Office-Based Elastographic Technique for Quantifying Mechanical Properties of Skeletal Muscle

Abstract

Objectives Our objectives were to develop a new, efficient, and easy-to-administer approach to ultrasound elastography and assess its ability to provide quantitative characterization of viscoelastic properties of skeletal muscle in an outpatient clinical environment. We sought to show its validity and clinical utility in assessing myofascial trigger points, which are associated with myofascial pain syndrome. Methods Ultrasound imaging was performed while the muscle was externally vibrated at frequencies in the range of 60 to 200 Hz using a handheld vibrator. The spatial gradient of the vibration phase yielded the shear wave speed, which is related to the viscoelastic properties of tissue. The method was validated using a calibrated experimental phantom, the biceps brachii muscle in healthy volunteers (n = 6), and the upper trapezius muscle in symptomatic patients with axial neck pain (n = 13) and asymptomatic (pain-free) control participants (n = 9). Results Using the experimental phantom, our method was able to quantitatively measure the shear moduli with error rates of less than 20%. The mean shear modulus ± SD in the normal biceps brachii measured 12.5 ± 3.4 kPa, within the range of published values using more sophisticated methods. Shear wave speeds in active myofascial trigger points and the surrounding muscle tissue were significantly higher than those in normal tissue at high frequency excitations (>100 Hz; P < .05). Conclusions Off-the-shelf office-based equipment can be used to quantitatively characterize skeletal muscle viscoelastic properties with estimates comparable to those using more sophisticated methods. Our preliminary results using this method indicate that patients with spontaneous neck pain and symptomatic myofascial trigger points have increased tissue heterogeneity at the trigger point site and the surrounding muscle tissue.

Ultrasonic Characterization of the Upper Trapezius Muscle in Patients with Chronic Neck Pain

“…This finding agrees with our group’s previous observations 7–9 : subjects with active MTrPs showed spherical or band-like hypoechoic (darker) regions with an increase in fiber alignment heterogeneity.…”

“…Following Travell and Simon’s diagnostic criteria, 1 this examiner determined the presence or absence of MTrPs in the muscle. Four sites (two sites per side) were marked on each subject, in the central region of the upper trapezius muscle within 6 cm of the muscle’s midline, approximately midway between the cervical vertebrae and the acromion process, as described in Ballyns et al 9 A site was classified as “active” if it was both spontaneously painful (pain present without provocation) and had at least one palpable nodule whose palpation reproduced the characteristic pain complaint, indicative of an active MTrP. Sites in symptomatic subjects were considered “normal in symptomatic” if no palpable nodule was found in that specified region of the upper trapezius muscle.…”

Ultrasound Elastography: The New Frontier in Direct Measurement of Muscle Stiffness

“…For persons with chronic muscular pain trigger points, ultrasound elastography appears to be able to detect changes in muscle stiffness (Figure 3) (13,14,48). Although the exact etiology of trigger points is unknown, one theory is that chronic muscle overuse leads to inflammation (64).…”

Ultrasonography in Diagnosis of Myofascial Pain Syndrome and Reliability of Novel Ultrasonic Indexes of Upper Trapezius Muscle

“…The results of the first step of the study were inves tigated with regard to the sensitivity and specificity of ultrasonography compared to the results of clinical diagnosis, which was considered a gold standard for the diagnosis of MPS [11].…”

“…In spite of the limitations in clinical diagnosis of MPS, physical manoeuvres such as palpation remain a gold standard for detecting MTrPs and diagnosing MPS [11].…”