85-90% of patients, according to most studies, achieve good to excellent results with relief of discomfort and significantly increased activity and mobility. They have little to no pain and are able to get back to their normal activity and often back to a reasonable level of sporting activity. Patients who are in better condition prior to surgery –normal weight, limited medical problems, playing sports before surgery– will typically return to their activity but with far less pain and restriction.
Most knee replacements are implanted in patients 60 years and older. Given the typical 20 year survival of 90% of implants, it is likely that the knee replacement will last the remainder of your life.