A histopathological study after vocal fold injection of calcium phosphate paste

Abstract

Problem: The injection of space-occupying materials into the lateral vocal fold is the commonly used technique for vocal fold (VF) medialization. The ideal injectable material would be biocompatible, nonreactive, nonvolatile, noncarcinogenic, and easily injected and would maintain its volume and position after injection. It is also clinically important that it be easily prepared. In Japan, aside from autologus tissue (fat, etc), the only available injectable material is atelocollagen. However, it is quickly absorbed and needs repeat injection; therefore, a new injectable material is needed. Calcium phosphate paste (CPP) (BIOPEX, Mitsubishi Materials Corporation, Tokyo) is currently used in a wide variety of surgical settings including orthopedic procedures and craniofacial reconstructions, and has been proved to be safe and injectable. In this study we examined if CPP could be used as an injectable material for VF medialization. Using rabbit models, soft tissue response and the migratory and absorption property of CPP were investigated. Methods: New Zealand white rabbits underwent left recurrent laryngeal nerve section for denervation and CPP was injected into the paraglottic space. One, 3, and 6 after the operation, the animals were painlessly euthanized, the larynges were excised, and histopathologic, volume, and migration analysis were performed. Results: The position of CPP was stable in the paraglottic space and the volume remained constant through all time periods. Thin fibrous encapsulation around CPP was also observed and remained unchanged when compared at one, three, and six months after injection. A very small number of local foreign body giant cells were observed; however, there was no apparent infiltration of inflammatory cells. Three and 6 months after injection, ossification adjacent to the thyroid cartilage was observed. Conclusion: After vocal fold injection using CPP in rabbit, soft tissue response was minimal, and the volume and position of CPP were stable. Significance: CPP could be used as a new injectable material for VF medialization. Support: None reported.