Objective sonographic measures for characterizing myofascial trigger points associated with cervical pain

Abstract

Objectives: The purpose of this study was to determine whether the physical properties and vascular environment of active myofascial trigger points associated with acute spontaneous cervical pain, asymptomatic latent trigger points, and palpably normal muscle differ in terms of the trigger point area, pulsatility index, and resistivity index, as measured by sonoelastography and Doppler imaging.

Methods: Sonoelastography was performed with an external 92-Hz vibration in the upper trapezius muscles in patients with acute cervical pain and at least 1 palpable trigger point (n = 44). The area of reduced vibration amplitude was measured as an estimate of the size of the stiff myofascial trigger points. Patients also underwent triplex Doppler imaging of the same region to analyze blood flow waveforms and calculate the pulsatility index of blood flow in vessels at or near the trigger points.

Results: On sonoelastography, active sites (spontaneously painful with palpable myofascial trigger points) had larger trigger points (mean ± SD, 0.57 ± 0.20 cm(2)) compared to latent sites (palpable trigger points painful on palpation; 0.36 ± 0.16 cm(2)) and palpably normal sites (0.17 ± 0.22 cm(2); P < .01). Analysis of receiver operating characteristic curves showed that area measurements could robustly distinguish between active, latent, and normal sites (areas under the curve, 0.9 for active versus latent, 0.8 for active versus normal, and 0.8 for latent versus normal, respectively). Doppler spectral waveform data showed that vessels near active sites had a significantly higher pulsatility index (median, 8.3) compared to normal sites (median, 3.0; P < .05).

Conclusions: The results presented in this study show that myofascial trigger points may be classified by area using sonoelastography. Furthermore, monitoring the trigger point area and pulsatility index may be useful in evaluating the natural history of myofascial pain syndrome.

Figures

Figure 1

Color Doppler images (top row) of the vibrating trapezius muscle and binary images (bottom row) for trigger point area calculation of stiffer tissue zones. Muscle tissue was scored as follows: 0, uniform echogenicity and stiffness; 1, noisy image, no clear nodule; 2, taut band; 3, focal stiff nodule; and 4, multiple nodules. Arrows denote focal trigger points, and red outlined areas denote measured trigger point areas.

Figure 2

Color Doppler waveform images (top tow) of blood flow through the trapezius muscle and binary images (bottom row) for pulsatility and resistivity index calculations. Waveforms were scored as follows: 1, high-resistance flow with no diastolic flow; 2, elevated diastolic flow; and 3, sustained retrograde flow in diastole.

Figure 3

Plots of pain pressure threshold (PPT) scores and trigger point areas. *Significant difference from normal sites; +significant difference from latent sites (P < .05).

Figure 4

Receiver operating characteristic curves for pain pressure threshold (PPT) scores (top row) and trigger point areas (bottom row) comparing the classification strength between latent and normal, active and normal, and active and latent sites. Red lines indicate receiver operating characteristic curves; black diagonals, random classifiers; and circles, cutoff points for a successful test.

Figure 5

Plots of the pulsatility and resistivity indices for normal, latent, and active sites. *Significant difference (P < .05).

Figure 6

Three-dimensional plots of the visual analog scale (VAS) versus the pain pressure threshold (PPT) versus the trigger point area (left) and the pulsatility index versus the visual analog scale versus the area (right) for patients with latent and active sites. The visual analog scale and trigger point area measures separate latent and active data the most, whereas the pulsatility index shows the largest amount of variance in patients with active sites.

Figure 7

Follow-up data plots of the visual analog scale (VAS), pain pressure threshold (PPT), trigger point area, and pulsatility index versus time. Data are from 3 patients with active sites and 1 patient with latent sites that underwent dry needling after the initial visit and sonographic examination.