Ultrasonic tissue characterization of the upper trapezius muscle in patients with myofascial pain syndrome

Abstract

Myofascial trigger points (MTrPs) are palpable, tender nodules in skeletal muscle that produce symptomatic referred pain when palpated. MTrPs are characteristic findings in myofascial pain syndrome (MPS). The role of MTrPs in the pathophysiology of MPS is unknown. Objective characterization and quantitative measurement of the properties of MTrPs can improve their localization and diagnosis, as well as lead to clinical outcome measures. MTrPs associated with soft tissue neck pain are often found in the upper trapezius muscle. We have previously demonstrated that MTrPs can be visualized using ultrasound imaging. The goal of this study was to evaluate whether texture-based image analysis can differentiate structural heterogeneity of symptomatic MTrPs and normal muscle.

Figure 1

Localization of MTrPs using vibration elastography. An external massager generates shear waves that can propagate orthogonal (A) and parallel (B) to the muscle fibers. Hypoechoic areas (MTrPs) in B-mode image are observed to be vibrating less than the surrounding muscle in color variance image (C).

Figure 2

Entropy filtering. (A): B-mode image; (B): entropy image; (C): yellow mask highlight the ROI, red region has entropy<4; (D): ROI with size threshold; (E): Crop of the ROI by 20% to exclude muscle near the fascial border; (Legend): Fuscia is subcutaneous tissue, green are fascia, yellow is upper trapezius, blue are underlying muscles.

Figure 3

Entropy analysis results. Mean entropy in symptomatic tissue is significantly (p<0.05) lower than in healthy ones. Blue bars: results from the analysis of the whole mask; Red bars: results from size threshold application; Green bars: results from cropped ROI.

Figure 4

Mean area estimation of the ROI with entropy less than 4. Blue bars: results from the analysis of the whole mask; Red bars: results from size threshold application; Green bars: results from cropped ROI.

Figure 5

Region size measurements from color Doppler images.

Figure 6

(A) Multiplanar view of a 3D volume of the upper trapezius acquired using a mechanically-scanned linear probe. (B) 3D volume rendering of the entropy-filtered stack of images in (A) showing the 3D structure of the regions with low entropy.