Conditions that cause knee pain and swelling include a broken knee, arthritis of the knee, bursitis of the knee, Osgood-Schlatter disease and osteomyelitis, according to the American Academy of Orthopaedic Surgeons. Pain can range from mild to excruciating, depending on the condition.
Osgood-Schlatter disease occurs in children who are active in sports in which they need to jump, run and change direction quickly, claims Mayo Clinic. The pain is concentrated in a lump just below the kneecap and can be severe in some cases. The condition tends to come and go until the child stops growing.
Like many joints in the body, the movement of the knee is facilitated by fluid-filled sacs called bursa. These sacs can become inflamed due to trauma, overuse of the knee or infection, according to MedicineNet. The knee experiences warmth, tenderness and swelling, though the pain is mild when the knee is not in use.
In osteoarthritis, the cartilage between joints begins to break down, sometimes to the point where they rub together, says the American Academy of Orthopaedic Surgeons. The knee becomes stiff, swollen and painful. These symptoms worsen first thing in the morning or after long periods of inactivity.
Osteomyelitis is an infection of the bone, according to Mayo Clinic. When it's in the knee it causes pain, swelling, warmth and redness.