Molecular engineering and emerging technologies

In 2002 the Food and Drug Administration (FDA) approved a form of bone morphogenic protein (BMP-2) for anterior lumbar interbody spinal fusion. The BMP product is called INFUSE™, and it is made by Medtronic Sofamor Danek.

Collagen-based sponges are used as carrier material for the BMP solution. These sponges are placed into cylindrical titanium cages (the LT-CAGE™, also made by Medtronic Sofamor Danek) that are inserted into the disk space through an anterior (front of the spine) approach. BMP is not approved for intervertebral fusions via a posterior (back of the spine) approach.

The FDA-approved study conducted to test the BMP for human use did not show any significant adverse reactions, and the implant seemed to grow bone as well as autograft (patient's own bone). This is the first recombinant technology (produced by molecular engineering techniques) that the FDA has approved as a true substitute for naturally-occurring proteins for achieving spine fusion. The major drawback of this product is that it is very expensive to use.

Much research is being conducted to find an adequate bone graft substitute for posterior lumbar spine applications. BMP is not approved for use in fusing the posterior spine. A proper carrier substance that can support this area and keep the BMP in place long enough to initiate a fusion has not been clearly identified. Research is being conducted with many different types of growth factors and carrier models.

Emerging technologies
Much research is underway in laboratories throughout the world to identify bone-growing BMP™s and other key growth factors and manufacture them via recombinant techniques.

These substances attract and alter cell lines into bone-producing cells. It is biologically one of the first steps that needs to happen before the body can start to grow bone. The body produces these proteins during the ordinary process of skeletal repair, but scientists have learned to isolate the proteins, and companies are developing ways to synthesize them. Work is also progressing in developing carriers to deliver the proteins effectively.

Another exciting development is a polymer-based bone void filler that can be injected into the fusion site to assist in stabilizing spinal anchors, such as pedicle screws (for example, CORTOSS^©, made by Orthovita). The material then hardens to provide immediate stability to the local environment stabilizing an implant in osteopaenic bone. CORTOSS^© is currently used in Europe, and preliminary work is being done for a U.S. study. An attractive spinal application would be for use in kyphoplasty or vertebroplasty procedures to help support bone that has been compromised by a compression fracture.

Synthetic bone wedges, cages and other shapes are also being studied (e.g. RHAKOSS™, made by Orthovita) as possible substitutes for structural autograft or allograft bone.

In addition to concerns about possible disease transmission, the supply of cadaveric bone is somewhat limited, and in the future there could be significant shortages. A synthetic replacement would eliminate these problems.