Cervico-thoracic and cranio-cervical strength differences between women with and without neck pain and the diagnostic performance of neck-strength tests

Background: Cervical strength and stability is often addressed in rehabilitation of people with neck pain. These functions may be associated with emergence and retention of neck pain in cases where the neck strength does not meet daily demands. However, clear empiric support for these notions are lacking, partly due to a scarcity of well controlled dynamometry studies with large samples. First, clarification is needed whether neck strength is in fact reduced in people with neck pain and to resolve the diagnostic performance of neck strength tests. Purpose: To compare neck muscle strength of women with non-specific long-term neck pain and healthy controls. Also, to assess the diagnostic performance of neck strength tests by assessing their discriminative ability to discern women with and without neck pain. Methods: The study had a cross-sectional design with data on cervical strength derived from the baseline measurement of a randomized controlled trial (RCT). 80 women with long-term non-specific neck pain (NP) were compared with 40 healthy women (CON). The NP group was a subsample from the RCT selected so that there were no group differences (NP-CON) for body weight and physical activity. Cervical strength assessment included dynamometry of cervico-thoracic extension (CTE) and flexion (CTF) in sitting and cranio-cervical flexion (CCF) in standing, all performed with isometric maximum voluntary contraction (iMVC). Independent samples Mann-Whitney U test and T-test were used to assess group differences for iMVC of the tests. Diagnostic accuracy was further assessed with a receiver operating characteristic (ROC) curve by plotting the true positive rate (sensitivity) as a function of the false positive rate (1 - specificity). The area under the ROC curve (AUC) with 95% confidence interval was used to determine discriminative ability of the tests. The optimal cut-off value to discern NP from CON with corresponding sensitivity and specificity was also determined. Results