Patterns of skeletal trauma resulting from motor vehicle collisions: a scoping literature review

Abstract

As a leading cause of fatality, motor vehicle collisions comprise a significant proportion of medico-legal cases worldwide. During death investigations into such events, forensic practitioners may be asked to make inferences about the relationship between traumatic injuries and the circumstances of the collision. These interpretations require a thorough understanding of the hard and soft tissue blunt force trauma that results from vehicle collisions. This scoping literature review aimed to assess what is currently known about skeletal fracture patterns in occupants of fatal motor vehicle collisions and how contextual variables influence those fractures. Upon screening the search results from several databases based on a set of pre-defined inclusion criteria, 133 articles were identified including case reports, case series and large empirical studies. Most studies investigated car occupants, followed by motorcyclists, with very few focusing on heavy vehicle occupants. Fractures patterns observed comprised a high prevalence of rib, lower limb, and skull fractures in motorcyclists and a high frequency of skull, vertebral and rib fractures in car occupants, whilst pectoral girdle fractures were rare in both occupant types. The level of contextual detail about the collision varied between studies, with most failing to consider the influence of occupant and crash-related variables on resulting fractures. Further, there was a strong focus on soft tissue trauma and a lack of differentiation between fractures in deceased adult vehicle occupants and other groups. The minimal fracture data available in these studies provides limited assistance to forensic practitioners interpreting motor vehicle collision trauma. Additional research on fracture patterns in the context of the variables that influence trauma is recommended.

Key points

• Limited literature exists on skeletal fracture patterns in occupants of fatal motor vehicle collisions.

• Motorcyclists and car occupants exhibit different fracture patterns.

• Few studies have examined skeletal blunt force trauma in heavy vehicle occupants.

• The literature inadequately considers the influence of contextual variables on fracture patterning.

• Additional research into fracture patterns from fatal motor vehicle collisions is necessary.

Introduction

Motor vehicle collisions (MVCs) are a leading cause of death worldwide [1], particularly within the young adult population [1]. According to the World Health Organization’s 2018 “Global Status Report on Road Safety” [2], an estimated 1.35 million people die annually in road traffic collisions. Whilst fatal MVC events may involve any type of motorised vehicle, including trucks, buses, vans, all-terrain vehicles, and mopeds; motorcyclists and car occupants constitute over half of all road fatalities [2]. As MVCs are recognised as an unnatural cause of death, many countries have legislated the reporting of road fatalities to a coroner, medical examiner, police officer, or equivalent authority [3–8]. Consequently, MVC events comprise a significant proportion of the global forensic caseload.

An MVC is a form of horizontal deceleration impact where a motorised vehicle collides with, or is impacted by, another object [9,10]. Due to the substantial blunt forces produced by MVCs, occupants may sustain severe, and sometimes fatal, trauma. In cases where a vehicle rolls or tips over, or an individual is ejected from a vehicle, the body is subjected to both horizontal and vertical deceleration blunt loads. As a moving vehicle impacts another object, a transfer of energy takes place with some, or all, of the vehicle’s energy being absorbed by deformation of the vehicle or by the object [9,11]. However, vehicle occupants are partially independent of the vehicle they are travelling in. As such, the occupants will continue moving at the same velocity upon impact until their momentum is arrested and kinetic energy is absorbed by safety restraints, or transferred to the vehicle’s internal structure or another object [9,10]. Consequently, the high-energy blunt forces involved in an MVC are the primary cause of blunt force trauma (BFT) to the skeleton [9,12], often resulting in extensive and complex fractures [9,13].

An MVC death investigation typically involves referral to the forensic pathologist for a determination of the cause of death, and in certain cases, to address questions by law-enforcement about the circumstances of the event [3–5,7,10]. Typically, these questions aim to improve understandings of the context and mechanism by which injuries were sustained, so that investigators can better comprehend how the MVC occurred and what future prevention measures may be implemented. The documentation of fracture patterns, as part of the examination of the cause of death, may also require specialist forensic anthropology [9,14,15] or radiology [10,15] opinions.

