The temporal development of fatty infiltrates in the neck muscles following whiplash injury: an association with pain and posttraumatic stress

Abstract

Background: Radiological findings associated with poor recovery following whiplash injury remain elusive. Muscle fatty infiltrates (MFI) in the cervical extensors on magnetic resonance imaging (MRI) in patients with chronic pain have been observed. Their association with specific aspects of pain and psychological factors have yet to be explored longitudinally.

Materials and findings: 44 subjects with whiplash injury were enrolled at 4 weeks post-injury and classified at 6 months using scores on the Neck Disability Index as recovered, mild and moderate/severe. A measure for MFI and patient self-report of pain, loss of cervical range of movement and posttraumatic stress disorder (PTSD) were collected at 4 weeks, 3 months and 6 months post-injury. The effects of time and group and the interaction of time by group on MFI were determined. We assessed the mediating effect of posttraumatic stress and cervical range of movement on the longitudinal relationship between initial pain intensity and MFI. There was no difference in MFI across all groups at enrollment. MFI values increased in the moderate/severe group and were significantly higher in comparison to the recovered and mild groups at 3 and 6 months. No differences in MFI values were found between the mild and recovered groups. Initial severity of PTSD symptoms mediated the relationship between pain intensity and MFI at 6 months. Initial ROM loss did not.

Conclusions: MFI in the cervical extensors occur soon following whiplash injury and suggest the possibility for the occurrence of a more severe injury with subsequent PTSD in patients with persistent symptoms.

Figure 1. Relationship between the independent variable (IV), dependent variable (DV) and mediator variable.

a = effect of IV on mediator, b = effect of mediator on DV after controlling for IV, c = effect of IV on DV and c' = effect of IV on DV after controlling for the mediator. Effects indicated by * must be significant and c' must be non-significant for mediation hypothesis to be confirmed.

Figure 2. Changes in MFI over time in each group.

* indicates significantly different from the recovered group at p<0.05 level. + indicates significantly different from the mild group at the p<0.05 level.