THE NEED FOR BONE SUBSTITUTES

Orthopedics to Take Center Stage in Coming Decade:


"The World Health Authority has decreed that 2000-2010 will be the Bone and Joint Decade, and this is now being supported by the United Nations. The rationale for this is that joint diseases account for half of all chronic conditions in people over 65; back pain is the second leading cause of sick leave; and osteoporotic fractures have doubled in the last decade so that 40% of all women over 50 will eventually suffer from one. It is estimated that 25°/( of health expenditure in developing countries will be spent on trauma-related care by the enc of the decade, and many children are deprived of normal development by crippling disease and deformities."

Many of these cases require bone graft substitutes to repair the injury or defect. There are currently on the order of 500,000 bone grafts performed annually in the U.S. For example there were an estimated 220,000 spinal 'fusion cases performed in 1998 requiring bone graft_ to secure areas of the spine affected by deformity, trauma, tumours, or degenerative disc disease. And there are approximately 170,000 fractures in the United States that fail to hear each year and are diagnosed as 'non-unions' ( i.e., fractures that have failed to heal within nine months) that require some form of bone substitute to repair the fracture.

Current Therapies:
To address the need for bone substitutes, current clinical therapies include:

1. Autografting, which represents about 58% of the current bone substitutes, involves harvesting a bone from one location in the patient's body and transplanting it into another part of the same patient. Using autologous grafts, when available, typically produces the best clinical results; successful clinical outcomes can exceed 80%. Auotgrafting is thus considered the 'gold standard'. An example one of the most commonly performed bone autografting procedure is for use in spinal fusion. In a fusion procedure, bone graft from the patient's hip is implanted in disc spaces between spinal vertebrae or along the back of the spine. The grafted bone fuses the vertebrae together over several months. The benefit from transplanting an autogenous tissue is obvious: immunogenicity is not an issue.

2. Allografting, which represents about 34% of the current bone substitutes, involves harvesting and processing bone from a cadaver then transplanting it to the patient. Allogenic implant are acellular and are less successful than autografts for reasons attributed to immunogenicity and the absence of viable cells that become osteoblasts. Another disadvantage of allografting is concern with transmitted disease.

3. Man-made materials, including metals, plastics, and ceramics represent approximately 8% of bone substitutes. These materials, however, are subject to fatigue, fracture, toxicity, and wear, and do not remodel with time.