Since the early 2000s, there has been a substantial increase in research on MVC events. Much of this research, particularly biomechanical and experimental studies, has endeavoured to improve vehicle manufacturing and safety [16–18]. Other studies, mainly in the fields of clinical medicine and forensic science, have examined the morbidity and mortality of individuals involved in MVCs [5,9,10,19–35]. By documenting injuries commonly observed in vehicle occupants under different conditions, researchers have attempted to achieve a range of outcomes; from better medical treatment for MVC survivors [36–39] to a greater awareness of trauma mechanisms [14,23,28,40,41]. However, despite this body of work, there remains a limited understanding of the fracture patterns that result in occupants of fatal MVCs [5,21,42,43]. Consequently, the aim of this scoping review was twofold. First, to investigate what is currently known about the skeletal fracture patterns sustained by occupants of motorcycles, cars, and heavy vehicles in fatal MVCs. Second, to assess how extrinsic variables (i.e., safety mechanisms, collision types, impact objects, vehicle velocity) and intrinsic variables (i.e., age, sex, body mass, height, pre-existing conditions) influence the distribution of those fractures.

Methods

Search strategy and inclusion criteria

A scoping literature review was deemed most appropriate due to the heterogenous study designs of the published literature. Peer-reviewed English language articles published between January 1st 2002 and November 27th 2023 were searched in Scopus, Web of Science, PubMed, and ProQuest. Articles were included if they noted skeletal fracture patterns sustained by adult (18 years or older) drivers or passengers in fatal motorcycle, car, and/or heavy vehicle (trucks and buses) collisions. Mopeds and scooters were grouped with motorcycles, whilst vans were grouped with cars. Over the past two decades, the influence of international regulatory and legislative changes, such as the United States of America’s Transportation Equity Act for the 21st Century (1998) [44], and the European New Car Assessment Program (1997) [45], have improved vehicle safety [46]. Therefore, focusing the search period on the last 21 years ensured the findings were reflective of modern vehicle safety standards, increasing their relevance to investigations of contemporary fatal MVCs.

Prior to undertaking the scoping search, keywords for relevant cohorts, fields of interest, incident and injury types were identified (Supplementary Table A) and entered into the four databases. Several articles known to meet the inclusion criteria were selected to test the effectiveness of the search strategy and keywords (Supplementary Table B). All of the “Gold Set” articles were found to be included in at least one of the database search results, confirming the ability of the keywords to capture relevant articles.

Documentation of study and trauma data

For the purposes of this scoping literature review, studies were categorised by their original study type, not by the number of cases deemed relevant to the review. Due to the differing level of trauma detail documented, case reports were considered separately to larger empirical studies (i.e., case series, cross-sectional studies, cohort studies). The skeletal trauma detail extracted from the literature was categorised according to seven skeletal regions: skull, pectoral girdle, upper limb, rib cage, vertebrae (including the hyoid bone), pelvic girdle, and lower limb.

Results

The database searches identified 7 873 articles of potential relevance. Upon review of the titles, abstracts, and full-body texts, 133 articles met the inclusion criteria (Figure 1). These articles consisted of case reports (n = 53), case series (n = 28), and a mixture of cross-sectional, retrospective, prospective and case–control studies (n = 52). As most studies derived from forensic pathology or clinical medicine, the majority of data originated from postmortem/autopsy examinations (n = 80), hospital-based trauma registries (n = 31), or a combination of both (n = 22). There was only one anthropological paper, by Marinho and Cardoso [14], which studied 21 individuals from a Portuguese identified skeletal collection of whom one had been an occupant of a car. The majority of studies investigated occupants of cars/vans (n = 69), followed by motorcycles (n = 48) and multiple vehicle types (n = 15), whilst only a small subgroup (n = 5) explicitly examined heavy vehicle occupants. Studies were undertaken in 38 countries and so were comprised of both left- and right-side drive vehicles (Supplementary Tables C1 and C2).

