Histological Analysis of a Displaced Femoral Ring Allograft Spacer Filled with a Recombinant Human Bone Morphogenetic Protein-2-Soaked Collagen Sponge: A Case Report

Abstract

R ecombinant human bone morphogenetic protein-2 (rhBMP-2) has been tested as a bone-graft substitute in randomized, prospective clinical trials since 19971-4. In certain procedures, its efficacy with regard to both arthrodesis rates and clinical outcome has equaled that obtained with iliac crest bone graft. The United States Food and Drug Administration recently approved the use of rhBMP-2 as a bone-graft replacement during anterior lumbar interbody arthrodesis in conjunction with a tapered, threaded intervertebral cage (LT-CAGE; Medtronic Sofamor Danek, Minneapolis, Minnesota). Although the Food and Drug Administration has approved the use of rhBMP-2 only in conjunction with the LT-CAGE device, an off-label use of rhBMP-2 with structural allograft bone in anterior lumbar interbody arthrodesis has been reported. A pilot clinical trial in which allograft bone dowels and an rhBMP-2-soaked absorbable collagen sponge were used for lumbar interbody arthrodesis demonstrated favorable outcomes and good arthrodesis rates3. There have been some concerns about the potential up-regulation of osteoclastic activity leading to rapid resorption of the allograft when the allograft is used with rhBMP-2. Some of this concern originates from the fact that rhBMP-2 can stimulate differentiation and enhance survival of some populations of osteoclasts5. However, thus far, this concern has not been clearly validated in basic science or clinical investigations. In fact, rhBMP-2 has been used to enhance healing of allograft fractures in rats6 and to enhance the biomechanical properties of allograft-native bone interface in dogs7. We report a case in which a femoral ring spacer filled with an rhBMP-2-soaked sponge was retrieved from a woman who had undergone a combined anterior and posterior spinal reconstruction but had early dislodgment of the interbody graft. To our knowledge, this is the first report of retrieval and analysis of an rhBMP-2-soaked collagen sponge in …