Expansion of 1 ML of Solution by Ultrasound-Guided Injection Between the Trapezius and Rhomboid Muscles: A Cadaver Study

Objective: An ultrasound-guided interfascial injection, which targets the space between the epimysia, is often performed for myofascial neck and shoulder pain. However, the relationship between the injection volume and clinical effectiveness has been controversial. We conducted an anatomical study with cadavers to measure the distribution of a small amount of pigment solution injected into the interfascial space.

Design: An experimental cadaveric study.

Setting: An institutional clinical anatomy laboratory.

Methods: We performed 20 ultrasound-guided injections with pigment solutions of 1.0 mL each into the space between the trapezius muscle and rhomboid muscle bilaterally on 10 cadaver specimens. Cadavers were then dissected and macroscopically evaluated for pigment distribution on the fascia of the muscular surfaces. The pigment distribution area of each injection site was visually confirmed and calculated using automatic area calculation software.

Results: Pigment solution exclusively within the interfascial space was visually confirmed in 95% (19/20) of injection sites. The median pigmented surface area (interquartile range) was 24.50 (16.17-30.76) cm2 on the deep side of the trapezius muscle and 18.82 (13.04-24.79) cm2 on the superficial side of rhomboid muscle; these measurements were statistically significantly different (P = 0.033).

Conclusions: A pigment solution comprising as little as 1.0 mL injected under ultrasound guidance separated two adjacent muscles and spread to the wide area within the interfascial space. The difference in the pigment distribution area between the two adjacent muscles can be explained by the path made by the injection needle and several layers of fascia between the epimysium.