Arthroscopy (also called arthroscopic surgery) is a minimally invasive surgical procedure in which an examination and sometimes treatment of damage of the interior of a joint is performed using an arthroscope, a type of endoscope that is inserted into the joint through a small incision. Arthroscopic procedures can be performed either to evaluate or to treat many orthopaedic conditions including torn floating cartilage, torn surface cartilage, ACL reconstruction, and trimming damaged cartilage.

The advantage of arthroscopy over traditional open surgery is that the joint does not have to be opened up fully. Instead, only two small incisions are made - one for the arthroscope and one for the surgical instruments. This reduces recovery time and may increase the rate of surgical success due to less trauma to the connective tissue. It is especially useful for professional athletes, who frequently injure knee joints and require fast healing time. There is also less scarring, because of the smaller incisions. Irrigation fluid is used to distend the joint and make a surgical space. Sometimes this fluid leaks into the surrounding soft tissue causing extravasation and edema

From http://en.wikipedia.org/wiki/Arthroscopy