One is cerebral palsy (CP), which is a neurological disorder that affects the way kids walk. About two children per 1,000 live births have cerebral palsy. In the United States, the average lifetime cost for people with CP is about $900,000 per individual, including lost income.
The overlap between CP and engineering is very strong because doctors analyze the biomechanics of the way children walk. Using gait analysis, digital cameras, sensors and force plates, a team of therapists, engineers and surgeons synthesizes all the data and tries to figure out the best list of surgeries to improve the patient’s function. “You might think a better way would be to treat them earlier so that they don’t develop issues, but we’re not there yet,” McCarthy says. “In the right patient, you can make a fairly significant improvement in biomechanical functioning. A lot of them walk more upright. A lot walk with less of a limp. You can make some pretty significant improvements in overall gait. That part ends up being fairly dramatic. It’s also possible surgery won’t help them at all and that is where the gait analysis comes in and is very useful.“
McCarthy’s other interest involves much less common limb deformities. Approximately one in 20,000 children have significant deformities of the lower extremities. His team works to correct those through placement of external fixtures. The devices go on the outside of the leg and the leg is manipulated either by cutting the bone or using another technique that changes it over time. “It’s very mechanical and very three-dimensional. What’s even more intriguing is when we ask if there are better ways of doing it,” McCarthy says. “Can we use an implantable device? That’s what I worked on at UW-Madison with Heidi Ploeg and Michael Zinn in the Department of Mechanical Engineering. By developing an implant, we’re trying to correct the deformity without having a large device attached to the outside of the leg.”
This approach would have huge advantages, especially for children, because braces or pins wouldn’t be visible on a patient’s leg. McCarthy says the challenge is to devise something that can be lengthened at a controlled rate and is strong enough to support the stresses of the body. Since only about 5,000 of these products would be needed per year, there isn’t much interest or funding available.