Four randomized controlled trials were included in this meta-analysis comparing the efficacy of a specific preparation of topical diclofenac, Pennsaid, to either placebo or oral diclofenac in the treatment of knee osteoarthritis. As compared to placebo, Pennsaid topical diclofenac was associated with significantly better clinical results of the Western Ontario and McMaster Universities Osteoarthritis Index for pain, stiffness, and function, and patient global assessment. In one study, clinical efficacy did not significantly differ between topical and oral diclofenac.