The Efficacy of Diclofenac Gel for Breakthrough Pain and the Neuropathic Components of Pain in Knee Osteoarthritis

• percent improvement in pain [ Time Frame: participants will be followed for the duration of hospital stay, an expected average of 5 weeks ] [ Designated as safety issue: No ]
  The primary outcome measure is the percent improvement in pain (prior to gel-1 hour after gel) after each diclofenac gel application for breakthrough pain. This is calculated from the pain ratings input into the ED just prior to and after gel application. Sample size calculations use a power of .85, an alpha level of .05, a pre-gel pain level of ~7/10, a standard deviation of response of 1.6, and T test comparisons. We estimate that 30 subjects will be needed to find a 30% improvement in breakthrough pain on average in the cohort.
  
  

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 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.