Forensic Science International 254 (2015) 18–25

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Case series analysis of hindfoot injuries sustained by drivers in frontal motor vehicle crashes Xin Ye a,*, James Funk a, Aaron Forbes b, Shepard Hurwitz b, Greg Shaw a, Jeff Crandall a, Rob Freeth c, Chris Michetti c, Rodney Rudd c, Mark Scarboro c a b c

Center for Applied Biomechanics, University of Virginia, 4040 Lewis and Clark Drive, Charlottesville, VA 22911, USA School of Medicine, University of North Carolina, 400 Silver Cedar Court, Chapel Hill, NC 27514, USA National Highway Traffic Safety Administration, 1200 New Jersey Avenue, SE, West Building, Washington, DC 20590, USA

A R T I C L E I N F O

A B S T R A C T

Article history: Received 29 December 2014 Received in revised form 4 June 2015 Accepted 17 June 2015 Available online 26 June 2015

Improvements to vehicle frontal crashworthiness have led to reductions in toe pan and instrument panel intrusions as well as leg, foot, and ankle loadings in standardized crash tests. Current field data, however, suggests the proportion of foot and ankle injuries sustained by drivers in frontal crashes has not decreased over the past two decades. To explain the inconsistency between crash tests results and real world lower limb injury prevalence, this study investigated the injury causation scenario for the specific hind-foot injury patterns observed in frontal vehicle crashes. Thirty-four cases with leg, foot, and ankle injuries were selected from the Crash Injury Research and Engineering Network (CIREN) database. Talus fractures were present in 20 cases, representing the most frequent hind-foot skeletal injuries observed among the reviewed cases. While axial compression was the predominant loading mechanism causing 18 injuries, 11 injured ankles involved inversion or eversion motion, and 5 involved dorsiflexion as the injury mechanism. Injured ankles of drivers were more biased towards the right aspect with foot pedals contributing to injuries in 13 of the 34 cases. Combined, the results suggest that despite recent advancement of vehicle performance in crash tests, efforts to reduce axial forces sustained in lower extremity should be prioritized. The analysis of injury mechanisms in this study could aid in crash reconstructions and the development of safety systems for vehicles. ß 2015 Elsevier Ireland Ltd. All rights reserved.

Keywords: CIREN Lower extremity Injury mechanism Injury classification

1. Introduction Lower extremity injuries are the most common injuries involved in frontal motor vehicle crashes, and within this body region, the foot/ankle complex is the most frequently injured [1]. Previous studies have documented the high incidence of lower extremity injuries with associated consequences and cost [2]. In addition, a recent study found that the relative proportion of lower extremity injuries has continued to increase and now accounts for 45% of all Abbreviated Injury Scale (AIS) 2+ injuries for frontal occupants in frontal crashes [3]. The relative importance of belowknee lower extremity injuries has increased in frontal crashes as seatbelt usage and airbag availability has improved [4]. Since the

* Corresponding author. Tel.: +1 434 466 8342; fax: +1 434 296 3453. E-mail addresses: [email protected] (X. Ye), [email protected] (J. Funk), [email protected] (A. Forbes), [email protected] (S. Hurwitz), [email protected] (G. Shaw), [email protected] (J. Crandall), [email protected] (R. Freeth), [email protected] (C. Michetti), [email protected] (R. Rudd), [email protected] (M. Scarboro). http://dx.doi.org/10.1016/j.forsciint.2015.06.015 0379-0738/ß 2015 Elsevier Ireland Ltd. All rights reserved.

late 1980s and the early 1990s, considerable changes have occurred in terms of the composition of the vehicle fleet, crashworthiness of the vehicles, and restraint systems. Improvements to vehicle frontal crashworthiness have led to reductions in toe pan and instrument panel intrusions as well as leg, foot, and ankle loads in standardized crash tests. However, the effects of these changes in mitigating the incidence of lower extremity injuries are not clearly understood. While frequency is one measure for prioritization, the long-term impairment and disability associated with a particular lower limb injury varies greatly depending on its location, the involvement of articular surfaces, and the fracture pattern. Classification schemes for lower limb injuries rely heavily on hypotheses supplemented with laboratory studies in which relatively simple loading were applied. Rational treatment of lower limb injuries and rigorous classification requires extensive knowledge. In addition to the variability associated with the direction, rate and magnitude of the external loading, the lower extremities of occupants in actual crashes vary in their initial position and level of muscle bracing. Given the detailed injury and

