Current Etiological Profile of the Spinal Cord Injury

Abstract

The causes of spinal cord injury are multiple; classically they can be divided into two large groups: those of medical origin (tumor, infectious, vascular, by compression, sclerosis, and congenital) and those of traumatic origin (traffic accidents, accidental falls, work accidents, sports accidents (dives), attempts of autolysis, and violence). Its incidence and prevalence by sex, age, occupation, leisure activities, and geographic location are variable. The objective of this chapter is to review the different causes of spinal cord injury, especially traumatic ones, according to the different variables mentioned. The analysis of these data will allow strategies for the prevention of new injuries to be focused on the best direction.

1. Introduction

Spinal cord injury (SCI) remains one of the most tragic disabilities that can happen to a person, for which there is still no regenerative or reconstructive cure. The holder of a SCI is affected with paralysis at different levels and degrees of extension, loss of sensation, and bowel, bladder, and sexual dysfunction. To this, the psychological, social, and economic consequences that this permanent physical disability involves must be added.

Spinal cord injuries are currently defined and classified according to the ASIA (American Spinal Injury Association) scale, in which a sensory and motor assessment is carried out, and a sensory, motor, and neurological level is established. This allows for homogenization of patient assessment and follow-up worldwide. It also allows to establish a prognosis, since neurological recovery is better in incomplete spinal cord injuries than in complete spinal cord injuries. Thus, different types of SCI can be distinguished according to the level, extent, and symptoms:

According to level: tetraplegia, if the paralysis affects both upper and lower limbs and paraplegia, if the paralysis only affects the lower limbs.

According to the extent: complete, when the lesion affects completely the spinal cord, and incomplete when there is a partial lesion of the spinal cord.

According to symptoms: spastic, when spasticity predominates below the level of the lesion, and flaccid, where flaccid musculature predominates below the lesion.

On the other hand, several incomplete clinical syndromes are distinguished according to their location and clinical features, such as Brown-Séquard syndrome (spinal cord hemisection), conus medullaris syndrome (sacral cord injury), and cauda equina syndrome (lumbosacral nerve root injury).

The incidence of SCI varies from country to country and among different regions. Likewise, the causes of SCI also differ from one country to another. It is therefore interesting to know these differences so that each country can work both, on treatment measures more adapted to the type of injury, above all, on prevention measures focused on working on those areas where they are most vulnerable.

1.1 Etiology of SCI

The etiology of SCI can be classically divided into two main groups: medical (or non-traumatic) and traumatic etiology.

1.2 SCI of medical origin

These represent a much lower frequency of reported cases of traumatic SCI; however, this proportion may not exactly correspond to reality due to the difficulty in recording them, which are often overlapped by the primary diseases that cause them. Thus, in Alito’s study [1] with a sample of 112 patients, 76% were of non-traumatic cause, with age being significantly higher than in those of traumatic origin. With regard to age, it has been observed that in industrialized countries, the percentage of non-traumatic injuries increases together with age [2].

Something remarkable is that there is no internationally accepted term for spinal cord damage not due to trauma. Many different terms have been used in the literature to describe these conditions, including non-traumatic spinal cord injury, spinal cord damage, spinal cord dysfunction, spinal cord lesion, medical paraplegia, myelopathy, and spinal cord myelopathy [3].

The following are some of the causes of non-traumatic SCI.

1.2.1 Tumor pathology

The tumor pathology that can induce a SCI can be a primary tumor in spinal cord (ependymomas are the most common glial tumor in adults, whereas astrocytomas are the most common intramedullary tumor in children) or a metastasis. Metastatic lesions are responsible for about 85% of neoplastic spinal cord compression cases, with the other 15% due to primary neoplastic lesions of the spine [4].

Spinal cord tumors may be classified as one of two different types depending on where they occur relative to the protective membranes of the spinal cord. These are the main types of intradural tumors: intramedullary tumors (begin in the cells within the spinal cord itself, such as gliomas, astrocytomas, or ependymomas) and extramedullary tumors (grow in either the membrane surrounding the spinal cord or the nerve roots that reach out from the spinal cord, such as meningiomas, neurofibromas, schwannomas, and nerve sheath tumors). Tumors from other parts of the body can spread (metastasize) to the vertebrae, the supporting network around the spinal cord or, in rare cases, the spinal cord itself [4].

