The purpose of this proposed study is to conduct a trial with knee OA patients using the diclofenac gel. The effectiveness of diclofenac gel in managing breakthrough pain or the neuropathic components of pain (e.g., the burning, soft tissue joint sensitivity, or allodynic components) in knee OA is unknown. It is likely that patients will use the gel in a as needed (prn) fashion, on top of other analgesics prescribed for their pain. The neuropathic components of a generally nociceptive or inflammatory condition, such as knee OA, are underappreciated, and typically not tracked in OA analgesic studies. Yet, evidence across a variety of chronic painful conditions suggests that these components are quite disabling. The results of this study would show whether diclofenac gel as a prn medication is beneficial to patients suffering from knee OA pain.