I have pain behind my knee and a swollen calf after a long flight. Could it be a clot?

Why this needs urgent attention

Sitting still for many hours slows blood flow in the leg veins, and a clot can form, often in the calf or behind the knee. The typical signs are swelling of one calf or ankle, an aching or cramping pain, warmth, redness or a darker skin colour, and tenderness when the calf is squeezed. A clot can travel to the lungs, which is a medical emergency.

The risk is higher with long-haul flights, recent surgery or injury, a leg in a cast or brace, pregnancy or the contraceptive pill, previous clots, cancer and significant obesity. Many expats in Qatar fly long distances home and back each year, so this is a practical concern, not a rare one.

What to do

• One swollen, painful calf after a flight: go to an emergency department the same day for an ultrasound scan of the veins
• Chest pain, coughing blood, sudden breathlessness or fainting: call 999 immediately
• Do not massage the calf or try to stretch it out
• Do not wait to see if it settles, and do not start your own blood thinners

Other causes of pain behind the knee after travel

Once a clot has been ruled out, other explanations are common. Stiffness after sitting cramped for hours, a Baker's cyst that has become more noticeable, or a cyst that has leaked into the calf can all cause aching behind the knee. A ruptured Baker's cyst can look very like a clot, which is why an ultrasound is needed rather than guessing.

Preventing problems on your next flight

Walk the aisle every hour or two when it is safe, do ankle pumps while seated, and drink plenty of water. People at higher risk, such as those who have just had knee surgery, should ask their doctor about compression stockings or preventive medication before flying. If you have had recent knee surgery with Dr. Gelber in Doha, discuss travel plans before booking.