In a retrospective evaluation in a Rehabilitation Unit in the USA, between 2003 and 2014, in which they included all the patients with SCI and a diagnosis of primary or metastatic spinal cancer, most tumors were located in the thoracic region (65.4%) and were primary central nervous system in origin (21.0%), including meningioma (7.4%), schwannoma (3.7%), and ependymoma (2.5%). The next most common origins of the spinal tumors were metastases from the lung (17.3%), prostate (9.9%), kidney (8.6%), lymphoma (7.4%), and multiple myeloma (7.4%) [5].

1.2.2 Infectious pathology

SCI of infectious origin can be caused by various etiological agents such as bacteria (tuberculosis, Mycobacterium spp), viruses (Cytomegalovirus (HCMV), Human Immunodeficiency Virus (HIV), Herpes Simplex Virus, Varicella Zoster Virus, poliovirus, HTLV-1, Zika virus), fungi (cryptococcus spp), and parasites (Toxoplasma gondii, Schistostoma mansoni).

At the National Paraplegic Hospital in Toledo (Spain), Morillo et al. [6] carried out a retrospective study of patients with SCI admitted to their center from 1997 to 2003: in the sample, infections accounted for 8% of neuropathies of medical cause, a higher figure than those reported in the classical literature. In this sample the most frequent cause of spinal cord injury was spondylodiscitis in 51% of cases followed by epidural abscesses (22.2%) and arachnoiditis (18.5%); the most frequent etiological agent was Staphilococcus Aereus in 51.9% of cases followed in frequency by Mycobacterium tuberculosis in 35.7% and brucellosis in 7.4%.

Other less frequent etiologies of SCI of infectious origin are viral infections and parasitosis, which represent 3.7% of the aforementioned sample, a figure that could increase in the coming years due to the migratory changes being experienced in Europe.

1.2.3 Rheumatological and degenerative diseases

Some rheumatological diseases such as Paget’s disease, rheumatoid arthritis, osteoporosis, or the ossification of the posterior longitudinal ligament could lead to medically induced SCI.

Cervical spinal cord compression (SCC) due to degeneration of the cervical spine is a frequent finding on magnetic resonance imaging. Degenerative changes include spondylosis, degenerative disc disease, ligamental hypertrophy, and ossification of the posterior longitudinal ligament. SCC mainly occurs during later stages of life and in most cases remains asymptomatic. Nevertheless, a subset of individuals will develop symptoms, causing a condition that has recently been termed degenerative cervical myelopathy, which is the most common non-traumatic, progressive spinal cord disorder with an estimated 2% prevalence [7].

1.2.4 Inflammatory diseases

Inflammatory diseases of the nervous system, such as Multiple Sclerosis or transverse myelitis, can cause damage at different levels of the central nervous system, including the spinal cord. The exact reason for transverse myelitis is unknown, sometimes there is no known cause, and sometimes it is associated autoimmune disease. In 2021, Yu-Ting Hsiao team published a case of acute transverse myelitis after vaccination against COVID-19 with the ChAdOx1 nCOV-19 vaccine (AZD1222), which was the first case reported in Taiwan [8].

In Multiple Sclerosis, the immune system destroys the myelin that surrounds the nerves in the spinal cord and brain, and this can lead to SCI at different levels and of varying severity.

1.2.5 Neurodegenerative diseases

Degenerative diseases of the nervous system are a term used to encompass any of the diseases or disorders that are due to a loss in the function or structure of neurons of the brain or spinal cord; examples of this kind of diseases, which could cause SCI, include Lateral Amyotrophic Sclerosis (LAS), hereditary spastic paraparesis, or spinal muscular atrophy.

1.2.6 Congenital origin

There are some congenital diseases that can damage the spinal cord; some of them are cerebral palsy, diastematomelia, spinal dysraphism, Arnold-Chiari malformation, or skeletal malformations.

1.2.7 Iatrogenesis

Iatrogenesis is unintended and unwanted damage to health caused as an unavoidable side effect of an active medical act, whether diagnostic or therapeutic. SCI secondary to iatrogenesis is common, and it is expected to grow, due to the increasing life expectancy of the population, which leads to an increase in the number of elderly patients with vascular risk factors undergoing invasive interventions. It is important to take into account whether the patient with SCI has required surgery to improve their prognosis or if, on the contrary, the SCI has been produced as a consequence of a surgical act.