Figure 1.

Preferred reporting items for systematic reviews and meta-analyses flowchart of the article screening process. BFT: blunt force trauma; MVC: motor vehicle collision.

Fracture patterns documented in case reports

Motorcyclists

Twenty-four case reports examined either an adult motorcycle rider [47–66] or pillion passenger [67–70] involved in a fatal MVC. The deceased were aged between 18 and 67 years old, with 22 males and only two females. The majority were drivers, with four pillion passengers including both female cases. Fractures were distributed across all skeletal regions in varying frequencies (Figure 2A). The most commonly fractured regions were the skull (n = 9), lower limbs (n = 10), and rib cage (n = 11), whilst pectoral and pelvic girdle fractures were least reported. Of the reports that specified the siding of the fractures, the majority exhibited BFT to both sides of the skeleton [48,51,53,54,60,62,66], whilst a few motorcyclists exhibited BFT to only one side [59,64,67]. Two pillion passengers [68,69] and two motorcyclists [55,61] did not exhibit any skeletal BFT.

Figure 2.

Anatomical regions exhibiting fractures in case reports involving (A) motorcycle (n = 24) [47–70], (B) car (n = 28) [28,29,71–96], and (C) heavy vehicle (n = 1) [97] occupants.

Car occupants

Of the 28 case reports investigating car occupants, 17 were drivers [28,29,71–85], six were passengers [86–91], and five were unspecified occupants [92–96]. The individuals ranged from 19 to 89 years old and included 24 males and four females. Like motorcyclists, skeletal BFT was reported in all major skeletal regions in car occupants, however, fractures of the vertebrae (n = 10) (typically the fourth to seventh cervical), and the rib cage (n = 10) were most prevalent (Figure 2B). Rib fractures tended to be distributed bilaterally [74,81,83,84], although the right side was more fractured than the left side in frontal and near-side impact collisions [74,83,84]. Skull fractures were also prevalent (n = 7), with several skull bones exhibiting trauma including the ethmoid [78], sphenoid [78], frontal [91], occipital [84], nasal, mandible and maxillae bones [72,78,92]. In contrast, pectoral girdle, pelvic, upper and lower limb fractures were rare (Figure 2B).

Overall, fractures were commonly distributed bilaterally across the skeleton [74,78,81,83,84,87,91,92]. Only three cases exhibited unilateral skeletal BFT [28,85,93]. However, due to a lack of contextual information, it was only known that one case with right-sided unilateral fractures had been involved in a right frontal impact [28]. Several cases did not report MVC-related fractures [79,80,86,88].

Heavy vehicle occupants

Only one case reported by Maiese et al. [97] noted skeletal trauma sustained in a heavy vehicle collision. The truck driver exhibited fractures of the right lower limb and vertebrae (Figure 2C). Given the data are anecdotal, it is not possible to say whether this pattern is representative of most truck occupants or a unique case.

Fracture patterns documented in larger empirical studies

Overall, the findings suggested that different patterns of skeletal BFT occur in motorcyclists and car occupants (Figures 3 and 4, Supplementary Tables D1 and D2). Fractures of the skull were reported most often, and pectoral girdle fractures least often, for both motorcycle and car fatalities. Several of the studies that explored multiple motor vehicle types within the same paper also reported skull fractures in both motorcyclists and car occupants [98–102]. Of the studies that examined the head region, skull fractures were more frequently reported in motorcyclists (85.2%) compared to car occupants (76.9%). This was consistent with the findings of the case reports. Fractures of the upper limbs, vertebrae, pelvis, and lower limbs were also more commonly reported in motorcycle studies than car occupant studies. In contrast to the case reports, trauma to the rib cage was reported proportionally more frequently in car occupants than in motorcyclists in larger empirical studies, though only by a small margin. Only four studies noted skeletal BFT in heavy vehicle occupants [34,98,103,104]. These included right-sided rib [103] and skull fractures [98] in truck occupants, pelvic [104] and skull fractures [98] in bus occupants, and vertebral fractures [34] in unspecified heavy vehicle occupants.

