James R. Funk

Snowboarder's Talus Fractures Experimentally Produced by Eversion and Dorsiflexion:

Background: Fracture of the lateral process of the talus is an unusual injury that has received heightened attention in recent years because of its association with snowboarding. The diagnosis is often confused with that of lateral ankle sprain. If left untreated, it can cause long-term impairment, including osteoarthritis and subtalar joint degeneration. It is generally thought to result from dorsiflexion and inversion. However, few experimental studies have been conducted to investigate the injury mechanism. Hypothesis: Eversion of a dorsiflexed ankle is more likely to fracture the lateral process of the talus than inversion of a dorsiflexed ankle. Study Design: Controlled laboratory study. Methods: Ten cadaveric leg specimens were subjected to dynamic inversion or eversion of an axially loaded and dorsiflexed ankle. Results: Inversion failed to produce any fractures in three injured specimens. However, all six specimens subjected to eversion sustained a fracture of the lateral process of the talus. Conclusions: The incidence of fracture of the lateral process of the talus was significantly higher in the eversion group compared with the inversion group. Clinical Relevance: Eversion of an axially loaded and dorsiflexed ankle may be an important injury mechanism for fracture of the lateral process of the talus among snowboarders.

Experiments for Establishing Pedestrian-Impact Lower Limb Injury Criteria

This paper discusses lower limb injury impacts to pedestrians. Previous lateral knee bending and shear tests have reported knee joint failure moments close to failure bending moments for the tibia and femur. Eight tibias, eight femurs and three knee joints were tested in lateral bending and two knee joints were tested in lateral shear. Seven previous studies on femur bending, five previous studies on tibia bending, two previous studies on knee joint bending, and one on shear were reviewed and compared with the current tests. All knee joint failures in the current study were either epiphysis fractures of the femur or soft tissue failures. The current study reports an average lateral failure bending moment for the knee joint (134 Nm SD 7) that is dramatically lower than that reported in the literature (284-351 Nm), that reported in the current study for the tibia (291 Nm SD 69) and for femur (382 Nm SD 103). While this research has demonstrated the importance of realistic boundary conditions, more research is necessary to determine a statistically valid impact threshold for the knee joint.

HOW FUTURE TRENDS IN SOCIETAL AGING, AIR BAG AVAILABILITY, SEAT BELT USE, AND FLEET COMPOSITION WILL AFFECT SERIOUS INJURY RISK AND OCCURRENCE IN THE UNITED STATES

The objective of this study was to quantify the importance of societal aging relative to other factors that are known to affect injury risk. An aging populations effect on Maximum Abbreviated Injury Scale (MAIS) 3+ injury trends for passenger car drivers in frontal crashes was projected and compared to the effects of projected changes in fleet composition, changes in seat belt usage, and changes in air bag availability. It was determined that increased frailty due to an aging population will result in 19,816 to 43,568 additional injuries to passenger car drivers in frontal crashes from 1996 to 2012. Aging was shown to have an effect similar to the increased presence of light trucks in the fleet (a cumulative increase of approximately 47,428 injuries). Aging and changing fleet composition were shown to have a smaller effect than the projected increases in seat belt use or air bag availability, though the effect of increased belt use is not much greater than the effect of aging. After 2012, however, air bag availability and seat belt use will plateau, while societal aging will continue.

THE ROLE OF AXIAL LOADING IN MALLEOLAR FRACTURES

Though rotation is thought to be the most common mechanism of foot and ankle injury in both automobile crashes and in everyday life, axial impact loading is considered responsible for most severe lower extremity injuries. In this study, dynamic axial impact tests were conducted on 92 isolated human lower limbs. The test apparatus delivered the impact via a pendulum-driven plate which intruded longitudinally to simulate the motion of the toepan in an automobile crash. Magneto-hydrodynamic (MHD) angular rate sensors fixed to the limbs measured ankle rotations during the impact event. Malleolar or fibula fractures, which are commonly considered to be caused by excessive ankle rotation, were present in 38% (12 out of 32) of the injured specimens. Ankle rotations in these tests were always within 10 degrees of neutral at the time of peak axial load and seldom exceeded failure boundaries reported in the literature at any point during the impact event. These results suggest that high-energy axial loading may be the cause of some of the injuries conventionally thought to be caused by excessive rotations in real-world car crashes. (A) For the covering abstract see ITRD E106349.

An Integrated Model of Rolling and Sliding in Rollover Crashes

Rollover crashes are often difficult to reconstruct in detail because of their chaotic nature. Historically, vehicle speeds in rollover crashes have been calculated using a simple slide-tostop formula with empirically derived drag factors. Roll rates are typically calculated in an average sense over the entire rollover or a segment of it in which vehicle roll angles are known at various positions. A unified model to describe the translational and rotational vehicle dynamics throughout the rollover sequence is lacking. We propose a pseudocylindrical model of a rolling vehicle in which the rotational and translational dynamics are coupled to each other based on the average frictional forces developed during ground contacts. We describe the model as pseudo-cylindrical because vertical motion is ignored but the ground reaction force is not constrained to act directly underneath the center of gravity of the vehicle. The tumbling phase of a rollover is modeled in three distinct phases: an initial brief airborne phase between roll initiation and the first ground contact, an early phase in which relative sliding between the perimeter of the vehicle and the ground causes the roll rate to increase, and a later phase in which the vehicle rolls without sliding and the roll rate decreases. In the early phase, the average vehicle deceleration is higher and is governed by sliding friction. In the later phase, the average vehicle deceleration is lower and is governed by geometric factors. Model predictions were fit to data from 12 well-documented rollover crashes in order to derive empirical values for the model parameters. In 11 out of the 12 rollovers studied, the model predictions matched the actual results with good accuracy. The results validate the underlying physical principles of the model and provide data that can be used to apply the model to real world rollovers. The proposed model provides a physical basis for understanding vehicle dynamics in rollovers and may be used in certain cases to improve the accuracy of a rollover reconstruction.

The Tibia Index: A Step in the Right Direction

Leg injuries are frequent occurrences for occupants involved in automobile crashes. This paper investigates the efficacy of a proposed injury criterion, the tibia index, to predict fractures of the leg. Using an interaction formula, the tibia index combines the applied compressive force and moment to predict mid-shaft fractures of the tibia and fibula. Quasistatic and dynamic test data of the leg are reviewed in an effort to establish critical threshold values of force and moment. The data indicate that there is minimal dependence of the fracture threshold on the direction of applied moment and suggest that a resultant moment is appropriate for the index. Meanwhile, axial loading of the leg results in bending of the tibia due to the curvature of the limb and eccentricity of the load through the ankle and knee. Since the distal and proximal ends of the fibula and tibia are weaker than the shaft, a supplemental compressive criterion is required for these regions. Validation of proposed indices relative to published experimental testing shows good correlation for dynamic results and verifies the dependence of the fracture threshold on an interaction between the applied moment and compressive force. Until additional testing can be conducted to generate injury risk functions, individual investigators must decide whether the static or dynamic criteria are most applicable for their test environment. Furthermore, implementation of the indices into dummy designs requires biofidelic response in order to provide accurate estimates of the injury risk.

Case Series Analysis of Hindfoot Injuries Sustained by Drivers in Frontal Motor Vehicle Crashes

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.