Not necessarily, they may have "medical history disregarded" policies. Much cheaper to get it through a company group scheme, but I suspect this isn't an option for you (and if it was, I'm assuming you didn't elect it and can only renew an anniversaries). It's pretty pricey otherwise unfortunately - when I was between jobs a few years ago it cost me about £40 a month to retain my BUPA cover as an individual.
Assuming this is around the knee, best to wait and see what the doctor says - a consultation with a specialist may be a much shorter waiting list than any potential surgery (sorry if I misled you here)