The popliteal artery is the single trunk that continues the superficial femoral artery at the knee and gives all the leg branches (anterior tibial, posterior tibial, peroneal). Collaterals around the knee are poor, especially in a young patient with no atherosclerotic collaterals, so ligating it devascularizes the whole leg and leads to amputation.

• Ligating one tibial artery alone is tolerated because the other leg vessels still perfuse the foot.
• Internal iliac supplies the pelvis, not the limb.