Stapes surgery for otosclerosis: Towards individualized patient care

Otosclerosis is a localized disorder that is characterized by a deposition of abnormal sponge-like bone in the otic capsule. Fixation of the stapes footplate in the oval window niche results in a conductive hearing loss, which can be treated conservatively using hearing aids, or surgically in a procedure called stapedotomy. In stapedotomy, the stapes arch is removed and a small fenestration is made in the stapes footplate. A prosthesis is placed between the incus and the fenestration in the stapes footplate. Success percentages of primary stapedotomy range between 72 and 94%.

The effect of prosthesis shaft diameter is one quality that has been the subject of research for the last few decades. Evaluation of the available literature revealed 12 cohort studies on this topic, the majority of which showed neither a statistically significant nor a clinically relevant difference between two prostheses with a different diameter piston. Two studies reached statistical significance and both of these studies favored the use of a larger-diameter piston with a difference in success of 31% and a difference in mean postoperative air-bone gap of 2 to 3 dB. The effects of different prosthesis shaft diameters were also evaluated in a temporal bone model. At midrange frequencies, between 500 and 4000 Hz, round window velocities increased by 2 to 3 dB using a 0.6-mm-diameter piston compared to a 0.4-mm-diameter piston. The use of a 0.8-mm-diameter piston led to a further increase in round window velocities of 2 to 4 dB.

Prostheses can be crimped to the incus in various fashions. Some prostheses do not require crimping at all whereas others are crimped using manual force or heat. In a systematic literature search, 22 studies were identified that evaluated the effect of different crimping techniques on hearing outcomes. The differences in success and mean postoperative air-bone gap were not consistently in favor of one crimping method. However, the differences that were statistically significant were consistently in favor of heat crimping over manual and no crimping with differences in success between 22 and 53%, and differences in mean postoperative air-bone gap between 4 and 9 dB. Furthermore, the differences that were statistically significant were consistently in favor of manual crimping over no crimping with a 30% difference in success and a difference in mean postoperative air-bone gap between 3 and 6 dB.

A substantial number of patients require revision stapes surgery because they suffer from a recurrent or residual conductive hearing loss following primary surgery. Surgical outcomes of revision surgery are less favorable than those of primary surgery with reported success percentages ranging between 40 and 80%. Furthermore, revision surgery is associated with a relatively high risk of postoperative sensorineural hearing loss of 1 to 8%. We developed an internally validated prediction model for success. Previous surgical technique, primary cause of failure leading up to revision stapes surgery and type of the prosthesis placed during revision surgery were associated with treatment success. We developed a similar model predicting sensorineural hearing loss following revision stapes surgery. Preoperative presence of vertigo, presence of oval window obliteration and type of the prosthesis placed during revision surgery were associated with postoperative sensorineural hearing loss.

Prosthesis dislocation is a positive factor for success compared to other primary causes of failure. A diagnostic test that accurately assesses crimping status following stapes surgery may be helpful in diagnosing the primary cause of failure before revision surgery and thus in preoperative counseling of patients. We investigated the role of wideband acoustic immitance measurements in assessing crimping status following stapedotomy in a temporal bone model. Stapedotomy changed the absorbance curve significantly, but the crimping conditions did not differ from one another.