A very interesting technique developed by the Harvard Medical School, Boston recently allows fat and muscle taken from a patient's own body to be converted to bone and cartilage. This process involves first putting a gene into muscle and fat cells and then transplanting them at the injury site. What this does is, it helps in the regeneration of bone and cartilage and quickens the injury healing process.

For example, a broken bone would mean that the patient would have to be put in traction, but using this new technique the time needed to be spent in traction will be considerably reduced. Normally a broken bone in an otherwise healthy adult would take several months to repair. However, using this technique broken bones could return to normal strength in just 8 weeks. Similarly it would assist in getting over cartilage damage in the knee, as proved by experiments conducted on rabbits. In short, as this new technique speeds up the recovery process, severe injuries could be treated by implanting genetically engineered muscle or fat tissues and to avoid risk of rejection, these muscle or fat could be taken from the patient themselves.

The essence of this technique is a kind of gene therapy that prods muscle and fat cells to first convert to cartilage and thereafter to bone.

Theoretical basis
Fibrodysplasia ossificans progressiva is a rare disease that causes bones to form in muscles. People with predisposition to this disease have a gene which codes for bone morphogenetic protein. Using a virus that gets into cell DNA, this defective gene is introduced to muscle and fat tissues. Gene transfer to muscle and fat is done using Ad.BMP-2 a first generation adenovirus vector carrying cDNA encoding human bone morphogenetic protein-2. Thereafter when this muscle and fat is implanted in the vicinity of the broken bone it converts itself to bone. For example, tests in rats transduced with genetically modified muscle and fat tissues showed that it took only a few days for rapid formation of a bridge between broken bones. Animal studies have indicated that muscle tissues used this way offers better treatment prognosis than fat tissues.

The fact that heterotopic ossification occurs in patients with total hip joint replacement procedures is indicative that bone can form from muscles. Earlier it was known that the repair of bone and cartilage can be done by tissues resulting from the ex vivo expansion of autologous progenitor cells that are seeded onto scaffolds and thereafter surgically implanted. Yet another earlier process was to use genetically modified bone marrow coagulates for repairing cartilage.

Therapeutic findings
Therapeutic findings have been encouraging as regards this new procedure. Although still in animal testing stage, according to Judith Hoyland a coauthor of this technique "implanted cells did migrate to injured tissue and were forming bone".

According to related scientific reports this new technique of introducing modified muscle and fat implants to aid the healing process in cases of broken bones not only did that, but also provided a rejuvenation to the body's own healing process in its ability to grow new bone.

How the procedure was deemed promising?
The differentiation into cartilage and subsequent endochondral ossification of the inserted grafts as established by histological tests is evidence of the tests being deemed successful. In female rats that underwent this procedure, some of the osteoblasts of the healed bone had originated from the implanted donor muscle. This was established by fluorescence in situ detection of Y-chromosomes.

It was also established that implanted fat tissue had set right bone defects albeit slowly. In short, there exists a possibility of using this technique for healing cartilage defects as confirmed in studies conducted on rabbit osteochondral defect models.

Prof. Evans, F.-J. Liu, V. Glatt, J.A. Hoyland together with a team of eminent scientists are credited with these findings. Professor Chris Evans a co-author of this technique is quoted as saying, "further development of these methods should provide ways to heal bone and cartilage more expeditiously, and at lower cost, that is presently possible." The researchers are conducting further animal trials before attempting the technique in human patients.

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