Biological Response to Platelet-rich Plasma and Corticosteroid Injections

The goal is to determine how two different injections, corticosteroid and platelet-rich plasma, are used to treat patients with knee osteoarthritis may affect a patient's pain and function. Secondarily, the investigators are also interested in knowing how the two types of injections that will be given may affect what happens in the joint cartilage. The participants will receive one of the two injection types at the initial visit. There will be surveys to complete (around 10 questions) about the participants' knee and overall function. The investigators will ask these same questions on seven separate occasions. In addition, the investigators will ask the participants to provide blood and urine samples at our clinic before the first knee injection and before any other injection that is needed over the course of the study. During the injections, synovial fluid will be aspirated from the participants' knee at the initial visit and the one month visit. If the participants decide to go to surgery to help relieve the pain from osteoarthritis at any point during the study, the investigators will collect the material from the participants' knee that would be normally discarded as medical waste. Previous studies have indicated that concentrations of inflammatory and degradative biomarkers in patient serum, urine, and synovial fluid may provide insight into OA pathophysiology. To our knowledge, no study has been performed to assess the impact of intra-articular PRP injection upon fluid concentrations of a comprehensive panel of proposed OA-related biomarkers. In this study, the investigators will evaluate the impact of intra-articular PRP injection upon markers of cartilage matrix turnover, inflammatory mediators, degradative enzymes, inhibitors of degradative enzymes, and markers of bone metabolism in serum, urine, and synovial fluid of knee OA patients.