The geography of fatty infiltrates within the cervical multifidus and semispinalis cervicis in individuals with chronic whiplash-associated disorders

Abstract

Study design: Cross-sectional.

Objectives: To quantify the magnitude and distribution of muscle fat infiltration (MFI) within the cervical multifidus and semispinalis cervicis muscles in participants with chronic whiplash-associated disorders (WADs) compared to those who have fully recovered from a whiplash injury and healthy controls.

Background: Previous research has established the presence of increased MFI throughout the cervical extensor muscles of individuals with WAD when compared to healthy controls. These changes appear to be greater in the deepest muscles (eg, multifidus and semispinalis cervicis) than in the more superficial muscles. A detailed analysis of the distribution of MFI within these deep extensor muscles in chronic WAD, recovered, and control groups would provide a foundation for further investigation of specific mechanisms, etiologies, and targets for treatments.

Methods: Fifteen participants (WAD, n = 5; recovered, n = 5; and control, n = 5) were studied using a 3-D fat-water separation magnetic resonance imaging sequence. Bilateral measures of cervical multifidus and semispinalis cervicis MFI in 4 quartiles (1 [medial] to 4 [lateral]) at cervical levels C3 through C7 were included in the analysis. Intrarater and interrater reliability were established. A mixed-model analysis was performed to control for covariates, identify interaction effects, and compare MFI distribution between groups.

Results: The limits of agreement confirmed strong intrarater and interrater agreement at all levels (C3-C7). Sex, age, and body mass index were identified as significant covariates for MFI. Significant interactions were found between group and muscle quartile (P<.001) and between muscle quartile and cervical level (P<.001). Pairwise comparisons for intraquartile MFI between groups revealed significantly greater MFI in the WAD group when compared to the recovered group in the first quartile (P<.001), second quartile (P<.001), and third quartile (P = .03). When compared to the control group, the WAD group had significantly greater MFI in the first quartile (P = .002) and the second quartile (P = .045). The control group had significantly higher MFI in comparison to the recovered group in the first quartile (P = .048).

Conclusion: This study provides preliminary data mapping the spatial distribution of MFI in the cervical multifidus and semispinalis cervicis muscles in individuals with chronic WAD, those who have recovered from a whiplash injury, and healthy controls. Muscle fat infiltration is more concentrated in the medial portion of the muscles in all participants. However, the magnitude of MFI in the medial quartiles (1 and 2) is greatest in the chronic WAD group.

Keywords: MRI; imaging; muscle; neck; spine.

FIGURE 1.

Regions of interest (ROIs) were drawn bilaterally around the Multifidus and Semispinalis Cervicis muscles (only one side shown above) at 5 cervical levels (C3-C7) for each participant. Each ROI was divided into quartiles (Q1 (medial) - Q4 (lateral)) for muscle fat infiltration (MFI) analysis.

FIGURE 2.

Intrarater and interrater reliability for the MFI quantification method. a) Bland-Altman Plot for intrarater reliability (Limits of Agreement (LOA)={−0.04, 0.06}), b) Bland-Altman Plot for interrater reliability (LOA={−0.07, 0.07}), c) Intrarater correlation (Intraclass Correlation Coefficient (ICC)[2,1] = 0.98, 95%CI = 0.97, 0.98), d) Interrater correlation (ICC[2,1] = 0.93, 95%CI = 0.90, 0.94).

FIGURE 3.

MFI means and standard deviations for between group comparisons at each quartile (Q1- medial, Q4- lateral) averaged over all cervical levels. The values are estimated marginal means and were based on the covariate values of age = 32.8 years, Body Mass Index (BMI) = 27.27 kg/m², and cervical level = C4. Significance is denoted as * for P<.05, ** for P<.01, and *** for P<.001.

FIGURE 4.

Mapping of MFI across quartiles of the Multifidus and Semispinalis Cervicis muscles for WAD (a), Recovered (b), and Control (c) groups and across cervical levels for WAD (d), Recovered (e), and Control (f) groups. There was a significant interaction between group and muscle quartile (P<.001) and between muscle quartile and cervical level (P<.001).