Novel applications of ultrasound technology to visualize and characterize myofascial trigger points and surrounding soft tissue

Abstract

Objective: To apply ultrasound (US) imaging techniques to better describe the characteristics of myofascial trigger points (MTrPs) and the immediately adjacent soft tissue.

Design: Four sites in each patient were labeled based on physical examination as active myofascial trigger points (A-MTrPs; spontaneously painful), latent myofascial trigger points (L-MTrPs; nonpainful), or normal myofascial tissue. US examination was performed on each subject by a team blinded to the physical findings. A 12 approximately 5MHz US transducer was used. Vibration sonoelastography (VSE) was performed by color Doppler variance imaging while simultaneously inducing vibrations (approximately 92Hz) with a handheld massage vibrator. Each site was assigned a tissue imaging score as follows: 0, uniform echogenicity and stiffness; 1, focal hypoechoic region with stiff nodule; 2, multiple hypoechoic regions with stiff nodules. Blood flow in the neighborhood of MTrPs was assessed using Doppler imaging. Each site was assigned a blood flow waveform score as follows: 0, normal arterial flow in muscle; 1, elevated diastolic flow; 2, high-resistance flow waveform with retrograde diastolic flow.

Setting: Biomedical research center.

Participants: Subjects (N=9) meeting Travell and Simons' criteria for MTrPs in a taut band in the upper trapezius.

Interventions: Not applicable.

Main outcome measures: MTrPs were evaluated by (1) physical examination, (2) pressure algometry, and (3) three types of US imaging including gray-scale (2-dimensional [2D] US), VSE, and Doppler.

Results: MTrPs appeared as focal, hypoechoic regions on 2D US, indicating local changes in tissue echogenicity, and as focal regions of reduced vibration amplitude on VSE, indicating a localized, stiff nodule. MTrPs were elliptical, with a size of .16+/-.11 cm(2). There were no significant differences in size between A-MTrPs and L-MTrPs. Sites containing MTrPs were more likely to have a higher tissue imaging score compared with normal myofascial tissue (P<.002). Small arteries (or enlarged arterioles) near A-MTrPs showed retrograde flow in diastole, indicating a highly resistive vascular bed. A-MTrP sites were more likely to have a higher blood flow score compared with L-MTrPs (P<.021).

Conclusions: Preliminary findings show that, under the conditions of this investigation, US imaging techniques can be used to distinguish myofascial tissue containing MTrPs from normal myofascial tissue (lacking trigger points). US enables visualization and some characterization of MTrPs and adjacent soft tissue.

Figures

Figure 1

Design for a vibration source that can be used for vibration sonoelastography imaging of the upper trapezius. This design can induce vibrations uniformly over a broad area both along the muscle fibers (A) and transverse to the muscle fibers (B).

Figure 2

Pain pressure thresholds (PPTs, in lb) measured using pressure algometry demonstrated lower thresholds in active and latent MTrPs compared to palpably normal muscle (N>A,L; p

Figure 3

Gray scale imaging of a trigger point in the upper trapezius. (A) An isolated MTrP appears as a well-defined focal hypoechoic nodule. (B) A series of four hypoechoic MTrPs in the upper trapezius.

Figure 4

3D imaging of trigger points. A mechanically-scanned 3D probe (3D9-3v) was used for 3D imaging in a subject with a latent trigger point. The MTrP is clearly identified (arrows) in all three planes as well as in a multi-slice view.

Figure 5

Simultaneous 2D grayscale and color variance imaging. (A and B) Normal upper trapezius muscle. The normal muscle appears isoechoic and has uniform color variance (TIS=0). (C and D) Muscle with a palpable MTrP. A hypoechoic region and a well-defined focal decrease of color variance indicating a localized stiffer region is visible (TIS=1). (E and F) Muscle with a palpable MTrP. Multiple hypoechoic regions and multiple focal nodules are visible (TIS=2).

Figure 6

3D color Doppler imaging of blood vessels passing through trigger points. A mechanically-scanned 3D probe (3D9-3v) was used for 3D imaging in a subject with a latent trigger point. The blood vessel is clearly visualized in all three planes.

Figure 7

(A) The main blood supply to the upper trapezius is through the ascending branch of the transverse cervical artery. (B) The ascending branch can be visualized using color Doppler imaging. The blood flow waveform in the ascending branch or other branches arising from this vessel can provide an indication of the flow resistance in the perfused tissue. (C) A blood vessel passing through an active MTrP.

Figure 8

(A) Subject with an active (symptomatic) MTrP visible as a hypoechoic region on the grayscale image, and an artery running through the MTrP visible on color Doppler (the Doppler sample volume is placed inside the MTrP). High-resistance blood flow waveform with retrograde diastolic flow was observed in the artery. (B) The same subject had a latent (non-symptomatic) MTrP on the contralateral side with an artery running through it, which showed elevated diastolic flow but no retrograde diastolic flow. (C) Four waveform shapes observed in our studies. C.1 shows arterial flow in muscle with no diastolic flow (BFS=0). C.2 shows elevated flow in diastole (BFS=1). C.3 shows oscillatory high-resistance flow with retrograde flow in early diastole (BFS=2). C.4 shows sustained retrograde flow in diastole (BFS=2).

Figure 9

Distribution of scores based on ultrasound imaging for active, latent and normal sites in upper trapezius muscle. Muscle with palpable trigger points on clinical exam (either active or latent) had a significantly higher tissue imaging score (TIS) compared to palpably normal muscle (p