In the study carried out by Montalva Iborra [9], the 18.18% of a sample of 265 patients with acute SCI were caused by iatrogenesis; the most frequent level of injury was the thoracic level (48%), and the main etiology was surgery for degenerative spine disease, where patients under the age of 30 were treated with intrathecal chemotherapy. The SCI rising during anesthetic practice is a rare event, which could be produced by direct (e.g., spinal nerve root damage due to incorrect pedicle screw placement) or indirect (e.g., cord ischemia following aortic surgery) factors [10].

1.2.8 Other causes of non-traumatic SCI

Other non-traumatic causes of SCI are vascular causes (spinal cord infarction), post-injury sequelae, such as Syrigomyelia, toxic causes, as radiation or chemotherapy, and genetical and metabolic disorders, such as vitamin B12 deficiency or abetalipoproteinemia.

The medical causes of SCI are included in Table 1 [11].

Tumor pathology	Primary tumor or metastases (intra and extramedullary).
Infectious pathology	Bacterial cause: Pott’s disease (tuberculosis), mycobacterium spp.; Myelitis of viral etiology: Cytomegalovirus (HCMV), Human Immunodeficiency Virus (HIV), herpes simplex virus, varicella zoster virus, poliovirus, HTLV-1.; Mycosis: cryptococcus spp.; Parasite: toxoplasma gondii, Schistostoma mansoni.
Rheumatological and degenerative diseases	Spondylosis, stenosis, disc pathology, Paget’s disease, rheumatoid arthritis, osteoporosis, ossification of the posterior longitudinal ligament.
Inflammatory diseases	Multiple Sclerosis, transverse mielitis.
Neurodegenerative disorders	Lateral Amiotrophic Sclerosis; Hereditary spastic paraparesis; Spinal muscular atrophy.
Congenital origin	Cerebral palsy, diastematomelia,…
Vascular	Spinal cord infarct
Iatrogenesis	Spinal taps, epidural catheter placement, aortic repair…
Post-injury sequelae	Syringomyelia
Toxic causes	Radiation, chemotherapy.
Genetical and metabolical disorders	Vitamin B12 deficiency, abetalipoproteinemia.

Table 1.

Medical causes of SCI.

1.3 Traumatic SCI

Traumatic cause is the most epidemiologically significant etiology, with a frequency ranging from 66 to 87% of all reported cases of SCI, according to ASPAYM (Table 2) [11].

Traffic accidents	Car accidents, motorcycle accidents, collision/knocking down.
Casual falls	From great height, from own height.
Accidents at work	Accidents with heavy machinery, falls…
Sports accidents /Recreative activities	Diving. Skiing. Horse riding.; Contact sports (rugby, American football).; Extreme sports (skydiving, paragliding).
Attempted self-injury	Suicide attempted
Others	Violence (firearms injuries, stab wounds, direct traumas).; Electrical injuries.

Table 2.

Traumatic causes of SCI.

It should be noted that the etiology of the injury is usually associated with the level, so that the majority of sports injuries, falls, and approximately 50% of traffic accidents correspond to the cervical level [12].

On the other hand, there are factors that increase the risk of SCI related to living conditions [12]; thus, the type of work activity, its category and the sector where it is carried out have a great influence on the incidence of SCI. Some jobs carry a higher risk of traumatic SCI. This is to some extend related to socioeducational variables, as some of the jobs with the highest risk of injury are often those with the lowest educational requirements. In relation to the socioeconomic situation of the place where the person lives as well as their particular conditions, the type of transport they use, the sport activities they do, and the climate of violence they may be exposed will differ.

Socioeconomic and occupational variables imply the emergence of a new profile of SCI worldwide, which takes into account the different development of each country as well as population movements, which deserve a detailed analysis.

2. Materials and methods

2.1 Design

This is a literature review in which a search for publications on etiology of traumatic and non-traumatic SCI worldwide has been carried out.

2.2 Selection criteria

Inclusion criteria: those dealing with the etiology of SCI publications within the last 30 years (due to the scarcity of publications in some geographic areas of the world) and those in English or Spanish.

Exclusion criteria: excluded epidemiological studies that did not provide a comprehensive analysis of the etiology of traumatic or non-traumatic SCI, studies without full text available and those found in other languages.

