KTP laser stapedotomy with a self-crimping, thermal shape memory Nitinol piston: follow-up study reporting intermediate-term hearing.

The aim of this study was an evaluation of the mid-term hearing results after the implantation of a self-crimping heat memory Nitinol piston in stapes surgery. The 12-month postoperative results were compared with those at a minimum of 3 years (maximum 6.7, average 4.4 years). The medical records of all 44 patients who underwent surgery with a Nitinol piston for stapes fixation between November 2005 and January 2007 were evaluated retrospectively. The prostheses used in all cases measured either 4.5 or 4.75 × 0.6 mm. We hypothesized that the 12-month postoperative hearing results would be permanent after an average follow-up of 4.4 years. Thirty-two of the 44 consecutive patients were females and 12 were males. Their mean age was 40.4 years (range 27-69). All underwent a 12-month postoperative audiometric evaluation. 38 (30 females, 8 males, average age 45, range 28-77 years) of the 44 were available for mid-term 4.4-year (minimum 3 years, maximum 6.7 years) postoperative audiometric evaluation. The mean air-bone gap (ABG) for the frequencies 0.5, 1, 2 and 3 kHz at the 12-month postoperative follow-up was 11 dB (SD 4.1) and that after an average 4.4-year postoperative evaluation was 6.4 dB (SD 3.6). The mean decrease in ABG after 12 months was 19.5 dB, and that after the average 4.4 years was 21.3 dB. ABG closure within 10 dB was achieved in 77.2 % after 12 months and in 89.5 % after the average 4.4 years. No patient with an ABG > 20 dB was recorded after the average 4.4 years. The mean air conduction threshold at 4 kHz was examined pre and postoperatively so as to indicate any possible inner ear damage. At the 12-month follow-up, the difference between the pre and postoperative values was -2.5 dB, whereas after the average 4.4 years the difference was surprisingly +13 dB. The individual AC improvements were also demonstrated with the use of Amsterdam Hearing Evaluation Plots (AHEPs). The Nitinol prosthesis allowed excellent intraoperative handling and no postoperative complication was reported. As compared with conventional stapes prostheses, the Nitinol-based SMart prosthesis is a safe and reliable stapes prosthesis. Our mid-term audiometric evaluations revealed that the audiometric parameters demonstrated a hearing improvement between the postoperative 12-month and average 4.4-year examinations. We consider the elimination of manual crimping and the use of a "non-touch" hand-held laser technique has a positive impact on the mid-term audiometric results. Most of the previous studies presented only relatively short-term (from 6 weeks up to 6-12 months) audiometric evaluations. Complications are rare, but a longer follow-up is needed to establish the long-term stability.