The qualitative grading of muscle fat infiltration in whiplash using fat and water magnetic resonance imaging

Abstract

Background context: The development of muscle fat infiltration (MFI) in the neck muscles is associated with poor functional recovery following whiplash injury. Custom software and time-consuming manual segmentation of magnetic resonance imaging (MRI) is required for quantitative analysis and presents as a barrier for clinical translation.

Purpose: The purpose of this work was to establish a qualitative MRI measure for MFI and evaluate its ability to differentiate between individuals with severe whiplash-associated disorder (WAD), mild or moderate WAD, and healthy controls.

Study design/setting: This is a cross-sectional study.

Patient sample: Thirty-one subjects with WAD and 31 age- and sex-matched controls were recruited from an ongoing randomized controlled trial.

Outcome measures: The cervical multifidus was visually identified and segmented into eighths in the axial fat/water images (C4-C7). Muscle fat infiltration was assessed on a visual scale: 0 for no or marginal MFI, 1 for light MFI, and 2 for distinct MFI. The participants with WAD were divided in two groups: mild or moderate and severe based on Neck Disability Index % scores.

Methods: The mean regional MFI was compared between the healthy controls and each of the WAD groups using the Mann-Whitney U test. Receiver operator characteristic (ROC) analyses were carried out to evaluate the validity of the qualitative method.

Results: Twenty (65%) patients had mild or moderate disability and 11 (35%) were considered severe. Inter- and intra-rater reliability was excellent when grading was averaged by level or when frequency of grade II was considered. Statistically significant differences (p<.05) in regional MFI were particularly notable between the severe WAD group and healthy controls. The ROC curve, based on detection of distinct MFI, showed an area-under-the curve of 0.768 (95% confidence interval 0.59-0.94) for discrimination of WAD participants.

Conclusions: These preliminary results suggest a qualitative MRI measure for MFI is reliable and valid, and may prove useful toward the classification of WAD in radiology practice.

Keywords: MRI; Muscle fat; Neck; Recovery; Spine; Whiplash.

Figure 1.

Left: Sagittal MR slice with vertebral level C4, C5, C6, and C7 marked. Middle: Axial Fat image at vertebral level C4, C5, C6, and C7. Right: Corresponding axial water image to the right. The image is from a 54-year old healthy female control.

Figure 2.

Top: Fat MR image with the multifidus muscle outlined. The muscle is then divided into eight regions for visual fat interpretation. Bottom: Example fat images of a healthy control, mild or moderate WAD, and a severe WAD participant.

Figure 3.

Average MFI for each region and cervical level for (Left) Healthy controls, (Middle) Mild or moderate WAD, (Right) Severe WAD. * p<0.03 Severe WAD compared to healthy controls, + p<0.02 Mild or moderate WAD compared to severe WAD.

Figure 4.

Frequency of MFI Scores across each group and level; Control, Mild or moderate WAD, severe WAD. * p = 0.03 Severe WAD compared to healthy controls, + p = 0.02 Mild or moderate compared to severe WAD.

Figure 5.

Results of ROC analyses discriminating mild or moderate WAD and severe WAD when, (Left) considering both diffuse (grades 0, 1, and 2) and distinct (only grade 2) MFI, and (Right) only considering distinct MFI.