X. Ye et al. / Forensic Science International 254 (2015) 18–25

crash information, cases from the Crash Injury Research and Engineering Network (CIREN) could demonstrate these complex conditions as injury patterns do not identically match with existing classification schemes that are predominantly based on experimental testing conditions. A recent study reviewed the biomechanics of ankle injuries from mechanical testing of human cadavers, and summarized the injury mechanisms based on the principle axis of force or torque applied to injured foot segment [5]. The proposed diagram deciphered experimental data for identifying injury mechanisms given an injury pattern and was referred in current study. The resulting flow-chart of initial foot and ankle positions along with the loading components provided a valuable tool for understanding injury mechanisms and associated injuries with contributing factors, including vehicle intrusions and foot panel contacts. The motion of the foot by a three-dimensional coordinate system in this study was illustrated using the Society of Automotive Engineers (SAE) sign convention (Fig. 1), with terminology describing the ankle kinematics [6]. The objective of this study is to analyze the current patterns and causes of lower extremity injuries sustained in moderate to severe frontal crashes, as a tool to provide forensic evidence and reference for crash reconstruction and injury mechanism analysis. 2. Methodology Crash Injury Research and Engineering Network (CIREN) is a U.S.-based research program designed to gather detailed records necessary to conduct multidisciplinary analysis on crash reconstruction and attribution of injury causation. Individual CIREN cases consisted of extensive information including crash summary, vehicular damage, countermeasure information, and injury biomechanics, with supporting radiology files. The crash investigation utilized physical evidence such as skid marks, vehicular damage measurements, and occupant contact points coupled with the investigator’s expert knowledge and experience of vehicle dynamics and occupant kinematics in order to determine the precrash, crash, and post-crash movements of involved vehicles and occupants. Medical experts and engineers went over the evidence for each case, and analyzed the documented photographs, X-ray films and CT scans of the patient’s injuries. Cases with complete CT scans and Digital Imaging and Communications in Medicine

Plantarflexion Y-axis

(DICOM) files were selected for 3-D reconstruction of injuries to examine more specific patterns and locations, adding detailed information on postulated injury causation and severity. Injury severity ranking and attribution was also conducted based on medical notes and relevant injury radiology files. Eligibility and criteria for case inclusion in this study consisted of drivers older than 16 years of age that were involved in a single event, frontal plane crash during the years 2005 to 2010. Frontal collisions was determined by occurrence of most severe vehicle crash damage (i.e., Rank 1) in the frontal plane with principal direction of force (PDOF) ranging between positive and negative 20 degrees. Collision Deformation Classification (CDC) was also tracked for crash type identification as per the CIREN coding guidelines. All case occupants must contain at least one ankle of hind foot injury with moderate or greater severity of injury, as defined by the Abbreviated Injury Scale (i.e., AIS2+) [7]. An in-depth analysis, using crash, occupant, and medical information, was performed on the selected cases to identify each hind foot injury: specifically, the injury mechanisms, contributing factors, involved vehicle components, injury causation scenarios, and applicable injury trauma codes. Fracture classification was conducted and each injury pattern was coded using the AIS codes. Additionally, the lower extremity injuries were further classified based on existing OTA classification developed by Orthopaedic Trauma Association to standardize the characterization of injury severity and potential associated impairment [8]. The Lauge– Hansen classification was not included in the injury summary results, as the classic classification system was not fully prognostic to represent all hind-foot injury mechanisms, including supination and external rotation injuries [9,10]. Involved physical components (e.g., instrument panel, toe pan) and initial foot orientation were then deduced based on the injury results coupled with crash statistics and kinematics knowledge. Vehicle intrusion and contacts for each injury were labeled with an injury causation scenario. The long term consequences of each injury was also analyzed based on post-injury observation notes and invasive procedures, in terms of their impact on cognitive, physical, psychosocial and economic factors. Decisions for each case were justified via utilizing the BioTab method to determining and documenting injury causation and injury mechanisms, which leveraged information available to develop evidence-based assessment and to improve the quality and accuracy of the findings [11]. Complete review of the crash scenario was performed in consideration of an extensive literature review of hind foot injuries for similar injury patterns. For cases involving multiple injury mechanisms, both primary and secondary attributing factors were documented. Consensus was reached with all judgments confirmed by biomechanical engineers, medical doctors, orthopaedic surgeons, and epidemiologists through case review sessions. 3. Results

Dorsiflexion Internal Rotation

Eversion Inversion X-axis

19

External Rotation Z-axis

Fig. 1. Diagram of terminology used to describe ankle kinematics.

