The purpose of this study is to determine whether hypnosis intervention added to usual care is more effective than usual care alone to control pain during lavage procedure in patients with knee osteoarthrosis

Joint lavage can be used in acute knee osteoarthritis, and can be repeated when it is effective. This procedure can generate pain and anxiety which are prevented by systematic prescription of analgesics and anxiolytics. To assess the benefit of hypnosis intervention, the investigators designed a monocentric prospective controlled randomised, single-blind study. Patients with acute and painful knee osteoarthritis, having an indication of lavage according to the rheumatologist, will be randomized to standard care, versus standard care and hypnosis. The hypothesis is that hypnosis intervention will decrease the level of pain during lavage, and the analgesics consumption during the week following the lavage. The sample size will be 100, 50 patients per group. Inclusion is scheduled for 18 months, and duration of the study will be 2 years. The main efficacy criterion is the pain score (assessed using VAS) difference between the 2groups; no interim analysis will be performed.

Inclusion Criteria:

• diagnosis of knee osteoarthritis
• indication for a lavage

Exclusion Criteria:

• People who have had both knees washed on the same day.
• People who have already received a joint lavage.
• Patients with psychotic disorders.
• Refusal to participate.
• People who do not understand and/or speak French or who are deaf.