<prompt> The part most commonly involved in otosclerosis is:Oval windowRound windowTympanic membraneMalleus  <response>: a Oval windowRef. Cummings, 6th ed., 2211Since the most common site of origin of otosclerosis is fissula ante fenestrum, the overgrowth from here comes over the footplate of stapes lying over the oval window. So the part most commonly involved in otosclerosis is oval window. 