A new method for lateral pterygoid intramuscular electrode placement

Electromyographic recordings of the lateral pterygoid muscle (LP) are difficult because of potential damage from intramuscular electrodes to nearby structures, e.g., maxillary artery, pterygoid venous plexus, and long buccal nerve, and, because of pain and reduced jaw mobility in some orofacial pain patients. Objective: To develop an intraoral placement technique, that minimises jaw displacement and reliably positions electrodes within the LP's inferior head (IHLP). Methods: In 7 human cadavers, it was estimated that, with the mandible in an ipsilateral closed position, a straight needle could position fine wire electrodes into the mid-portion of the IHLP, by inserting the needle 26 mm through the mucosa adjacent to the distal root of the maxillary second molar, and angled towards the external auditory meatus and parallel to, and close to, the buccal alveolar bone of the maxilla, avoiding the maxillary artery and long buccal nerve. Using this approach in two adult volunteers, two teflon-coated stainless steel fine wires with bared tips were placed using a spinal needle (25 Gauge, 51 mm) into the right IHLP. Right lateral jaw position was maintained with a custom-made rubber jig. Electrode placement was verified by computer tomography scans (CT) and electromyography. Results: In both subjects, the needle hub was located adjacent to the maxillary premolar/molar interproximal space just prior to needle withdrawal, and activity was observed for typical tasks: jaw opening, contralateral jaw movement and protrusion. CT verified electrode placement in the IHLP mid-portion. Conclusion: With further testing, this technique could be a reliable method of IHLP electrode placement for patients with impaired jaw function, which minimises risk of damage to nearby structures, and also minimises jaw movement to enable electrode placement. This technique could also be used for diagnostic/therapeutic injections. Support: NHMRC; The Bella Schwartz Foundation.