Which veins empty into the Popliteal vein behind the knees?

The gastrocnemius veins are correctly identified as the veins that empty into the popliteal vein behind the knees. These veins arise from the gastrocnemius muscle in the calf and are typically responsible for draining blood from this muscle group. They merge to form the popliteal vein, which is located in the popliteal fossa behind the knee joint.

The soleal veins, while they also contribute to venous drainage in the lower leg, primarily drain the soleus muscle and typically empty into the posterior tibial veins, not directly into the popliteal vein. The femoral veins are situated in the upper leg and do not drain into the popliteal vein, as they are superior to it in the venous system hierarchy. Lastly, the great saphenous vein runs along the length of the leg and typically drains into the femoral vein in the groin area, well above the level of the popliteal vein. Therefore, the gastrocnemius veins are specifically positioned to contribute blood flow into the popliteal vein in the described location.