Figure 3.

Number of motorcycle studies reporting fractures by anatomical region. See Supplementary Table D1 for a full list of the case series and larger empirical studies summarised in this figure [19–22,31,37,43,98–102,105–128].

Figure 4.

Number of car occupant studies reporting fractures by anatomical region. See Supplementary Table D2 for a full list of the case series and larger empirical studies summarised in this figure [5,14,23–25,27,30,32–36,39–42,98,99,101,103,104,108,110,126,129–154].

Influence of intrinsic and extrinsic variables on fracture patterns

Motorcyclists

Despite the significant number of motorcycle studies, very few examined the role of extrinsic variables in fracture patterning (Table 1) and even less investigated the relationship between intrinsic variables and fracturing [19,43]. Saunders et al. [43] found that rib, pelvic, and cervical vertebrae fractures were significantly more likely to occur in older motorcyclists, whilst Anh et al. [19] determined that occipital bone fractures occurred significantly more frequently in individuals 40 years and older. Furthermore, females were found to be at significantly greater risk of obtaining basilar skull fractures [19].

Table 1.

Extrinsic variables influencing fracture patterning in motorcyclists involved in fatal motor vehicle collisions (MVCs).

Variable	Category	Skeletal region
		Skull	Pectoral girdle	Upper limbs	Rib cage	Vertebrae	Pelvic girdle	Lower limbs
Helmet status	Yes	[19,20,31,58,107,114,119,124]	-	-	-	[31,114]	-	-
	No	[19,31]	-	-	-	[31]	-	-
Impact object	Fixed/stationary object	[20]	-	-	-	Cervical, thoracic [20]; C4, hyoid [56]	-	-
	Car	Temporal bone [19]	-	-	-	-	[43]	-
	Motorcycle	Temporal bone [19]	-	-	-	-	-	-
Collision type	Frontal impact	[31]	-	[51]	[31,51]	[51]	[31,51]	[51]
	Rear impact	[31]	-	-	[31]	-	[31]
	Self-skid/single motorcycle incident	[31]; basilar skull [19]	-	-	[31]	-	[31]	-
	Side-swipe	[31]	-	-	[31]	-	-	-
	Runover by vehicle	[48]			[48]		[48]

Note: specific bones/anatomical regions fractured are listed and italicised where available.

Of the studies examining extrinsic variables, most investigated the effect of helmets on fracturing; finding that skull [19,31] and cervical vertebrae [31] fractures occurred with and without helmets due to head impacts with other vehicles [48], fixed objects [20,58,65], or the ground [119]. A relatively small number of studies investigated the effects of collision type and object impacted on fractures. Skull, rib and pelvic fractures were identified in most collision types [31], whilst vertebral fractures were only observed in frontal impacts [51] and collisions with fixed objects [20,56]. Bambach and Mattos [20] suggested that fixed object collisions where the motorcyclist is ejected and slides in a prone position may produce basilar skull and upper cervical vertebrae fractures due to frontal or lateral impacts to the head, causing lateral flexion and hyperextension.

Car occupants

Like for motorcycles, the influence of extrinsic (Table 2) and intrinsic [23,140] variables on fracturing was only considered by some car studies. The main intrinsic variable investigated was age, with Bertrand et al. [23] and O’Donovan et al. [140] finding that the odds of rib fracture increased with age.

Table 2.

Extrinsic variables influencing fracture patterning in occupants of fatal car collisions.

