Mortality due to traumatic spinal cord injuries in Europe: a cross-sectional and pooled analysis of population-wide data from 22 countries

Traumatic spinal cord injuries (TSCI) remain a serious public health and social problem. While the incidence rates of TSCI are relatively low, it is a high-cost condition which has been associated with high mortality rates [1]. Along with skull-brain injury, TSCI resulted in the highest burden due to permanent disability in a study including six European countries [2]. They disrupt lives and come along with substantial human and societal toll [3]. Globally, they affect primarily the population of young males, and in high income countries – due to population aging – the elderly population [1, 3, 4]. Transport accidents (especially in low income countries with high increase of motor-vehicle use), falls (dominating in elderly populations of high income countries), and violence [1, 3] are globally among the three main causes of TSCI.

While world-wide epidemiological data are limited, it has been estimated that in 2007 between 133 and 226 thousands of incident cases of TSCI would occur resulting from accidents and violence (estimated global incidence rate of 23 per million) [1, 3]. Substantial variations have been observed between various regions of the world: a recent review reported an incidence of 40 per million inhabitants in US, 16 in Western Europe and 15 in Australia [3]. Another review reported incidence rates from single country studies ranging from 12.1 per million in The Netherlands to 57.8 per million in Portugal [5]. Incidence and mortality rates also differ between developing and developed countries [6]. The mortality risk in persons after TSCI largely depends on the level and severity of the injury in general. The victims are two to five times more likely to die prematurely than the general population [1]. A clear influence of age has been observed - much higher death rates were detected in elderly populations, compared to the young [4]. Similarly to incidence rates, substantial variation in population mortalities attributable to TSCI exist between countries or regions [1, 2, 6].

Improvements in prevention and outcome of TSCI must be supported by valid and timely epidemiological data. Several reviews have aimed to summarize the incidence and prevalence of TSCI, and their mortality globally [3‐5, 7‐9] – all reporting heterogeneity of findings across the studies. These could reflect true variations, but could also stem from varying methodological approaches, time-span, and case ascertainment used in the included studies. Such methodological differences are inherited in systematic reviews and may hinder the comparability of studies and the estimation of the burden of TSCI [7, 10]. In an endeavor to overcome these limitations, we present a cross-sectional analysis of population-based mortality rates, using data collected in a standardized manner and for the same time period.

The aim of this study was to calculate the age-standardized population mortality rates attributable to TSCI in 22 European countries, along with the pooled age-standardized mortality rate attributable to TSCI in Europe.

A total of 1840 TSCI-related deaths were identified, of which 1084 (59%) were males. The age-standardized mortality rates ranged from 1.0 (95% CI: 0.7 to 1.4) in Turkey to 21.4 (95% CI: 17.6 to 25.7) in Finland. The mortality rates were in general higher in males, where they ranged from 1.5 (95% CI: 0.9 to 2.3) in Turkey to 30.0 (95% CI: 23.3 to 38.1) in Finland, compared to rates in females ranging from 0.6 (95% CI: 0.3 to 1.1) in Turkey to 14.3 (95% CI: 10.3 to 19.4) in Finland. Using the random effects model, pooled population mortality rates were estimated for Europe: based on age-standardized rates we estimated a mortality of 6.7 per million (95% CI: 5.2 to 8.2) overall, 9.4 (95% CI: 7.3 to 11.5) for males and 4.5 (95% CI: 3.4 to 5.6) for females; based on crude rates we estimated an overall pooled mortality rate of 6.2 (95% CI: 4.8 to 7.7), a pooled rate of 8.0 (95% CI: 6.1 to 9.8) in males, and 4.6 (95% CI: 3.6 to 5.6) in females. Substantial heterogeneity was observed between the countries in both sexes – I² = 100%. See Fig. 1 for details and Additional file 1: Table S1 for an overview of crude and age-standardized TSCI-related population mortality rates by a country, sex and age group.

Most deaths occurred in the older age groups, especially in the female population, where 83% of deaths were in the group of 65 years old or older; this proportion was 63% in males and 70% overall (ranging from 17% in Latvia to >90% in Switzerland, United Kingdom, or Cyprus). Figure 2 presents the proportions of deaths in age groups by sex and clearly demonstrates the shift towards older age groups, with a peak at 80–84 years of age in both sexes. In Table 2 and Additional file 1: Table S2 ratios of mortality rates are presented, quantifying the relative differences among age-groups (the age-group of 45–64 years old was chosen as the reference group and all ratios are in relation to the rate in this group). Clearly, mortality rates are substantially higher within the 65 years or older group, compared to all younger age groups. On average the rates in this group were higher by a factor of 9.5 when compared to the reference group, 1.7 in Romania, to 33.3 in Switzerland.

Table 3 presents the rate ratios of age-standardized mortality rates between sexes, and suggests that mortality rates in males are on average higher by a factor of 1.5 (95% CI: 1.4–1.6); rate ratios ranged from 1.1 in Austria and Croatia to 3.9 (95% CI: 2.5 to 6.2) in Romania. Thus, men were about 50% more likely to die of TSCI, compared to women in the analyzed countries.

The most common recorded external causes of injury were falls and traffic accidents. On average, 53% of deaths occurred after a fall and 23% after a traffic accident. These proportions were similar in both sexes: on average 51% of deaths occurred after falls in males and 58% in females; 25% of deaths were traffic related in males and 20% in females. Figure 3 presents a graphical overview of age-standardized mortality rates by external cause for each country and confirms the dominance of falls as the primary external cause (see Additional file 1: Figure S1 for sex-specific data).

The most common site of fatal TSCI overall was the cervical area where 61% of all cases were located (66% in males and 55% in females), followed by lumbar TSCI with 23% (19% males, 26% females) and thoracic TSCI contributing 14% overall, 14% in males and 16% in females. Expressed in rates, cervical TSCI was associated with an overall mortality of 4.22, lumbar TSCI 1.4 and thoracic TSCI with a mortality of 0.95 per million. See details in Fig. 4 and in Additional file 1: Figure S2 where the site distributions are presented for each country separately.

To evaluate the potential influence of the general economy level of the country on the observed heterogeneity between mortality rates, we have categorized the included countries based on their GDP per capita to a group with a per-capita GDP of <45,000 USD and a group with per-capita GDP of ≥45,000 USD; we found a pooled crude rate of 5.3 (95% CI: 3.8 to 6.3) per million in countries with lower GDP, and a pooled rate of 8.4 (95% CI: 5.0 to 11.8) in countries with higher economy level.

TSCI-related deaths were a relatively minor contributor to the overall injury-related mortality (Table 4 and Fig. 5) with proportions ranging from <1% in Cyprus, Latvia or Turkey up to 5.9% (95% CI: 5.0% to 6.8%) in Finland – on average they contributed 2% (95% CI: 1.8% to 2.2%). When extrapolating the pooled crude TSCI-mortality rates from the analyzed 22 countries to the whole population of the EU-28, in 2012 a total of 3152 (95% CI: 2441 to 3915) TSCI deaths would occur. The number of deaths in the population of the whole Europe (48 countries) would be 4570 (95% CI: 3538 to 5675). See Table 5 and Additional file 1: Table S3 for details.

Our study presents a comprehensive and large-scale overview of TSCI-related population mortality in Europe. With an estimated toll of nearly five thousand lives that could be potentially saved by prevention, our findings confirm TSCI as an important cause of injury related deaths in Europe. Further action towards harmonization of case ascertainment and towards prevention strategies targeted mainly on the elderly is warranted.