Autologous Bone Graft or BMP-2 for Spinal Fusion
Combined interbody and posterior or posterolateral techniques seem to have the highest clinical fusion rates.
In the past, the best source of bone cells for fusion was autogenous cancellous bone. Now there is an alternative.
Bone graft harvest requires an additional incision (even if done through the same skin incision, there is still a separate fascial incision). This second surgical site results in the risk of nerve damage – classically cluneal nerve damage – with the potential sequelae of painful neuroma formation, blood loss, muscle disruption, iliac bone disruption with possible fracture, sacroiliac joint violation, donor site infection and chronic pain.
Bone graft harvest requires additional operating room time and thus additional cost. Currently rhBMP-2 and rhBMP-7(OP1) are available as bone graft substitutes. These osteoinductive/cell differentiation factors cause undifferentiated cells to selectively differentiate into bone rather than fibrous tissue. RhBMP-2 has been shown to increase fusion rates. The patient wants the highest probability of bone fusion success. BMP provides that opportunity. In addition, it appears that BMP causes fusion to occur faster than autogenous bone. It may cause the bone to be more robust as well.
RhBMP-2 is FDA approved, on label, for use in the lumbar tapered fusion device (LT cage) done as an anterior interbody fusion. OP-1 has an FDA humanitarian device exemption (HDE) for high risk patients that requires institutional review board oversight and limits use to 4000 cases per year in the US. Surgeons are free to use rhBMP-2 in “off label” fashion, but the company cannot promote such use. It is currently used extensively in an off label fashion, with increasing clinical experience and clinical reports demonstrating the efficacy of its use in that fashion. There has been some concern about rhBMP-2 in a posterior lumbar Interbody fusion application and whether or not there is bone formation in the spinal canal. It has not been a clinical issue to date.
Finally, there is the spurious argument that BMP costs too much. This is based only upon looking at implant or procedure costs. This is an easy-to-measure but short-sighted parameter for evaluation. The most expensive part of any fusion is the revision. If the success rate is improved, the overall cost of the process of care is lessened which should be the long term societal goal. Overall BMP is an excellent investment for procedural and clinical success. It is the state of the art for fusion surgery and if I needed this procedure, I would want the best. Why would you offer patients less than what you would want for yourself? Physicians are ethically bound to advocate for their patients for the best possible treatment. This is the best.
The FDA recognizes that physicians have the right and duty to use any approved product to help their patients even when it is used in a manner different than its original intent.
Because of very brief clinical experience within the spinal surgery community related to the use of BMP-2, I am sure that all the safety issues related to BMP-2 have not been addressed.
One well-recognized problem with BMP-2 is unintended bone formation. Therefore, the material may spill out to unintended sites and cause bone formation. Indeed, when degenerative disc disease is treated by a posterior lumber interbody fusion technique, some surgeons have noted overgrowth of bone around the nerve roots after using BMP-2.
There are potential dangers of cancer related to BMP-2. Some studies have shown that BMP-2 does promote tumor angiogenesis and growth in some laboratory studies. Application of large exogenesis BMP-2 may result in fetal death or malformation. Rarely, patients receiving BMP-2 have developed antibodies to BMP-2 and it has been theorized that this may prevent successful pregnancy. Furthermore, it is possible that fetal expression of BMP-2 could re-expose mothers who were previously antibody positive, eliciting a more powerful immune response with adverse consequences for the fetus. Currently, it is recommended that the BMP-2 is not used for women of childbearing age.
Another point that illustrates the problem related to lack of clinical experience is the company notification to the surgeon for BMP-2 use for anterior cervical surgery. To date, three cases of acute and severe edema of the prevertebral soft tissue requiring surgical intervention have been reported including a case which required tracheostomy.