2.3 Search strategy

A bibliographic search was carried out from January 1989 to August 2022 in the following database: PubMed and Cochrane. The following keywords were used: spinal cord injury, traumatic, non-traumatic, etiology, epidemiology. A combination of these terms was used thanks to the Boolean operator “and” and “or.”

3. Results and discussion

A total of 58 documents were reviewed, of which 50 were scientific articles according to the inclusion and exclusion criteria mentioned in the previous section. In addition, a doctoral thesis, a paper of a conference, a reference of three books, two web pages, and an informative guide were included, all of which were referenced in one of the articles reviewed.

The results found are collected discussed below, separated by non-traumatic and traumatic etiology as well as by geographical area.

3.1 Non-traumatic SCI

3.1.1 Results

The etiology of non-traumatic SCI was reviewed worldwide by New PW¹³, which included the abstracts of 377 publications and 45 reports from 24 countries in 12 of the 21 WHO global regions. The results were the following:

3.1.1.1 Asia

Pacific Asia presented a high rate of degenerative deformity of the spine (59%) and tumors (19%). South Asia (India) showed a high rate of tuberculosis (38–25%), followed by tumors.

3.1.1.2 Australia

Tumors, degenerative and vascular conditions were the main causes of non-traumatic SCI.

3.1.1.3 Europe

Western Europe presented high rates of tumors and degenerative conditions (25% and 32% medians, respectively), quite likely influenced by the age profile of the western European population. Spina bifida was reported as a cause of non-traumatic SCI in Spain, Italy (both 5%), and Denmark (2%). Myelitis was lower in Israel (7%) and higher in Denmark (14%) and Italy (23%).

3.1.1.4 Africa

In north Africa/middle east, spinal tumors and degenerative causes of non-traumatic SCI were the most commonly diagnosed conditions. Tumors and degenerative conditions were slightly higher in Ankara (29% for both causes) than in Istanbul (22% and 25%, respectively). Inflammatory conditions were common in Ankara (23%) and in Istanbul (20%). Six percentage of non-traumatic SCI cases reported in Istanbul were spina bifida.

In east sub-Saharan Africa, tuberculosis was a major cause: this etiology was highest in Kenya and Malawi (33% in both countries) and lower in Ethiopia (20 and 27%). HIV-related non-traumatic SCI was common in Ethiopia (17%) and was not reported in Kenya or Malawi. Tumor-related non-traumatic SCI cases were highest in Kenya (33%), Malawi (25%), and Ethiopia (22%). Myelitis was low in Ethiopia (4%) and Malawi (7%).

In southern sub-Saharan Africa, tumors and tuberculosis-related non-traumatic SCI cases were high (28% and 27%, respectively). Transverse myelopathy accounted for 11% of the non-traumatic SCI cases.

In west sub-Saharan Africa, tuberculosis was relatively common in both Ghana and Nigeria (30% and 25%, respectively), and the proportion of neoplastic SCI and myelitis was similar in both countries (about 15% and 12%, respectively).

3.1.1.5 America

According to literature, in North America, spinal stenosis and tumors were common (54% and 26%, respectively) and myelitis was low (5%).

3.1.1.6 Oceania

In Oceania, the most frequent cause of non-traumatic SCI was infection (32%), and tumors only represented 9%.

An overview of the etiology of non-traumatic SCI can be seen in Figure 1, extracted from New PW [13].

Figure 1.

Global maps of NTSCI epidemiological outcomes (1959–2011) by WHO global regions [13].

3.1.2 Discussion

There tended to be more reports of better quality from high-income countries compared with medium- and low-income countries [13]. Developed countries tended to have a higher proportion of cases with degenerative conditions and tumors causing SCI [11]. Developing countries, in comparison, tended to have a higher proportion of infections, particularly tuberculosis and HIV, although it was interesting that a number also reported tumors as a major cause [13].

3.2 Traumatic SCI

3.2.1 Results

The different causes of traumatic SCI vary greatly in incidence and prevalence from country to country and are discussed in detail below according to the various published studies.

In developing countries, motor vehicle collisions were the cause of traumatic SCI in 41% of cases, followed by falls in 34.8%, although there are differences between countries that will be discussed below, according Rahimi-Movaghar’s review (Table 3) [14].

