When you think of knee pain during or after walking or jogging, what likely comes to mind is pain in the front of the knee or below the kneecap. While this is a classic symptom of cartilage damage and other injuries walkers and joggers commonly face, pain in the area behind the knee, called the popliteal fossa, is also a frequent complaint. The pain is often vascular in origin.
Deep Venous Thrombosis
Pain behind the knee after walking can signal a very serious condition called a deep venous thrombosis, or DVT. These are blood clots that form in veins, usually in the legs and after long periods of inactivity or immobility, as in when flying or lying in bed. Smoking and oral contraceptives are also predisposing factors. These clots can dislodge and travel to the lungs as emboli. If they become stuck in the lung, brain or heart vessels, they can be damaging and even fatal. Swelling and warmth usually accompanies pain, If you suspect a DVT, seek medical care immediately.
Pain behind the knee can affect the arteries in the popliteal area as well as the veins. An aneurysm is a bulging of the arterial wall thanks to local mechanical weakness, which most often results from hardening of the arteries owing to advancing age. As with DVTs, clots may form and break off, but in this case the clots travel not toward the heart but toward the feet. This can result in foot and calf pain that can progress to a cold, numb foot, which is a medical emergency.
A Baker's cyst can masquerade as venous pain behind the knee. This kind of cyst forms when synovial fluid within the knee capsule, the purpose of which is to provide lubrication to the joint, leaks backward into the popliteal fossa and collects around a structure called the popliteal bursa, which also provides lubrication. The swelling caused by this fluid-filled cyst may be visible to the naked eye, but in any case almost always causes pain behind the knee and swelling of the lower leg.
While a DVT or a Baker's cyst are the most common causes of popliteal pain, they are not alone. Other culprits include benign or malignant connective-tissue tumors, which can be very serious if not identified early; inflammation of the popliteal tendon, which is most severe during squatting; injury to the back of the meniscus, a C-shaped structure providing padding within the knee joint capsule; hamstring tendinitis and calf tendinitis. These may often be differentiated from venous pain in that the pain may worsen with walking instead of occurring afterward.