Final answer:
The recommended protocol for a femoral nerve block using an ultrasound-only technique is to insert the needle immediately medial to the femoral artery to target the femoral nerve accurately.
Step-by-step explanation:
The recommended protocol for performing a femoral nerve block using an ultrasound-only technique is to identify the femoral artery and insert the needle immediately medial to it. This is because the femoral nerve lies just medial to the femoral artery. By inserting the needle in this position, the chances of accurately targeting the femoral nerve are higher.