Confirming the geography of fatty infiltration in the deep cervical extensor muscles in whiplash recovery

Abstract

Previous preliminary work mapped the distribution of neck muscle fat infiltration (MFI) in the deep cervical extensor muscles (multifidus and semispinalis cervicis) in a small cohort of participants with chronic whiplash associated disorders (WAD), recovered, and healthy controls. While MFI was reported to be concentrated in the medial portion of the muscles in all participants, the magnitude was significantly greater in those with chronic WAD. This study aims to confirm these results in a prospective fashion with a larger cohort and compare the findings across a population of patients with varying levels of WAD-related disability one-year following the motor vehicle collision. Sixtyone participants enrolled in a longitudinal study: Recovered (n = 25), Mild (n = 26) and Severe WAD (n = 10) were studied using Fat/Water magnetic resonance imaging, 12-months post injury. Bilateral measures of MFI in four quartiles (Q1-Q4; medial to lateral) at cervical levels C4 through C7 were included. A linear mixed model was performed, controlling for covariates (age, sex, body mass index), examining interaction effects, and comparing MFI distribution between groups. The recovered group had significantly less MFI in Q1 compared to the two symptomatic groups. Group differences were not found in the more lateral quartiles. Results at 12 months are consistent with the preliminary study, indicating that MFI is spatially concentrated in the medial portions of the deep cervical extensors regardless of WAD recovery, but the magnitude of MFI in the medial portions of the muscles is significantly larger in those with severe chronic WAD. Various investigations across three continents (United States 1-3 , Australia 2,4-6 , and Sweden 7,8) have used similar manual segmentation methods with magnetic resonance imaging (MRI) to demonstrate widespread fatty infiltrates in the neck muscles of individuals with acute and chronic whiplash associated disorders (WAD). Comparably high levels of muscle fat infiltration (MFI) were not identified in individuals who (i) had recovered or reported lower levels of WAD-related disability 1,3,4,7,8 , (2) had chronic non-traumatic neck pain 9 , or (3) those without a history of neck disorders 10. Knowledge of a precise mechanism for MFI expression and distribution (e.g. extra-or intra-fascicular MFI) would provide a target for clinical remediation of any adverse symptoms; but this is largely unknown. There remains conjecture in the literature about what constitutes extra-or intra-fascicular MFI, which likely centres on our ability to reliably distinguish the epimysium/perimysium and associated muscle fascicles on MRI. Some have proposed standardised, anatomical definitions of regions of interest in quantifying spinal muscle composition 11,12 , which we concede can be difficult for the cervical spine (eg transversospinal muscles like multifidus).

Fatty infiltration in cervical flexors and extensors in patients with degenerative cervical myelopathy using a multi-muscle segmentation model

“…MRI findings of altered muscle adiposity are present across a number of spinal pathologies. For example, patients with severe WAD have higher MFI in cervical flexors and extensors as compared to healthy controls and patients with mild/moderate WAD [ 15 – 19 ]. Elevated levels of MFI in chronic whiplash may be reduced through a regimen of neck specific exercises [ 38 ].…”

“…These studies suggest that MFI may be an important pathophysiological marker in variety of conditions affecting the appendicular skeleton and the axial spine such as rotator cuff injury [ 40 – 42 ], WAD [ 15 – 19 ], disc herniation [ 43 , 44 ], degenerative disc disease [ 45 ], and DCM [ 14 ], respectively. However, studies on comprehensive examination of cervical muscle composition and its effects on symptomology, diagnostic, and prognostic utility in patients in DCM are limited.…”

“…Muscle fat infiltration (MFI) is commonly observed in patients with cervical spine diseases including whiplash associated disorders (WAD) from a motor vehicle collision [ 15 ], traumatic spinal cord injury [ 16 ], and DCM [ 14 ]. Increased MFI in cervical flexors (longus capitis/colli and sternocleidomastoid muscles) [ 17 ] and extensors (multifidus and semispinalis cervicis) [ 18 , 19 ] is associated with increased pain and clinical disability in patients with WAD. In a smaller clinical cohort of the patients used in this study, we previously showed that in patients with DCM there is an increased MFI in the multifidus muscles that may be associated with clinical disability, as measured by mJOA, and Nurick scales [ 14 ].…”

Multi-muscle deep learning segmentation to automate the quantification of muscle fat infiltration in cervical spine conditions

“…While the pathophysiological and pathomechanical mechanisms underlying these spinal conditions differ, the characteristic pattern of MFI appears to occur with greatest magnitude in the deep muscular layers of the cervical extensors (i.e., multifidus and semispinalis cervicis (MFSS)) and cervical flexors (i.e. longus colli and longus capitis (LC)) [18][19][20] . The ubiquitous nature of muscle compositional changes in these spinal conditions suggests MFI may be one common biological explanation or risk factor for persisting neck-related disability.…”

microRNA let-7i-5p mediates the relationship between muscle fat infiltration and neck pain disability following motor vehicle collision: a preliminary study

“…In addition to microRNAs as blood-based predictors of adverse posttraumatic outcomes, substantial research efforts have focused on understanding the contribution of skeletal muscle changes to post-trauma recovery, including how fatty infiltration of cervical muscle (MFI) influences tissue/stress injuries in the neck [27][28][29][30][31][32][33] . Recent longitudinal studies have demonstrated that MFI is predictive of 28 and associated with [31][32][33][34] PNPD, yet the molecular mechanisms mediating this association are not yet clear.…”