Bone Morphogenetic Proteins

Bone morphogenetic proteins (BMPs) are substances that are used in place of bone grafts for spinal fusions to stimulate bone growth. While BMPs are found naturally in the body, they can also be created in the lab. Eventhough BMPs are approved for use in spinal fusion surgeries, they cannot be used for cervical spinal procedures due to the possibility of adverse reactions that may interfere with swallowing or breathing.

There are a few types of BMPs. Recent research has shown one type in particular to be effective when treating chronic kidney disease.

What Are the Different Types Of Bone Morphogenetic Proteins?

Originally, seven BMPs were discovered. This was in the 1960s. Since then another seven have been added. These all occur in the body and can also be created in the lab. Of the 13 BMPs the two most focused upon are BMP-2 and BMP-7. BMP-2 has been studied thoroughly and has been found to successfully stimulate spinal fusion equal to or better than the patient’s own bone. BMP-2 has received FDA approval for use in anterior lumbar interbody fusion in titanium cylindrical cages. This is the only “approved” use, although BMP-2 is used with other cages “off-label.”

Bone Morphogenetic Proteins Benefits

There are multiple benefits to the surgical use of BMPs as opposed to bone grafts. Bone grafts may be harvested during a fusion from another part of the patient’s body or from a donor bank. In either situation, there are potential complications to be considered that do not apply when using BMPs. Also, BMPs do not just serve as fillers, but actually help stimulate bone growth, yielding successful results.

Bone Morphogenetic Proteins Disadvantages

Although BMPs represent advancement in bone fusion procedures, they do carry certain disadvantages. While there are allergic reactions that can sometimes be dangerous, these substances can also be costly. In addition, BMPs are a developing treatment, therefore their long-term side effects remain unknown. Currently, BMPs are contraindicated for pregnant women, children, and patients with tumors or infections adjacent to the surgical site.

Who Is A Good Candidate For Bone Morphogenetic Proteins For Fusion?

Patients who are at risk for potential side effects and complications from traditional bone grafting are good candidates for BMP use for their spinal fusion, as it produces the same results (or even better bone growth) without the potential side effects of bone graft site morbidity. These are consequences that can occur from harvesting of the patients’ own bone, usually from the iliac crest of the hip.

These side effects include early post-operative pain, chronic pain, scarring, bleeding, infection, and more. Pain can last up to two years in up to one third of patients after the bone graft is harvested.

How Do Morphogenetic Proteins Work?

It’s not fully understood how BMPs work to grow new bone. The BMP is placed at the fusion site, fully incorporated into a bone implant. Then the proteins are released gradually to allow bone formation, which is stimulated by the cytokines and metabologens in these proteins. The doses of BMP-2 released are thousands to millions of times the amount normally found in the body. Research has shown that BMP-2 stimulates fusion equal to or better than the patient’s own bone.

How Are Bone Morphogenetic Proteins Administered?

These are six-step processes:

1. Implantation — For these procedures, Dr. Girardi applies the BMP to an absorbable collagen sponge (ACS) carrier. This is implanted at the fusion site, usually within a cage, between the vertebrae after the disc is removed. The BMP and the absorbable collagen sponge need to work together to produce new bone tissue.
2. Chemotaxis — Bone-forming cells migrate to the area of the BMP/ACS implant. This cell migration stimulated by a chemical response is known as chemotaxis. Mesenchymal stem cells move from bleeding bone, muscle, and the periosteum to infiltrate the implant.
3. Proliferation — The stem cells around the BMP/ACS implant now increase in number. Some of these differentiate into osteoblasts, or bone-forming cells.
4. Differentiation — Binding to specific receptors on the surface of the stem cells, BMP causes them to differentiate into bone-forming cells. This differentiation plays an essential role in the induction of new bone.
5. Bone formation — As the collagen sponge degrades or dissolves, these stem cells differentiate into osteoblasts and begin to form bone. This bone formation process starts from the outside of the BMP/ACS implant and it moves toward the center until the entire implant is replaced by bone.
6. Remodeling — The body continues to remodel bone in response to the local environment and mechanical forces, resulting in normal bone formation. Various methods of evaluating this new bone has shown that it functions biologically and biomechanically as native bone.

Is The Use Of Bone Morphogenetic Proteins Safe?

Bone morphogenetic protein use has proven to be safe and effective for lumbar fusion. It is not to be used for anterior cervical fusions because it has been shown to cause massive soft tissue swelling. This can restrict the patient’s airway.

BMP is also not to be used in pregnant women, as there hasn’t been adequate study on its possible effects on the fetus. Patients also cannot have tumors or infections near the surgical site.

Are There Any Risks With The Use Of Bone Morphogenetic Proteins?

The main risks are if these proteins are used outside of the FDA’s approval for anterior lumbar fusion. Dr. Girardi only uses them for lumbar fusion, and only when there is more risk involved in harvesting the patient’s own bone graft. In patients where there is risk with this harvesting, or if their own bone production is overly slow or not of good quality, the use of BMP is a great alternative.