Joint pain can be a result of an injury that affects any of the tendons, ligaments, or bursae surrounding the knee joint. A physical trauma can also affect the bones, ligaments, and cartilage within the joint. Knee pain is also a characteristic of an infection in the knee joint, joint inflammation, arthritis, or maybe in rare cases due to cancer of the knee joint. The severity and the affected structure of the knee joint mainly define the symptoms a person is experiencing. Knee pain within the joint is very common among the older population and athletes due to the overuse and wear and tear of the knee structures. The pain of the knee joint is a whole another condition medically known as arthralgia, which can develop from various knee problems.  The symptoms of the knee pain vary widely due to the underlying cause, but the most commonly prevailing signs and symptoms that accompany knee pain are as follows:
Redness of the knee joint is a commonly occurring symptom of active arthritis, especially in the case of rheumatoid arthritis. Redness around the joint might appear due to an injury to surrounding structures or to the knee joint directly. There are numerous causes of joint redness which appear mainly because of arthritis of the knee joint. 
The redness around the joint might develop in multiple joint or in a single joint in the body at the same time. Some rare causes of knee joint redness are the tumors of the joint lining i.e., the synovium or the bone.