United Kingdom, June 23 -- Madonna has a "bad knee" after years of dancing in high heels.

The 67-year-old pop star has explained that she doesn't work out every day because of the damage caused to her knee.

Speaking to Interview magazine, Madonna said: "I have a bad knee now.

"I have no cartilage in it, thanks to dancing for so long in high heels and running on pavement and doing Ashtanga yoga."

Madonna has been forced to change her gym plan over the last 12 months.

The chart-topping singer - who is one of the best-selling musicians of all time - shared: "Up until a year ago, I was jumping on trampolines and doing dance cardio and doing a lot of what a doctor would call loading on my joints. Can't do that anymore."

Madonna still wor...