Introduction: Long-term follow-up studies focusing on the posterior extensor muscles in patients suffering from whiplash injury are scarce. The purpose of this study was to elucidate the changes in the posterior extensor muscles 10 years after whiplash injury. Methods: Twenty-three patients who had suffered from whiplash injury in 1994-1996 and had undergone MRI using a 1.5-T superconductive imager participated in this follow-up study (13 males, 10 females, mean age 51.8 years, mean follow-up 11.5 years). In addition, 60 healthy volunteers who had undergone MRI in the same period were included as controls (36 males, 24 females, mean age 47.8 years, mean follow-up 11.1 years). All participants underwent follow-up MRI. The cross-sectional areas of the deep posterior muscles (CSA) including the multifidus, semispinalis cervicis, semispinalis capitis, and splenius capitis were digitally measured at C3-4, C4-5, and C5-6 using NIH image. The long-term changes in the CSA were compared between the two groups. In addition, correlations between the CSA and cervical spine-related symptoms were evaluated. Results: The mean total CSA per patient (the sum of the area from C3-4 to C5-6) was 4811.6 ± 878.4 mm 2 in the whiplash patients and 4494.9 ± 1032.7 mm 2 in the controls at the initial investigation (p = 0.20), and 5173.4 ± 946.1 mm 2 and 4713.0 ± 1065.3 mm 2 at the follow-up (p = 0.07). The mean change in CSA over time was 361.8 ± 804.9 mm 2 in the whiplash patients and 218.1 ± 520.7 mm 2 in the controls (p = 0.34). Ten whiplash patients (43.5%) had neck pain and 11 (47.8%) had shoulder stiffness. However, there was no difference in the change in CSA over time between the symptomatic and asymptomatic patients. Conclusions: There was no significant difference in the change in CSA between whiplash patients and healthy volunteers after a 10-year follow-up period. In both groups, the cross-sectional area slightly increased at follow-up. In addition, there was no association between the change in CSA and clinical symptoms such as neck and shoulder pain. These results suggest that whiplash injury is not associated with symptomatic atrophy of the posterior cervical muscles over the long term.
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