Position and anatomical landmarks
Infiltration is carried out with the patient in the supine position with the head in a slightly backward flexion position. The head is positioned in the midline.
The upper margin of the orbita is located and the supra-orbital fissure palpated and marked. The distance between the infra-orbital foramen and median line is about 2.5 cm (see figure).
The surrounding area is disinfected and covered with sterile drapes. A needle (22-G, 5 cm, 1 cm active tip) is inserted perpendicularly (under ultrasound guidance) just medial to the supra-orbital fissure until there is contact with bone. The thermocouple is connected to the needle. The location of the nerve is confirmed when the patient experiences reproducible paresthesia in the forehead by stimulation with 50 Hz, 0.5 V. Then, a pulsed radio-frequency current of 45 V lasting for 120 seconds is administered without preceding local anaesthetic. The maximum temperature should not exceed 42°C, but if this occurs the output should be reduced. If necessary, a second treatment period of 120 seconds can be administered if the impedance is above 500 Ω, prior to injection of 1 ml NaCl 0.9% solution.
- The most serious complication of the injection is infection.
- Small subcutaneous bleedings may result in a temporary increase in pain after the injection.