The femoral vein can become blocked and this is a medical emergency. My neighbor called us for help at 5am one day a few years ago because she couldn't move her leg or get out of bed. I rushed over and saw her leg swollen, her toes were blue, and the femoral vein was palpable and extremely painful. She was a nurse at the Naval hospital and was taken in immediately. Deep vein thrombosis in the legs can happen with little to no warning and almost 600,000 people die from this yearly. It's worth reading up on.