The case inclusion criteria resulted in 34 cases with detailed information in terms of driver characteristics and lower limb injuries to further investigate the mechanisms of injuries to the foot/ankle complex (Table 1). A statistical summary of demographic information showed that female drivers accounted for 62% of queried cases, with passenger cars attained the highest proportion in vehicle types (Table 2). Injury with the highest AIS code was assigned with Rank 1 injury, and if two or more injuries meet the criteria of the highest AIS, ranking was based on the source of injury and confidence of data from CIREN database. As a result, lower extremity injuries accounted for 50% of Rank 1 injuries in these cases, with hind foot and ankle injuries contributed to 38% of Rank 1 injuries (Table 3).

X. Ye et al. / Forensic Science International 254 (2015) 18–25

20 Table 1 Occupant information from 34 CIREN cases. No.

CIRENID

Age

Sex

Height (cm)

Weight (kg)

MAIS

ISS

Lower limb injuries

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

100074559 100088587 100090373 119607 153427 100091816 100093806 159356 385119819 385123861 385143614 385116467 590144220 781129518 591139760 590132942

39 40 72 38 25 48 37 31 16 58 51 51 38 25 39 19

Female Male Male Female Female Female Female Female Male Female Female Female Male Male Female Female

160 178 180 173 168 169 157 160 178 157 160 163 173 183 158 163

68 80 78 64 82 113 63 68 77 109 61 79 82 82 61 66

2 2 3 4 2 3 3 5 2 3 3 3 4 4 3 5

5 9 19 29 5 10 10 38 5 17 17 19 26 34 10 43

17 18

160143724 122168

36 76

Male Female

185 152

118 60

3 3

22 22

19 20 21 22 23

590109776 857097660 100106878 116194 164689

17 16 29 52 54

Female Male Female Female Female

170 168 157 157 168

62 60 59 96 154

3 2 3 5 3

19 5 10 33 22

24 25 26 27

165430 160153577 385143723 137759

55 55 27 39

Male Male Male Female

173 173 173 150

82 70 66 70

3 3 3 3

19 11 27 10

28 29 30 31 32 33 34

128697 119737 160124426 160131058 160141872 163674 160132288

22 54 18 49 19 49 40

Female Male Male Female Female Female Male

157 183 193 160 175 160 175

59 70 107 104 56 54 90

3 3 3 3 3 4 3

14 22 22 10 27 29 14

Calcaneus fx, medial malleolus fx (R) Talus fx (R) Tibia fx, fibula fx, talus fx, medial malleolus fx (R) Bimalleolar fx (L) Talus fx, tibia fx (R) Talus fx, medial malleolus fx (R) Tibia shaft fx, fibula fx, talus fx, malleolus fx (R) Bimalleolar fx, talus fx (R) Medial malleolus fx (R) Bimalleolar fx (L,R) Medial malleolus fx, talus fx (R) Talus fx (R) Calcaneus fx, talus fx, deltoid ligament rupture (R) Talus fx (L), Bimalleolar fx (R) Talus fx, tibia shaft fx (R) Medial malleolus fx, posterior malleolus fx, fibula fx (L); calcaneus fx, talus fx, fibula fx (R) Trimalleolar fx (R) Bimalleolar fx, calcaneus fx, talus fx (L); talus fx, calcaneus fx, fibula fx (R) Talus fx (R) Bimalleolar fx, fibula fx (R) Trimalleolar fx (R) Calcaneus fx, medial malleolus fx (R) Tibia shaft fx, fibula fx, medial malleolus fx (L); Tibia fx, fibula fx, trimalleolar fx, talus fx (R) Bimalleolar fx (L) Malleolus fx (R) Bimalleolar fx (R) Calcaneus fx, bimalleolar avulsions, talus fx, peroneal tendon avulsions (R) Calcaneus fx, talus fx (R) Tibia shaft fx, bimalleolar fx (L); Tibia fx, fibula fx (R) Talus fx (L) Bimalleolar fx (R) Tibia pilon fx (R) Medial malleolus fx (L);Bimalleolar fx, fibula fx, talus fx (R) Tibia shaft fx (L); Calcaneus fx, talus fx (R)

