You are both right. Up until age 90, more women than men have total knee replacements (TKR). According to a study of Medicare claims for adults over age 65, two-thirds of the TKRs were done in women. One-third were men. Presumably this is because more women have arthritis than men do.
Fewer women have TKRs as they get older because older women are more likely than older men to be living alone. Lack of family or social support might explain fewer numbers of older women having TKR.