I was hit by a bus while crossing the street. An MRI showed a torn piece of cartilage and bone in the back of my knee. The doctors don't think they can repair the damage without opening the knee up. Why can't they use a scope like they did last year when they repaired the meniscus in my other knee?

You may have to ask your doctors to know for sure. Without all the details, we can only make an educated guess.

Most areas inside the knee joint can be reached with an arthroscope. This depends on where the doctor inserts the tool from outside the joint. The damage to your knee may be too hard to reach even with an arthroscope. In cases like this, the doctors can do surgery the "old-fashioned" way by opening the joint up.

Or they may be able to combine the use of the arthroscope with a small incision. This is called a mini-open procedure. As surgical instruments become more and more specialized, companies are making newer and better tools for use in arthroscopy.

Recently, a group of doctors in Italy reported on just such a case. A 25-year old man was involved in a car accident that left a hole in the knee. A piece of cartilage deep enough to include attached bone was ripped away from the joint. Cartilage was harvested from the joint, grown in a lab, and reinserted into the hole. A special glue was used to hold the graft in place.

The entire operation was done arthroscopically. The authors report they couldn't do this type of operation without instruments made just for the procedure. It's probably only a matter of time before all joint operations are done this way.