Variable	Category	Skeletal region
		Skull	Pectoral girdle	Upper limbs	Rib cage	Vertebrae	Pelvic girdle	Lower limbs
Seatbelt status	Yes	-	[27]	-	[27,30,40,135]	[29,30,82,142];	-	-
	No	Occipital, mandible [41]	-	-	-	C2-C7 [90]	-	-
Airbag deployment	Yes	Occipital, mandible [41]	-	-	Left [10]; right [3–6] [83]	T4-T5 [144]; C6 [71]	-	-
	No	-	-	-	-	-	-	-
Seating position	Driver	[5,25,78,135]	-	Left humerus [25]	[135]; left-sided [25]	-	[25]	[5]
	Front seat passenger	-	-	-	Right-sided [25]	-	-	-
	Rear seat passenger	Skull base (except hinge/ring fractures) [5]	-	-	-	-	-	-
Collision type	Frontal impact		-	-	Bilateral [23]	-	-	-
	Side impact	-	-	-	Left-sided [23]	-	-	-
	Rear impact	-	-	-	[152]	T7-T8 [152]	-	-
	Rollover	[72]	-	-	-	C7 [72]; C6 [95]	-	-
Impact object	Fixed object	[41,138]	-	-	-	-	-	-
	Another occupant	Skull base [148]	-	-	-	-	-	-
	Stationary vehicle	[135]	-	-	-	-	-	-
Velocity	>240 km/h	[75]	-	-	-	-	-	-

Note: specific bones/anatomical regions fractured are listed and italicised where available.

Most studies analysing extrinsic variables focused on safety mechanisms (Table 2). Skull and vertebral fractures were related to the lack of a restraint [41,90], whilst rib [27,40], sternal [27] and clavicle [27] fractures concentrated along the diagonal path of seatbelt, were reported in restrained individuals. Due to contact loading [40,142], seatbelt-related fractures were often accompanied by distinctive patterned neck and/or upper torso abrasions known as the “seatbelt syndrome” [27,40,82,84,87,142]. Cervical vertebrae fractures were also observed in belted individuals [142], possibly attributable to the hyperflexion and hyperextension of the unrestrained head and neck relative to the restrained torso [29,142]. Similar to the motorcycle studies, few car studies examined the role of collision type and impact object on fracture patterns, whilst almost no analysis of vehicle velocity and fracturing was performed. Slight differences in the patterning of rib fractures were associated with frontal and side impacts [23], whilst cervical [72,95] and thoracic [152] vertebral fractures were related to rollover and rear-impact collisions, respectively. Moreover, multiple impact objects were found to be associated with skull fracturing.

Regarding seating position, a significantly greater prevalence of skull base, facial, pelvic, and limb fractures [5,25], as well as a higher frequency of left-sided rib fractures [25], have been observed in drivers. Moreover, multiple rib fractures have been associated with steering wheel contact [135], whilst lower limb fractures may be related to the influence of the pedals on the driver’s leg and foot position [5,155]. In contrast, right-sided rib fractures were more prevalent in front seat passengers [25]. In rear-seat passengers, hinge fractures of the skull and lower limb fractures were found to be significantly less prevalent [5], whilst other skull base fractures were sustained more often in comparison to drivers [5]. It has also been suggested that contact with the door and the roof pillars that frame the windscreen and divide the passenger compartments can result in fatal skull and rib fractures [135].

Heavy vehicle occupants

No study detailing heavy vehicle occupants investigated the influence of intrinsic and extrinsic variables on the observed skeletal fracture patterns [34,97,98,103,104].

Discussion

Fracture patterns resulting from fatal MVC events

In general, motorcyclists are considered to be particularly prone to injury in MVC events due to their status as “vulnerable road users” [1]. This is because they are not protected by an enclosed vehicle structure like car occupants, nor do they have access to as many protective devices like seatbelts and airbags [2,9]. Consequently, motorcyclists may have a greater risk of severe skeletal BFT. When considering the overall findings of the literature, fractures of the skull, limbs, and pelvic girdle were reported in proportionately more motorcycle than car fatalities. The greater frequency of upper limb fractures observed in motorcyclists is consistent with literature examining hospitalised MVC patients [156,157] and could be due to their increased vulnerability to direct impacts with the road or other objects [9]. Similarly, the higher proportion of lower limb fractures may be related to the vulnerability of the lower limbs to being crushed under the load of the motorcycle, directly impacted by the road’s surface/another object [54,63], or injured during attempts to stabilise an out-of-control motorcycle with the leg and foot [117]. A possible explanation for the greater degree of pelvic fractures reported in motorcyclists is their proneness to obtaining “straddle injuries” [51]. Such injuries occur when the individual's body continues forward after impact, in opposition to their motorcycle, thrusting them with substantial force into the motorcycle’s fuel tank and handlebars [48,51].

