Osteoarthritis is a condition that affects your joints and is common in the knee. When a knee joint develops OA, some of the cartilage covering the ends of the bones gradually roughens and becomes thin. Associated features include stiffening and weakening of the surrounding muscles, ligaments and tendons.
A knee sprain can occur when you injure or twist your knee awkwardly. This may cause damage to the tissues in and around the knee such as the muscles, ligaments and/or cartilage.