Introduction: Magnetic Resonance Imaging (MRI) is the gold standard for imaging muscle and fatty infiltrate has featured in low back pain. However, there is little knowledge about in vivo features of neck muscles in chronic WAD. The purpose of this study was to quantitatively compare fatty infiltrate in the cervical extensors in patients with chronic WAD and controls across muscle and segmental level.

Methods: Volunteer subjects were gained through referral from local practitioners and the local university fraternity. A previously established MRI measure was performed in 113 female subjects (79- WAD & 34 healthy controls). Subjects with chronic WAD (> three months – < three years) were included if, classifiable as WAD II per the Quebec Task Force. The cohort was restricted to females (18–45 years) as they best represent those with chronic WAD. Volunteers were excluded when

classified as WAD I, III or IV

The measure was performed for the rectus capitis minor/major, multifidus, semispinalis cervicis/capitis, splenius capitis and upper trapezius. The values for all muscles were plotted for level and side and linear regression analysis was used to determine segmental trends (C3-7). A multi-factorial analysis of variance (MANOVA) was applied to investigate group means of whiplash and controls for fat indices across muscle, side and level. Bonferroni post-hoc comparisons were used to compare group by muscle interactions at each level. Multiple regression analyses were performed to determine if the score on the Neck Disability Index (NDI), age, Body Mass Index (BMI), compensation status and duration influenced fatty infiltrate. Significance was set at p < 0.05. Data presented as mean ± SD.

Results: The demographic characteristics of the two groups are: WAD (n = 79): age: 29.7 ± 7.8 years, BMI (kg/m2): 25.1 ± 5.7; duration: 20.3 ± 9.6 months and NDI: 45.5 ± 15.9. Healthy Controls (n = 34): Age: 27.0 ± 5.6 years, BMI: 23.0 ± 4.4.. NDI was not collected in controls.

MANOVA revealed significant main effects for group, muscle, segmental level and side (p < 0.0001), and significant interactions between Group:Muscle, Group:Level, Muscle:Level and Group:side (p < 0.0001). Sides were averaged for each muscle and level for post-hoc analysis.

There was a linear decrease in the fat indices from C3 – C7 for each muscle in both groups. No significant differences in fat indices across muscle, levels and side were noted in controls (p = 0.09). For the WAD subjects, the multifidus muscle had significantly higher fat content at each level compared to the other segmental muscles (p < 0.0001) and was highest at C3 (p < 0.0001).

There were higher fat indices in the whiplash group compared to the controls for the rcpmin and rcpmaj muscles (p < 0.0001).

No relationship was found for fat indices in all WAD muscles and NDI scores (p = 0.81), age (p = 0.14), duration (p = 0.99), compensation (p = 0.37) or BMI (p = 0.74).

Discussion: There is significantly greater fatty infiltration in neck extensors, especially in the deeper muscles, in females with chronic WAD when compared with controls. Future studies are required to investigate relationships between muscular degeneration and symptoms.