300 patients with knee osteoarthritis were included in this 2x2 factorial randomized controlled trial. The objective of this trial was 2-fold; 1) determine if the addition of manual therapy to exercise therapy provided improvements in pain and function outcomes, and 2) determine if the use of booster sessions sustained the improvements observed at the short-term follow-up. Patients were randomized into 4 groups; 1) exercise therapy for 9 weeks with no booster sessions, 2) exercise and manual therapy for 9 weeks with no booster sessions, 3) exercise therapy for 9 weeks with booster sessions, or 4) exercise and manual therapy for 9 weeks with booster sessions. There were no differences between groups in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at 1 year. Manual therapy was associated with a transient effect of improving outcome on the WOMAC and the likelihood of being a treatment responder within the first 9 weeks, though these were not sustained at 12 months. The only significant effect observed with booster sessions was a significantly increased likelihood of being a treatment responder at 12 months.