Neck pain is a condition that is commonly treated by health care professionals. It has been estimated that the annual prevalence of neck pain in the general population is 30-50%, with the prevalence of activity limitations due to neck pain ranging between 11-14%
[1, 2]. Neck pain can be categorized based on the duration of symptoms as acute (less than 7 days), sub-acute (between 7 days and 3 months), or chronic (greater than 3 months)
. Whereas the majority of individuals who experience acute symptoms do not seek professional care, chronic neck pain has a prolonged negative impact on health and health care expenditures
Several studies have investigated the reliability of cervical impairment measures such as strength
[5, 6], endurance
[5, 6], and range of motion
[6, 7] among individuals with neck pain. As reviewed by Nordin and colleagues
, a large number of these studies examined patients with acute or whiplash associated neck pain, in which measurement reliability may be reduced by limited tolerance for maximal performance testing after an acute injury. Moreover, the natural time course of symptom resolution is more predictable in patients with acute compared to chronic neck pain
, which ultimately limits the ability to generalize findings from an acute pain population to patients who are experiencing chronic symptoms. Given that chronic symptoms tend to fluctuate over time, it is important to establish the between-day reliability and minimum detectable change (MDC) for cervical impairment measures so that clinicians can identify meaningful improvement in patients treated for chronic neck pain. Finally, the reliability of cervical impairment measures has most often been examined within a single session
[8–11] limiting the ability to generalize these findings to a clinical setting where impairments are typically reassessed days or weeks apart, often by different therapists.
In addition to establishing the reliability and MDC of cervical impairment measures, it is also important to identify whether there are systematic differences in the range of values typically observed among individuals with and without chronic neck pain. Normative data from healthy individuals can help identify which impairments should be targeted for assessment in patients with neck pain, and provide an empirical basis for judging the severity of impairments for individual patients.
In the absence of quantitative assessment tools for neck pain that are both valid and feasible, clinicians often rely on the subjective categorization of musculoskeletal impairments. For example, muscle length is often categorized as “within normal limits” or “short” as compared to the contralateral limb
[8, 12]. Similarly, muscle strength is often categorized on an ordinal scale based on manual muscle testing (MMT) as described by Kendall and McCreary
. Although the MMT scale is commonly used in clinical practice, it lacks sensitivity to detect improvements in strength among individuals whose muscles are neurologically intact and able to withstand a relatively high magnitude of manual resistance
. Recent studies have demonstrated the utility of hand held dynamometry (HHD) as a robust alternative to MMT which shows acceptable reliability for a variety of different tests of isometric strength across several muscle groups
[9, 13]. Although scapulothoracic muscles such as the rhomboids, middle trapezius, and lower trapezius are thought to contribute to postural stability of the cervical spine and reduce biomechanical loading of cervicoscapular musculature
[14, 15], we are aware of only one study that has investigated the use of HHD to measure scapulothoracic muscle strength in individuals with neck pain
. It is currently not known whether scapulothoracic muscle strength is impaired in patients with chronic neck pain compared to healthy individuals, or whether the strength of these muscles can be reliably assessed over time.
Whereas numerous studies have reported the intra- and inter-rater reliability of cervical impairment measures, systematic differences between individuals with and without neck pain and the MDC required to detect clinically significant improvement over time have not been established for the majority of these measures. This limits the ability of clinicians to identify meaningful thresholds of cervical impairment, and to track quantitative changes in these impairments following treatment. The reliability and validity of scapulothoracic impairment measures are also not known, despite being commonly addressed in interventions for chronic neck pain. Therefore, the purpose of this study was to assess the inter-rater reliability, MDC, and group differences in quantitative cervical and scapulothoracic impairment measures among individuals with and without chronic neck pain.