Ten RA subjects with unilateral knee synovitis, who have not responded to methotrexate, will be recruited from our early RA Clinics. Following enrollment, the subjects will have a technetium sulfur colloid scan performed on both lower extremities followed by a baseline 3 Tesla contrast-enhanced magnetic resonance imaging (3T CE-MRI) study and Doppler US on the involved knee as described below. The overall disease activity will be determined by the DAS 28 and activity in the involved knee with the RAOS instrument; an outcome measure that quantifies the degree of tenderness, swelling and function in monoarthritis. The subjects will then receive 18 weeks of certolizumab and three of the ten subjects will undergo repeat technetium sulfur colloid scans. To test our hypotheses, we will select three responders based on the RAOS response. We will select only three of the 10 for repeat nuclear studies because this number of subjects will allow us to test our hypothesis without the need to perform the scan on all the subjects. All ten subjects with have 3T CE-MRI, Doppler US and clinical evaluations performed at the 18 week time point. The subjects will continue on certolizumab for a total of 24 weeks.