Pain Behind the Knee: Causes

Pain behind the knee is not a separate diagnosis but a point where several different structures converge: blood vessels, nerves, tendons, and the joint capsule. Below — what is located in the popliteal fossa, which causes produce such pain, and when a doctor is needed without delay.

What is located in the popliteal fossa

The popliteal fossa (fossa poplitea) is a diamond-shaped depression behind the knee joint filled with adipose tissue. Above and medially it is bounded by the tendons of the semimembranosus and semitendinosus muscles, above and laterally by the tendon of the biceps femoris muscle, and below by the medial and lateral heads of the gastrocnemius muscle.

The tibial and common peroneal nerves, the popliteal vein, and the popliteal artery, which lies adjacent to the joint capsule, pass through the adipose tissue; lymphatic vessels and nodes lie along the popliteal vessels. The skin here is thin and mobile; the small saphenous vein and superficial nerves run in the subcutaneous layer.

Main causes of pain behind the knee

One possible cause is a Baker's cyst (popliteal cyst), a fluid-filled formation behind the knee. Its main symptom is a soft swelling that is more noticeable in the standing position. There is sometimes no separate cause, especially in children; in adults, the cyst usually arises when another condition damages the knee joint:

• knee injury;
• osteoarthritis;
• rheumatoid arthritis;
• gout.

A Baker's cyst occurs at any age, more often in people aged 35–70. The most common knee disease is osteoarthritis: cartilage gradually wears away, and pain and swelling appear. Ligament and tendon injuries also cause pain: a typical example is anterior cruciate ligament damage during a sudden twisting movement, a common sports injury.

Pain behind the knee when walking

With a Baker's cyst, symptoms worsen after walking. In addition to swelling, there may be pain in the knee or leg, tightness, stiffness, aching pain, difficulty bending the knee, and clicking.

Swelling behind the knee that is visible when standing is a reason to show the leg to a general practitioner, even if it does not hurt.

Pain behind the knee and in the calf: what to watch for

Pain in the leg below the knee together with swelling requires attention: it may be a ruptured cyst or deep vein thrombosis. Warning signs are a sudden increase in pain or swelling, a bruise and hot skin on the leg, redness or darkening of the skin (harder to notice on dark skin), and swelling that becomes firmer or softer.

Acute pain and tightness behind the knee

Tightness, stiffness, and aching pain are part of the picture of a popliteal cyst. Sharp pain behind the knee occurs with a ruptured cyst: symptoms become stronger than usual until the swelling subsides — this takes several weeks.

The timeframes are as follows: a Baker's cyst may cause discomfort from several months to several years, and in children it often resolves on its own. If the cause is joint disease, symptoms usually subside when it is treated.

When pain behind the knee requires urgent medical attention

A routine visit is needed if swelling of unclear origin appears anywhere on the body. An urgent consultation is needed for a sudden increase in pain or swelling in the leg, a bruise and hot skin, redness or darkening of the skin, or swelling that changes firmness. The doctor will examine the leg, rule out other conditions, and if necessary refer for ultrasound or MRI or to a specialist.

Pain behind the knee by itself is not a reason to call an ambulance. Call 103 or 112 if, against the background of pain and swelling in the leg, shortness of breath or chest pain appears — this may be a thrombus that has reached the lungs, that is, pulmonary embolism; such a condition is life-threatening.

This material is for reference: it helps you understand what to ask the doctor but does not replace a consultation — the final cause of your pain is determined during an examination.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer