Baker's cysts and gout, a form of arthritis, are causes of pain behind the knee, notes MedlinePlus. People who have pain behind their knee and cannot bear weight on that leg, have severe pain, still have pain after three days of home treatment, or who have pain, swelling, numbness, tingling or discoloration in the calf below the knee should seek medical attention.
Baker's cysts, also called popliteal cysts, are pockets of fluid that form when excess joint fluid pushes into the small sacs behind the knee, notes WebMD. Some people with Baker's cysts do not experience pain, while others have slight pain behind the knee and into the upper calf. Swelling behind the knee that worsens when standing, tightness and stiffness behind the knee are other symptoms of Baker's cysts. Baker's cysts may go away on their own, or doctors may treat them by draining the fluid with a needle or administering steroid medications to reduce swelling.
Gout causes pain in the back of the knee due to a buildup of uric acid in the blood that forms crystals that cause joint inflammation, notes MedlinePlus. While the exact cause of gout is unknown, as of 2015, risk factors include diabetes, obesity, kidney disease, anemia and blood cancers. People who drink alcohol, men and those with a family history of gout are at greater risk of contracting the condition. Throbbing pain, tender and swollen joints, and in some cases fever are symptoms of gout.