IMPAIRMENT IN MUSCLE function is a feature of chronic mechanical neck pain and has been implicated as a signif-
icant factor in the maintenance of this disorder that is characterized by periods of remission and exacerbation.
Impairments of the cervical extensor muscles have been identified in patients with mechanical neck pain disorders
and exercise to train and improve their performance is advocated in management.
However, there is a paucity of studies investigating their role in mechanical neck pain. Further information on the topic could be useful to better inform decision making in the clinical management of neck pain.
Studies investigating the neck extensor muscles in patients with mechanical neck pain have observed changes in their
physical structure, including alterations in cross-sectional area, and changes in fiber type.
Studies have also identified deficiencies in extensor muscle strength and endurance in patients with neck pain compared with healthy subjects. However, while clinical evidence exists for the flexors, there has been little exploration into the effect of painful neck disorders on the differential activation of the extensor muscles.
Within the multiple layers of the cervical extensor muscle group, there is a distinct division between the superficial cer-
vical muscles (splenius capitis [SpC] and semispinalis capitis [SCa]), which span the entire cervical spine and the deeper
layered muscles (semispinalis cervicis [SCe] and the multifidus [Mul]), which span only the typical cervical vertebrae (C2-7).While imaging studies have attempted to quantify changes in cervical extensor muscle activity in response to exercise,
no studies to date have compared the activity patterns of the different cervical extensor muscles in patients with and without chronic mechanical neck pain disorders. It is therefore pertinent to compare the differential activity of the extensors in people with and without mechanical neck pain. Varied morphologic changes have been shown to occur in the presence of neck pain,and it is thus plausible to also expect variable
changes in motor output in the presence of pain. Muscle functional magnetic resonance imaging (mfMRI) is
a useful method to noninvasively evaluate muscle activity of multiple-layered cervical extensor muscles.
The mfMRI method is based on an increase in T2 relaxation time of muscle water after exercise. Specifically, there is a slower decay of the muscle water signal in response to exercise, causing an enhancement in signal intensity of the activated muscles on T2-weighted images (appears brighter) that can be quantified.
Changes in the T2 value recorded from the pre- and postexercise image are calculated and referred to as the T2 shift per-
mitting quantification of activity levels of specific muscles in response to exercise. Accordingly, T2 shift measures have
shown to be concordant with other measures of muscle activity (eg, electromyography and dynamometry measures of
force) and have shown high measurement reliability with intraclass correlation coefficients ranging from 0.87 to 0.94.
The purpose of this study was to compare the activity of the cervical extensor muscles in patients with mechanical neck
pain to that of healthy controls during 2 different cervical exercise conditions using an mfMRI method. We hypothesized
that there would be evidence of altered activity of the multi-layered extensor muscles in patients with mechanical neck pain compared with healthy controls. It was anticipated that the findings would enhance our understanding of motor impairments in mechanical neck pain disorders.