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A proposed alternative that may improve outcomes is an allograft engineered from multipotent stem cells. Francis H. Shen, MD, associate professor of orthopaedic surgery at the University of Virginia, is studying the utility of an allograft engineered from cells derived from human fat tissue.

AAOS Now

Published 5/1/2010
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Jay D. Lenn

Engineering tissue for spinal fusion

Spinal fusions are common orthopaedic procedures, with about 450,000 fusion surgeries performed annually in the United States. Although grafts from a patient’s ilium are considered the gold standard for spinal fusion, autologous bone grafts still present significant risks. Failure to fuse occurs in as many as 40 percent of cases, and chronic hip pain and other morbidities are common.

Francis H. Shen, MD

Dr. Shen is the recipient of two grants from the Orthopaedic Research and Education Foundation (OREF) that have supported this endeavor: a $300,000 OREF Clinician Scientist Award given in 2007 with support from the Dr. Dane and Mrs. Mary Louise Miller Endowment Fund, and a $100,000 OREF Research Grant awarded in 2009 and funded by the Musculoskeletal Transplant Foundation.

Engineering tissues
Engineering new tissue for spinal fusion depends on the following three factors:

  • appropriate multipotent stem cells that, in the right environment, can be coaxed into cells capable of producing bone
  • a growth factor that can prompt the appropriate differentiation in cells
  • a three-dimensional structural scaffold that helps protect cell development, serves as a template for tissue growth, and can eventually be absorbed by the body

“Basically, we create new tissue of nonnative ingredients,” explained Dr. Shen. Identifying these ingredients and testing them in cultures with cells harvested from rats was the focus of the work supported by his OREF Clinician Scientist Award.

Bone marrow is a reliable source for partially differentiated or stromal cells, though the harvesting procedure is invasive and yields very few cells. Dr. Shen and his colleagues demonstrated that stromal cells derived from rat adipose tissue (body fat) can, under the right conditions, become uncommitted stromal cells capable of differentiation that leads to the growth of bone tissues.

His research team has also performed a series of experiments to identify an appropriate growth factor to direct cell differentiation. The most promising candidate is a protein called growth and differentiation factor-5 (GDF-5).

To create a scaffold for tissue engineering, Dr. Shen and his team—in collaboration with one of his mentors, Cato T. Laurencin, MD, PhD—have used a technique that thermally fuses polymer microspheres to create a three-dimensional, interconnected pore system with mechanical and structural properties similar to trabecular bone. The scaffold can be engineered to be resorbed at a rate that parallels the fusion of bone (Fig. 1).

A proposed alternative that may improve outcomes is an allograft engineered from multipotent stem cells. Francis H. Shen, MD, associate professor of orthopaedic surgery at the University of Virginia, is studying the utility of an allograft engineered from cells derived from human fat tissue.
Fig. 1 Hematoxylin and eosin (H&E) staining of in vivo rat specimens demonstrates a compact layer of bone on the surface of bioengineered scaffold in the GDF-5 treated group (A) but not in the control group (B). By 8 weeks, most of the scaffold has been resorbed and replaced by the new bone in the treatment group, while gaps (*) persisted in the control group (×200 magnification).
Courtesy of Francis H. Shen, MD
Fig. 2 Von Kossa staining at 3 weeks demonstrates that human adipose tissue treated with GDF-5 in osteogenic medium (A) have significantly greater mineralization and calcium deposition (dark staining regions) than the control group (B).
Courtesy of Francis H. Shen, MD

Their investigations have shown that this scaffold allows for cellular adhesion, proliferation, migration, and differentiation that leads to bone formation. Preliminary studies with rats have shown that the engineered tissue is capable of fusing vertebrae.

Translating work for clinical studies
With support from the 2009 OREF Research Grant, Dr. Shen and his team are replicating the experiments using stromal cells derived from human adipose tissue (Fig. 2).

Dr. Shen has also begun testing engineered human tissues in nude rats, immuno-incompetent rats incapable of mounting a response to the human cells. This environment provides a laboratory for identifying and solving problems with human tissue engineering that cannot be addressed in cell cultures.

Moving beyond spinal fusion
“Spinal fusion is just the beginning,” Dr. Shen explained. “As a true bone graft substitute, adipose-derived stromal cells that could achieve bony fusion would dramatically alter the way a variety of orthopaedic conditions could be treated. For example, these techniques could be extended to the management of delayed unions, nonunions, and the treatment of primary fractures.”

Theoretically, his work may inform efforts to engineer other tissues, such as nerves, tendons, and cartilage.

Supporting the future of orthopaedic surgery
As a clinician scientist, Dr. Shen continues to contribute much beyond his own laboratory work to enhance future practices in orthopaedic surgery. An active spine surgeon at the University of Virginia, he reviews clinical cases and mentors fellows, residents, and medical students on the hospital wards, in the emergency department, in outpatient clinics, and in the operating room. He has also served on the faculty of AAOS continuing education programs.

Describing the value of his OREF grants, he reported, “I cannot emphasize enough how immensely important it is to receive encouragement and financial support when you first begin pursuing research. You can develop ideas, you can create novel research techniques, and you can obtain data, but to truly succeed and progress, you need help and support from people, societies, and institutions like OREF.”

Jay D. Lenn is a contributing writer for OREF and can be reached at communications@oref.org