Reliability of muscle thickness measurements of the deep neck flexors in the upper cervical spine

Musculoskeletal ultrasound(MSK-US) has demonstrated acceptable validity and reliability for measuring muscle thickness(MT) in the mid-cervical spine(C4–C6). No standardized protocol exists for assessing MT of the deep neck flexors (DNF) above the C4 level. Developing a novel protocol in asymptomatic individuals is a crucial step in bridging the gap between measurement and clinical relevance, enhancing the applicability of ultrasound assessment in cervical spine evaluation.

Describe a novel protocol for MSK-US MT measurements at the C3 level and determine the inter and intrarater reliability of MSK-US measurement for this novel protocol. The secondary objective is to establish a clinically useful measure for Minimum Detectable Change(MDC) for MSK-US measures of MT in the upper cervical spine.

25 participants completed this cross-sectional study. Two clinicians independently captured ultrasound images of participant right sided deep neck flexors. Three ultrasound images of the DNF musculature were obtained and the average MT of the images was used for analysis. Four separate intra-class correlation coefficients(ICC_2,1 and ICC _2,3) with 95 %CI were calculated, and standard error of measurement(SEM) were used.

The ICC for intrarater reliability for rater 1 was “moderate”(ICC_2,1.52,95 %CI-.04 -.78,P = .034). Rater 2 was “moderate”(ICC_2,1.64,95 %CI.17-.84,P = .008). The ICC for interrater reliability for day 1 was “moderate”(ICC_2,3.73,95 %CI.38-.88, P = .001). Day 2 was “high”(ICC_2,3.79,95 %CI.55-.91, P < .001). The SEM range was .16-.23 cm. The MDC range was .65-.44 cm.

Measuring MT of the DNF at the C3 level is a novel, reliable protocol which can be implemented clinically and in future research to measure physiological adaptations to prescribed cervical interventions.