As shown in the injury distribution, talus fracture was the most common ankle/hind foot injury from the reviewed cases, accounting for 33% of all the injuries. Bi-malleolar and calcaneal fractures comprised 21% and 15% of all injuries, respectively. Lower extremity injuries were recorded as the most severe injury (Rank 1) of all injuries recorded in 50% of all 34 cases, with 71% of the injuries involved the right aspect of ankle/hind foot. Multiple injury mechanisms were identified for each case. The primary and secondary injury mechanism for each lower extremity injury was summarized, as some of the injuries could be a Table 2 Demographic and vehicle information.

combination of multiple contributing factors resulted from external force and moment (Fig. 2). Similar to the findings from Dischinger et al. which examined 42 patients with below-knee lower limb injuries, axial loading was the predominant injury mechanism in this study, contributing to 43% of the injuries [12]. External rotation, inversion and eversion accounted for 14% of the attributing injury mechanisms in all the Table 3 Attributes and distribution of case injuries. Injury information

Mean or percentage (%) 3 (serious severity), 65% 19 42

Age (year) Gender Male (%) Female (%) Weight (kg) Height (cm)

38 62 78.5 168

MAIS* (mode) ISS* Hind foot/ankle injuries Rank 1 injury (%) Lower extremity Hind foot/ankle Hind foot/ankle aspect (%) Right Left

Vehicle

Mean or percentage (%)

Below-knee injury distributiony

Percentage (%)

Passenger cars (%) SUVs (%) Trucks (%) Vans (%) Delta-V (km/h)* Left toe pan intrusion (cm) Left instrument panel intrusion (cm)

59 15 11 15 55 19 12

Tri-malleolus Bi-malleolus Medial malleolus Lateral malleolus Pilon Talus Calcaneus

5 21 17 3 6 33 15

Occupant

Mean or percentage (%) 39

* Unknown Delta-V for case no. 9 and case no. 32 (Table 1), estimation of 40– 55 km/h for case no. 7 and case no. 33.

* y

50 38 71 29

MAIS = maximum abbreviated injury score; ISS = injury severity score. Injury distribution based on all 63 lower limb injuries of 34 cases.

X. Ye et al. / Forensic Science International 254 (2015) 18–25

External Rotaon

Table 5 Injury description and mechanism summary of Case I.

44% 43%

Axial loading 0%

Injury description and mechanism summary

14%

Inversion

14%

Eversion

14%

Dorsiflexion

5%

Other

5% 3% 0%

Right Vertical, comminuted medial malleolar fx (AIS 853414.2). SAD, OTA 44-a2.1 - Talar neck-body junction, including the lateral process (AIS 853200.2). Hawkins IV, OTA 81-b2.3 - Lateral retinaculum tear with subluxing peroneal tendons, accompanied by subtalar, tibiotalar, and talonavicular involvement/subluxations Mechanism Dorsiflexion + inversion with axial loading

28% 18% Dischinger et al.

12%

10%

21

Current Study

20%

30%

40%

50%

Fig. 2. Distribution of hind foot/ankle primary injury mechanisms.

cases, while dorsiflexion made up 12% of the primary injury mechanism. Consequently, five of the 34 cases were presented as exemplars for how these ankle and hind foot injuries can occur given the aforementioned crash conditions. Table 4 summarized the crash and vehicle characteristics of these five cases, with subsequent texts provided a more detailed description of the crash events and occupant injury mechanisms. Related radiology information and 3D reconstruction of DICOM files of these five cases was included in Appendix A. 3.1. Case I (385143614)—Pole impact The case occupant is a 51-year-old, female driver of a 2003 Dodge Durango utility vehicle that was involved in a frontal impact with a pole. While the driver was negotiating the curved section of the roadway, an animal approached and entered the roadway across the path of the vehicle. The driver steered left, crossed the painted median, subsequently traversed a paved shoulder, a grass covered drainage ditch and a sidewalk before striking a traffic support pole, located at the east side of the intersection. The injury pattern of the case suggests forced dorsiflexion of the hindfoot causing a transverse fracture of the talar neck (Table 5) [13]. The high energy and added inversion force were likely

