Voltaren Gel (diclofenac sodium topical gel) is a topical gel nonsteroidal anti-inflammatory drug (NSAID) used to treat pain of osteoarthritis of joints that are amenable to topical treatment such the hands and knees. Voltaren Gel contains diclofenac a nonsteroidal anti-inflammatory drug (NSAID). Diclofenac works by reducing substances in the body that cause pain and inflammation. Voltaren Gel is used to treat joint pain caused by osteoarthritis in the hands wrists elbows knees ankles or feet. Voltaren Gel may not be effective in treating arthritis pain elsewhere in the body.