Understanding the vascular environment of myofascial trigger points using ultrasonic imaging and computational modeling

Abstract

Myofascial pain syndrome (MPS) is a common, yet poorly understood, acute and chronic pain condition. MPS is characterized by local and referred pain associated with hyperirritable nodules known as myofascial trigger points (MTrPs) that are stiff, localized spots of exquisite tenderness in a palpable taut band of skeletal muscle. Recently, our research group has developed new ultrasound imaging methods to visualize and characterize MTrPs and their surrounding soft tissue. The goal of this paper was to quantitatively analyze Doppler velocity waveforms in blood vessels in the neighborhood of MTrPs to characterize their vascular environment. A lumped parameter compartment model was then used to understand the physiological origin of the flow velocity waveforms. 16 patients with acute neck pain were recruited for the study and the blood vessels in the upper trapezius muscle in the neighborhood of palpable MTrPs were imaged using Doppler ultrasound. Preliminary findings show that symptomatic MTrPs have significantly higher peak systolic velocities and negative diastolic velocities compared to latent MTrPs and normal muscle sites. Using compartment modeling, we show that a constricted vascular bed and an enlarged vascular volume could explain the observed flow waveforms with retrograde diastolic flow.

Figures

Figure 1

Schematic of a lumped parameter compliant vessel model with two vessels simulating blood flow through muscle with a MTrP.

Figure 2

(A). Color Doppler image showing a blood vessel very close to a palpable MTrP, which appears as a hypoechoic nodule on ultrasound images (arrow). (B) Four types blood flow waveforms that are representative of the findings in our study.

Figure 3

Difference in blood flow waveform parameters between active, latent and normal sites. The bars correspond to median values, and the error bars represent the interquartile range.

Figure 4

Simulated blood flow waveforms reproduces several features of the observed blood velocity waveforms, such as the flow oscillation at the dicrotic notch and retrograde flow in diastole. (A) The simulated arterial pressure waveform with 10 harmonic components. (B) Inflow waveforms through the two vascular pathways in Fig. 1(B). (C) Doppler velocity spectrum near L-MTrP. (D) Doppler velocity spectrum near A-MTrP.

Figure 5

Dependence of flow waveform on the initial vascular volume and outflow resistance. As the outflow resistance increases, the inflow decreases. However for a larger initial vascular volume, the pulsatility of the flow waveform increases with larger retrograde diastolic flow.