responsible for the observed rotation and subluxation seen at the talonavicular joint resulting in a Hawkins IV injury (OTA 44-a2.1). The inversion/adduction moment was also responsible for the vertically oriented, comminuted medial malleolus fracture and rupture of the lateral retinaculum [14]. 3.2. Case II (590132942)—Massive intrusion The driver of the case vehicle (V1, 2004 Hyundai Accent) was travelling eastbound, but crossed onto the opposite side (westbound) of the road. The opposing vehicle (V2, 2008 Honda Pilot, 4door utility) was traveling westbound in the same lane. V2 had been stopped at a traffic signal and had begun accelerating uphill as the vehicles met. The front of V1 struck the front of V2 in a headon collision. The resulting injury pattern suggested that the right foot underwent forced dorsiflexion due to a midfoot load producing a non-displaced (Hawkins I, OTA 81-b1) fracture of the talar neck [15] (Table 6). Concomitant axial compression through the heel resulted in a comminuted, intra-articular (Sanders 4, OTA 82-c4) calcaneal fracture. Forced external rotation of the right foot was the likely cause of the comminuted, oblique fibular shaft fracture. Delta-V reached 107 KPH prior to the occurrence of the impact, and was partly responsible for the massive intrusion occurred at toe pan and instrument panel. The deformed instrument panel indicated the contact between the bolster and both knees. The left lower extremity suffered a Ru¨edi–Allgo¨wer II (OTA 43-c1.1) tibial plafond fracture; non-displaced fractures of the

Table 4 Descriptive information for selected five cases. Case no.

Case I

Case II

Case III

Case IV

Case V

CIREN ID Crash summary Crash year Crash vehicle Vehicle summary Delta-V (km/h) PDOF (degrees) CDC (rank no. 1 event) Case occupant Age (y)/sex (M/F) Height (cm)/weight (kg) Belt use (y/n) Pre-tensioner actuation Frontal airbag deployment Pre-crash braking Involved physical components Toe pan intrusion (cm)

385143614

590132942

590109776

100106878

164689

2009 2003 Dodge Durango

2008 2004 Hyundai Accent

2006 2002 Mercedes Benz

2006 2001 Toyota Corolla

2010 2010 Kia Forte

43 0 12FZEW03

107 0 12FDEW05

47 0 12FDEW04

56 0 12FDEW03

54 -10 12FYEW03

51/F 160/61 Yes Yes Yes Yes

19/F 163/66 Yes Yes Yes Unknown

17/F 170/62 Yes Yes Yes Yes

29/F 157/59 Yes Yes Yes Unknown

54/F 168/154 Yes None Yes Unknown

6 Longitudinal 2 Lateral 2 Vertical Yes Yes No

30 Longitudinal 10 Longitudinal 10 Vertical No Yes Yes

4 Longitudinal 3 Longitudinal 5 Vertical Yes Yes No

0

0

8 Longitudinal 2 Longitudinal 0

No Yes No

Yes Yes Yes

Instrument panel intrusion (cm) Floor pan intrusion (cm) Pedal contact Knee bolster contact Floor contact

0

22

X. Ye et al. / Forensic Science International 254 (2015) 18–25

Table 6 Injury description and mechanism summary of Case II. Injury description and mechanism summary Right - Comminuted, intra-articular calcaneus fx (AIS 851400.2). Sanders 4, OTA 82-c4 - Non-displaced talar neck fx (AIS 853200.2). Hawkins 1, OTA 81-b1 - Comminuted fibula fx (junction of middle & distal 1/3) (AIS 851606.2). Weber C, OTA 44-c2.1 Mechanisms: Dorsiflexion, axial compression, external rotation, eversion Left - Tibial plafond fx. Ru¨edi–Allgo¨wer II, OTA 43-c1.1(AIS 853414.2), medial malleolus fx and posterior malleolus fx(AIS 853416.2) - Segmental fibular shaft fx. Weber C, OTA 44-c2.3(3) (AIS 851606.2) - Nondisplaced anterior Navicula fx, Cuboid fx, Medial, middle and lateral cuneiform fx. OTA 89-b - Metatarsal neck fx (2,3,4) OTA 87-a3.1 Mechanism: Plantarflexed foot position with axial compression and active calf muscle tension, eversion and external rotation. Medial to lateral directed force (right to left)

