Background: Myofascial pain syndrome (MFPS) causes chronic shoulder pain. Supraspinatus and infraspinatus, rotator cuff muscles innervated by the suprascapular nerve, are commonly affected. Intramuscular botulinum neurotoxin (BoNT) injections near motor points (i.e., visible nerve branch entry sites used as a proxy for motor endplates) are an effective treatment for such pain. However, current techniques limit accessibility. This study aimed to develop a patient-specific, landmark-guided technique for BoNT delivery into supraspinatus and infraspinatus using scapular dimensions.
Methods: Ten pairs of cadaveric shoulders (n=20) were dissected to identify supraspinatus and infraspinatus motor points. Distances from scapular landmarks to these motor points were measured in two axes. These distances were correlated with scapular dimensions (height, spine length, width) using linear regression. Patient-specific predictive formulae were derived. For validation, landmark-guided methylene blue dye injections were performed on four additional shoulders using calculated coordinates.
Results: For supraspinatus, motor points were predicted using deltoid tubercle and root of the scapular spine (r = 0.58–0.64, p = 0.0016–0.021). For infraspinatus, root of the scapular spine and lateral acromion were used (r = 0.46–0.60, p = 0.0054–0.0500). In all validation specimens, injected dye accurately reached the motor points.
Conclusion: This study provides a validated, patient-specific, landmark-guided technique for BoNT delivery into the rotator cuff, offering an approach for accessible analgesia.
Keywords: Rotator cuff, Botulinum neurotoxin (BoNT), Myofascial pain, Landmark-guided, Injection, Cadaveric, Suprascapular nerve, Variation, Patient-specific, Motor points