People over age 65 who suffer from osteoarthritis (OA) of the knee may have an effective treatment option with Voltaren (diclofenac sodium) gel, a new study suggests. In the trial, 492 patients received either the gel or a placebo four times per day on a knee affected by OA. Patients who received the Voltaren gel showed significantly less pain and better movement in the joint than those who were given the placebo.