A Study of Liquid Certolizumab Pegol as Additional Medication to Methotrexate in the Treatment of Signs and Symptoms of Rheumatoid Arthritis and in Prevention of Joint Damage in Patients With Active Rheumatoid Arthritis

Inclusion Criteria: * Patients must be at least 18 years old at the screening visit. * Patients must have a diagnosis of adult-onset RA of at least six months duration but not longer than fifteen years as defined by the 1987 American College of Rheumatology classification criteria. * Patients must have active RA disease as defined by: * 9 tender joints at Screening and Baseline. * 9 swollen joints at Screening and Baseline. and fulfilling 1 of the following 2 criteria during the screening period: * 30 mm/hour ESR (Westergren), or CRP \>15 mg/L. * Patients must have received treatment with MTX (with or without folic acid) for at least 6 months prior to the Baseline visit. The dose of MTX and route of administration must have been stable for at least 2 months prior to the baseline visit. The minimum stable dose of MTX allowed is 10 mg weekly. * Patients must be willing to complete an X-ray of the hands and feet 24 weeks after randomization even if they are no longer receiving study treatment in the present study, provided they have not withdrawn their informed consent. Exclusion Criteria: * Patients must not have a diagnosis of any other inflammatory arthritis (e.g., psoriatic arthritis or ankylosing spondylitis). * Patients must not have a secondary, non-inflammatory type of arthritis (e.g. OA or fibromyalgia) * Female patients who are breast feeding, pregnant, or plan to become pregnant during the trial or for three months following last dose of study drug. * Patients with a history of tuberculosis or positive chest X-ray for tuberculosis or positive * Patients at a high risk of infection (e.g. leg ulcers, indwelling urinary catheter and persistent or recurrent chest infections and patients who are permanently bed ridden or wheelchair bound). * Patients with known human immunodeficiency virus (HIV) infection. * Patients with an active malignancy of any type or a history of malignancy (except basal cell carcinoma of the skin that has been excised prior to study start). * Patients with a current or recent history, as determined by the Investigator, of severe, progressive, and/or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, cardiac, neurological, or cerebral disease which would interfere with the patient's participation in the trial. * Patients with a history of, or suspected, demyelinating disease of the central nervous system (e.g. multiple sclerosis or optic neuritis).