Country	First author	Motor vehicle	Fall	Gunshot wound	Violence	Sport
Bangladesh	Hoque et al., 1999	18	63
Brazil	Brito et al., 2011; Barros Filho et al., 1990	41.4; 26.9	42.6; 22.4		36,.7	7.9
China	Ning et al., 2011	34.1	56.9		1.4	0.2
India	Manjeet et al., 2009	30.3	50		2.7	0.7
Russia	Kondakov et al., 2002	16	34			2
Sudáfrica	Velmahos et al., 1995; Hart y Williams, 1994	30; 28	3	61; 62
Irán	Rahimi-Movaghar et al., 2009	64	12
Nigeria	Obalum et al., 2009	77.4	9.4	7.3	2.1	1.7

Table 3.

Etiology of traumatic SCI in developing countries (table extracted from Rahimi-Movaghar et al., 2013) [14].

In countries such as Bangladesh, where urbanization and motorization are less developed, falls remain the leading cause (63%), related to fruit picking and loading as part of agricultural practice, rather than osteoporosis as in developed countries. This is also the case in Pakistan (82% due to falls from trees or roofs) and Nepal (61%) [15]; in both countries road traffic accidents account for around 7% of traumatic SCI [16, 17, 18].

However, in Vietnam and Thailand, transport accidents are the leading cause (47%), most of them involving motorbikes, as they are the main means of transport [15]. In 31 of the studies analyzed by Rahimi-Movaghar [14], road traffic crashes were more frequent, and in one, both causes had similar percentages. Thus, in two studies from Nigeria and one from Saudi Arabia, motor vehicle collision accounted for more than 80% of cases [14].

In two studies from South Africa, with more than 50% of the cases, and in one from Brazil, violence was the first cause. In South Africa, the etiology has shifted from stab wound (38% in 1998 to 17.5% in 1992) to firearm (28.5% in 1988 to 47% in 1992) as the most frequent cause, with only 3% fall injuries [19].

In the Nigerian city of Plateau, in contrast, tunnel collapse in illegal mines was the most prevalence cause [14]. However, in a hospital in Enugu, Nigeria, the most cause of traumatic SCI in their sample was car accident (55.3%), with a decrease in injuries caused by falling from a palm tree from 40.2% of SCI in 1988 to 3.5% [20].

In Rahimi’s systematic review [14], an annual increase of 0.9% in the relative frequency of traumatic SCI-related falls was detected during the study period between 1975 and 2009. Male gender, age, or type of complete or incomplete injury and neurological damage (tetraplegia or paraplegia) showed no association with mechanism of injury in these countries [14]. Etiologies were also studied by groups or seasons; in India, an increase in injuries was detected during the summer period, related to an increase in population movements during this period, with injuries being more frequent in natives than in visitors to the country, and Nigeria recorded the highest peaks of SCI during the celebration of the most important festivals [20].

Other articles published between 2011 and 2013 that were not included in the Rahimi-Movaghar systematic review are listed below. In the Emergency Unit of Haydarpasa Hospital in Ankara, falls from height (50.6%) represent the first cause of traumatic SCI, associated with lumbar injuries, followed by falls from small heights (20.8%), more related to thoracic injuries [21]. On the other hand, a clear relationship was observed between traffic accidents and cervical (p = 0.00001) and lumbar injuries (p = 0.004) and sports accidents and cervical injuries (p = 0.014). The season with the highest number of injuries was summer [21].

In Anhui province in China [22], the leading cause in the sample of 761 traumatic SCI patients analyzed was fall from height (52.6%) in both men and women, followed by road traffic accidents (21.2%), something also observed in Tianjin [23], where a review of cervical SCI was conducted, with 49.7% of injuries caused by falls (an increase in incidence in low falls and a decrease in high falls with age), and 36.4% by traffic, while in Mainland [24], in the same country, in a review of 82.720 patients, the majority of traumatic SCI was caused by motor vehicle accidents (33.61%), closely followed by falls from height (31.25%) and trivial falls (23.23%). A subsequent study in Guangdong province (China) has shown an increase in the number of people suffering from SCI and a rising trend; the leading causes were falls and motor vehicles collisions. The low-falls (height < 1 m) group has expanded over this period, related to population aging [25].

In contrast, in Malaysia, in the review conducted at Kuala Lumpur Hospital between 2006 and 2009, 66% of traumatic SCI cases were caused by motor vehicle accidents and 28% by falls [26].

