Modulation in Elastic Properties of Upper Trapezius with Varying Neck Angle

Abstract

Background: Neck and shoulder complaints caused by poor posture may influence upper trapezius stiffness. The relationship between the shear elastic modulus of the upper trapezius and cervical flexion angles is unknown. Therefore, it is essential to assess upper trapezius stiffness during cervical flexion. The objectives of this study were to (1) determine the intra- and interoperator reliabilities of evaluating upper trapezius stiffness and calculate the minimal detectable change (MDC); (2) examine the elastic modulus alterations of the upper trapezius during cervical flexion; and (3) explore the difference of upper trapezius stiffness between the dominant and nondominant sides.

Methods: Twenty healthy male participants were recruited in this study. The shear modulus of the upper trapezius was evaluated by two independent investigators using shear wave elastography (SWE) during cervical flexion at 0° and 50°.

Findings: The intraoperator (intraclass correlation coefficient (ICC) = 0.85-0.86) and interoperator (ICC = 0.94-0.98) reliabilities for measuring the shear elastic modulus of the upper trapezius during the cervical flexion ranged from good to excellent. An increase of 35.58% in upper trapezius stiffness was found at 0° to 50° of cervical flexion, and the MDC was 7.04 kPa. In addition, a significant difference was obtained in the elastic modulus of the upper trapezius muscle between the dominant and nondominant sides (P < 0.05).

Conclusions: Our findings revealed that SWE could quantify the elastic modulus of the upper trapezius and monitor its changes. Therefore, further studies are required to delineate the modulation in upper trapezius muscle stiffness among subjects with neck and shoulder pain.

Figure 1

Participant position at 0° of cervical flexion with a Goniometer Pro assessing upper trapezius stiffness.

Figure 2

SWE maps of the upper trapezius muscle. Upper images: color-coded box presentations of the upper trapezius elasticity are shown in the upper image (the image color represents stiffness degree: red indicates stiff, while blue indicates soft). Lower images: B-mode images of the upper trapezius (UT: upper trapezius).

Figure 3

Bland-Altman plots of intra- and interoperator reliabilities for measuring the upper trapezius at 0° of cervical flexion. (a, b) Intra- and interoperator reliabilities of assessing upper trapezius stiffness at 0° of cervical flexion. (c, d) Intra- and interoperator reliabilities of assessing upper trapezius stiffness at 50° of cervical flexion (the continuous lines represent the mean difference, while the dotted lines show the 95% upper and lower limits of agreement).

Figure 4

Mean and standard deviation of upper trapezius shear modulus examined during 0° (white bar) or 50° (gray bar) of cervical flexion. ^∗Significant intergroup difference (P < 0.05).

Figure 5

Mean and standard deviation in upper trapezius shear modulus examined between the dominant (white bar) and nondominant (gray bar) sides during 0° and 50° of cervical flexion. ^∗Significant intergroup difference (P < 0.05).