Cross-sectional area of posterior extensor muscles of the cervical spine in asymptomatic subjects: a 10-year longitudinal magnetic resonance imaging study

Abstract

There has been no prospective study on age-related changes of the extensor muscles of the cervical spine in healthy subjects. This study was conducted to elucidate any association between the changes in cross-sectional area of the extensor muscles of the cervical spine on MRIs and cervical disc degeneration or the development of clinical symptoms. Sixty-two subjects who underwent MR imaging by a 1.5-Tesla machine between 1993 and 1996 as asymptomatic volunteers in a previous study were recruited again 10 years later for this follow-up study. The mean interval between the studies was 11.0 ± 0.7 years. The cross-sectional areas of the multifidus, semispinalis cervicis, semispinalis capitis, and splenius capitis at C3-C4, C4-C5, and C5-C6 intervertebral levels were measured on T2-weighted axial images using Image J 1.42. The mean cross-sectional areas of the deep extensor muscles were 1,396.8 ± 337.6 mm(2) at the C3-C4 level, 1,514.7 ± 381.0 mm(2) at the C4-C5 level, and 1,542.8 ± 373.5 mm(2) at the C5-C6 level in the previous investigation. The cross-sectional areas were 1,498.7 ± 374.4 mm(2) at the C3-C4 level, 1,569.9 ± 390.9 mm(2) at the C4-C5 level, and 1,599.6 ± 364.3 mm(2) at the 10-year follow-up. An increase in the cross-sectional area of the muscles was more frequently observed in subjects in their tens to thirties in the initial study, while a decrease was more frequently observed in those in their forties and older in the initial study. Disc degeneration was not correlated with a change in extensor muscle volume. Development of shoulder stiffness during follow-up was significantly negatively correlated with a change in the cross-sectional area of the deep extensor muscles.

Fig. 1

Sagittal alignment of the cervical spine. A line (“A”) was drawn between the lower posterior corners of C2 and C7. Perpendicular lines were drawn from the lower posterior edge of the bodies of C3–C6 to this line, and their lengths were denoted as a1–a4. If every line a1–a4 was anterior to “A” and one was more than 2 mm, the curvature was defined as lordosis. If every line a1–a4 was less than 2 mm, the curvature was defined as straight. If a1–a4 was measurable both anterior and posterior to “A,” and one was more than 2 mm, the curvature was defined as sigmoid. If every line a1–a4 was posterior to “A” and one was more than 2 mm, the curvature was defined as kyphosis

Fig. 2

Posterior extensor muscles, visualized on an axial T2-weighted image at the C5–C6 level. The cross-sectional area of the a multifidus, b semispinalis cervicis, c semispinalis capitis, and d splenius capitis was measured using Image J 1.42 software, calibrated to the scale of the MR image

Fig. 3

Changes in the total cross-sectional area of the posterior extensor muscles by age group