anterior navicula, cuboid, medial, middle and lateral cuneiform bones (OTA 89-b); medially angulated fractures of the second, third and fourth metatarsal necks (OTA 87-a3.1); and a segmental fibular shaft fracture (OTA 44-c2.3(3)). The likely cause of this constellation of injuries was a compressive force with a slight laterally directed vector through the metatarsal heads while the foot was in a plantarflexed position. This compression caused fracture and lateral displacement of the metatarsal heads as well as a crush injury at the Lisfranc joint. Given the plantarflexed ankle position and active tensing of the calf muscles, the load transmitted through the talus possibly caused the posteriorly angulated fracture of the tibial plafond. External rotation of an everted foot resulted in a combination of bending and compressive forces to the fibula resulting in segmental fracture. 3.3. Case III (590109776)—Pedal-related injury This case involved a belted driver of a 2002 Mercedes Benz CL240, 4-door sedan in a head-on collision with another passenger vehicle. The case vehicle V1 was travelling eastbound. The opposing vehicle (V2, 1995 Saturn Wagon) was traveling westbound, negotiating a sweeping right curve, just prior to the crash site at a speed too great to keep the vehicle from crossing into the opposing eastbound lane. According to the driver of V1, she only saw headlights approaching her vehicle and attempted to brake before the front of V1 struck the front of V2. The right foot underwent forced dorsiflexion of the ankle with impaction of the talar neck against the anterior tibia (Table 7). This finding was similar from the study by McMaster et al. which found that the key to talar neck fracture was the resistance of talar body rotation when the foot was forced into dorsiflexion [13]. Levering through the neck caused a Hawkins II (OTA 81-b2.2) fracture with subsequent anterior dislocation of the subtalar joint [16,17]. The significant comminution was evidence of a high-energy mechanism and the medial femoral condyle fracture indicated that a varus load at the knee was also present.

3.4. Case IV (100106878)—No intrusion This case involved a belted driver in a head-on impact with another passenger vehicle. The case vehicle (V1, 2001 Toyota Corolla) was travelling southbound. The 29-year-old female driver was using the belt restraint as evidenced by the actuated pretensioner which locked the retractor with enough webbing spooled out to appropriately fit a driver. The opposing vehicle (V2, 2004 Chevrolet Silverado C1500 pickup) was traveling northbound. The driver of V1 became distracted when she turned to address the children in the back seat. As the driver looked over her right shoulder toward the rear seat she inadvertently turned the steering wheel to the left causing the vehicle to veer left across the center turn lane, into the northbound lanes and into the path of V2. The front of V1 struck the front of V2 in a head-on impact. The right foot began in a plantarflexed position and an axial compressive force combined with inversion caused impaction of the tibial plafond with vertically oriented fractures of the posterior and medial malleoli (Ru¨edi–Allgo¨wer II, OTA 43-b3.2) [14]. The posterior malleolar fracture resulted from external rotation coupled with the axial compressive loading from the foot [5]. Further inversion resulted in an avulsion fracture of the lateral malleolus and displacement of the medial tibial plafond superiorly (Table 8). 3.5. Case V (164689)—Moderate intrusion In this case, the driver of case vehicle V1 (2010 Kia Forte) was traveling eastbound lane on a two-lane, two-way road. Vehicle 2 (2010 Ford Escape) was traveling westbound and approaching the same intersection. An unidentified, non-contact vehicle (NCV) was stopped in westbound lane waiting to make a left turn. The driver maneuvered V2 to the right of the NCV in an attempt to pass through the intersection on the right shoulder. The driver of V2 dropped right wheels off the paved surface and steered left in attempt to regain the road. V2 re-entered the road in a sharp left turn maneuver and then entered the eastbound lane. Front of V1 struck the right side of V2 in an L-type configuration. Bilateral tibial pilon fractures resulted from high-energy axial loading of the plafond was found in this case (Table 9) [18]. Sparing of the calcanei indicated that the driver was actively tensing the calf muscles in both legs prior to impact [20,21]. On the right a Ru¨edi–Allgo¨wer III, (OTA 43-c3.3) injury was seen along with medial talar articular surface impaction (OTA 81-c1.1). On the left a Ru¨edi–Allgo¨wer III, (OTA 43-c2.3) injury with a spiral posterior tibial component and associated oblique fibular shaft fracture suggested an axial compression plus external rotation mechanism possibly due to intrusion of the toe pan. 4. Discussion Below-knee lower limb injuries, especially hind-foot injuries, have been a problem and remain the highest proportion of AIS2+ injuries [3]. This study analyzed the injury patterns and

