Bones: How to grow new ones

James P King

Bones: How to grow new ones

The recipe is as follows: Take a bone (usually from a cadaver, but it can be from the patient’s own body), pulverize it into a powder, soak it in a hydrochloric acid solution (HCl), then wash it with distilled water. Extract (dry) the powder in ethyl alcohol for an hour, followed by an hour in anhydrous ether. Sterilize the material by cathode ray irradiation. The resulting product from this straightforward but exacting process is called “demineralized bone powder.” (See Fig 1.) For the past year and a half, physicians on the staff of Harvard Medical School, Children’s Hospital Medical Center and Brigham and Women’s Hospital, Boston (see list) have placed this demineralized bone powder (and, in some cases, demineralized bone chips or strips) into patients in areas where no bone previously existed. The 34 patients receiving the demineralized bone ranged in age from 15 months to 59 years, with mean age 18 years. Some of the patients had acquired bone defects, while the majority had congenital deformities. Remarkably, shortly after the de-

James P King is assistant vice-president for corporate communications in theoffice of Public Relations, Brigham and Women’s Hospital, Boston. Copyright @ Brigham and Women’s Hospital, 1981. Reprinted with permission.

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mineralized bone was introduced into the patients in body areas where no bone existed, bone began to grow. How and why are intriguing questions, but they point to dramatic implications for future research-as well as present solutions to medical problems. Writing in the May 1, 1981, issue of the British medical journal Lancet, the researchers reported that a biological process unlike that occurring in existing bone-transplantation techniques was utilized to produce new bone. (See Figs 2 and 3.) Upon the introduction of demineralized bone powder (rehydrated), host fibroblasts (cells that would ordinarily become fibrous tissue) come into contact with the powder. By day 10, the fibroblasts have been converted to cartilage-forming cells. The cartilage is formed free of blood vessels; but by day 12, new blood vessels penetrate the cartilage and trigger conversion of cartilage to new bone. The biological process is called induced osteogenesis or osteoinduction. The study of this process progressed in animals for three years in the laboratories of Judah Folkman, MD, supported by a gift to Harvard University from the Monsanto Company, before the first clinical trials in humans occurred. In humans, the same process occurs, but it usually proceeds more slowly than depicted in Figs 2 and 3, generally taking three to four months. The demineralizing process literally

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removes all minerals from the bone (whether it be in chunks, strips, or powder). Since minerals are what cause hardness in bone, the resulting texture of the demineralized bone is soft and pliable, allowing it to be carved or molded easily. When the material is used in the form of blocks, discs, or chips, the surface area of the demineralized bone plays an important role in determining the amount and location of the new bone formation. Large blocks of demineralized bone, according to the physicians, induce only a thin layer of new bone on their surfaces, so osteogenesis proceeds more slowly in response to blocks than to powders. However, the size of the powder particles is also crucial to successful osteoinduction. If the particles are too small, osteogenesis does not occur; if they are too big, induction is not successful. “The extent of bone induction is a function of the surface area of the implanted powders. As expected, healing is more rapid in patients who receive powdered implants,” the physicians said. The “powdered” implant is actually applied in a paste form. Apparently, the implant produces a signal, perhaps electrical, in the cells immediately adjacent to the implant, thereby causing these cells to become bone-producing cells. Studies by Dr Glowacki and her associates have shown that any step in the demineralizing process that alters the electrochemical properties of the final product diminishes its effectiveness. For example, sterilization procedures, such as soaking in iodine, have an adverse effect. The demineralized bone implantation process differs substantially from current bone repair techniques. Implanted demineralized bone material can cause new bone to grow in soft tissues, even when the implant is not in contact with the existing bone. Further, in patients

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DEMl N ER A L IZE (HC I )

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(Ethanol. Ether)

I STERILIZE-IRRADIATION I

Fig 1 . The recipe for preparing demineralized bone powder. The source of bone can either be the patient’s own body, such as a rib, or a bone bank.

who were followed by x-ray, healing occurred not from the edges of the defect, but uniformly throughout the site, the authors reported. Conventional bone repair procedures use cadaver bone or transplantation of living bone such as rib or iliac bone, from the patient’s own body. Growth and healing occur to the extent that cells from existing bone migrate to the edges of the transplant-a process called osteoconduction. The trans-

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BONE INDUCTION IN RAT

Fig 2. Stages in the biological process leading from demineralized bone through new bone formation. Demineralized bone induces the host to form cartilage, which arises free of blood vessels. Later, new blood vessels penetrate the cartilage; this triggers the conversion of cartilage to bone. (In humans, this process proceeds more slowly than depicted here.)

planted bone, if it is not resorbed, serves as a scaffold for cells from adjacent living bone. However, resorption occurs in 40% to 50% ofthe cases, and, frequently, the harvesting of the patient’s bone for transplantation carries substantial risk. With the new process, the need for a major operation-to harvest the patient’s own bone for implanting-is eliminated. In the future, animal bone may also be used in this new technique. Dr Glowacki and h e r associates have shown that both human and cow demineralized bone material induces bone growth in laboratory animals, thereby

BONE INDUCTION

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Fig 3. Sequence of events at the cellular level begins when host fibroblasts are converted to cartilage-forming cells. New blood vessels enter the cartilage and trigger conversion of cartilage to new bone.

