The part most commonly involved in otosclerosis is:
(a) Oval window(Ref. Cummings, 6th ed., 2211)Since 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.
Oval window
Round window
Tympanic membrane
Malleus
Otosclerosis