Knee Osteoarthritis occurs when the cartilage that provides a cushion between your knee bones wears down, resulting in the bones rubbing together. This causes you to experience pain, swelling, stiffness and a decreased ability to move your knee. You are more likely to develop osteoarthritis as you age, if you have had repetitive stress injuries to your knee or are overweight. It is characterized by pain in your knee when you first wake up, and it takes you awhile to get moving. Once you are moving, your knee typically feels better. However, if you are more active and on your feet for a while, your knee can often become sore, tight or swollen.