Medtronic submits PMA for added rhBMP-2 indication

Using rhBMP-2 may accelerate fusion mass maturation in posterior lumbar spinal fusion patients.

Medtronic Inc. has submitted a premarket approval application to the FDA to expand the indications for its bone morphogenic protein, rhBMP-2, to include posterior lumbar spinal fusions, the company announced. If approved, this will mark the third orthopedic indication granted to the drug.

RhBMP-2 (Infuse) was originally approved for use in anterior lumbar interbody fusions. The FDA expanded the drug’s indications in May 2004 to include the treatment of certain tibial fractures.

The new premarket approval submission covers a new formulation and carrier for the rhBMP-2 called Amplify (rhBMP-2 Matrix), which Medtronic designed specifically for posterior lumbar spinal fusion cases.

Infuse Bone Graft is currently the only bone graft replacement to receive FDA premarket approval, which supports its efficacy for treating lumbar spine degenerative disc disease. It has also been approved in more than 37 countries, company officials noted in the press release.

Clinical cohort study

The premarket approval submission was based on data from a randomized, prospective, clinical study involving more than 460 patients. However, a separate prospective study presented by Kern Singh, MD, at the North American Spine Society 20th Annual Meeting also supports the efficacy of rhBMP-2 for posterior lumbar spinal fusions.

Singh, an orthopedic spine surgeon in Chicago, and colleagues at Emory University in Atlanta, used computed tomography (CT) to evaluate osseous fusion in 22 women and 12 men. These patients had a mean age of 65.5 years, and all underwent posterolateral lumbar spine fusion using pedicle screw instrumentation, iliac crest cancellous bone graft and rhBMP-2 (12 mg), which surgeons delivered using an absorbable collagen sponge. For bulking agents, the researchers used autogenous laminectomy bone in 22 patients and allogeneic demineralized bone matrix in 12 patients, according to the study’s abstract.

Overall, the researchers analyzed 118 arthrodesis sites in a blinded fashion. Of these, 110 levels (94%) were graded as definitely fused, four levels (3%) as probably fused, and two levels each (1.5%) as probably not fused and definitely not fused.

“The fusion masses attained full maturation by the one-year time interval,” the authors said in the abstract. “This fusion rate appears higher than in other similar populations fused with iliac crest bone graft alone,” they added, noting these studies found one-year fusion rates ranging from 50% to 75%.

In the current study, the researchers rated fusion mass quality as excellent in 27 patients (79%), good in five patients (15%) and fair in two (6%) patients. Only one patient had a bilateral fusion mass rated as fair. Additionally, 33 of the 34 patients (97%) had at least one side at each level graded as definitely fused, according to the study.

At six months follow-up, 30 patients (89%) had attained a mature fusion. In four patients (11%), the fusion mass underwent additional maturation and consolidation between six and 12 months follow-up. However, fusion masses showed no additional maturation in five patients available for follow-up at two years, according to the study.

CT studies showed no evidence of soft tissue ossification, dural ossification or laminar bone regrowth in any patients, the authors noted.

For more information:
Singh K, Smucker J, Rhee J, et al. Use of recombinant human bone morphogenetic protein-2 as an adjunct in posterolateral lumbar spine fusion CT-scan analysis at one and two years. #60. Presented at the North American Spine Society 20th Annual Meeting. Sept. 27-Oct.1, 2005. Philadelphia.