Mortality Rates Associated With Odontoid and Subaxial Cervical Spine Fractures

Our gender-specific analyses revealed that older men with odontoid injuries exhibited higher mortality compared with an age-matched male cohort, with 6 of the 8 deaths occurring within 3 months. However, after this exaggerated decline in survival, the rate normalized towards general population mortality rates (Figure 3B). As in the younger cohort, these earlier deaths were largely attributable to multisystem trauma, whereas medical comorbidities were implicated in those who died later. In contrast, the Kaplan-Meier curve of older women with odontoid fractures closely approximates that of age-matched women at every time point (Figure 3C), indicating that these injuries do not decrease survival as they do in their male counterparts.

When comparing the survival of older patients with subaxial cervical spine fractures with that of gender- and age-matched controls, the mortality rates of women were, once again, essentially equivalent. However, the survival of older men was significantly compromised by these injuries. In men, 7 of the 9 deaths were within 3 months, with the remaining 2 deaths occurring within 7 months. Nevertheless, beyond this initial period of elevated mortality, the survival curve again stabilized and paralleled that of the general population. As with odontoid fractures, there was no sustained increase in the mortality of male patients who lived at least 3 months after injury.

The mortality rates of odontoid and subaxial fractures were also compared in the older population. When controlled for age, there was no difference in mortality rates between these 2 groups. When individually analyzed in both men and women, the mortality rates of both fracture types matched those of the general population at all time points.

It is useful to contextualize our findings alongside the mortality of older individuals with other fracture types. Based on our results, we believe that the survival curves of geriatric men with odontoid or subaxial cervical spine fractures most closely resemble the characteristic pattern seen in hip fractures. Hip fractures have shown an early spike in mortality by as much as 8% to 49% in the first 6 to 12 months that returns to baseline after 1 year.^1-10 This presumably reflects the natural history of these injuries in response to appropriate therapeutic interventions. Interestingly, the male mortality rates for both odontoid and subaxial cervical spine fractures in this study are largely analogous to those reported by various hip fracture surveys.^1,5,55-58 In contrast, similar to prior studies of rib or wrist fractures, older women with these cervical spine fractures did not show a survival decrease after their injuries.^12,16-18

While the reasons underlying the differential effects of cervical fractures on the mortality of men and women have not been established, one explanation is that the female geriatric population is relatively more osteoporotic; thus, cervical injuries may occur after lower-energy forces, leading to less severe associated trauma that could otherwise decrease survival. Another explanation is that men are more likely to be involved in high-energy accidents,^59,60 thus decreasing their overall survival after injury.

This investigation is not without limitations. Our primary concern is the determination of survival. The NDI maintained by the NCHS is an extremely reliable tool regularly employed by epidemiologists to collect mortality data. However, it is possible that deaths may have been missed. We believe this number would be small, because the NDI database provided multiple probable matches that were carefully compared with supplemental personal information. It is also possible that deaths that were not appropriately registered with the NDI are not represented in this series. Another limitation lies in the determination of controls. As with any case–control study, the patients sustaining these odontoid fractures may differ in some significant way from the average population. A final limitation is that a small portion of patients in the study have only 1-year follow-up, because patient data was collected through 2006, although access to NDI data ended in 2007.

Conclusion

Our results indicate that the survival of older men with either odontoid or subaxial cervical spine fractures shares many of the same mortality characteristics as hip fractures, with diminished survival in the first 3 months that normalizes to the survival rate of the age-matched population. Interestingly, and perhaps because of disparate rates of osteoporosis and traumatic forces, the mortality rates in the female cohort were similar to that of the age-matched general population at all time points. These trends were nearly identical for both odontoid and subaxial cervical fractures.