showing that crossing species lines may be possible in humans, too, and demineralized bone need not come from the same species as the host. Dr Glowacki,who conducted the basic biochemical and animal studies, credits t h e 1972 work of Nobel Laureate Charles Huggins, MD, with providing the foundation that ultimately led to human application of the process. However, as early as 1899, Nicholas Senn, MD, reported his attempts to correct long-bone defects in patients using bone treated with acid. This concept was examined briefly around the turn of the century, but was never pursued in extended clinical trials with humans. Dr Huggins, in reporting his experiments with demineralized bone mate-

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This series of x-rays and diagrams of a patient’s jaw illustrates one use of demineralized bone. A large cyst in a patient’s lower jaw had failed to heal, jeopardizing teeth supported in that area. Four months after implantation of demineralized bone powder, x-rays show new bone formation, and after 74 months, nearly complete healing with new bone, as confirmed by biopsy.

rial in 1972, observed that it induced phenotypic change in fibroblasts, resulting in the formation of cartilage and bone. It remained for Dr Glowacki and her associates to go beyond these observations, to recognize the potential clinical use in humans for demineralized bone, to refine and perfect the process of preparing it, and to use it successfully in a large number of human patients. They accomplished this by demonstrating that new bone could be consistently in-

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duced to grow in animals, that this new bone was not resorbed, and that the procedure was safe. The first human application of this process in this study was accomplished by John Mulliken, MD, who treated a series of patients with craniofacial defects. Cadaver bone was obtained from the Interhospital Organ Bank and was demineralized by the research team. At the American Surgical Association’s annual meeting in Chicago, Dr Mulliken reported on the current status of the 34 patients cited in the Lancet article, as well as an additional 10 patients treated with demineralized bone. To date, the material and the surgical procedure have been used to augment a bony contour (ie, in a forehead or cheek); to fill gaps (ie, replacing jawbone, repairing cleft palate); to construct new bone in soft tissue (replacing a congenitally absent nose); and in dental and periodontal surgery. In addition, several orthopedic patients have been treated using this material, but, according t o Dr Mulliken, it is too soon to know whether their treatment has been wholly successful. He explains, “It will require several years of careful followup, but we are hopeful this approach may have application in selected orthopedic cases.” Dr Kaban is optimistic about the potential applications of induced osteogenesis i n oral and maxillofacial surgery: “This is a very significant breakthrough with major public health implications. Periodontal disease is fast approaching 100% of our population in the over-40 age group. Its occurrence increases with age.” This condition, he said, often leads to loss of the bones that support the teeth, and subsequent loss of the teeth themselves. Double-blind clinical trials of demineralized bone in the treatment of periodontal disease are under way in collaboration with Stephen Sonis, MD, a member of the

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The researchers The individuals involved in the project are: Julie Glowacki, MD, associate in surgery at Harvard Medical School and research associate at Children’sHospital Medical Center (CHMC), Boston. She conducted the basic biochemical and animal studies that led to the implantation of demineralized bone in humans. Leonard B Kaban, MD, assistant professor of oral and maxillofacial surgery at Harvard Medical School and associate in surgery at Children’sHospital Medical Center and Brigham and Women’s Hospital. He was the surgeon for the dental and oral surgical applications of this technique. Joseph E Murray, MD, professor of surgery at Harvard Medical School and chief of the Division of Plastic Surgery at Children’s Hospital Medical Center and Brigham and Women’s Hospital. Dr Murray also led the surgical team that performed the first successful kidney transplant in humans in 1954. Judah Folkman, MD, professor of pediatric surgery and anatomy at Harvard Medical School and surgeon-in-chiefat Children’sHospital Medical Center. He is one of the principal scientists involved with the Harvard Monsanto program and is director of the surgical research laboratory at CHMC. John Mulliken, MD, assistant professor of surgery at Harvard Medical School and associate in surgery at Children’s Hospital Medical Center and Brigham and Women’s Hospital. Dr Mulliken perforitled the first operation in humans using ’, 9 demineralized bone materi? rld was the surgeon in the craniofacial cases. faculty in oral medicine at Harvard and chief of dental services at the Brigham and Women’s Hospital. “We hope t o determine whether we can create new bone to hold teeth in place,” Dr Kaban says. Dr Sonis says, “What we have been and are trying to do is take patients

with advanced periodontal diseaseclinical disease-and give them a second chance. On the trials we are running, things look very promising. The procedure is safe, it has been tolerated well by patients and it looks like it’s working. But I won’t feel comfortable saying that it works until we’ve had several more years of clinical testing and experiences to analyze.” Another potential application of this technique is in the treatment of atropic mandible. Dr Kaban points out: “Some 20 million Americans have lost all their teeth, and when this happens, the jawbone becomes smaller o r shrinks. In 10% of these cases, the jawbone is too small to effectively fit dentures. The first animal studies to ascertain whether induced osteogenesis is applicable to this problem are just getting under way.” Dr Mulliken stresses the potential application for the new procedure in orthopedics, neurosurgery, and pediatric surgery. Dr Kaban adds that 1 out of every 800 newborns suffers from cleft palate, indicating that the implications in this area could be substantial. Dr Murray, the surgeon who led the surgical team in the first successful kidney transplant at the Peter Bent Brigham Hospital in 1954, emphasizes the importance of this technique for trauma patients. Collagen Corporation, a company that is 30% owned by the Monsanto Company, is assembling the appropriate documentation for submission to the Food and Drug Administration to begin a multicenter clinical investigation of the process, and is moving as rapidly as is clinically and scientifically prudent to make this material widely available. The hope is that this can all be accomplished within 12 to 18 months. 0

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