Severe head, chest and vertebral column trauma is often associated with a higher likelihood of mortality given the vital organs contained within these regions [33,39,98,100,102,144]. As such, the high representation and reporting of skull, rib cage, and vertebral fractures found across most of the reviewed MVC literature is not unexpected. The absence of lumbar vertebrae fractures amongst the car case reports, in comparison to the motorcycle case reports, may be attributed to their lower likelihood of being subjected to whiplash forces or impacts from the steering wheel [9,29]. It could also be due to the introduction of three-point shoulder restraints, said to reduce the incidence of flexion injuries to the lumbar spine [158], or be a consequence of the relatively small number of case reports. Moreover, the finding that cervical vertebrae fractures were particularly prevalent amongst the car case reports [29,71,72,89,90,95], may be explained by the multiple ways in which neck hyperextension and/or hyperflexion occurs in car collisions. This includes whiplash-induced injuries [29], airbag-related facial trauma [71], head impact with the vehicle’s roof or the road during a rollover [72,95], and injuries associated with unstrained individuals [90].

Of all skeletal regions, fractures of the pectoral girdle were reported the least often in both motorcyclists and car occupants. This is consistent with medical and forensic literature, which has suggested that scapula fractures are rare even in high-energy MVC events [9,159–162]. The low frequency of pectoral girdle fractures could be due to its anatomical position and the protection afforded by the scapula’s overlying muscles and the rib cage [9,160]. Given the scapula is a mobile and unfixed bone, its anatomical structure may also contribute to its ability to dissipate blunt loads and thus avoid fracturing [9,160]. Alternatively, the low occurrence of pectoral fractures may indicate that direct loading and energy transfer to this region is uncommon in MVCs.

Influence of intrinsic and extrinsic variables on fracture patterns

In medico-legal casework, the accuracy of interpretations about the manner in which skeletal injuries occur relies upon available contextual information [12,14]. For example, Lindquist et al. [40] identified challenges with distinguishing between the respective contributions of the seatbelt, airbag, and steering wheel, in producing rib fractures. In such situations, if intrinsic and extrinsic variables are unknown, or as many variables as possible are not considered in analyses of skeletal BFT, understanding the context behind fracture patterns remains challenging. Despite this, multiple studies in the literature noted only basic information about the occupant and the circumstances of the MVC event, potentially due to a lack of access to in-depth contextual data. Furthermore, few studies evaluated the effect of intrinsic and extrinsic variables on resulting skeletal BFT. The limited variable data available restrict the ability of forensic practitioners to make informed interpretations of skeletal BFT and the circumstances that influence fracturing in MVCs.

Of the small proportion of studies that investigated contextual variables, many focused on the influence of safety measures. In motorcyclists, the finding that skull and cervical vertebrae fractures occurred regardless of helmet status [19,31] suggests the effectiveness of helmets is limited when significant impact velocities are involved [112]. Furthermore, though seatbelt use may reduce morbidity and mortality in car collisions [163,164], seat belt loading and associated whiplash have been documented to cause fractures in restrained car occupants, commonly to the ribs and vertebrae [29,40,135]. Evidently, despite their status as safety mechanisms, skeletal fractures may still occur regardless of helmet and seatbelt use.