Table 8 Injury description and mechanism summary of Case IV. Table 7 Injury description and mechanism summary of Case III. Injury description and mechanism summary Right - Hawkins II talar neck fx. OTA 81-b2.2 (AIS 853200.2) - Medial femoral condyle fx, and subtalar joint dislocation and flexor hallucis longus tendon rupture Mechanism: Forced dorsiflexion through midfoot with varus load to the knee

Injury description and mechanism summary Right - Tibial plafond with large posterior malleolus component and vertical medial malleolus. Ru¨edi-Allgo¨wer II, OTA 43-b3.2(6) (AIS 851614.3) - Nondisplaced, transverse, distal lateral malleolus fracture at the level of the joint line. Weber B Mechanism: Plantarflexed foot position with axial compression, inversion, and active calf muscle tension

X. Ye et al. / Forensic Science International 254 (2015) 18–25 Table 9 Injury description and mechanism summary of Case V. Injury description and mechanism summary Right - Tibial plafond fx. Ru¨edi–Allgo¨wer III, OTA 43-c3.3 (AIS 853422.3) - Talar body fx, medial dome impaction. OTA 81-c1.1 (AIS 853200.2) - Fibula distal diaphysis fx, Weber C, comminuted. OTA 44-c2.4 (AIS 851606.2) - Tri-malleolar fx. Ru¨edi–Allgo¨wer III, comminuted, OTA 43-c3.3 (AIS 851612.2) Mechanism: Axial compression with active calf muscle tension Left - Tibial plafond fx. Ru¨edi–Allgo¨wer III, OTA 43-c2.3 (AIS 853422.3) - Fibular shaft fx. Weber C, OTA 44-c2.2 (AIS 851606.2) - Medial malleolus fx. Ru¨edi–Allgo¨wer III comminuted, OTA 44-c2.2 (AIS 853414.2) - Left-sided intra-articular fx of posterior aspect of talus near subtalar joint noted in CT report Mechanism: Axial compression with active calf muscle tension, possible external rotatory component given oblique fibula and spiral component to posterior tibia

mechanisms for selected hind-foot injuries, with associated identification and categorization of each injury for assessment. There are multiple reasons that may account for the high incidence of lower limb injuries in frontal crashes. Intrusion of the toe pan was a sufficient mechanism of injury but not a necessary one, given that a large number of crashes occur without large intrusion. A more direct causal relationship exists between the deceleration of the vehicle components and the injury outcome [3]. Active musculature bracing is one potential contributing factor. In real world crashes, up to two thirds of occupants sustaining lower extremity injuries were associated with pre-impact tension of leg muscle [19]. Axial loading was shown to be the dominant injury mechanism in this study. Axial loading could be generated by the active muscle tension applied through the Achilles tendon during pre-impact bracing, accompanied by vehicle deceleration and toe pan intrusion. Muscle bracing could also possibly alter or aggravate the internal load distribution and transmission in the foot/ankle complex. Biomechanical studies on cadavers have shown that tibia pilon fractures with sparing of the calcaneus almost always require a significant amount of active calf muscle tension (two to three times of body weight) through the Achilles tendon [20,21]. As a result, Achilles tension applies a plantar-flexion moment on the ankle joint and a compressive force on the distal tibia. Chang et al. also pointed out that muscle tension could affect the force transmitted through the knee-thigh-hip by increasing the coupling of soft-tissue mass distal or proximal to the hip [22]. Driving posture is another contributing factor for high prevalence of hind-foot injuries. Changes in lower limb orientation could potentially result in various kinematic responses during the crash event. Splayed knees could generate abduction movement of the legs but result in less axial loading to the tibia shaft. Inversion or eversion of the ankles could potentially increase the bending moment of ankles during a frontal collision. Additionally, leg orientation and injury risk varies with different vehicle types and compartment space. From the previous NASS-CDS data analysis, the distribution and risk of injury by vehicle type revealed that vans, followed by SUVs, were less likely to cause lower-limb injury compared to passenger cars, with light pick-up trucks being the worst for sustaining lower limb injuries [3]. Another study showed that initial position of the foot and the interaction with the pedal structures strongly affected the lower extremity loadings [23]. Smaller drivers, with decreasing driver stature or foot length, sustained a higher likelihood of sustaining lower extremity injuries with increasing heel rise, which would result in an increase heel height during braking. Lastly, footwear could alter the injury risk to

