Knee Osteoarthritis (OA) is a leading cause of premature disability in Veterans who develop knee OA at higher rates and younger ages than the population in general. For those with symptomatic early knee OA, who are years to decades away from meeting clinical indications for knee replacement surgery, knee injections have been a key treatment option. In recent years, platelet rich plasma (PRP) injections have gained increasing attention for improving pain and function in patients with knee OA. Basic science studies also suggest that PRP may also potentially stimulate repair responses to articular cartilage. However, the mechanisms of action of PRP in the treatment of knee OA are unknown. Because autologous blood is used, the PRP composition differs between patients. It is also unknown whether these differences in PRP composition affect clinical outcomes. This study will address these gaps and provide critical new and objective information on PRP treatment effects in Veterans and additional women with early knee OA important to improving clinical use of this new treatment.