In Jordan, the leading cause is four-wheeled vehicle accidents, related to high speed and lack of seat belts, but not alcohol, given the high percentage of Muslims; in this country, accidental gunshots account for 26% [15].

In Turkey, road traffic accidents account for almost half of the cases (49%), followed by falls (37%) from trees and roof (more in the summer months, when people sleep on roofs), mainly among children and elderly people [15].

In Central and South America, information is only available from Brazil: road accidents account for 35% of traumatic SCI, more frequent in cars than on motorbikes; those related to violence, specifically gunshot wounds, account for 30% of cases [15]. However, in the study conducted at the UFMA University Hospital in the state of Maranhao in Brazil, between January 2008 and June 2009, falls accounted for 42.6%, traffic 41.4%, gunshot wounds 12.6%, and dives 3.4% [27].

In developed countries, road traffic accidents continue to be the most frequent cause of traumatic SCI, although their proportion, especially in young men, has decreased in recent years with respect to falls, especially in older people, and even non-traumatic SCI. The results are broken down by continent.

3.2.1.1 Asia

The review carried out at the Yunsel University College of Medicine Hospital in Seoul between 2004 and 2008 places car accidents as the leading cause of traumatic SCI, with a statistically significant increase in injuries caused by falls, and a decrease in those caused by firearm or penetrating wounds. Likewise, there is a decrease in traumatic SCI with an increase in non-traumatic SCI (traumatic causes represented between 1987 and 1996 91.2% and between 2004 and 2008 76.5% [28]).

In Japan, falls account for 42% of cases, which is probably related to an aging population [29, 30].

3.2.1.2 North America

In the 2005–2011 review of SCI of any etiology collected in NSCID and NSSCID, two SCI databases in the USA, the most frequent causes of SCI were car accidents (31.5%) and falls (25.3%), followed by firearms injuries (10.4%), motorbike accidents (6.8%), diving accidents (4.7%), and those due to medical or surgical complications (4.3%) [31]. Road traffic accidents remain the leading cause of SCI in the USA, although the percentage of injuries caused by falls increased from 17% in the 1970s to 28% in 2005–2011 [32]. There has been a little change in SCI caused by motor vehicle accidents: in the 1970s, the motor vehicle etiology accounted for 47.6% and in 2000 48.3% [33]. In a review conducted at a major trauma center in California between 1996 and 2008, 32.6% of traumatic SCI cases were caused by motor vehicle accidents; although traffic accidents were also the leading cause in this study, a decrease was noted, which was related to improved vehicle safety and traffic regulations [34].

In the United States, SCI caused by violence increase by 29% between 1973 and 1999, with a significant decrease (14%) after 2000, values that are well above those reported in Western Europe and Australia, being a frequent etiology in urban settings in developed countries [30]. DeVivo [33, 35], analyzing NSCISC data, notes that acts of violence, specified as firearm injuries, constitute the third leading cause of SCI globally, at 17%.

Sport or recreationally motivated SCI is on the other hand decreasing (from 14% in 1970s to 8% between 2005 and 2011 [31] and from 14.2% in 1970s to 10% in 2000 [33]. Injury prevention initiatives have reduced cases of SCI, such as diving, American football, or trampoline jumping; however, they are increasing in relation to winter sports [33]. In the USA, diving ranks fourth in frequency with 7.3%, behind violent acts [34]. These percentages are very variable when comparing different countries [22, 36, 37, 38]: Russia with 23%, Poland with 19.8%, Australia 10.4%, Brazil with 9.3%, or the state of Florida in the USA with 8.5%.

In Canada [39], very similar percentages were found for motor vehicle collision (35%) and falls (31%), the latter being the leading cause in people over 60 (57%) and even more so in those over 80 (89%), which is consistent with other publications where falls are the leading cause of traumatic SCI in women over 60 and men over 70 [40].

3.2.1.3 Europe

Data on traumatic SCI in Europe also varies from one country to another.

In Estonia, according to Saber’s study [41], 41% of traumatic SCI cases were caused by falls, which were the most frequently recorded etiology in the over 30 age group (thus, above the age of 60, accounting for 72.4% of traumatic SCI) and only 29% were caused by road traffic accidents, which proved to be the most frequent cause below the age of 30. Alcohol consumption preceded such injuries in 43.2% of cases.

In a study conducted in Oslo [42], in which only traumatic cervical fractures were studied, 60% of them were caused by falls, more associated with older people, 21% were caused by car accidents, 8% were associated with cycling, and 4% with diving, the latter being more frequent in younger people.