23

the lower extremity, as high heels from female drivers could potentially result in inversion/eversion instability of the ankles. In real-world driving scenarios, drivers do not generally maintain exactly the same postures as in standardized crash tests, and tend to change the driving posture in multiple driving conditions (e.g., under the stressful conditions of pre-impact braking or bracing). As a consequence, the response of restrained system may react differently and the efficiency may reduce [24]. In addition, approximately 90% of U.S. adult drivers were associated with incorrect seatbelt use, with the lap belt being placed further forward and higher relative to the pelvis [25]. As a result, the percentage of population whose driving posture was identical to standardized crash tests was marginal. The frequency and severity of lower limb injury has also been related with the pedal interactions [26]. The examination of NHTSA standardized crash tests showed higher loads in the right tibia than the left tibia, indicating that interaction with the pedal may be significant in lower limb injuries. A parametric study from simulations in the same study suggested that loading of lower limb could be more sensitive to the rate, peak, and onset of toe pan intrusion than the absolute intrusion magnitude [27]. Investigation from crash test data and simulation results suggest that factors such as the vehicle’s change in velocity and the rate and timing of intrusion must be considered when examining injury mechanisms of the lower extremities [28]. A fair amount of high degree of comminuted fractures was observed from this study, suggesting a combination of high Delta-V of vehicles and bone fragility (i.e., osteoporosis) for elderly drivers. Moreover, although relatively few talar fractures have been generated in biomechanical experimental studies from the laboratory, talar fractures were the most common injuries in the reviewed cases [29]. While this finding could not be generalized given the small sample size and potential over-estimation of overall crash severity in the real-world, the results suggested more emphasis on the evaluation and quantification of injuries from the foot/ankle complex. 5. Conclusion This study examined the injury patterns and injury mechanisms from 34 cases selected from the CIREN database. Crash, occupant and medical information were extensively reviewed and analyzed to illustrate the inconsistency between improved dummy performance in crash tests and the increased incidences of lower limb injuries in real world crashes, in addition to providing improved clarity on the likely mechanisms of these injuries. Results indicated that talar fractures, malleolar fractures, and calcaneal fractures were the most frequent hind-foot skeletal injuries observed among the reviewed cases. Despite the overarching improvements made to reduce toe pan intrusion observed from vehicle crash tests, axial loading continues to be the dominating injury mechanism among lower limb injuries. Axial compression was most prevalent in this study causing 18 injuries, while 11 injured ankles involved an inversion or eversion motion, and the 7 remaining injuries resulted from dorsiflexion as the primary injury mechanism. As such, the reduction of axial forces sustained in lower extremity should be a greater focus and priority for the mitigation and prevention of lower limb injuries. The analysis of injury mechanisms in this study could also aid in crash reconstruction and the development of safety systems for vehicles. Acknowledgements The National Highway Traffic Safety Administration provided both technical and financial support via Cooperative Agreement no. DTNH22-10-H-00293. Note that the views expressed by the authors do not necessarily represent those of the sponsors.

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Appendix A. Radiology information Fig. A.1.

Fig. A.1. Injury schematics and radiology information for selected cases.

X. Ye et al. / Forensic Science International 254 (2015) 18–25

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