The objective of this study is to assess the efficacy of certolizumab pegol (CZP) with methotrexate (MTX) compared with MTX-alone in patients with early-stage rheumatoid arthritis (RA) who are naive to MTX and have with poor prognostic factors, using inhibition of radiographically confirmed joint damage progression over a one-year period as a primary endpoint. Following a year of treatment with CZP plus MTX treatment, CZP will be discontinued, and the subjects will be monitored for one more year (the follow-up period) to investigate the sustainability of efficacy of CZP during the MTX monotherapy for exploratory purposes.