Seating position was a variable of interest in several car studies, with different fracture patterns being identified between drivers and passengers [5,25]. As evidenced in Blandino et al. [25], differences in the siding of rib fractures may be associated with the side of the car in which the occupant was seated. Further, researchers have hypothesised that the higher frequencies of lower limb fractures observed in drivers [5,155] are caused by impacts of the knee with the dashboard [155,165], and the feet with the pedals and intruding toe and floor-pans [5,139,155,165,166]. Interestingly, rear-seat car passengers and motorcycle pillion passengers have remained relatively disregarded in considerations of fracture patterns potentially due to a dominance of drivers in samples [5,22,25,150] and a lack of specification of the occupant’s seating position [37,39,91,95,112,128]. Given there may be medico-legal importance in identifying seating position, and particularly the individual in control of the vehicle at the time of the MVC, additional research is required to reliably differentiate between fracture patterns in drivers and the various passenger types.

Despite few motorcycle and car studies investigating collision type and impact object, the literature suggests that the nature of a collision may have implications regarding the region and extent of skeletal BFT (Table 2). This is because the way an occupant and a vehicle responds in an MVC is heavily dependent upon factors like the direction of impact, the area and degree of vehicle deformation, and the size and shape of the object impacted [9,10]. Therefore, given the importance of understanding the nature of a collision when investigating injury patterns, more studies examining fractures in the context of different collision types and impact objects are needed.

Vehicle velocity is a significant variable in MVC events given its legal implications, potential to be a causative factor in collisions, and its significant association with the risk of serious injury and fatality [167,168]. Despite this, the influence of vehicle impact velocity on fractures was not well examined. Whilst multiple studies [22,112,139] noted that high speed impacts may play a significant role in injury severity and trauma outcomes, few actually analysed exact collision speeds and their influence on the observed fracture patterns [105,117,139,148]. The challenges involved in estimating a vehicle’s impact speed, particularly with unwitnessed MVCs, and the fact that it is not often recorded in incident or autopsy reports [43], may explain the lack of studies accounting for this variable.

Whilst many of the motorcycle and car occupant studies included in the review noted basic demographic information like age and sex, very few examined the influence of these intrinsic factors on fracture patterns. Furthermore, almost no investigation was undertaken into the effect, if any, of other relevant intrinsic variables, such as height, body mass, pre-existing conditions, and post-MVC medical interventions. Bone strength and stiffness, and therefore fracture risk, can differ due to pathological conditions like osteoporosis, diabetes, rickets, metastasizing cancers and rheumatoid arthritis [9]; whilst Body Mass Index has been correlated with the risk of fractures and serious injury in MVC occupants [169,170]. Additionally, cardiopulmonary resuscitation has been known to cause rib fractures which may mask or mimic MVC-related rib fractures [171]. The lack of analysis of intrinsic variables in the current literature makes it challenging for forensic practitioners to hypothesise the effects of such variables on the skeletal trauma observed during MVC death investigations.

Limitations of the current literature to forensic medicine

This scoping literature review has provided some important insights into the skeletal regions commonly fractured, and the circumstances that result in fractures, in MVC events. However, gaps and weaknesses identified in the literature constrain its usefulness for medico-legal practice. To date, the available information on skeletal BFT in motorcyclists and car occupants, while vast, offers only a superficial understanding of fracture patterns and the variables that contribute to them. Furthermore, the investigation and documentation of fractures in truck and bus occupants has been negligible compared to other vehicle types [34,97,98,103,104], potentially because they make up a smaller proportion of MVC fatalities [172]. Consequently, the evidence base of MVC fracture patterns is unrepresentative for forensic practitioners.

