Anurag Soni

Effect of Active Muscle Forces on Knee Injury Risks for Pedestrian Standing Posture at Low-Speed Impacts

Objectives: The objective of the present study is to investigate the effect of muscle active forces on lower extremity injuries for various impact locations and impact angles for a freely standing pedestrian. Methods: FE simulations have been performed using a validated lower extremity FE model with active muscles (A-LEMS). In all, nine impact orientations have been studied. For each impact orientation, three different pre-impact conditions of a freely standing pedestrian, representing a cadaver, and an unaware and an aware braced pedestrian, have been simulated. Stretch-based reflexive action was included in the simulations for an unaware pedestrian. Results: Strains in knee ligaments and knee joint kinematics have been compared in each impact orientation to assess the effect of muscle activation. It is observed that strain in knee ligaments is dependent on impact locations and angles and the MCL is the most vulnerable ligament. Further, due to muscle effects, except when the impact is on the knee, peak strain values in all the ligaments are lower for an unaware pedestrian than either for a cadaver or for a fully braced pedestrian. Conclusions: It is concluded that active muscle forces significantly affect the knee kinematics and consequently reduce strains in knee ligaments.

Response of Tonic Lower Limb FE Model in Various Real Life Car-Pedestrian Impact Configurations: A Parametric Study for Standing Posture

This paper investigates the effect of muscle contraction on lower extremity injuries in car-pedestrian lateral impacts. Three variables, viz. height of impact, pedestrian offset with respect to car centre and impact speed, are considered. Full-scale car-pedestrian FE simulations have been performed using the full body pedestrian model with active lower extremities (PMALE) and front structures of a car model. Two pre-impact conditions of a symmetrically standing pedestrian, representing a cadaver and an unaware pedestrian, have been simulated. It is concluded that (1) with muscle contraction risk of ligament failure decreases whereas risk of bone fracture increases; (2) ligament and bone strains are dependent on the impact location; (3) chances of ligament injuries are higher when the impact occurs near the outer corner of the car; (4) risk of bone fracture increases with speed and (5) bone fracture reduces the risk of ligament failure.

Response of lower limb in full-scale car–pedestrian low-speed lateral impact – influence of muscle contraction

This paper investigates the effect of muscle contraction on lower extremity injuries in car–pedestrian lateral impact. A full-body pedestrian model with active muscles has been developed. Finite element simulations have then been performed using the full-body model and front structure of a car. Two pre-impact conditions, that of a symmetrically standing pedestrian, representing a cadaver and an unaware pedestrian, have been simulated. Stretch-based reflexive action was included in the simulations for an unaware pedestrian. The results show that due to muscle contraction (1) peak strain in all the knee ligaments reduces, (2) von Mises stresses in tibia and fibula increase and may fail and (3) knee joint effective stiffness increases by 58% in lateral bending.

Effect of Active Muscle Forces on the Response of knee Joint at Low Speed Lateral Impacts

In vehicle-pedestrian collisions, lower extremities of pedestrians are frequently impacted by the vehicle front structure. The aim of the current study is to understand the role of muscle activity in knee joint injuries at low velocity lateral impacts, characteristic of vehiclepedestrian collisions. Therefore, a group of muscles in the lower extremity are modeled using bar elements with the Hill material model. The reflex response of the muscle is then included. Simulations indicate that muscle activation decreases the probability of failure in knee ligaments.

Effect of Muscle Contraction in High-speed Car-Pedestrian Impact: Simulations for Walking Posture

This paper investigates the effect of muscle contraction on lower extremity injuries for pedestrian walking posture in car-pedestrian lateral impact at 40 kmph. The full body model, PMALE, which was configured in symmetric standing posture, has been repositioned in the walking posture. Finite element simulations have then been performed using the PMALE in the walking posture and front structures of a car. Two impact configurations, i.e. impact on right (trailing) and on left (leading) leg have been simulated. Two pre-impact conditions, that of a symmetrically standing pedestrian, representing a cadaver and an unaware pedestrian have been simulated for both the impact configurations. Stretch based reflexive action was included in the simulations for an unaware pedestrian. It is concluded that (1) with muscle contraction risk of ligament failure decreases (2) in lateral impacts, MCL could be considered as the most vulnerable and LCL as the safest ligament (3) for a walking pedestrian, PCL would be at higher risk in case of impact on trailing leg whereas, ACL would be at higher risk if car strikes the leading leg (4) active muscles may not affect bone fracture in high speed car-pedestrian crashes.

Effects of Boundary Conditions in Dynamic Tests for Pedestrian Safety: A Finite Element Simulation Study

Dynamic impact tests on post mortem human subjects (PMHSs) have been used to understand the injury mechanism and to devise countermeasures for pedestrian safety. Available experimental studies of impacts to the lower limbs simulating those encountered in automobile crashes is limited in number. However, the current European and Japanese standards have been devised from such tests. These tests have a degree of uncertainty associated with their boundary conditions due to the dynamic loading which are difficult to quantify during the test and hence usually not reported. This can lead to the erroneous results. It is concluded that the experiments should be designed to limit the effect of such dynamics based parameters or the final results should be compensated/normalised for the dynamic loading.

Effect of impactor mass on the response of knee joint during finite element simulations

In our previous studies, we have observed that active muscles affect the response of the knee joint under impact. This paper investigates if the mass of the impactor affects our earlier observations. Therefore, simulations of lateral impact just below the knee have been performed using impactors of two different masses (i.e., the heavy and the light impactor). Two pre-impact conditions of a freely standing pedestrian, representing a cadaver and an unaware pedestrian have been simulated. Stretch-based reflexive action was included in the simulations for an unaware pedestrian. The results indicate that: the light impactor does not load the knee joint to the extent a car does in real-life car-pedestrian crashes; irrespective of the impactor mass, active muscle forces significantly alter the ligament strains.

Sensitivity Analysis of Muscle Parameters and Identification of Effective Muscles in Low Speed Lateral Impact at Just below the Knee

Finite Element simulation of a lower extremity model is used to (1) determine which of the muscle parameters maximum force capacity (Fmax), initial activation levels (Na) and maximum muscle contraction velocity (Vmax) affect ligament strains the most and (2) to identify which muscles affect the knee response the most in low speed, just below the knee, lateral impact. Simulations have been performed with Fmax, Na and Vmax varying from their reference values. Sensitivity of ligament strains to variation in muscle parameters has been studied. It is observed that knee response is more sensitive to Fmax and Na than Vmax. Amongst the muscles varied, reduction in the Fmax and the Na in the hamstring and the gastrocnemius muscles affects the knee ligament strains the most. The hamstring parameters significantly affects the ACL, the PCL as well as the MCL strains whereas, change in the gastrocnemius parameters affects only the MCL strain.