The aim of this study is to compare the analgesic effect of 1% Hedera helix extract gel with 1% Diclofenac gel on knee pain in osteoarthritis patients. It is a double blind randomized clinical trial. The 1% Hedera helix extract, 1% Diclofenac gel and placebo gel will all be set in A,B, and C tubes by a trustworthy third party and will be handed over to the researcher. 150 patients seeking medical care in orthopedic clinics will randomly receive one of the tubes. The main inclusion criteria is primary osteoarthritis in at least one knee confirmed radiologicaly in the knee plain x-ray, presence of pain for at least 2 weeks before the visit and age of 45 years and older. The main exclusion criteria is secondary osteoarthritis, peptic ulcer, taking corticosteroids for any reason, and using any analgesic topical gel on the knee before the study. Before receiving the gel, patient pain will be assessed using VAS and WOMAC questionnaires. Patients will rub the gel on the affected knee for 6 weeks three times a day, each time for 15-20 minutes. All three groups will receive 200 mg Celecoxib capsules simultaneously to subside the pain. After 6 weeks of administration, patients pain, morning stiffness, daytime stiffness and physical function will be assessed again by VAS and WOMAC.