The human body has tremendous bouncebackability, but when its biologic response isn't enough to regenerate bone lost to injuries or defects, surgeons can reach for a wide array of bone grafts, bone substitutes and biologics to speed the healing process. Bone grafting gives the body a bone-building boost and helps surgeons fuse spines, revise failed joint replacements and fix complex fractures.

Before appreciating how the various graft materials work, you must first understand the 3 mechanisms of action involved in new bone growth: osteoinduction, which involves cells that induce new bone growth; osteoconduction, which involves spacer material on which new bone grows; and osteogenesis, which is when new bone actually fuses with a graft. Bone graft materials and bone graft substitutes have some or all of these properties.

• Autograft bone grafts are taken directly from the patient's body, most often at the iliac crest, and demonstrate all 3 properties of bone growth. Donald Corenman, MD, DC, a board certified spine surgeon in Vali, Colo., says spinal fusion procedures can involve obtaining a local autograft by recycling bone spurs or lamina from the vertebra.

Dr. Corenman points to several benefits of using autograft bone: no risk of disease transmission, easy acceptance by the body and optimal healing for a healthy fusion. Potential drawbacks include longer surgical times to harvest the graft and additional post-op pain for the patient. During spine surgery, fusion rates (the percentage of full incorporation of the graft bone with the native vertebrae) involving autograft bone is 95 to 98% at a single disc level, according to Dr. Corenman. He says healing time (how long it takes new bone to become fully incorporated in the body) takes about 6 weeks.

• Allograft bone grafts are taken from donors and provide a framework for new bone cells to grow in and around before they eventually replace the donor bone. An allograft is 100% conductive and hardly inductive because it does not contain growth factors.

"Implanting allograft bone does not require additional surgical time, but does carry a small risk of disease transmission," says Dr. Corenman. "In addition, disinfecting the allograft bone before implantation to reduce infection risk eliminates growth cells and the proteins that strengthen the bone after implantation."

Dr. Corenman points out that fusion time is lengthened when allograft bone is used because there are no host cells present in the graft to speed the healing process. He says fusion rates are 92% to 95% and healing takes 3 to 4 months.

Bone substitutes

Many bone alternative materials designed to help new bone growth are available in various moldable forms — including injectable paste, putty or gel. Your surgeons might prefer a certain material, but they should focus on using cost-effective products that demonstrate osteoconduction and osteoinduction. Here's a quick review:

• Bone morphogenetic protein (BMP) is a naturally occurring protein found in human bone and is a strong stimulant for bone formation, according to Dr. Corenman. He says the substance has significantly improved outcomes of spinal fusions involving iliac crest bone grafts. Without the use of BMP, Dr. Corenman says fusions following posterior fusion surgeries typically take 1 year to mature and have a fusion percentage with local bone grafts between 85% and 90%. When using BMP, Dr. Corenman's patients achieve fusion in 5 to 6 months and have a fusion percentage of 99%.

The FDA has approved BMP for use during posterior spine fusion procedures, including transforaminal lumbar interbody fusion (TLIF) and posterior lumbar interbody fusion (PLIF). Dr. Corenman says many insurance companies now reimburse for BMP use during PLIF, but acknowledges that many surgeons don't use the protein because of problems getting pre-authorization from payers due to its expense. Some surgeons instead combine synthetic bone extender grafts — ?such as a collagen-calcium sulfate mixture — ?with autografts or use stem cell derivatives aspirated from the iliac crest to increase fusion rates.

• Demineralized bone matrix (DBM) is allograft bone that has had its mineral content (calcium) removed to leave behind protein-based growth-stimulating substances such as collagen, proteins and growth factors. Dr. Corenman says DBM, which has osteoinduction and osteoconduction capabilities, comes in a variety of forms and has a low risk of disease transmission. However, he points out, DBM isn't strong enough to promote bone fusion by itself, so it's typically combined with other types of grafts.

• Human recombinant proteins such as bone morphogenetic proteins are effective but expensive growth factors with limited FDA-approved indications, says Philip F. Stahel, MD, FACS, chief medical officer at North Suburban Medical Center in Thornton, Colo., and a professor of orthopedics and neurosurgery at Rocky Vista University College of Osteopathic Medicine in Parker, Colo.

The benefits of using synthetic bone grafts are that they carry no infection risks and can be molded into various shapes and sizes for easier placement. They provide a framework for bone to grow, but don't stimulate bone growth.

"Operative times are shorter with synthetic bone substitutes because surgeons don't have to harvest local grafts," says Dr. Stahel. "Risks of complications, including infection, bleeding and post-op pain, are also lower."

However, the likelihood of successful fusion is less than if autografts are used, says Dr. Stahel. Autograft bone is also free, but you have to factor in the costs of additional OR time and the risks of anesthetizing patients for longer periods and adding an operative site to harvest the graft.

Dr. Stahel says bone substitute manufacturers do an excellent job of marketing their products, as evidenced by patients seeking out facilities that use the latest synthetic grafting materials.

Bone grafts are reserved for treating bone loss during revision surgery after implants fail or to augment bone around fractures that occur in replaced joints, less so for primary fracture fixation and primary joint replacements.

Dr. Stahel says the burden of proof is on manufacturers to show through human studies and case reports that synthetic products are equivalent or superior to natural grafting materials. His research showed autologous iliac crest bone grafting and compression plating were safer and more effective than other grafting methods — ?allograft, an allograft-autograft combination and recombinant human bone morphogenetic protein-2 (rhBMP-2) with or without adjunctive bone grafting — in the treatment of complicated fracture nonunions.

"Nothing trumps proper indication and excellent surgical technique," he says, "but when in doubt, go with natural bone grafts to promote healing." OSM