Novel Use of Ultrasound Elastography to Quantify Muscle Tissue Changes After Dry Needling of Myofascial Trigger Points in Patients With Chronic Myofascial Pain

Abstract

Objectives: To compare a mechanical heterogeneity index derived from ultrasound vibration elastography with physical findings before and after dry-needling treatment of spontaneously painful active myofascial trigger points in the upper trapezius muscle.

Methods: Forty-eight patients with chronic myofascial pain enrolled in a prospective interventional trial of 3 weekly dry-needling treatments for active myofascial trigger points. Trigger points were evaluated at baseline and at treatment completion using palpation, the pressure-pain threshold, and the mechanical heterogeneity index. Thirty patients were reevaluated at 8 weeks. Trigger points that "responded" changed to tissue that was no longer spontaneously painful, with or without the presence of a palpable nodule. Trigger points that "resolved" changed to tissue without a palpable nodule. The mechanical heterogeneity index was defined as the proportion of the upper trapezius muscle that appeared mechanically stiffer on elastography. Statistical significance for comparisons was determined at P < .05.

Results: Following 3 dry needle treatments, the mechanical heterogeneity index decreased significantly for the 38 myofascial trigger points (79% of 48) that responded to treatment. Among these, the baseline mechanical heterogeneity index was significantly lower for the 13 trigger points (27% of 38) that resolved, but the decrease after 3 dry needle treatments did not reach significance. The pressure-pain threshold improved significantly for both groups. At 8 weeks, the mechanical heterogeneity index decreased significantly for the 22 trigger points (73% of 30) that responded and for the 10 (45% of 22) that resolved. The pressure-pain threshold improvement was significant for trigger points that responded but did not reach significance for resolved trigger points.

Conclusions: The mechanical heterogeneity index identifies changes in muscle tissue properties that correlate with changes in the myofascial trigger point status after dry needling.

Keywords: dry needling; musculoskeletal ultrasound; myofascial pain syndrome; myofascial trigger points; ultrasound elastography.

© 2015 by the American Institute of Ultrasound in Medicine.

Figures

Figure 1

Examples of heterogeneous soft tissue properties in the upper trapezius muscles of 4 patients with active myofascial trigger points. The top row shows the B-mode images enhanced with histogram equalization to enhance contrast, and the bottom row shows the corresponding elastograms. On physical examination, the tissue was described in A and B as ropey, in C and D as having a chain of nodules, in E and F as lumpy, and in G and H as inhomogeneous.

Figure 2

Grayscale image (left) and color Doppler image (right) of an upper trapezius muscle with an active myofascial trigger point (arrows). The fascia borders (bright lines in the grayscale image) were used as guidelines to mark the upper trapezius muscle manually (yellow borders). Vibration elastography allows measurement of the mechanical heterogeneity index from the color Doppler variance image.

Figure 3

Myofascial trigger point (arrows) size evolution. Top row, Color Doppler variance images. Middle row, Binary images of the mechanical heterogeneity region. Bottom row, Yellow borders indicate B-mode images of the upper trapezius muscle, and red borders indicate regions with a lower vibration amplitude (red line).

Figure 4

Bland-Altman plots of the cross-sectional areas of the upper trapezius muscle. Left, Repeatability of the upper trapezius area between 2 consecutive measurements. Right, Repeatability of the mean upper trapezius area between measurements performed at baseline and follow-up visits.

Figure 5

Bland-Altman plots of the mechanical heterogeneity area. Left, Myofascial trigger point area. Right, Mechanical heterogeneity index.

Figure 6

Changes in tissue status after dry needling at the 3- and 8-week follow-ups. Left, Open circles represent individual mechanical heterogeneity indices (MHI) of upper trapezius muscles with treated active myofascial trigger points at different visits; gray lines are drawn between individual active trigger points that responded at week 3 or 8; unconnected circles represent trigger points that did not respond; open diamonds represent mean mechanical heterogeneity indices of upper trapezius muscles with trigger points that responded at week 3; and open squares represent mean mechanical heterogeneity indices of upper trapezius muscles with trigger points that responded at week 8. Right, Open circles represent individual mechanical heterogeneity indices of upper trapezius muscles with treated active trigger points at different visits; gray lines are drawn between individual active trigger points that resolved at week 3 or 8; unconnected circles represent trigger points that did not resolve; open diamonds represent mean mechanical heterogeneity indices of upper trapezius muscles with trigger points that resolved at week 3; and open squares represent mean mechanical heterogeneity indices of upper trapezius muscles with trigger points that resolved at week 8. *P < .01; **P < .001.

Figure 7

Changes in pressure-pain threshold (PPT) scores after dry needling at the 3- and 8-week follow-ups. Notations are as in Figure 6.