"Lavage" means 'washing'. To lavage a joint means to wash out any blood, fluid or loose debris from inside the joint space.

Arthroscopic lavage is generally combined with arthroscopic

Arthroscopy

Arthroscopy 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...

 debridement

Debridement

Debridement is the medical removal of a patient's dead, damaged, or infected tissue to improve the healing potential of the remaining healthy tissue...

, where fronds of joint material or degenerative tissue are removed using a combination of injected fluid and a small vacuum, i.e. both washing (rinsing) and sucking. 'Arthroscopic' means that this is done using a tiny incision at the joint, where a thin arthroscope is pushed into the joint to inspect the structures.

Excessive growth of irritated synovial membrane causes it to increase its surface area by buckling into fronds, and the fronds may become inflamed and pour destructive enzymes into the joint space, causing joint swelling and joint surface destruction. Removing this excess material via lavage frequently resolves arthritic knee inflammation or pain.

Arthroscopic lavage is a minor part of an armamentarium of procedures which are now available to help reverse the damage of early arthritis

Arthritis

Arthritis is a form of joint disorder that involves inflammation of one or more joints....

. There is, however, controversy about the value of simple lavage and debridement for the older patient with established osteoarthritis

Osteoarthritis

Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...

.