PORTLAND, Ore. - Osteo-arthritis of the knee is a painful and often debilitating condition, and a new study reveals that nearly half of all Americans will suffer from it.

When the cartilage that cushions the joint is worn away, the pain worsens over time and there is no cure.

Dr. Jim Chesnutt, the medical director of sports medicine at Oregon Health and Science University, said the study's findings are no surprise and that rising obesity rates are the reason.

Hospitalizations related to the disease are also on the rise, mostly due to knee replacement surgery.  But that can be costly, and it's not always an option.

The good news? There are a few other promising therapies.

The first is injections.      

The so-called joint lubrication is injected directly into the knee. The lubricant provides a barrier between the bones and lasts anywhere from four to six months.

The shots can be expensive but Chesnutt puts it in perspective: "Compared to the cost of a knee replacement surgery, they are quite a bit less expensive."

Exercise is also a very effective way to manage the pain.

There are a couple of reasons why it works. First you have stronger muscles that are better shock absorbers for your joints. Secondly, if you are active you produce a better joint fluid to lubricate your joints. Finally the subsequent weight loss also helps ease knee pain.

Surgery is the ultimate therapy for arthritis patients, but, according to doctors, you can only get one replacement for each knee in your lifetime. So if patients get one too soon they run the risk of wearing it out.