7:52 Recombinant human bone morphogenic protSD stem–2 in a posterior lumbar interbody fusion construct: 2-year clinical and radiologic outcomes

Abstract

Purpose of study: Recombinant human bone morphogenetic protein (rhBMP)-2 has been demonstrated to form bone in various spine fusion applications as effectively as autologous iliac crest bone, without the morbidity of the graft harvest. Posterior lumbar interbody fusion (PLIF) constructs are commonly used in the treatment of degenerative spinal disease. This study evaluates the use of rhBMP-2 in a PLIF construct.Methods used: This is a prospective, randomized, Food and Drug Administration–approved, IDE study comparing the outcome of PLIF using cylindrical titanium cages loaded with either InFuse Bone Graft (rhBMP-2 in a collagen sponge; Medtronic, Minneapolis, MN) or autologous iliac crest bone graft. Enrollment in the study was stopped at 67 patients after “excess” bone formation was noted posterior to the cage in some patients. Clinical and radiographic assessment of the patients has continued, with a minimum of 2-year follow-up now available. Radiographs were evaluated in a blinded fashion by a panel of surgeons and critically compared to the clinical data.of findings: Recombinant human BMP-2 is at least as effective as autologous iliac bone in this PLIF construct, in terms of promoting radiographic fusion. However, 58% of the rhBMP-2 patients demonstrated “greater than expected bone formation” dorsal to the cage, a finding seen in none of the controls. In 30% of the rhBMP-2 cases, this bone compromised the central canal, the neural foramen or both. At a mean 2-year follow-up, there was no correlation between the clinical outcome (Oswestry, back pain, leg pain or neurological score) and the radiological outcome in either group.Relationship between findings and existing knowledge: Recombinant human BMP-2 is an effective substitute for autogenous iliac crest bone in PLIF constructs. This is the first clinical study to document “excessive” bone formation with the use of BMP, although there was no discernable effect on the clinical outcome. The cause of the bone formation seen in selected cases is not understood, and theories to explain this finding are currently being evaluated.Overall significance of findings: BMP should not be used in PLIF constructs outside of clinical trials at this time.Disclosures: Device or drug: recombinant human bone morphogenetic protein–2. Status: investigational.Conflict of interest: Joseph Alexander, Speaker's Bureau, Mediatronic Sofamor Danek.