Too much stress can fracture bones, as any long-distance runner or orthopaedic surgeon knows. Too little stress and bone fails to develop properly. Traumatic stress and cellular stress from diseases such as cancer can also lead to bone loss.

Robert L. Satcher, MD, PhD, is among the researchers studying ways to replace lost bone. A recipient of a 2002 Career Development Award sponsored by the Orthopaedic Research and Education Foundation (OREF) and Zimmer, Dr. Satcher is also a mission specialist astronaut candidate.

Dr. Satcher’s interest in how bone responds as a whole to the various stresses thrust upon it and, conversely, how it responds to the absence of those stresses goes back to his postdoctoral work at Northwestern University’s Feinberg School of Medicine.

The stresses bones face
To gain a better understanding of how various forces affect bones, Dr. Satcher—then an assistant professor of orthopaedic surgery at the Feinberg School of Medicine, a researcher at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University, and an orthopaedic surgeon at Northwestern Memorial Hospital—investigated bone at the cellular level.

Bone is made up partly of living tissue and partly of an inorganic and organic matrix. Proteins make up the organic portion, while calcium and phosphates constitute the inorganic part. It is the living portion, however, that reacts to stress placed upon it.

“It’s been known for a long time that if you subject bone to physical stress, such as loading it, the bone will become larger in size,” Dr. Satcher said. “What that means is that the bone cells—the smallest living units that make up the bone—are helping to build up that bone to make it stronger in response to that physical stress.”

Using bone cells harvested from rats, Dr. Satcher and a team of researchers were able to study how bone reacts to different physical forces using several methods. In one study, Dr. Satcher observed flowing fluid across the bone cells to see how they were affected. The side of the cell exposed to the flowing fluid represented how a physical force would affect the bone.

Dr. Satcher was also able to grow cells on a deformable membrane. “When you deform the membrane that the cell is growing on, it subjects that cell to the same deformation,” he explained, “which is equivalent to a physical stress that would cause deformation in the bone.”

This enabled Dr. Satcher to test the cells’ response to controlled loading. “We can specify how much straining the cells experience, or the deformation they experience because we artificially input the load,” he said. “This lets us observe the patterns of response.”

These initial studies led Dr. Satcher to his more recent investigation of designing materials that promote bone growth and that could be used to reconstitute areas of bone lost due to trauma, surgery, or cancer.

“We took what I had learned from working on the more fundamental process of how physical stresses affect bone and applied it to practical applications,” he explained.

Research beyond Earth
Dr. Satcher may someday have the opportunity to study this process in a completely different setting. He was selected as a NASA astronaut candidate in 2004.

He has nearly completed the 2-year basic training course that combined both didactic and experiential lessons. For example, classroom training covered the specifics of the space shuttle and international space station, while training in a large pool simulated the weightlessness of space.

“We also had a trip that involved leadership training, where we were put in scenarios of hostile environments and had to work together as a team to solve the problem under stressful situations,” Dr. Satcher said.

Once he has completed a technical assignment to support ongoing activities at NASA, Dr. Satcher will be eligible for assignment to either a space shuttle mission or a research project on the international space station. In either case, at least part of Dr. Satcher’s role will be that of researcher.

“Some NASA experiments have specifically studied how bone cells respond to a low gravity environment, but I won’t necessarily be conducting orthopaedic research,” Dr. Satcher said. “NASA has a review process similar to the National Institutes of Health or OREF. They accept research proposals and select the experiments that will be flown on the space shuttle and on the space station. Most likely I’ll be a proxy scientist for the principle investigator, doing some experiments that were selected by the peer-review process.”

Discovering the future of orthopaedics
Dr. Satcher stresses, however, that it is important to support orthopaedic research. “Orthopaedics as a whole has been expanding throughout the years, and the capabilities of the surgeries have become better as technology has improved,” Dr. Satcher said. “As we age, most of us will need orthopaedic care, even if it’s not operative. Our joints are going to start to bother us, or our back is going to give us problems. If orthopaedics is going to continue to improve, it will be through research that is carried out intelligently and effectively. Supporting research is essential to the continuing improvement and evolution of orthopaedics.”

Each year Zimmer supports six $50,000 awards through OREF. According to Ray Elliott, Zimmer’s board chair, “When we realized that young, practicing clinicians did not have the resources that were available to residents or veteran clinicians, we decided to help these young researchers by providing funding through OREF for a new grant program. Since then, we’ve granted to OREF more than a quarter of a million dollars each year to help these younger surgeons pursue additional research, education, travel, or any legitimate endeavor to help them advance orthopaedic science or care.”

For more information on the Zimmer/OREF Career Development Awards or ways you can support research through OREF, visit the OREF Web site, www.oref.org