Knee pain can be caused by a sudden injury, an overuse injury, or by an underlying condition, such as arthritis. Treatment will vary depending on the cause. Symptoms of knee injury can include pain, swelling, and stiffness. Most people experience knee pain at some point in their lives. Sports, exercise and other activities can cause muscle strains, tendinitis, and more serious injuries to ligaments and cartilage. For some, knee pain can be so severe that it limits daily activities. For others, mild knee pain may be a chronic hindrance to the active lifestyle they desire. In either case, chances are that you’re dealing with a knee problem that shouldn’t be ignored.