My mother is suffering from pain behind the knee, she barely moves. could that indicates vein thrombosis?

Get it checked: Pain behind the knee could be something as benign as a muscle strain or a Baker's cyst, but it could also indicate a deep vein thrombosis. Someone with these symptoms should see a physician for a physical exam and possibly an ultrasound of the veins of the legs.

Bakrs Cyst,tight ham: When knees develop arthritic change, there can be periods of flare where inflammation and fluid can develop behind the knee. This is also called a Bakers cyst. Some patients with tight hamstrings also have pain behind the knee due to muscle spasm, a secondary effect of knee arthritis. It is thus best to see a Sports Medicine MD or PMR to diagnose what is going on and make sure there is not a clot.