The stapes is the smallest and lightest bone in the human body, shaped like a stirrup (Latin: stapes). Its head articulates with the lenticular process of the incus, and its footplate occupies the oval window of the cochlea, transmitting sound vibrations directly to the perilymph of the inner ear. Two crura (anterior and posterior) connect the head to the oval footplate. The stapedius muscle tendon attaches to the posterior crus.
Otosclerosis, a pathological fixation of the stapes footplate by new bone deposition in the oval window niche, is the most common cause of progressive conductive hearing loss in adults. Stapedotomy (creating a small fenestration in the fixed footplate and placing a piston prosthesis from the incus to the fenestration) has 90-95% success in restoring hearing. The acoustic reflex, tested by impedance audiometry, evaluates stapedius muscle contraction in response to loud sound, providing information about facial nerve and auditory pathway integrity.
Pathological bony fixation of the stapes footplate in the oval window niche produces slowly progressive bilateral conductive hearing loss in adults, with characteristic audiometric findings of a Carhart notch at 2000 Hz, managed with hearing aids or stapedotomy with piston prosthesis placement.
Traumatic disruption of the annular ligament around the stapes footplate, from forceful Valsalva, direct head trauma, or extreme pressure change, allows perilymph leakage into the middle ear, producing fluctuating sensorineural hearing loss, tinnitus, and vestibular symptoms.
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