In Iceland, the most frequent cause of SCI is traffic accident: Knutsdottir et al. [43] reported 42.5% of traumatic SCI caused by road traffic accidents, most of which were associated with non-use of seat belts; the second cause was falls with 30.9% with an increase in falls from height in the elderly group, associated with cervical injuries and incompleteness. Sports accounted for 18.8%, related to horse riding and winter sports, especially in the female group [42].

In Poland [44] and Romania [45], road traffic accidents are the first cause, as in the rest of Western European countries.

Bicycle accidents are highly representative in the Netherlands, Greece, Denmark, and Ireland [15]; motorbike accidents are more frequent in Greece and Italy compared with other European countries.

Given that Europe has a high proportion of people over 60 years of age, falls account for 32% of traumatic SCI in Western Europe.

SCI related to self-harm attempts varies from 1 to 26% with an average of 8%: thus, Scandinavian countries have a high suicide rate, where only intentional precipitation accounts for 8% of all cases of traumatic SCI [36]. Greenland (Denmark) has the highest rate of all: 15% of traumatic SCI cases are caused by accidental shooting, according to Pedersen et al. [46]; on the other hand, transport accidents, especially motorbike accidents, account for 4%, the lowest figure of all articles reviewed, as do skiing accidents (4%); 50% of all SCI occur under the influence of alcohol [46].

Riding-related SCI cases are highest in Ireland, Switzerland, and Iceland [15].

In Spain, between 2000 and 2008 (Working Group of the Spanish Society of Epidemiology, 2011), 50% of cases were caused by a traffic accident, 20–30% by a casual fall, 8% by an accident at work, 4–11% by sport or leisure activity, and 1% by violence. Traffic accidents are therefore the leading cause of traumatic SCI in this country, and of these, those produced in four-wheeled vehicles are the most common. Mazaira’s team [47] related it to 52.4% of the total traumatic etiology and García Reneses [48, 49] to 45%. According to the latter author, 84% occur in four-wheeled vehicles, 9.6% in two-wheeled vehicles, and 6.4% in pedestrians. In those produced in four-wheeled vehicles, 58.2% affected drivers and 41.8% affected passengers, although it was not differentiated whether the passengers occupied the front or rear passenger seat. There was a significant increase in the incidence of traumatic SCI with road traffic accident etiology and a predominance of males, with a Male/Female ratio greater than 4 [47]. During the last decades, safety measures have been implemented, many of them aimed at increasing the severity of traffic laws. The second most frequent cause was falls from height, casual falls, and falls at work. In the study carried out in eight Spanish autonomous communities [47], casual falls accounted for 22.8%, more related to advanced age, and work-related falls accounted for 13.6%; these data coincide with those found in the Canary Islands [50], where the occupational accident was also assessed in isolation and related to the etiology. In Aragon [51], falls account 24.6% of traumatic SCI, a figure that is increasing while traffic accidents causing this type of injury are decreasing, with the highest number of cases found in the second decade of life in women, and fifth and eighth in both sexes. In terms of sporting etiology, most of them occur in people under 30 years of age. In Van den Berg’s study [52], it accounted for 1.9% behind violent causes, while Mazaira and his team [47] put it at third place with 5.3%, with diving being the main etiology in all the studies reviewed, a figure that coincides with those provided for the Canary Islands (10.4% of all traumatic etiologies are due to diving) [50]. The study by Alén Garabato [53] examines diving as a significant etiology in this country between 1974 and 1995; it is the fifth cause of SCI, with 3.4% of all injuries. Of all those affected, 87.7% were under 30 years of age, with a distribution of 76.5% on beaches, 21.5% in swimming pools, and 2% in lakes. Cervical injuries accounted for 98% of the injuries, with summer being the season with the highest incidence. Data on SCI secondary to violence are scare with ranging from 0.95% [39], 1.3% [47], 1.8% [50] to 3.9% [53]. All these results are below those found in other studies in developed countries, such as the United States. The data found for international falls from height, or precipitation, are variable: in the Canary Islands, it is 2.8% [51]; in the ASPAYM’s study, it is 2.5% [13]; and in the Mazaira study [47], it is 2.3%, all of them below 8% of the Nordic countries, which have the highest figures in Europa.

