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.