Subcutaneous Trigeminal Nerve Stimulation to Relieve Neuropathic Facial Pain

Take an anesthetized patient suffering from neuropathic facial pain, in which trigeminal nociceptor fibers in the face relay pain to spinal projection neurons, which transmit signals to the brain.

Mark along the trigeminal branches for electrode implantation.

Insert cannulas to tunnel subcutaneously from the painful facial region to the area above the ear, known as the supraauricular area.

Insert electrodes in the painful region and guide the distal ends to the supraauricular area.

Then, remove the cannula and secure the electrodes.

Create a subcutaneous pocket below the collarbone, known as the infraclavicular site.

Extend the tunnel to this site and pass electrodes through it.

Attach the electrodes to an internal pulse generator, or IPG, secure it to the infraclavicular site, and close the incisions.

The IPG sends electrical signals to stimulate the trigeminal nerve's mechanoreceptors. These fibers activate the spinal inhibitory interneurons, which inhibit projection neurons and reduce pain transmission.

After a patient has carried out a 12-day stimulation trial according to the text protocol, turn the anesthetized patient's head to the side, contralateral to the pain, then place a pillow under the ipsilateral shoulder to expose the clavicle. Shave the area around the ear on the painful side of the face. Then, remove any loose hair. If necessary, tape away the surrounding hair to prevent it from moving into the surgical field.

Next, thoroughly disinfect the surgical field from the facial area around the ear and down to the clavicle area. From the X-rays of the outpatient appointment, use a sterile surgical pen to mark the desired position of the permanent electrodes in the marks of the previous skin punctures for guidance.

For the first trigeminal branch, choose a position on the lateral side of the forehead at which to puncture the skin, roughly 10 centimeters lateral and 1 centimeter above the medial border of the eyebrow. For the second trigeminal branch, choose a position that is located roughly 1 centimeter anterior to the tragus. Do not perform a skin puncture 2 centimeters or more anterior to the tragus to spare facial nerve fibers from injury. For the third trigeminal branch, choose a position that is located roughly 1 centimeter anterior and 4 centimeters below the tragus.

Correct planning of electrode insertion is crucial to the success of this technique as the paresthesia provoked by the stimulation should cover the entire painful area.

Use a 14-gauge Tuohy needle to perform a skin puncture at a previously marked position.

As the subcutaneous tissue of the facial area is thinner than on other body parts, make sure to stay half a centimeter below the skin surface to prevent skin perforation or direct muscle stimulation.

Make a 1 centimeter long vertical incision in the auricular area and form a small subcutaneous pocket. Take the stylets from the Tuohy cannulas and subcutaneously tunnel them from the site of the skin puncture to the auricular incision. Insert another Tuohy cannula to subcutaneously tunnel from the supra auricular incision to the site of the skin puncture, and then insert the electrodes into the Tuohy cannula with the contacts located in the painful area.

Remove the Tuohy cannulas, in the electrode stylets, and insert the distal end of the electrode into the cannula. Remove the Tuohy cannula, while using forceps to keep the electrode in place.

Then, use a 3-0 non-absorbable silk suture to fix the electrode to the muscle fascia to prevent electrode dislocation. Next, perform a 6-centimeter long infraclavicular incision and manually form a subcutaneous pocket to house the IPG. Use bipolar electrical forceps to coagulate any bleeding vessels. Insert a tunneling spear into the infraclavicular incision and subcutaneously tunneled behind the ear towards the supra auricular incision. Make a small retroauricular incision for the spear to exit the skin.

Then tunnel with a second spear from the super-uricular to the retroauricular incision. Remove the spear stylets and insert the electrodes until the electrodes are buried in the subcutaneous tissue, without any loops or kinks. After tunneling the electrodes to the retroauricular incision, tunnel them from here to the infraclavicular incision.

Then, remove the spear by pulling it out of the infraclavicular incision while using forceps to keep the electrodes in place. Connect the electrodes to the IPG and use torque screws to secure them. Use a non-absorbable 3-0 silk suture to suture the IPG to the pectoralis muscle fascia to prevent IPG dislocation.

Perform skin closure with absorbable 3-0 subcutaneous sutures and non-absorbable 3-0 cutaneous sutures in the facial area and absorbable 3-0 intracutaneous sutures at the site of the IPG. Then disinfect all wounds. Clean the surgical field with saline, and apply sterile draping. Carry out post-operative care according to the text protocol.