Optimal routes of administration of trigger point injections into the trapezius muscle: a prospective study

Abstract

Background: We compared the efficacy of intramuscular and interfascial routes of local anesthetic administration for trigger point injections (TPI). Methods: We investigated 50 patients with myofascial pain syndrome (MPS) of the trapezius muscle who were assigned to an intramuscular injection group (Group M, n＝25) and an interfascial injection group (those who received the TPI between the trapezius and the supraspinatus muscle) (Group F, n＝25). The primary outcome was the efficacy after the first injection, and the secondary outcome was efficacy of injections after four subsequent TPI. Results: The mean numerical rating scale (NRS) was significantly reduced in both groups (p＜0.001) after the first TPI, although this intergroup difference was statistically insignificant (p＝0.766). The mean NRS was significantly lower in Group F than in Group M (p＝0.016) with each subsequent TPI. Conclusion: Both intramuscular and interfascial injections are effective routes of administration for TPI. Repeat TPI showed greater efficacy with interfascial than with intramuscular injections.