Inflammatory Characteristics of rhBMP-2 In Vitro and in an In Vivo Rodent Model

Study Design. In vivo and in vitro model. Objective. Investigate soft-tissue inflammation caused by rhBMP-2. Summary of Background Data. Although rhBMP-2 produces excellent rates of fusion in the spine, dysphagia and respiratory compromise have occurred when used in the neck. The mechanism of the swelling and inflammatory response has yet to be fully elucidated. Methods. ELISA kits (IL-6, IL-10, TNF-alpha) were used to measure cytokine levels at different concentrations of rhBMP-2. Absorbable collagen sponges were implanted with or without different concentrations of rhBMP-2 into the backs of rats subcutaneously (SC) and intramuscularly (IM). Magnetic resonance imaging was used to measure inflammation at 3 hours and 2, 4, and 7 days. The inflammatory volumes were measured and compared using MIPAV software. Rats were killed after 7 days and studied. Results. IL-6, IL-10, and TNF-alpha release was dose-dependent. Soft-tissue edema after rhBMP-2 implantation was also dose-dependent, peaking at 3 hours SC, after SC and IM implantations, and on day 2 IM after IM implantation. All formed a granuloma-type mass after SC insertion. The mass was much larger in the 10 and 20 mu g/10 mu L (high-concentration) groups. The inflammatory response did not diffuse across physiologic barriers (subcutaneous fascia). Both high-dose groups were associated with encapsulated hematomas and a significant increase in the inflammatory zone. Conclusion. Swelling and inflammation after rhBMP-2 use are dose-dependent. Swelling may be due to direct contact as well as spread in the plane of access. The causes are a robust inflammatory reaction as well as sterile seroma and encapsulated hematoma formation.