In stapedectomy for otosclerosis, the prosthesis is placed from the long process of the incus to the vestibule (oval window). The Carhart's notch seen in the bone conduction audiogram of otosclerosis patients at 2000 Hz improves after successful stapedectomy because:

• A Cochlear blood supply improves due to vascular spread of otosclerosis being reversed
• B New bone remodeling from otosclerosis at the cochlear endosteum is halted by surgery
• C The notch represents a mechanical impedance artifact due to stapes fixation, not true cochlear loss, and resolves when stapes mobility is restored ✓
• D The inflammatory mediators from otosclerotic foci are removed, allowing hair cell recovery

Explanation

Carhart's notch is a mechanical artifact — the stapes normally contributes to the inertia mechanism of bone conduction by vibrating along with the ossicular chain. When the stapes is fixed (otosclerosis), this inertial component of bone conduction is abolished specifically around 2000 Hz (the resonant frequency of the ossicular chain), producing a characteristic 2 dB dip at 500 Hz, 5 dB at 1000 Hz, 10–15 dB at 2000 Hz, and 5 dB at 4000 Hz. After successful stapedectomy (restoration of stapes mobility), the inertial component returns, Carhart's notch disappears, and bone conduction improves by the corresponding amounts — confirming that this bone conduction loss was mechanical (apparent) rather than true sensorineural.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.