Medplay is an incredibly common kink - and it has a few iterations and subcategories. For obvious reasons, anything specifically gynaecological is particularly popular. Speculums, stimulating or numbing creams, sensation testers such as pinwheels and physical examinations are all appealing both physically and psychologically. Fans of the gyno fetish enjoy them for both the sensations they create and the mindfuck or dynamics they can lead to. There's something uniquely exposing of sitting in a gyno chair and being examined "down there" - and there are plenty of ways for a couple interested in that side of BDSM to use that to their kinky advantage.
Many people love a bit of sexualised roleplay, and medical situations are a pretty common theme in a lot of folk's fantasies. Doctors, nurses, patients and hospitals are all the subject of any number of sexy imaginary scenarios--and while you woudn't want situations like this to arise in real life, they can be an incredibly hot fantasy to act out in the privacy of your own relationship or bedroom!
Medical play is actually a very common and highly varied kink. Fans of the fetish often own plenty of leather and latex, enjoy dressing up in fetishised versions of medical uniforms, and get a big kick out of play that involves various medical accoutrements such as pinwheels, enemas, tongue depressors and metal gags.