One explanation for the current lack of in-depth fracture pattern data is that almost all studies were undertaken from a clinical medicine or forensic pathology perspective. Consequently, their focus was on examining soft tissue injuries to address questions around effectively treating patients [24,36,39,49,134] and/or determining cause of death [47,71,73,110]. Hard tissue trauma, although often complex and extensive [9], was frequently considered tangentially to soft tissue injuries, with many studies over-simplifying and/or under-reporting skeletal trauma [57,77,94]. For the larger empirical studies, this is probably due to a lack of differentiation in statistical analyses, including between fatal and surviving cases [112,137], and/or adults and subadults [116,122], which reduced the depth of fracture and variable information that could be extracted. For the case reports, this is most likely because the reports aimed to bring attention to unique and significant medical findings or circumstances, and the reported fractures may not have appeared particularly noteworthy in their own right. Lastly, the majority of the forensic and clinical studies used data from observations taken during hospitalisation or autopsy instead of advanced imaging techniques considered to be superior in identifying detailed skeletal trauma, like computed tomography scanning [145,173,174]. Overall, the level of skeletal fracture detail provided in many studies was inadequate to assist forensic practitioners in understanding MVC fracture patterns.

Lastly, MVCs are complex events that involve many different variables. Although several studies examined the influence of different circumstances on skeletal BFT patterns in motorcyclists and car occupants, much of the existing literature did not thoroughly consider many of the demographic and/or incident-related variables that could potentially influence the presentation of trauma. In addition, the association between contextual variables and fracture patterns in bus or truck occupant fatalities remains completely unexplored. To achieve the best understanding of the true relationship between blunt force impacts from MVCs and resulting fracture patterns in occupants, future studies should consider a multivariable analysis of relevant intrinsic and extrinsic variables in the context of skeletal BFT.

Limitations of the scoping literature review

This scoping literature review had several limitations. First, since scoping literature reviews aim to provide an overview of the current evidence base by identifying and investigating knowledge gaps in the available literature [175], it is possible that not all existing studies examining fractures in MVC occupants were captured. However, given that almost 8 000 articles originating from four separate databases were assessed (Figure 1), the authors consider the included studies to be a good representation of the current literature. Second, the review examined studies with data from 38 different countries (Supplementary Tables C1 and C2). Whilst the majority examined vehicles that drove on the right-hand side of the road, some studies examined vehicles that drove on the left-hand side. As such, this variation may have influenced the siding of the skeletal BFT produced and the overall findings of this study.

Conclusion

This scoping review synthesises, for the first time, the current literature on skeletal fracture patterns in motorcyclists, car and heavy vehicle occupants involved in fatal MVCs for forensic medical specialists. The review demonstrates that, although there has been extensive work published on MVC fatalities, there remains a limited, and statistically non-validated, understanding of not only the resulting skeletal fracture patterns, but also how the extrinsic and intrinsic variables associated with these collisions influence those fracture patterns. This is particularly notable for occupants of heavy vehicles, such as trucks and buses. Despite the limitations of the current literature and the complex nature of MVC events, the findings of this review suggest that motorcyclists and car occupants sustain different patterns of skeletal fractures. Building upon details provided in the existing literature, further research into the fracture patterns resulting from MVCs in the context of the intrinsic and extrinsic variables that influence trauma is recommended. Obtaining access to a more in-depth and reliable evidence base of fracture patterns in vehicle occupants will enable medico-legal investigators to make better informed inferences regarding the circumstances in which skeletal BFT is produced.

Authors' contributions

Alexandra Wulff conceptualised the study, created the methodology, undertook the literature search, reviewed and analysed the papers, drafted and edited the manuscript and created all figures and tables. Richard G. D. Fernandez provided ideas, reviewed and edited the manuscript. Joanna F. Dipnall provided ideas, reviewed and edited the manuscript. Soren Blau reviewed and edited the manuscript. Samantha K. Rowbotham was also involved in the conceptualisation of the study and creation of the methodology, as well as reviewing and editing the manuscript and supervising the study. All authors contributed to the final text and approved it.

Compliance with ethical standard

Given the nature of this study as a scoping literature review, no ethical approval was required for the conduct of this research.

Disclosure statement

Soren Blau holds the position of Editorial Board Member for Forensic Sciences Research and is blinded from reviewing or making decisions for the manuscript.

Funding

During this research, Alexandra Wulff was supported by an Australian Government Research Training Program Scholarship and a Westpac Future Leaders Scholarship. These funding sources had no influence nor involvement in the conduct of this research nor the article’s preparation.