Biocompatibility of Nitinol Stapes Prosthesis

Abstract

OBJECTIVE: Use of the SMart piston, a nitinol-based, self-crimping prosthesis in stapes surgery may allow improved functional results because of better sound transmission properties at the incus-prosthesis interface because of the elimination of manual crimping. Possible disadvantages include thermal damage or strangulation of the incus and its mucoperiosteum or nickel intolerance. The goal of this study was to morphologically assess the fixation of this prosthesis to the incus, investigate the reaction of the middle ear mucosa to the prosthesis, identify alterations to the incudal bone, and detect deposits of nickel in the tissue around the prosthesis. STUDY DESIGN:: Prospective consecutive case analysis. SETTING:: Tertiary referral center. PATIENTS: Four patients with an unfavorable functional result after primary SMart-piston stapedotomy. INTERVENTION: Revision malleostapedotomy with explantation of the incus and prosthesis for further analysis. MAIN OUTCOME MEASURES: Analysis of intraoperative findings and postoperative examination of the explants using light- and scanning-electron microscopy, energy dispersive x-ray analysis, and atom absorption spectrometry. RESULTS:: The intraoperative, macroscopic, and scanning electron microscopic investigation showed tight circular fixation of the prostheses, whereas a gap between the prosthesis and the lateral incus was found in 1 case. All prostheses were overgrown by mucosa. Superficial localized erosion of the incudal bone was found in 2 cases. There was no elevation in nickel content in the removed tissue samples. CONCLUSION:: The lateral gap between prosthesis and incus did not affect fixation of the prosthesis, neither did covering by a mucosal layer. Bone erosion was most likely caused by laser in one and by the prosthesis in another explant. No signs of increased nickel deposits could be found on energy dispersive x-ray analysis or atom absorption spectrometry. We conclude that a nitinol stapes prosthesis is safe for treatment of stapedial fixation.