The synovial membrane is thought to play an important role in both the clinical and the anatomical evolution of osteoarthritis. Arthroscopy performed under local anaesthesia on an outpatient basis has been proposed as a means of cartilage and synovial assessment for research purposes. The authors propose a scoring system for assessing anterior synovial abnormalities at arthroscopy in knee osteoarthritis. This synovitis score takes into account the intensity and the extent of synovial lesions.