Measurement of segmental cervical multifidus contraction by ultrasonography in asymptomatic adults.

The deep muscles that play significant roles in maintaining segmental stability have been measured using ultrasonography (US). However, few studies have been carried out to determine the reliability and validity of US for measuring the cervical multifidus during contraction. The aims of this investigation were to evaluate the reliability of the dimensions of the cervical multifidus as measured using US and compare the US measurements with those determined with magnetic resonance imaging (MRI), the gold standard. Ten asymptomatic adult subjects (age, 28.5+/-3.5 years) participated in testing-retesting of muscle dimensions at rest and during isometric head extension with the cranio-cervical spine maintained in a flexed position against individual maximum resistance. Ten asymptomatic adult subjects (age, 28.1+/-4.1 years) participated in testing to compare US and MRI measurements of the thickness, width, area, and shape ratio of the cervical multifidus at the C4, C5, and C6 levels. US measurements of muscle thickness at the C4, C5, and C6 levels at rest were 0.67+/-0.14, 0.70+/-0.20 and 0.73+/-0.09 cm, respectively; the corresponding measurements as determined by MRI were 0.70+/-0.12, 0.67+/-0.15 and 0.70+/-0.06 cm. The within-subject coefficient of variation (CV(w)) for thickness at rest and during contraction was less than 10%, indicating acceptable reliability. US measurement of thickness had better reliability and validity. The range of limit of agreement for muscle thickness at the C4, C5, and C6 levels was -0.20 to 0.20 cm, and the range of R(2) was 0.42-0.64. The thickness of the cervical multifidus muscle increased significantly during contraction (1.13+/-0.20, 1.19+/-0.20 and 1.17+/-0.12 cm for the C4, C5, and C6 levels, P<0.05). However, no significant differences were noted among the three levels. The results indicate that US can detect changes in segmental cervical multifidus during contraction.