The nerves that supply the hip joint come from branches of the sciatic nerve, the femoral nerve and the obturator nerve. These main nerve trunks all pass down the leg. Unlike with the fingertips, where there is a large area of the sensory cortex in the brain devoted to small areas of the body, with the hip joint the brain is often not very good at localizing the exact origin of the pain impulses that it is receiving. Therefore, hip pain is often felt in the groin, the thigh or the knee.
Particularly with children, any child presenting with knee pain should first have their hip checked very careful to ensure that the actual underlying cause of the pain isn’t actually the hip joint.