Comparison of Individual and Group Segmentation of Longus Colli and Longus Capitis Muscles in Whiplash-Associated Disorder: An MRI Analysis

This study aims to determine whether intramuscular or intermuscular fat contributes to changes in muscle size and FI in the deep cervical flexor muscles (longus colli and capitis) in WAD. This will be achieved by comparing muscle volume and FI when the longus colli and capitis muscles are segmented individually compared to together on MR images of control and chronic WAD participants. The results will inform the standardization of segmentation methods for interpreting muscle size and FI in WAD.

Magnetic resonance T1-weighted images were acquired using a 3 T MR scanner from participants with chronic WAD (n=14) and age- and sex-matched healthy controls (n=14). Manual segmentation of the left and right longus colli and capitis muscles, individually and together, was performed by trained blinded researchers using a Mat-lab based program. Muscle volume and FI were calculated. Mixed linear regression models were used, with each individual muscle or the muscles together set as the dependent variable, group (chronic WAD, healthy control) as the independent variable, and sex and age as covariates (fixed effects).

The chronic WAD and control groups each comprised 11 females and 3 males, with a mean (± SD) age of 27.1 ± 4.3 years and 27.8 ± 3.1 years, respectively. When the longus colli and capitis were segmented individually, group did not predict muscle volume (p=0.61 and p=0.97, respectively) or FI (p=0.096 and p=0.13, respectively). Similarly, group did not predict muscle volume (p=0.53) or FI (p=0.41) when the muscles were segmented together.

Segmenting the longus colli and capitis individually versus together did not affect the assessment of muscle volume or FI in individuals with chronic WAD compared to healthy controls. Assessing deep flexor muscles together rather than individually has the potential to save time and increase the potential to develop automated processes.

The segmentation of deep cervical spine flexor muscles individually versus together does not appear to influence the identification of changes in muscle size and FI due to chronic WAD. The results inform the development of standardized time-efficient segmentation methods for interpreting muscle size and FI to inform the accurate diagnosis and management of WAD.