By Tom Keppeler, Knee1 Staff
Picture this: with a broken leg, you hobble into the doctor's office, expecting to be wrapped in plaster and sent home with crutches. Instead, the doctor pulls out a needle and injects a synthetic fluid into your leg that will harden enough in one week to let you walk on it.
Such far-flung fantasy may not be far off, if some Texas researchers have their way. By injecting the synthetic material into a broken, missing, or diseased bone, they claim, the fluid does more than provide structural stability—it can actually help a bone heal itself.
Researchers are undertaking an enormous challenge with the injection. Here's how it works:
- First, a porous liquid plastic is injected into the broken bone. Within a week, the substance hardens enough to support the weight the bone used to.
- Once it hardens, proteins known as "growth factors" encourage new blood vessels to grow into the scaffolding. The blood vessels will bring nutrients for new bone cells to grow.
- Eventually, the body's own bone cells build around and inside the scaffolding. Over time, the plastic breaks down and washes out of the body, leaving behind only healthy bone.
Many challenges have plagued the research, however. First, nearly every bone in the body has a unique set of properties. For instance, the heavy and dense femur has much different characteristics than the small bones within your feet. As a result, the amount of support the scaffolding provides and rate at which it decomposes must be adjusted for each bone.
Artificial bone presents a viable alternative to the existing method of bone replacement, the allograft. In the procedure, a bone graft is taken from another patient's bones, usually the hip, and transplanted where it is needed. While the procedure presents little or no risk of rejection, it presents a "robbing Peter to pay Paul" scenario, leaving the patient with a damaged hip. In addition, those who most need a bone graft—those with degenerative bone disease—often can not afford to lose more bone than they already have lost. Bone grafts also provide no structural support while the bone heals.
Dr. Antonios Mikos, president of the Tissue Engineering Society in Houston, Texas, told CNN that a biodegradable plastic bone scaffold will soon become the option of choice for diseased or missing bone. Mikos and his fellow researchers are currently working on combining the right amount of plastic, growth factors and stem cells—primitive cells that can become any type of cell, whether it is bone, cartilage, muscle, or otherwise—in the injectable bone. "The main obstacle to the stem cell approach is in large defects, larger than half a millimeter," Dr. Mikos told CNN. "The cells on the interior of the scaffold tend to die because they can't get enough nutrients from adjacent blood vessels."
Some plastics that scientists have used to create the bone scaffolding have already been approved for use in the body, possibly paving the way for a quicker-than-average acceptance rate. For now, however, researchers need to figure out the proper ratios of stem cells, support, and growth factors. Some studies have even suggested that growth factors may not be necessary in human bone healing, as it is in lower mammals.
One of the first areas that injectable-bone researchers have targeted is the spinal cord. If a patient ruptures a disk in the spine, doctors often have to fuse two vertebrae together with surgical screws to provide the support necessary and eliminate the pain of the ruptured disc. Mikos said the work will eventually expand into the most commonly broken or diseased bones. Currently, an estimated 300,000 to 600,000 patients need doctors to help along the body's bone-healing process every year, CNN reported.
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