I have had two arthroscopies and was diagnosed withchronic arthritis. Most of the times, I get jaw inflamation andpain. How can TMJ synovitis be treated?

Anti-infamammatory . Synovitis is an of inflammation of the fluid in the joint. Non surgical treatment of inflammation options include anti-inflammatory medication, steroids, iontophoresis of medications, and sometimes electrical acupuncture can be helpful. It may be that you will need to take anti-inflammatoiries until the arthritis is reduced.
Various. The are various ways to treat your condition, from non invasive bite splints, cold laser, physiotherapy, to invasive injections and surgical procedures. Best to see a dentist who has experience in all phases of TMJ and facial pain.
Resting Jaw. Resting jaw, moist heat and cold packs and limit the jaw to small motions and diet to soft foods to avoid further irritation. It is the same condition as any other arthritic joint in the body. Motrin helps with the pain and a bite guard will help lessen pressure on the joint.
TMJ expert. It sounds like your arthroscopies were not successful. See another surgeon who specialized in TMJ for another opinion. Make sure you're also being managed by a true TMJ expert (non-surgical).