stapes

The stapes, commonly known as the stirrup bone, is the innermost of the three auditory ossicles in the middle ear, along with the malleus (hammer) and incus (anvil). It is one of the smallest bones in the human body, measuring roughly 3.5 millimeters in length. The stapes consists of a head that articulates with the incus, a neck, and two limbs called the anterior and posterior crura, which merge into a slender footplate that fits into the oval window of the cochlea. The bone is stabilized by ligaments and surrounding tissues in the middle ear.

In its role within the auditory chain, the stapes transmits sound-induced vibrations from the eardrum via the malleus and incus to the perilymph of the inner ear through the oval window. The movement of the footplate causes pressure waves in the cochlear fluids, enabling hair cells to convert mechanical energy into neural signals. The ossicles collectively provide impedance matching, enhancing the efficiency of sound transmission from air to the fluid-filled inner ear.

The stapedius muscle attaches to the neck of the stapes. When the muscle contracts, it dampens the movement of the stapes, reducing vibration transmission to protect the inner ear from loud sounds—a reflex known as the acoustic or stapedius reflex.

Clinically, impaired mobility of the stapes, as in otosclerosis, can cause conductive hearing loss. Surgical procedures such as stapedectomy or stapedotomy with a prosthetic replacement are used to restore mobility and hearing in selected patients.