Hi!
I am sorry to hear about your medical problems. I am sorry, but you cannot fix this on your own. You need to see an orthopedic specialist for this. But your GP may be a good place to start with.
If the pain comes on bending the knee as in walking step or running downhill or down a flight of stairs, then it could be due to Patellofemoral syndrome or runners knee. This happens due to mal-alignment of the knee cap on bending the knee (and hence any imaging study has to be taken with the knee bent), injury to the knee (you may have sustained it in past), flat feet, over tight or over lax muscles around the knee joint. All these aspects will have to be investigated by your doctor. Other possibilities are bursitis (inflammation of fluid filled sac over joints), tendonitis (inflammation of cords joining muscles to bones) or due to weakness of patellar bone. Please discuss all these possibilities with your treating doctor. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.
I partially disagree with DR. Kokil on this one.
I suspect he is correct about the "runner's knee," but most medical persons (and people in general) over look some important soft tissue issues. Number one being uneven muscle/soft tissue development or rehab.
Males tend to have more knee problems than females, and one reason is something I like to call the "Suzanne Somers Thigh Master exercise."
Males tend to not do this sort of muscle strengthening/toning, so they get tighter lateral quads than inner. Therefor, the knee tends to be pulled of of tracking alignment. Look at your knees while relaxed. I bet the inner muscles look more puffy than the outer? That's because they are not as toned/tight.
Now Dr. Kokil is probably right that at this point you need to make sure there is no damage. However, if there is no structural damage, the exercises should do you a world of good. Even if there is damage, it would most likely allow that to heal, or greatly improve the healing.