3.2.1.4 Oceania

In Australia [54] and New Zealand [55], the leading cause of traumatic SCI is road traffic accidents due to motor vehicles; SCI of sporting etiology is approximately 3% more frequent in New Zealand, with rugby accounting for 8% of all those in this category. In both, falls account for a quarter and a third of all traumatic SCI, respectively.

In the Fiji Islands, falls account for 39% followed by sports (28%); road accidents account for no more than 25% [56].

3.2.2 Discussion

The most common etiologies in developing countries are road traffic accidents and falls from height. Both of them are increasing due to urbanization and increased use of motor vehicles; the WHO foresees a further growth in traumatic SCI due to road traffic accidents if preventive measures are not put in place. In contrast, in developed countries, although road traffic accidents continue to be the most frequent cause of traumatic SCI, this proportion is decreasing due to an increase in falls, especially in older people, as well as an increase in non-traumatic etiology.

Figure 2 provides an overview of the etiology of both traumatic and non-traumatic SCI worldwide from the Lancet 2019 [57].

Figure 2.

An overview of the etiology of SCI [57].

3.3 Analysis of the etiology in terms of age

The etiology profile was analyzed by age group by Price [58]: motor vehicle collision is the leading cause in the USA up to the age of 45 years, and above this, falls (75% of the cases recorded in people aged 76 years and over, are caused by falls). Between the ages of 16 and 30, firearm injury ranks second (19%) and third between the ages of 10 and 15 (8.1%), with this etiology declining as the age of the persons affected increases. Motorbike accidents represent the third most frequent cause between 31 and 45 years (10.9%) and 46–60 years (7.1%). Medical-surgical complications are the second most frequent cause under the age of 16 (12.8%) and the third most frequent cause over the age of 60 (10.9%).

If one looks only at what happens in childhood [3], non-traumatic SCI was mostly due to tumors (30–63%) and inflammatory/autoimmune causes (28–35%), and traumatic SCI was mostly caused by land transport (46–74%), falls (12–35%), and sport or recreation (10–25%) .

3.4 Analysis of the etiology in terms of sex

Analyzing the etiology according to sex, the two main causes of SCI, car accidents and falls, accounted for 53.5% of the total among males and 68.6% among females, while firearm injuries (11.7% in males and 5.8% in females), motorbike accidents (8% in males and 2.4% in females), or dives (5.3% in males and 2.4% in females) were more numerous among males. In contrast, medical-surgical complications represent the third cause of SCI in women (7.6%) and the sixth among men (3.3%), according to Price [58].

3.5 Analysis of the etiology in terms of ethnicity

Price et al. pointed out that the largest differences in the etiological profile were found in the ethnicity: firearm injuries caused 33% of SCI in blacks, 14.6% in Hispanics, 9.5% in other races, and only 3% in whites [58].

3.6 Analysis of the etiology in terms of temporality

There are notable differences between the days of the week and the season in which most traumatic and non-traumatic SCIs occur. On the one hand, most traumatic SCI takes place on weekends: Price et al. [58] found that most SCI occurred on Saturday (18.9%) and Sunday (17.3%), which is explained by the higher number of motorbike accidents and dives during the weekend; in contrast, medical-surgical complications are more frequent on Monday or Tuesday (19.8% and 21% respectively).

On the other hand, the month with the highest number of SCI was July (10.9%), compared with February (6.3%), which was the lowest, which is also related to the increased use of water sports and motorbikes in the warmer months [58].

3.7 Relationship between etiology and type of SCI

The level and complexity (complete and incomplete) of the injury were associated with the etiology: firearms injuries and medical-surgical complications result in paraplegia, especially at the D7-S3 level [58]. In contrast, falls generally result in tetraplegia [57]. A large number of falls and medical-surgical complications result in incomplete injuries, while firearm and motorbike injuries result in complete injuries [58].

4. Conclusions

A more comprehensive understanding of the epidemiology of SCI is required to better plan health services that can meet the future demand for prevention and rehabilitation of people with spinal cord damage from any cause.

4.1 Limitations

A limitation of this review is that there is a scarcity of quality research in the field of SCI epidemiology; most studies are single-center, with the potential for selection bias to influence the results. Furthermore, there was no internationally accepted classification of non-traumatic SCI available at the time that the studies included in this review were carried out. This limited the ability to report and compare the etiology across many countries and regions.