This name is given to acute or chronic inflammatory conditions that affect the joints and are accompanied by swelling of the synovial membrane. When only one joint is affected, it is called mono-arthritis. When more than two joints are affected, it is called oligo-arthritis (2 to 4 joints affected), or polyarthritis (more than 4 joints). The term arthritis should not be confused with that of arthralgia which refers to pain, without swelling, of one or more joints.