So far my knees are still working just fine! It's one of the few parts of my body I can say that about.
My wife has had arthroscopic surgery on both knees so I have some personal knowledge of knee problems. It worked fairly well for her but it’s been about six months and she still can’t squat.
She is still very limited in how far she can bend her knees. Her doctor tells her it will take time but eventually she should be 100 percent.

Knee pain is the most common musculoskeletal complaint that brings people to their doctor. With today’s increasingly active society, the number of knee problems is increasing. Knee pain has a wide variety of specific causes and treatments. My wife damaged her knees by jogging. This is a very common way of hurting your knees. You have to be careful of the type of surface you run on and it’s very important you run correctly. The average person has no idea that they are probably running incorrectly and will damage their knees if they continue to run in this manner. If you are thinking about starting to run please see a physical therapist or doctor so that they can watch you and improve your running style before you do damage.

Other Causes:

Arthritis. Osteoarthritis,Bursitis,Fractures,Ligament injury or instability are just a few.

Diagnosis:

Knee pain can be diagnosed and treated by an orthopedic surgeon.
The knee will be bent to determine the range of motion and palpated (felt with the hands) to detect the presence of any abnormalities. The physical exam may include any of a number of different tests designed to detect injuries by manipulating the knee and leg. X-rays may be taken. In some cases more advanced testing may be carried out using MRI's,CT or contrast arthrography(X-ray following injection of a contrast solution).

Treatments:

Rest, Ice, Elevation are all things you can try on your own.
Your doctor can try Anti-inflammatory medications, Physical Therapy, and Cortisone injections.
Surgery again is a last option Arthroscopy is usually a outpatient procedure and you will be up and walking the same day. This is the procedure my wife had. She had both knees done at the same time. She was in pain for a while but it has gotten much better over time. Total Knee replacement is becoming easier and more effective than ever. They have new artificial joint (prostheses) made of metal alloys, high-grade plastics and polymers. They usually have you walking the same day, which is incredible.