The effective zone of botulinum toxin A injections in the sternocleidomastoid muscle.

PURPOSE: The aim of this study was to document the anatomical landmarks of the motor entry point (MEP) and the intramuscular motor point (IMP) of the sternocleidomastoid (SCM) muscle for effective botulinum toxin injections.

MATERIALS AND METHODS: Thirty-five specimens from 20 adults bodies donated to science were investigated. The reference points were the mastoid process and the most medial point of the clavicle.

RESULTS: The mean length of the reference line was 165.2 ± 12.8 mm. 97.0% of the total number of MEP in this study were located at 20-40 and 85.0% of the total number of the IMP was located at 20-70% from the mastoid process. The intersection with the great auricular nerve was located at 22%, it was 45% for the transverse cervical nerve and 28% for the external jugular vein.

CONCLUSIONS: In clinical practice, the mass in patients with torticollis or cervical dystonia might be formed at the lower part or upper part of the SCM muscle. For a mass in the upper portion of the SCM muscle, the injection area using alcohol, phenol or botulinum toxin was determined to be 20-40%. However, to inject the area at 20-40%, ultrasound guidance is recommended because of the cervical cutaneous nerves and veins. For a mass in the lower portion of the SCM muscle, the injection area of botulinum toxin was 50-70%. These areas can be used with botulinum toxin injections or other agents for motor point blocking in patients with torticollis or cervical dystonia.