Making Bone Grow Faster
Speeding up distraction’s consolidation phase would make the procedure easier to bear. Several approaches seem promising.
Distraction osteogenesis proceeds at its own pace, optimally about one millimeter per day. But for every day a bone is distracted, more than one day is required for consolidation, during which newly formed bone hardens. “Consolidation is the time killer,” says Michael Longaker, director of the Children’s Surgical Research Lab at the Stanford School of Medicine. “There’s no reason we can’t accelerate that phase.”
Longaker’s lab is pursuing four strategies to speed hardening. The first calls for isolating mesenchymal stem cells from bone marrow or fat. These stem cells can become other kinds of cells, including those needed for bone formation. “During the surgery to cut the bone, you could insert a scaffold that mimics the structure of bone so stem cells immediately start forming bone,” Longaker says.
The second explores the potential of boosting the effect of bone morphogenic proteins (BMPs), which the body manufactures naturally to heal fractures. These proteins are already commercially available, and Longaker imagines “either adding BMP-type substances, or decreasing the effects of BMP antagonists (which inhibit the action of BMPs), or both.”
Third, because distraction is faster and has fewer complications in the face than in the long bones (because the face is highly vascular), Longaker is researching whether having more blood vessels at the distraction site would speed bone formation. Vascular endothelial growth factor creates blood vessels when it is released by tumors or by stem cells after a bone injury. “If you created a matrix that released VEGF and added cells that formed bone, that would hasten healing,” says Longaker.
The fourth possibility would use mechanical loading to stimulate bone formation. Bone demineralizes quickly when no force is applied. Longaker is experimenting with devices to see whether movements as imperceptible as one-millionth of a millimeter might make bone harden more quickly. “If we could reduce the consolidation period by half,” he says, “that would be great.”