Objective. To study the (1) temporal development of muscle fatty infiltrates (MFI) in the cervical multifidi after whiplash, (2) differences in multifidi MFI between those who recover or report milder pain–related disability and those who report moderate/severe symptoms at 3 months, and (3) predictive value of multifidi MFI outcomes.

Summary of Background Data. The temporal development of MFI on conventional magnetic resonance image has been shown to be associated with specific aspects of pain and psychological factors. The replication of such findings has yet to be explored longitudinally.

Methods. Thirty-six subjects with whiplash injury were enrolled at less than 1 week postinjury and classified at 3 months using percentage scores on the Neck Disability Index as recovered/mild (0%–28%) or severe (>=30%). A fat/water magnetic resonance imaging measure, patient self-report of pain-related disability, and post-traumatic stress disorder were collected at less than 1 week, 2 weeks, and 3 months postinjury. The effects of time and group (per Neck Disability Index) and the interaction of time by group on MFI were determined. Receiver operating characteristic curve analysis was used to determine a cut-point for MFI at 2 weeks to predict outcome at 3 months.

Results. There was no difference in MFI across groups at enrolment. MFI values were significantly higher in the severe group than those in the recovered/mild group at 2 weeks and 3 months. The receiver operating characteristic curve analysis indicated that MFI levels of 20.5% or above resulted in a sensitivity of 87.5% and a specificity of 92.9% for predicting outcome at 3 months.

Conclusion. Consistent with previous evidence, muscle degeneration occurs soon after injury but only in those patients with poor functional recovery. This study provides further evidence that (1) multifidi MFI occur in tandem with known predictive risk factors (older age, pain-related disability, and post-traumatic stress disorder) and (2) routine imaging protocols may need to be reconsidered in the vast majority of patients after whiplash.