Arthroscopy is used by rheumatologists for research purposes in cases with knee osteoarthritis and inflammatory arthritis. This chapter explains the technical characteristics of 'research arthroscopy' including the simplification of the procedure, video-recording, as well as risks and training. Lavage of the knee joint is proposed as a treatment procedure for osteoarthritis and inflammatory and septic arthritis. Tidal irrigation and the two-needle technique of lavage are described. In the absence of clear predictive factors for efficacy, the indications for these techniques are a matter of debate.