@ TD,yes 2 new knee's will be required at some stage.Although I have other problems with my leg.Some years ago while I was waiting for the bus to move off before I crossed the road a drunk driver skidded across the road and ploughed into me and my ex wife.
My right leg was badly broken,it was a compound fracture that took ages to heal.I spent 9 months in a full leg cast and nearly two years off work.I also had a broken arm and fractured shoulder.My ex wife had a fractured pelvis and broken leg.The impact knocked her through a privet hedge into a garden.
I went back to doing my job of a joiner,but over the years the physical strain of all the kneeling,climbing etc took its toll and now my knee's,bones and ankles all have severe arthritis.