The Effects of Patient and Visit Characteristics on Health Outcomes in Knee Osteoarthritis

The goal of this clinical trial is to understand the patient and clinic visit characteristics that affect health outcomes for individuals with knee osteoarthritis (OA) pain using topical diclofenac gel. The main questions it aims to answer are:

• What baseline patient characteristics predict response to topical diclofenac?
• Does patient physiology during the study visit predict response to topical diclofenac?
• Do study visit characteristics predict response to topical diclofenac?

Participants will:

• attend 2 study visits to complete study questionnaires and have blood drawn
• apply topical diclofenac to their knee for 8 weeks
• complete biweekly questions about knee pain and diclofenac use between study visits

220 older adults with symptomatic knee OA will attend a single research clinic visit (one of four different types of study visits) with a study clinician. The investigators will video record the visits and measure participant heart rate and skin conductance during the visit. Participants will complete baseline questionnaires immediately prior to the study visit. All participants will receive diclofenac gel (a topical over-the-counter non-steroidal anti-inflammatory drug [NSAID]), a guideline recommended treatment for knee OA-related pain at the end of the first study visit. Participants will identify an "index" knee (worst pain, right or left) that they will treat and follow during the study. Between study visit 1 and the 8-week follow-up visit, participants will receive an every other week text message asking them to report on pain and diclofenac use to better understand changes in pain over time. Final questionnaires will be completed at the second study visit at week 8.