Certified Surgical Technologist (CST) Practice Exam

Which anatomical structure is affected by a bony overgrowth encountered in otosclerosis?

1. Incus

2. Stapes

3. Malleus

4. Tympanic membrane

The correct answer is: Stapes

The bony overgrowth encountered in otosclerosis primarily affects the stapes, which is the smallest bone in the human body and is located in the middle ear. In otosclerosis, abnormal bone growth occurs around the stapes or in the area where it articulates with the oval window of the cochlea. This overgrowth leads to stiffness in the ossicular chain, resulting in conductive hearing loss. The stapes is critical for transmitting sound vibrations from the outer ear to the inner ear, and when it becomes immobilized due to otosclerosis, it disrupts the normal hearing process. In contrast, while the incus and malleus are also part of the ossicular chain, they are not the primary structures impacted by the disease. The tympanic membrane is the eardrum, which doesn't undergo bony overgrowth but rather functions as a barrier between the outer ear and the middle ear. Understanding these anatomical relationships helps clarify why the stapes is the most significantly affected structure in cases of otosclerosis.