Otosclerosis and Stapedectomy: Surgical Treatment of Hearing Loss

Otosclerosis is a remodelling disorder characterised by abnormal osteoclast and osteoblast activation in the temporal bone. This process affects otherwise normal bone tissue; in otosclerosis, ectopic foci begin primarily from the fissula ante fenestram area at the anterior margin of the oval window. The densifying bone tissue fixes the stapes base and impedes sound conduction. Cochlear otosclerosis is less common and adds a sensorineural loss component by disrupting endocochlear fluid biochemistry.

The genetic basis is strong: 25-40% of otosclerosis cases are familial. Variants identified in genes such as TGFB1 (transforming growth factor beta-1), COL1A1 (Type I collagen) and BMP2/4 increase disease risk. Autosomal dominant inheritance is transmitted with 25-40% penetrance, meaning a carrier individual will not always develop symptoms. Evidence exists that rubella infection may be a triggering factor.

Epidemiologically, prevalence in the Caucasian race is 0.3-1%. It is 2:1 more common in women than men; pregnancy coincides with symptom flares (oestrogen effect). The disease typically begins in the 2nd-4th decade; new diagnosis in old age is rare. Bilateral involvement is seen in 70-80% of cases, potentially starting in one ear and progressing to the other.

The main symptom of otosclerosis is usually slowly progressing bilateral hearing loss beginning with difficulty hearing whispered speech. The paradoxical hearing phenomenon called paracusis Willisii — hearing better in noisy environments (crowds, traffic) — is nearly pathognomonic for the disease; the sound pressure effect of background noise masking the conductive loss explains this. Tinnitus accompanies the condition in 50-80% of patients.

Pure-tone audiometry is the cornerstone of diagnosis. Conductive hearing loss pattern: elevated air conduction thresholds, relatively preserved bone conduction thresholds. The noteworthy finding is the Carhart notch: specific to otosclerosis, a mechanical dip (typically 5-15 dB) in the bone conduction threshold at 2000 Hz. This notch is not a true sensorineural loss but a mechanical effect of stapes fixation on bone conduction; it usually corrects after successful surgery.

Impedancemetry (tympanic membrane movement measurement) helps exclude other causes of conductive loss (otitis media, malleus fixation) with the As-type (reduced compliance, flat, plateau) tympanogram pattern. Otoscopic examination is usually normal; middle ear disease is excluded. Flamingo pink appearance (Schwartze sign) reflects an active vascular otosclerotic focus; rare but characteristic on physical examination.

Sodium fluoride (NaF) slows disease progression by reducing the elevated bone turnover in otosclerotic foci. Daily 20-40 mg fluoride supplementation is used in patients with positive Schwartze sign (active vascular focus) or evidence of active progression. Literature exists supporting its effectiveness in stabilising hearing thresholds; however, it does not reverse existing hearing loss.

Side effects include gastrointestinal discomfort (minimised by taking with calcium), bone fluorosis (at high doses) and rarely renal toxicity. Not recommended in pregnancy. The definitive indications for fluoride capsule therapy are debated; some guidelines only recommend it in young patients showing active progression or when cumulative radiological findings are present before surgery.

Bisphosphonates (alendronate, risedronate) have a theoretical mechanism of action by suppressing osteoclast activation, but the evidence level in ear otosclerosis is low. Assessment and replacement of 25-OH vitamin D level is a rational complementary approach, since vitamin D deficiency may increase aggressive bone turnover.

In classic stapedectomy, the entire stapes is removed and a connective tissue patch and prosthesis are inserted. Stapedotomy — now the more widely preferred technique — is performed by creating a small fenestration (0.6-0.8 mm diameter hole) in the stapes footplate; there is no need to remove the entire stapes. Laser-assisted stapedotomy (KTP or argon) reduces mechanical trauma and cochlear blast risk when perforating the footplate.

Prosthesis selection is a critical factor. Teflon piston prostheses (0.4-0.6 mm diameter), once connected to the incudostapedial joint, transmit fluid vibrations to the inner ear through the oval window. Titanium prostheses are preferred for MRI compatibility. Prosthesis length is individually selected between 4.0-4.5 mm; insufficient or excess length impairs long-term outcomes.

Surgery is performed under local or general anaesthesia. The tympanic membrane is elevated through an endaural incision and the middle ear is exposed. Surgical time is typically 45-90 minutes; hospital admission is same-day. Dizziness is an expected transient complication in the first 24-48 hours post-surgery. Sudden hearing worsening or severe vertigo are alarm signs requiring immediate reporting.

In successful stapedotomy, the air-bone gap is expected to close to 10 dB or less. Results from series: clinically significant hearing gain in 85-95% of patients, normal or near-normal hearing thresholds in 70-80%. Success criteria vary by surgeon experience, prosthesis choice and disease stage. In long-term follow-up at 10 years, the rate of preservation of initial gain is approximately 80-85%.

Complications are rare but serious. The most severe risk is total cochlear hearing loss (SHL): occurs in 0.5-1% of cases. Other complications: chorda tympani nerve damage (taste disturbance, 3-10%, mostly transient), vertigo (persistent form 1-3%), tinnitus increase, facial nerve paresis (rare, <0.5%), prosthesis dislocation (1-3%). Because of cochlear damage risk, simultaneous bilateral surgery is never performed; at least 6-12 months apart.

Hearing aid is a strong alternative for those not wishing surgery or with poor general health. Traditional behind-the-ear (BTE) devices are appropriate for otosclerosis. Bone-conducted hearing aids (BAHA, Osia, Sophono) are preferred when there is active middle ear infection or a significant cochlear component. All treatment options are presented after multidisciplinary assessment.

If hearing loss worsens again after initial stapedotomy, revision stapedotomy is considered. Revision cases are technically more challenging: fibrous adhesions, prosthesis displacement and debris (granulation tissue) complicate surgery. Success rates are below those of primary surgery (60-80%), but satisfactory results are reported in experienced surgeons.

A significant sensorineural component can develop in cochlear otosclerosis or after prolonged failed stapedotomy. Cochlear implant guidelines apply when moderate-to-deep hearing loss accompanies a good speech discrimination score. Cochlear implant surgery in otosclerosis patients is somewhat more challenging (dense channels, potential facial nerve aberration); however, success rates are comparable to the general population in experienced centres.

Individual assessment for each patient is critical. Thyroid supplementation, vitamin D deficiency, cardiac status and anaesthesia risk are all factored into determining surgical suitability. All cases and treatment plans are evaluated at our clinic's multidisciplinary otology board; for international patients, a detailed English report is provided through tele-tip consultation.