Treatment protocol for injecting into lateral pterygoid muscle

Figure 1. Cutaneous puncture site through the sigmoid notch and inferior to the zygomatic arch.

A facial or transoral approach can be utilized in the administration of Botox to the lateral pterygoid muscle. The technique that we employ is a transoral approach that is similar to that used for administering an extra-oral second or third division trigeminal nerve block. This technique is achieved with the insertion of a needle via a transcutaneous approach inferior to the zygomatic arch and within the sigmoid notch. In this injection technique, the zygomatic arch and the condylar head/neck are palpated both at rest and at maximal opening, and the needle is inserted inferior to the arch and anterior to the condylar neck (see Figure 1). The needle is inserted until a hard stop at the lateral pterygoid plate is encountered (approximately 40-45 mm), at which point the needle is retracted to a depth of 30-35 mm, bloodless aspiration is confirmed, and the desired therapeutic injection is performed.

This technique for local anesthesia is consistently reliable due to the diffusion of the local anesthetic to all of the local structures, including the second and/or third divisions of the trigeminal nerve However, the administration of botox into the lateral pterygoid muscle needs to be more exacting. First, because the botox must be injected directly into the muscle and second because the lateral pterygoid muscle is in close proximity to numerous other muscular, vascular, and neural structures (including the pharyngeal musculature, the medial pterygoid, the internal maxillary artery and its branches, the pterygoid plexus, and various branches of the third division of the fifth cranial nerve), which if affected by the botox could cause significant adverse effects, such as dsyhagia.

To ensure the precise delivery of botox into the lateral pterygoid muscle the planning and administration of the botox is facilitated by CT measurements and EMG guidance. Non-contrasted maxillofacial CT scans are usually available as a component of the patient assessment. Using an axial image the depth of insertion from skin to muscle can be determined. This provides a good estimate as to the depth required. The procedure is then performed with a 35 mm 25 gauge EMG needle. The needle is inserted as described above to the CT estimated distance. Intramuscular placement is confirmed with the patient performing small mandibular opening movement, which activates the EMG. The Botox is then administered incrementally with multiple negative needle aspirations to confirm non-intravascular placement. Post-operatively, the patients have restricted movement which may entail physical restraints. The patients are then monitored at sequential follow-up for recurrent episodes of TMJ open lock.