Stapes prosthesis attachment: The effect of crimping on sound transfer in otosclerosis surgery

Objectives/Hypothesis: Although in stapes surgery successful hearing improvement may be achieved in the majority of patients, unsatisfactory closure of the air-bone gap can be recorded. One of many reasons for unexpected failures of stapes surgery may be the insufficient crimping of a stapes prosthesis onto the incus. The objectives of the study were to assess the amount of sound transmission loss in response to the quality of prosthesis crimping and to identify a required loop attachment pattern to obtain good sound transmission results. Study Design: Experimental. Methods A temporal bone model was developed to measure the sound transmission properties between incus and prosthesis on 17 fresh human temporal bones. The attachment of a titanium stapes piston was assessed without crimping, followed by loose crimping and tight fixation to the incus, using scanning laser Doppler interferometry, endoscopic photography, micro grinding technique, and scanning electron microscopy. An algorithm had to be developed to simulate acoustical stimulation using electromechanical stimulation. Results: Optimal tight crimping of the stapes piston revealed consistent good sound transfer function ranging from 0 to 7 dB loss, and loss remained, on average, at 2 dB. The mean transmission losses for conditions of loose crimping and no crimping were surprisingly small (within 10 dB). However, these unusual crimping conditions allowed a wide range of losses up to 28 dB. A close coupling at least at two opposite points was obligatory to obtain consistently good results. Conclusions: Perfect hearing reconstruction necessitates ideal crimping of a prosthesis to obtain consistently good results. However, the final functional gain depends on many different intraoperative and postoperative factors.