Introduction Botulinum neurotoxin injection is a valuable treatment method for patients with myofascial pain syndrome in the infraspinatus muscle. However, there is no botulinum neurotoxin injection guideline, and the most appropriate injection site based on topographical anatomic information for this injection to effectively treat myofascial pain syndrome in the infraspinatus muscle is unclear. The purpose of this study was to evaluate the intramuscular nerve terminal of the infraspinatus muscle and to suggest the most efficient botulinum neurotoxin injection sites.

Methods This study used 5 formalin-embalmed and 10 fresh frozen cadavers with a mean age of 78.9 years. Sihler’s staining was applied to evaluate the intramuscular nerve terminal of the infraspinatus muscle. The ultrasound scanning of the infraspinatus muscle was performed based on the surface landmarks and internal structures near the scapular region.

Results The intramuscular nerve terminal was mostly observed in the medial third area of the infraspinatus muscle. The deltoid tubercle, inferior angle, and acromion of the scapula are useful as surface landmarks to scan the infraspinatus muscle.

Discussion The proposed injection sites based on the intramuscular nerve terminal and surface landmarks can be regarded as accurate locations to reach the cluster area of the intramuscular nerve terminal and each compartment of the infraspinatus muscle to manage the myofascial pain syndrome in the infraspinatus muscle.