New York Times health writer Jane Brody says artificial knees, while certainly an improvement over severely arthritic ones, are not like normal, healthy knees.

Brody had knee replacements three years ago and has returned to dancing, hiking, skating and the active life she lived before developing arthritis.

However, Brody also says that, in some cases, the device fails or there are lasting injuries to internal tissues.

Click here to read her column.